A Durif

⁎⁎ M Richou

G Kermouche

M Lenci

J-M Bergheau

Impact of tungsten recrystallization on ITER-like components for lifetime estimation

For ITER divertor, plasma facing components are made with tungsten as armor material. In previous papers, it has been shown that plasma facing components are prone to crack, appearing in tungsten block during thermal cyclic heat loading. In order to predict component lifetime, a numerical simulation is proposed in this paper. With regard to previous studies, tungsten (raw and recrystallized) real mechanical behaviors are taken into account. To be used as inputs for numerical simulations, compressive tests at different temperatures and strain rates were realized on raw and recrystallized tungsten. Raw tungsten tests reveal a linear elastic and ideal plastic behavior that is sensitive to strain rate. Concerning recrystallized tungsten, an elastic-viscoplastic behavior is observed on the entire explored temperature range (up to 1150 °C), that can be described by an elastic-plastic model with kinematic hardening. Manson-Coffin relationships are used to estimate the lifetime. When taking into account real mechanical behaviors for raw tungsten and recrystallized tungsten, we show that lifetime estimation is mainly driven by recrystallized thickness in the component, by the ductile to brittle transition temperature and finally by strain rate.

Introduction

The fusion reaction could become a viable way to generate electricity. To perform this reaction, reactors confine magnetically plasma in a vacuum chamber. However, plasma confinement is imperfect and due to the magnetic plasma configuration, energy losses are directed toward the main wall, mainly on the lower part of the vessel called divertor. For the ITER divertor, plasma facing components have to withstand cyclic high heat flux (stationary and transient) up to 20 MW/ m 2 [START_REF] Ezato | Progress of ITER full tungsten divertor technology qualification in Japan[END_REF]. High Heat Flux (HHF) experimental campaigns were performed [START_REF] Pintsuk | Characterization of ITER tungsten qualification mock-ups exposed to high cyclic thermal loads[END_REF] and proved that actively cooled plasma facing components made with tungsten as armor material, bonded on a copper alloy tube as heat sink structural material are able to satisfy the ITER heat exhaust requirements (20 MW/m 2 ) [START_REF] Hirai | Status of technology R&D for the ITER tungsten divertor monoblock[END_REF]. However, due to high heat flux, strong temperature gradients are generated on a thickness of 7 mm, leading to extreme temperature values from 2000 °C at the loaded surface to 500 °C near the cooling tube [START_REF] Hirai | Use of tungsten material for the ITER divertor[END_REF]. 2000 °C is large enough to alter the tungsten microstructure causing recrystallization and mechanical properties losses and then damages such as macro cracks in the material [START_REF] Pintsuk | Characterization of ITER tungsten qualification mock-ups exposed to high cyclic thermal loads[END_REF][START_REF] Gavila | High heat flux testing of mock-ups for a full tungsten ITER divertor[END_REF][START_REF] Riccardi | Preliminary results of the experimental study of PFCs exposure to ELMs-like transient loads followed by high heat flux thermal fatigue[END_REF][START_REF] Pintsuk | Qualification and post-mortem characterization of tungsten mockups exposed to cyclic high heat flux loading[END_REF]. It is thus necessary to identify which phenomena have to be taken into account to predict the lifetime of tungsten armored component, this identification is the aim of this paper. M. Li et al. pointed out that recrystallization is a key phenomenon regarding lifetime prediction [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF][START_REF] Li | Structural impact of armor monoblock dimensions on the failure behavior of ITER-type divertor target components: size matters[END_REF]. Indeed, they show that the loss of mechanical properties induced by recrystallization leads to an increase of plastic strain increment per thermal cycle. From Manson-Coffin relationship they conclude on the drastic reduction of the component lifetime. However, thermomechanical model uses by assumption an linear elastic and ideal plastic behavior for recrystallized tungsten. In this paper, it is proposed to investigate the effect of the actual mechanical behavior of tungsten grades (in recrystallized and no recrystallized states) on lifetime prediction. For this, the model proposed by M. Li et al. [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF] is used and assumed mechanical behaviors of tungsten are replaced by the actual ones. In the first part of this paper, compressive tests of raw and recrystallized tungsten for different temperatures and strain rates are presented. The thermomechanical model is then described. Numerical simulations are performed to estimate the equivalent plastic strain increments depending on various parameters: thickness of the recrystallized layer and constitutive relations. Manson-Coffin relations are used to estimate the number of cycles to failure. A conclusion is ⁎⁎ Principal corresponding author. ⁎ Corresponding author.

E-mail addresses: alan.durif@cea.fr (A. Durif), marianne.richou@cea.fr (M. Richou).

T

finally brought on the key parameters that govern the lifetime prediction of plasma facing components.

High temperature compressive tests

Materials and methods

ITER requirements request tungsten manufacturers to supply material with strong grains orientation [START_REF] Hirai | Status of technology R&D for the ITER tungsten divertor monoblock[END_REF]. Usually, oriented microstructure is obtained by a forming or rolling process. Rolling process involves grain orientation, strain rate sensitivity and promotes tungsten recrystallization. Microstructure change, such as recrystallization, decreases significantly the mechanical properties of the material [START_REF]ITER Structural Design Criteria for In-vessel Components (SDC-IC) Appendix[END_REF].

Compressive tests are thus performed on rolling tungsten provided by Advance Technology and Materials (AT&M) which is one of the ITER tungsten grade suppliers. Tungsten samples are cut from tungsten blocks (28 * 28 * 12 mm 3 ) into cylindrical shape (dimensions are displayed in Fig. 1). 24 samples are prepared. Samples are cut in the transversal direction (T) (Fig. 2) and half of them are then annealed (15 h at 1350 °C) to obtain a recrystallized microstructure.

Compressive tests are performed using a hydraulic machine (Schenk) on raw and recrystallized tungsten at 500 °C, 750 °C, 900 °C and 1150 °C (Fig. 1). The test device is equipped with an infrared heating system, capable of reaching temperature up to 1200 °C and an enclosure to perform compressive tests under argon atmosphere. Argon is used to avoid oxidation on surfaces samples. For each test, sample is coated by spray with graphite and boron in order to avoid friction during the compression. Then, sample is placed in the enclosure on TZM (Tungsten-zircon-molybdenum) heaps. Two thermocouples are placed in a fixed position on the test line, at the sub-surface in the heaps, close to each of the faces of the sample to measure sample temperature. Once samples reached test temperatures, they were maintained 10 min to ensure a homogeneous temperature in the whole sample. Compressive tests were performed for several strain rates for the same temperature range. For each test, constant strain rate is obtained assuming a constant volume and a homogeneous deformation of the sample during the test. Strain rates were chosen based on the expected thermal strain rate (ε˙t h ) under stationary thermal heat flux in ITER (Eq. ( 1)):

= - ε TT α T t ˙() * ( ) ∆ ss th 0 (1)
where T s corresponds to the block surface temperature and α corresponds to the thermal expansion coefficient (5.08 × 10 -6 K -1 at 1400 °C [START_REF]ITER Structural Design Criteria for In-vessel Components (SDC-IC) Appendix[END_REF]). Previous simulations [START_REF] Hirai | Use of tungsten material for the ITER divertor[END_REF] show that at 20 MW/m 2 , the surface temperature can reach up to 1400 °C in approximately 1.2 s (t = 1.2 s). T 0 is representative of the initial temperature of the tungsten block under cooling condition before plasma shock (T 0 = 120 °C) [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF].

Finally, strain rate is estimated around 6 × 10 -3 s -1 . Also, fast transient heat loadings are expected in ITER [START_REF] Du | FEM study of recrystallized tungsten under ELM-like heat loads[END_REF]. These particulars heat loadings (edges localized modes) have strong impact on the tungsten surface temperature. In this context, it was decided to test samples also at higher strain rates (6 × 10 -2 /s and 6 × 10 -1 /s).

Results

In Fig. 3, stress-strain curves are plotted for 500 °C (at 6×10 -3 s -1 ) and 1150 °C (at 6 × 10 -3 s -1 and 6×10 -1 s -1 ). Curves reveal that tungsten is ductile between 500 °C and 1150 °C and that tungsten has a linear elastic and ideal plastic behavior. Moreover, yield stresses (estimated at 0.2%) decrease from 559 MPa at 500 °C to 426 MPa at 1150 °C, showing that temperature has an impact on tungsten mechanical property. Also, strain rate effect is observable, indeed, yield stresses (estimated at 0.2%) decrease from 459 MPa at 6×10 -1 s -1 to 426 MPa at 6 × 10 -3 s -1 . To conclude, Fig. 3 highlights that raw tungsten recrystallizes dynamically at 1150 °C (at 6×10 -3 s -1 ). In this case, once the tungsten reached the yield stress, a stress decrease is noticed during the test.

In Fig. 4, stress-strain curves are plotted for 500 °C at 6 × 10 -3 s -1 and 1150 °C (at 6 × 10 -3 s -1 and at 6×10 -1 s -1 ). Recrystallized tungsten is ductile between 500 °C and 1150 °C. This clearly involves that Ductile to Brittle Transition Temperature (DBTT) is below 500 °C. In the literature, several tungsten grades were studied and large differences were obtained concerning the estimation of the DBTT [START_REF] Reiser | Tungsten foil laminate for structural divertor applicationstensile test properties of tungsten foil[END_REF][START_REF] Farre | Étude de la transition fragile-ductile d' un tungstène[END_REF]. In a further study this effect will be studied. The increase of temperature has a strong impact on mechanical properties of recrystallized tungsten. Yield stress (estimated at 0.2%) decreases from 61 MPa at 500 °C to 49 MPa at 1150 °C. Contrary to the linear elastic and ideal plastic case, described for raw tungsten, recrystallized tungsten exhibit a strong hardening. Once the yield stress is attained; stress has to be endlessly increased to ensure plastic strain. Tangent moduli obtained are presented in Table 2. Tangent modulus corresponds to the plastic (hardening) slope of the material. In this paper, slope are measured between strain corresponding to yield stress (estimated at 0.2%) and expected strain after 3 thermal cycles at 20 MW/m 2 estimated at 2.3% in [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF]. Recrystallized tungsten is also sensitive to strain rate. Same quantitative results are obtained for each studied temperature. These observations lead to conclude that recrystallized tungsten has elasticviscoplastic behavior.

Here below, correlation of obtained mechanical characteristics with other published characteristics [START_REF] Wirtz | Material properties and their influence on the behaviour of tungsten as plasma facing material[END_REF] is presented. In Table 1, yield stresses and stresses values obtained at 0.2% at 750 °C (representative of the described compressive test obtained at 6 × 10 -3 s -1 on raw tungsten) and at 800 °C [START_REF] Wirtz | Material properties and their influence on the behaviour of tungsten as plasma facing material[END_REF] (obtained on AT&M tungsten grade during tensile test at 10 -4 s -1 ) are presented. Comparable yield stresses (=5%) are obtained, revealing that plastic constitutive relation obtained in compression are representative to that obtained in traction.

Finite element analysis

Geometry, meshing

Geometry presented in Fig. 5, is representative of an ITER divertor block. Thanks to the use of two symmetry planes only quarter part block is modeled. Dimensions are identical to the ones implemented in the numerical model used by M. Li et al. [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF] (28 * 14 * 6 mm 3 ). Tungsten block dimension is 28 mm (width) * 28 mm (height) * 12 mm (depth). The minimum distance from tungsten upper surface to the copper interlayer is 6.5 mm. Tube inner diameter is 12 mm, while the outer diameter of the tube is 15 mm. The thickness of the Cu-OFHC interlayer is 1mm. ANSYS 17.2 commercial finite element analysis code is used to perform this geometry. 12952 quadratic elements are used to mesh the 3D geometry.

Materials properties

Based on described mechanical tests, raw tungsten is assumed to be linear elastic and ideal plastic (tangent moduli are set to 0, Table 2). Despite the slight anisotropy effect [START_REF] Wirtz | Material properties and their influence on the behaviour of tungsten as plasma facing material[END_REF], tungsten is assumed isotropic in this model. Elastic-visoplastic behavior with hardening was observed for recrystallized tungsten. Moreover, in literature [START_REF]Nuclear Fusion Programme Annual Report of the Association Forschungszentrum Karlsruhe/EURATOM[END_REF] cyclic tests were performed on recrystallized tungsten at 800 °C. Constitutive relation obtained revealed kinematic hardening over cycles. To take into account this in our upcoming simulations, kinematic hardening model is used. In stress space, kinematic hardening models allow a translation of the yield surface and hence that cyclic effects like softening, hardening or Bauschinger effect [START_REF] Clavel | Endommagement et rupture des matériaux -Volume 1, Hermes -Lavoisier[END_REF] can be modeled. Bilinear kinematic hardening model is used in simulations. This model assumes that the stress-strain curve can be described as two straight line segments. For the elastic part, slope is young modulus and for the plastic part, slope is tangent modulus. Tungsten mechanical properties obtained under compressive tests (yield stress and tangent modulus) used in dedicated simulations are summarized in Table 2. Bold characters presented in upcoming equations denote tensorial quantities. The yield criteria (f(σ, χ)) of bilinear kinematic hardening model used is commonly defined as [START_REF] Prager | The theory of plasticity: a survey of recent achievements[END_REF]:

=- - σχ σ χ f Jσ (, ) ( ) y
With χ the back stress and σ y the material yield stress, both depending on temperature. J(.) denotes the von Mises invariant. In uniaxial case, χ is defined as follow:

= χH ε P (2)
With ε P plastic strain and H: Fig. 4. Stress-strain curves obtained on recrystallized tungsten at 500 °C (at 6×10 -3 s -1 ) and 1150 °C (at 6 × 10 -3 s -1 and at 6 × 10 -1 s -1 ).

Table 1

Raw tungsten mechanical properties obtained under compressive and tensile tests.

Tensile test [START_REF] Wirtz | Material properties and their influence on the behaviour of tungsten as plasma facing material[END_REF] Compressive test (800 °C, 10 -4 s -1 ) (750 °C, 6 × 10 = -

H EE EE T T ( 3
)
The Young modulus (E), and the tangent modulus (E T ) are temperature dependent.

E, heat conductivity and coefficient of thermal expansion used are those presented for the raw tungsten and recrystallized tungsten in [START_REF]ITER Structural Design Criteria for In-vessel Components (SDC-IC) Appendix[END_REF]. Also, mechanical properties used for Cu-OFHC and CuCrZr are extracted from stress-strain curves presented in [START_REF]ITER Structural Design Criteria for In-vessel Components (SDC-IC) Appendix[END_REF]. Stresses and strains generated in the both copper materials are not studied.

Studied cases

In this paper, several simulations are performed.

1. The Reference simulation (Ref, Fig. 6) assumes raw tungsten obtained experimentally at 6 × 10 -3 s -1 of strain rate. 2. Second simulation which aims to analyse the effect of the strain rate (SR, Fig. 6); assumes raw tungsten and uses mechanical properties obtained experimentally at 6 × 10 -1 s -1 of strain rate. 3. Another simulation which aims to analyse the effect of tungsten recrystallization (RXX thickness 2, Fig. 6); assumes 2 mm thickness of recrystallized tungsten on the upper part of the model. 2 mm thickness of the recrystallized tungsten is chosen as it is representative to that observed on the center of the block after 300 high heat flux cycles [START_REF] Pintsuk | Characterization of ITER tungsten qualification mock-ups exposed to high cyclic thermal loads[END_REF]. This model uses, for raw tungsten and recrystallized tungsten, related mechanical properties obtained experimentally at 6 × 10 -3 s -1 of strain rate. 4. Another simulation which aims to analyse the effect of tungsten recrystallization thickness (RXX thickness 4, Fig. 6); assumes 4 mm thickness of recrystallized tungsten on the upper part of the model and uses, for raw tungsten and recrystallized tungsten, related mechanical properties obtained experimentally at 6 × 10 -3 s -1 of strain rate. Conservative 4 mm thickness of the recrystallized tungsten is chosen as it is representative to that observed on the block edge after 300 high heat flux cycles [START_REF] Pintsuk | Characterization of ITER tungsten qualification mock-ups exposed to high cyclic thermal loads[END_REF]. 5. Another simulation which aims to analyse the effect of tungsten recrystallization combined to the effect of strain rate (SR+RXX,) Fig. 6); assumes 4 mm thickness of recrystallized tungsten on the upper part of the model and uses for raw tungsten and recrystallized tungsten related mechanical properties obtained experimentally at 6×10 -1 s -1 of strain rate.

Boundary conditions and thermal loads

For comparison, same thermal loads as M. Li et al. are applied on the block upper surface. Convective boundary condition is applied to the cooling pipe inner surface. Schlosser et al routine [START_REF] Schlosser | Finite elements calculations for plasma facing components[END_REF], is used to calculate heat transfer coefficients taking into account coolant conditions (pressure 3.3 MPa, temperature 120 °C and water velocity 12 m/s). Calculated coefficients are presented in Table 3 and are representative of those given by M. Li et al.

Simulations presented by M. Li et al. in [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF] were reproduced in order to compare M. Li et al. results with the upcoming simulations. As in M. Li et al. model [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF], free nodes displacements are allowed only in the pipe axial direction for pipe surface (surface with chequered pattern, Fig. 5). To obtain consistent results, it was necessary to constrain tungsten by fixing point A (Fig. 5). This boundary condition was used for each upcoming simulation. In realistic condition, tungsten blocks are either mechanically constrained or free at the block bottom surface. In future, simulations should be performed by fixing the whole bottom surface of tungsten block. In this way conservative study will be achieved due to an increase of stress and strain in the tungsten block. Moreover, it is assumed that residual stresses generated in tungsten block during the manufacturing process are fully released over the first thermal cycles.

Finite element results

Temperature field

Thermal loadings at 20 MW/m 2 involve strong temperature gradient in tungsten (1674 °C) on a thickness of 6.5 mm. Indeed, temperature of 2132 °C is reached at the loaded surface and 458 °C is reached at tungsten to Cu-OFHC interface (Fig. 7).

Mechanical response

Maximum plastic strains are expected to be observed in the center of the block where the maximum temperature gradient is located (point B, Fig. 4). Indeed, during experimental campaigns, this region corresponds to macro crack opening location [START_REF] Pintsuk | Characterization of ITER tungsten qualification mock-ups exposed to high cyclic thermal loads[END_REF]. Mechanical model used in simulations stabilized quickly. Indeed, Fig. 8 highlights the evolution of the equivalent plastic strain at point B (Fig. 5) for simulation Ref. After 4 thermal cycles, mechanical response becomes stable. Same quantitative observation is obtained for all performed simulations. Consequently, following mechanical results are the ones obtained at the 5th cycle. Equivalent plastic strain increment (Δε p ) is estimated for each simulation in order to perform lifetime calculations. Δε p corresponds to half of the plastic strain generated over the 5th thermal cycle [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF]. For the different simulations, Δε p is summarized in Table 4. Fig. 9 shows the evolution of plastic strain over the 5th thermal cycle for each simulation.

Raw tungsten

According to transient calculations, Δε p is equal to 0.069% for Fig. 6. Simulations.

Table 3

Representative heat transfer coefficient data used in simulations. simulation Ref and 0.020% for simulation SR (Table 4). These reveal that strain rate has an important effect on the mechanical plastic strain estimation for raw tungsten.

Recrystallized tungsten

Between RXX thickness 4 and M. Li et al. simulations [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF], the only change is the mechanical tungsten behaviors inputs. Comparing Δε p obtained for the RXX thickness 4 simulation (0.585%), with the ones obtained by M. Li et al. [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF] (0.325%.), one can note that use of the actual elastic-plastic behavior of recrystallized tungsten involves important Δε p difference (nearly twice higher). As presented by M. Li et al. [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF], Fig. 9 reveals that tungsten recrystallization thickness play an important role on the evolution of material plastic strain. Indeed, Δε p obtained for Ref simulation is about seven times lower than the one obtained for simulation RXX thickness 2 and about eight times lower than the one obtained for simulation RXX thickness 4. According to Fig. 9, Δε p is equal to 0.585% for RXX thickness 4 simulation and 0.587% for SR+RXX simulation (Table 4). These reveal that, strain rate has marginal effect on the estimation of the equivalent plastic strain increment for recrystallized tungsten.

Discussion on lifetime prediction

In order to optimize the use of plasma facing components in thermonuclear reactors and so ensure the mechanical vacuum chamber integrity over plasma shocks, numerical life time prediction has to be performed. In the literature, experiments are commonly performed to link equivalent plastic strain increments (Δε p ) directly to number of cycles to failure (N f ) [START_REF] Praveen | Effect of heat treatment on Coffin-Manson relationship in LCF of superalloy IN718[END_REF]. Manson-Coffin power law is used to estimate lifetime [START_REF]ITER Material Properties Handbook[END_REF]. Low cycle fatigue data are available for several tungsten grades.

Methodology and data used to compute the component fatigue lifetime referred to the work of M. Li et al. This is based on the observation that the low cycle fatigue lifetime of tungsten at 815 °C is greater than at room temperature. This is usually assumed as a consequence of the Ductile to Brittle Transition Temperature (DBTT). Hence it is considered that low cycle fatigue data at room temperature are relevant to estimate fatigue lifetime below the DBTT and that low cycle fatigue data at 815 °C are relevant above. Here, three Manson-Coffin relations displayed by M. Li et al. [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF] are used. Two of them are given for raw tungsten (stress-relieved) at two different temperatures (23 °C and 815 °C) and the third one is given for recrystallized tungsten (annealed) at 815 °C. Although, these are not corresponding to the studied tungsten grade, these experimental data are used in this paper in order to estimate lifetime. Moreover, to obtain Manson-Coffin relationships, fatigue tests were performed at isothermal temperature. According to Fig. 9 and M. Li et al. [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF], equivalent plastic strain increments obtained for each simulation is generated during transient temperature phase. The use of this low cycle fatigue data is a strong assumption, however, because of the lack of experimental anisothermal data, available isothermal Manson-Coffin relations are used in this paper.

To study the effect of the DBTT on components life time, numbers of

)6 × 1 0 -3 6×10 -1 6×10 -3 6×10 -3 6×10 -1
Δε p (%) 0.069 0.020 0.506 0.585 0.587 Fig. 9. Evolution temperature and equivalent plastic strain occurring for each simulation at the 5th thermal cycle at point B.

cycles to failure calculations are performed at two different DBTTs (350 °C and 500 °C) [START_REF] Reiser | Tungsten foil laminate for structural divertor applicationstensile test properties of tungsten foil[END_REF][START_REF] Farre | Étude de la transition fragile-ductile d' un tungstène[END_REF]. In this manner, part of Δε p generated above the DBTT are used to estimate number of cycles to failure (N 2 ) with the related Manson-Coffin relations obtained at 815 °C (annealed for recrystallized and stress relieved for raw tungsten) and the part of Δε p generated below the DBTT will be used to estimate number of cycles to failure (N 1 ) with the Manson-coffin relation obtained at 23 °C. Then, thanks to the following relation (equation ( 4)), related N 1 and N 2 are used to estimate final number of cycles to failure (N f ) [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF]:

=+ NN 1 Nf 1 1 1 2 (4)
For simulations RXX thickness 2, RXX thickness 4 and SR+RXX, Fig. 9 shows that during transient (heating and cooling) phases, part of Δε p appears below DBTTs. This can be explained due to the use of low yield stresses for recrystallized tungsten. Recrystallized tungsten low yield stresses promote plasticity in the tungsten block. Plastic strain are involved throughout the thermal cycle at equivalent amplitude during the heating and the cooling phase leading to 98% released of plastic strain at the end of the thermal cycle. On the other hand, no plastic strain occurs below DBTTs during the heating phase for Ref and SR simulations. This reveals that quantitatively, cooling phase has stronger impact on the monoblock damage process. Off-set and time delays observed for simulations Ref and SR are explained by the use of high yield stresses of the raw tungsten.

Table 5 and Table 6 summarize related numbers of cycles to failure obtained for each simulation. Component lifetime is drastically reduced due to recrystallization. Also, tungsten thickness recrystallized layer play a role on the component life time. In this way, recrystallization phenomenon will be investigated further in the future to better define and model this phenomenon. Besides, Table 5 and Table 6 reveal an effect of DBTT on components lifetime for simulations providing important Δε p . Indeed, for the simulation RXX thickness 2, component life time reduces significantly from 390 to 52 cycles. In future, the actual DBTT of rolled tungsten should be consequently accurately defined.

In the past, high heat flux experimental campaigns achieved and revealed that macro crack appears in tungsten block after a few tens (up to a few hundreds) of thermal cycles depending on tungsten supplier, geometry (width, tungsten thickness), and experimental coolant conditions [START_REF] Hirai | Status of technology R&D for the ITER tungsten divertor monoblock[END_REF]. Although numerical model used in this paper are not exactly corresponding to the experimental cases presented in [START_REF] Hirai | Status of technology R&D for the ITER tungsten divertor monoblock[END_REF], number of cycles to failure (N f ) obtained in upcoming calculations are compared. In the case of RXX thickness 2, calculated number of cycles to failure is consistent to the one observed experimentally for the same recrystallized layer condition at the center of the block [START_REF] Pintsuk | Characterization of ITER tungsten qualification mock-ups exposed to high cyclic thermal loads[END_REF]. Preliminary study is performed in this paper to highlight the effect of tungsten recrystallization and tungsten viscoplasticity on lifetime estimation. Simulations are performed assuming (or not) recrystallized tungsten layer on the upper part of the block and using mechanical property obtained either at 6 × 10 -3 s -1 or 6 × 10 -1 s -1 . According to M. Li et al. [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF], the state of the material (recrystallized or raw material) plays a major role on the equivalent plastic strain increment. Regarding strain rate effect, the smaller the equivalent plastic strain increment, the higher the strain rate influence. Future simulations should be performed using dedicated mechanical model able to account for tungsten recrystallization and actual elastic-viscoplastic behavior of raw tungsten and recrystallized tungsten, even though tungsten viscoplasticity would have a marginal effect.

Conclusion

This paper proposes to estimate tungsten armoured component life time taking into account actual mechanical behavior of raw and recrystallized tungsten. For that, compressive tests were performed at several temperatures from 500 °C to 1150 °C and at several strain rates from 6×10 -1 s -1 to 6 × 10 -3 s -1 . Raw tungsten tests reveal an elastic-plastic behavior that is sensitive to strain rate. Concerning recrystallized tungsten, it showed an elastic-viscoplastic behavior on the entire explored temperature range. This behavior was described by an elastic-plastic model with kinematic hardening constitutive relation in the modeling. Up to now, in the literature, mechanical behavior of tungsten and recrystallized tungsten were assumed as linear elastic and ideal-plastic using mechanical data displayed in [START_REF]ITER Structural Design Criteria for In-vessel Components (SDC-IC) Appendix[END_REF]. Using mechanical behaviors experimentally obtained which are implemented in finite element modeling simulations; it shows that higher numbers of cycles to failure are obtained compared to previous simulations performed by M. Li et al. [START_REF] Li | Interpretation of the deep cracking phenomenon of tungsten monoblock targets observed in high-heat-flux fatigue tests at 20 MW/m 2[END_REF]. Moreover, simulations reveal that: recrystallization phenomenon and DBTT have major effect on the component life time whereas strain rate has marginal effect. Also, consistent life time estimations were obtained compared to the one observed experimentally in literature even if the exact boundary conditions (geometry, heat loading, cooling) are not exactly the same as the one which were simulated. These observations highlight that in the future, more accurate estimations could be performed by using dedicated mechanical model capable of taking into account the actual behavior of tungsten and modeling tungsten recrystallization phenomenon under thermal loadings.

Fig. 1 .Fig. 2 .

 12 Fig. 1. Compressive test device.

Fig. 3 .

 3 Fig. 3. Stress-strain curves obtained on raw tungsten at 500 °C at 6 × 10 -3 s -1 and 1150 °C obtained at 6 × 10 -3 s -1 and 6 × 10 -1 s -1 .

Fig. 5 .

 5 Fig. 5. Numerical model.

Fig. 7 .Fig. 8 .

 78 Fig. 7. Tungsten temperature at 20 MW/m 2 .

Table 2

 2 Material properties.

	Material	Temperature	Strain rate	Yield stress at	Tangent modulus
		(°C)	(s -1 )	0.2% (MPa)	(MPa)
	Raw tungsten	500	6 × 10 -3	559	0
			6×10 -1	678	0
		1150	6 × 10 -3	426	0
			6×10 -1	459	0
	Recrystallized	500	6 × 10 -3	61	5913
			6×10 -1	46	9618
	Tungsten	1150	6 × 10 -3	49	3906
			6×10 -1	58	4985

Table 4

 4 Equivalent plastic strain increments (Δε p ) obtained for each simulation after 5th thermal cycle.

	Ref	SR	RXX	RXX	SR
			thickness 2 thickness 4 +RXX
	Strain rate (s -1

Acknowledgements

The authors express their deep gratitude to Séverine Girard who performed compressive tests at Ecole Nationale Supérieure des Mines de Saint-Etienne. This work has received CEA funding from the "Programme Transverse de Compétence, Matériaux et Procédés" (PTC-MP). This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under Grant Agreement No. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Δε p < 500 : part of Δε p which appeared bellow the DBTT (%) fixed at 500 °C. N 1 < 500 : number of cycles to failure obtained below the DBTT fixed at 500 °C. N 2 > 500 : number of cycles to failure obtained above the DBTT fixed at 500 °C. N f500 : final life time estimation assuming DBTT at 500 °C.


Philippe Lagacherie
email: philippe.lagacherie@supagro.inra.fr

Jorge Álvaro-Fuentes

Mohamed Annabi Martial

Bernoux Sami

Bouarfa Abdelkader Douaoui

Olivier Grünberger

Ali Hammani

Luca Montanarella

Rachid Mrabet

Mohamed Sabir

Damien Raclot

Mohamed Annabi

Martial Bernoux

Sami

Abdelkader Douaoui

Mrabet

Mohammed Sabir

Managing Mediterranean Soil Resources Under Global Change: Expected trends and mitigation strategies

Keywords: Soil, Erosion, carbon, Salinization, Climate Change Soil, erosion, carbon, salinization, climate change

The soils of the Mediterranean basin are the products of soil processes that have been governed by a unique convergence of highly differentiated natural and anthropogenic drivers. These soils are expected to be dramatically affected by future climate and societal changes. These changes imply that suitable adaptive management strategies for these resources cannot simply be transposed from experiments that are performed in other regions of the world. Following a framework that considers the chain of "drivers -soil process -soil capital -Ecosystem Services/Disservices" the paper review the research undertaken in the Mediterranean area on three types of Mediterranean soil degradation than can be expected under Global Change i) soil losses due to the increase of drought and torrential rainfall, ii) soil salinization due the increase of droughts, irrigation and sea level and iii) soil carbon stocks depletion with the increase of temperature and droughts. The possible strategies for mitigating each of these degradations have been

largely addressed and are still studied in current research projects. They should include changes in agricultural practices, soil-water management and vegetal material. As a pre-requisite for the site-specific adaptations of such mitigation strategies within viable Mediterranean agro-systems, it is highlighted that methodological advances are necessary in integrated assessment of agricultural systems and in finer resolution soil mapping.

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Author Comments: Following the editor-in chief's requests, the title, the abstract and the figures have been modified. Minor changes in the text and in the reference list (including adding doi) have been performed. Along with its water, coastlines and biodiversity, soils constitute one of the Mediterranean basin's 64 vulnerable natural resources. Their productivity enhancement and the care given to their 65 conservation and management have been a big contributor to the spread of successive past 66 civilisations. By contrast, their degradation has been a cause of crisis and constant decline in the 67 past and has inflicted a high cost on most of its countries (World Bank, 2010). Even today, soil 68 degradation in its various forms constitutes a significant threat to the future of the Mediterranean 69 basin [START_REF] De Franchis | Threats to Soils in Mediterranean Countries[END_REF][START_REF] Lahmar R Ruellan | Dégradation des sols et stratégies coopératives en Méditerranée : la pression sur les ressources naturelles et les stratégies de développement durable[END_REF]. 70

The Mediterranean basin hosts a unique combination of soil-forming factors, climate conditions, 71 parent material and reliefs [START_REF] Yaalon | Soils in the Mediterranean region: what makes them different?[END_REF][START_REF] Ryan | Drylands of the Mediterranean Zone: Biophysical Resources and Cropping Systems[END_REF]. Furthermore, Mediterranean soils have 72 been heavily impacted, if not built, by the most ancient agriculture in the world (De Franchis and 73 Ibanez, 2003). This impact makes the Mediterranean soils and soil patterns very different from 74 other regions of the world.

75

The Mediterranean basin is also a global change hotspot. Most general circulation models forecast 76 drastic changes in temperatures and rainfall regimes for this area (Dubrovsky et al, 2014). Some of 77 these changes have been observed recently [START_REF] Lionello | The climate of the Mediterranean region: research progress and climate change impacts[END_REF]. In addition, increasing population 78 and market pressures have induced important land use changes (García-Ruiz et al, 1996;Sluiter et 79 De Jong, 2007) that could become even greater in the future (IPCC, 2014). 80

Both the Mediterranean's soil peculiarities and its strong regional dynamic relations with global 81 change imply that suitable adaptive managing strategies for Mediterranean soil resources cannot be 82 simply transposed from experiments that were performed in other regions of the world. Instead, 83

research should be performed on strategies that specifically address Mediterranean soil conditions. 84

In this paper, a multidisciplinary group of soil scientists reviews the current research on managing 85

Mediterranean soil resources through a common framework [START_REF] Dominati | A framework for classifying and quantifying the natural capital and ecosystem services of soils[END_REF], highlighting the 86 primary challenges that should be faced to conserve the ability of these resources to provide their 87 expected services. 88 89 90

Specificities of Mediterranean soil resources 91 92

The soils of the Mediterranean region are products of soil processes that have been governed by a 93 unique convergence of highly differentiated natural drivers (climate, relief, and parent material) and 94 strong historic human activity. These drivers have provided some remarkable characteristics to the 95

Mediterranean soil cover that are highlighted in the following section. We use in the following the 96 World Reference Base for Soil Resources terminology and classification system (IUSS Working , 2005[START_REF] Jones | Soil Atlas of Africa[END_REF][START_REF] Zdruli | Soils of the Mediterranean Region, Their Characteristics, Management and Sustainable Use[END_REF]. These characteristics reflect the natural 102 predominance of erosion processes, which are enhanced by the conjunction of i) a marked relief in 103 which 45% of the areas have slopes greater than 8% because of active tectonics at the contact of the African and Eurasian plates [START_REF] De Franchis | Threats to Soils in Mediterranean Countries[END_REF], ii) the high frequency of very intense rainfall events (> 100 mm/h) during the autumn and winter seasons and iii) lesser protection by vegetation against erosion because of the severe summer droughts, burning, overgrazing and deforestation that reduce the vegetation coverage (García Ruiz et al, 2013). The evolution towards shallow soils is often counterbalanced by human practices such as terracing in hilly areas [START_REF] Tarolli | Terraced landscapes: From an old best practice to a potential hazard for soil degradation due to land abandonment[END_REF]. Conversely, farming is known to greatly accelerate the erosion rates relative to soil production (Amundson et al, 2015), particularly when cultivated fields replaced the natural vegetation that was originally dominated by Mediterranean scrublands and forests. Finally, shallow and skeletal soils in Mediterranean landscapes are often closely associated with Cambisols -youngaged soils-that have formed on the downhill colluvium of eroded material and represent large areas in this region too.

Soil carbon contents

Mediterranean soils have not been consciously managed to store or sequester carbon. Hence, most of these soils exhibit low to very low soil organic carbon (SOC) contents. This information is particularly well-documented for the European countries in the Mediterranean basin [START_REF] Jones | Estimating organic carbon in the soils of Europe for policy support[END_REF][START_REF] Zdruli | Organic Matter in the Soils of Southern Europe[END_REF]. For countries along the southern side of the Mediterranean sea, [START_REF] Henry | Soil carbon stocks in ecoregions of Africa[END_REF] calculated a mean SOC content of 1.1% in the top 0-30 cm for the North Africa region, with mean national SOC values ranging from 0.67-0.79% for Morocco, Tunisia, Algeria and Egypt. National-scale studies have confirmed those values, e.g., for Tunisia, [START_REF] Brahim | Pedotransfer functions to estimate soil bulk density for Northern Africa: Tunisia case[END_REF] organized a soil database with 238 soil profiles corresponding to 707 soil horizons. The authors reported that the mean and median SOC contents of the top-soils (depth < 40 cm, 249 horizons) were 1.17% and 0.86%, respectively. Limited SOC content is the result of several biotic and abiotic processes and factors, with climate and management being the two most influential factors in the Mediterranean region. Rainfall shortage limits the net primary productivity, and, in turn, soil C buildup. Low C inputs driven by limited soil moisture availability are exacerbated by the adoption of certain management practices. Crop residue competition for livestock feeding or the introduction of long fallowing in the crop rotation are two examples of typical management practices in the Mediterranean region that have contributed to the reduction of C inputs that are returned to the soil. In addition to decreases in C inputs, agricultural management may also boost SOC losses. In the Mediterranean region, the use of intensive deep-tillage implements (e.g., mouldboard ploughing) has been a common practice for centuries. Inversion tillage generates favourable soil conditions for microbial activity (i.e., it homogenizes the moisture content along the soil profile, favours soil oxygenation and incorporates crop residues into the soil), thus accelerating soil organic matter mineralization and loss. Another important consideration is that those soils usually contain an important amount of inorganic carbon, most of which is present as carbonates as a result of the dissolution of calcareous parent material by winter rainfalls and precipitation during dry summer periods [START_REF] Yaalon | Soils in the Mediterranean region: what makes them different?[END_REF]. This composition results in soils with calcareous material accumulations in their profiles (Calcisols, Kastanozem), which are more frequent in the Mediterranean basin than everywhere else in the world [START_REF] Ryan | Drylands of the Mediterranean Zone: Biophysical Resources and Cropping Systems[END_REF]. However, there have been few investigations concerning the short-term pattern of inorganic C stocks because of complex interactions and balances between atmospheric C and organic and inorganic forms of soil C [START_REF] Bernoux | The effect of soil drying on humus decomposition and nitrogen availability[END_REF].

Irrigation and salinity

The Mediterranean basin is also characterized by a large surface of irrigated soils, usually in the flat areas. In the Near East/North Africa countries, the irrigated area is estimated by the FAO to be 31 million hectares (2012). This figure does not take the north side of the Mediterranean into account. The International Commission of Irrigation and Drainage estimates a lower area of 25 Mha for all Mediterranean countries that are equipped with irrigation systems (ICID, 2014). This difference is likely linked to informal (and private) groundwater irrigation and small-scale irrigation systems. Irrigated soils are prone to secondary salinization (or human-induced salinization) related to imbalances in the soil salt budget. Human-induced salinization is as old as irrigation. Salinization forced the early settlers of Mesopotamia, the Indus river basin and China to abandon their land [START_REF] Ghassemi | Salinisation of land and water resources: human causes, extent, management and case studies 544[END_REF]. More than fifty years ago, modern states promoted the development of irrigation, primarily for orchards and fruit production. The primary model of irrigation development was based on large irrigation schemes using water stored in large and medium dams. These systems generally faced water management problems (water supply-demand coordination issues and inefficient water transport and field application), leading to a rise in groundwater levels and to the so-called twin menace of "waterlogging and salinity" (Bouarfa and Kuper, 2012). Despite this wellknown challenge, there is still no accurate estimation of how the corresponding soils were affected by secondary salinization in irrigated areas. [START_REF] Paranychianakis | Irrigation of Mediterranean crops with saline water: from physiology to management practices[END_REF] estimated that salinization in the Mediterranean basin is a serious problem with some 16 million ha out of 74 million ha of today irrigated lands, under the assumption that the ratio of 25% of salt affected soils of irrigated areas soils in 1974 put forward by [START_REF] Szabolcs | Salt-affected soils[END_REF] is still valid in spite of progresses in irrigation techniques. For example, salinization occurs in most Moroccan irrigated systems. The available data on salinity indicates that approximately 500.000 ha that are located primarily in the command areas are threatened by salinity (Dahan et al, 2012).

Spatial soil patterns

Apart from the above-evoked characteristics, Mediterranean soil cover is also remarkable for the occurrence of extremely complex soil patterns with large short-scale and anisotropic variations caused by the rapid successions of contrasting parent materials, erosion and re-deposition of soil material within short distances and the long-term impacts of human practices. Many detailed studies across this region have revealed such complex patterns (e.g., [START_REF] Pardini | Distribution Patterns of Soil Properties in a Rural Mediterranean Area in Northeastern Spain[END_REF][START_REF] Gomez | Using Vis-NIR hyperspectral data to map topsoil properties over bare soils in the Cap-Bon Region, Tunisia[END_REF]…). It is worth noting that the existing soil data in the Mediterranean area are available at a spatial resolution that is much too coarse for mapping such complex patterns. The most recent review on the data available for Mediterranean soils was compiled by the European Commission [START_REF] Yigini | Soil resources of Mediterranean and Caucasian countries[END_REF]. It updates the previous assessment that was completed within the Soil Atlas of Europe (European Soil Bureau Network, 2005). A large amount of additional information was collected by the EU-funded project MedCoastLand [START_REF] Zdruli | The EU-funded MEDCOASTLAND Thematic Network and its Findings in Combating Land Degradation in the Mediterranean region[END_REF]. The harmonisation of national soil surveys allowed for the production of the European Soil database (EUSIS) at 1:1,000,000, further extending among other countries to those of the southern part of the Mediterranean Basin. Few Mediterranean countries have developed their own national database at a larger scale than 1:1,000,000. Some 1:250,000-scale soil databases are available in Italy (http://eusoils.jrc.ec.europa.eu/library/data/250000/Italy.htm), Albania [START_REF] Zdruli | Soil surveys in Albania[END_REF], Lebanon (Darwich, T., 2008) and Mediterranean France [START_REF] Bornand | Les banques régionales de données-sols. Exemple du Languedoc-Roussillon[END_REF]. Larger-scale soil maps cover entire or at least substantial portions of Mediterranean countries. Israel (Crouvi et al, 2013), southern Portugal [START_REF] Goncalves | Progress of soil survey in Portugal[END_REF], and the coastal part of Albania [START_REF] Zdruli | Soil surveys in Albania[END_REF] are covered by a 1:50,000-soil map. Complete coverage at 1:25,000 and 1:100,000 exists for Bulgaria and Turkey, respectively. Badraoui and Stitou (2001) have developed a comprehensive report on the availability of soil information and maps in Morocco. Finally, there have been many local surveys in most countries at various scales that are hard to locate and describe, with the notable exception of Tunisia, for which a database of scanned soil survey reports (BEST) has been developed (Derouiche, 2011, pers. communication).

Analysing the future of Mediterranean soil resources under global change

The latest Global Change Model projections (Dubrovsky et al, 2013) have indicated the presence of clear climate change in the Mediterranean area. The results show an increase in temperature during all seasons and for all parts of the Mediterranean with good inter-model agreement. The precipitation is projected, with a lower degree of model agreement, to decrease in all parts and all seasons (most significantly during the summer), except for the northernmost parts in winter. Furthermore, increased mean daily precipitation sums on wet days are expected for some seasons, and some parts of the Mediterranean, which may imply higher daily precipitation extremes. A decreased probability of wet day occurrence will imply longer drought spells all across the Mediterranean. All these projections converge towards an even more aggressive climate that may highly impact Mediterranean soils. In addition, the demographic projections indicate a less-than-expected but still clear increase in the population of the Mediterranean area with a total population of 500 million inhabitants in 2010 that is expected to reach 563 million inhabitants by 2025 [START_REF] Carella | Demographic trends and challenges in the Mediterranean[END_REF]. This increase will primarily concern urban and coastal areas, and the population of rural areas will remain stable. This change will lead to reconfigurations of national spaces into a mosaic of mushroom cities and rural areas (ARP Parme, 2011). The two above-evoked trends will work together to substantially increase the pressure on Mediterranean soil resources, i.e., producing more on less arable lands that have been depleted by urbanization.

In the following section, the future of Mediterranean soil resources is examined by considering the expected impacts of the trends evoked above and by exploring the most promising levers that humans can use to counterbalance the negative impacts. For that reason, we followed the holistic soil assessment approach proposed by [START_REF] Dominati | A framework for classifying and quantifying the natural capital and ecosystem services of soils[END_REF] by considering the chains of "drivers soil processsoil capital -Ecosystem Services/Disservices". The central concept is soil capital, which is defined as the stocks of natural and human-added assets in soils that yield a flow of valuable ecosystem goods or services. This soil capital can be described through a list of measurable soil properties (e.g., soil carbon stocks or available water capacity). The soil capital is included in a broader chain that considers i) the upstream processes governing the soil capital formation, maintenance and degradation and their associated natural and human drivers and ii) the downstream soil ecosystem services, with beneficial flows arising from soil capital stocks and fulfilling human needs and dis-services and adverse changes in soil capital leading to a loss of ecosystem services. The processes are themselves impacted by a set of drivers among which one can distinguishes the actual observable trends and the mitigation strategies that could alleviate and even delete the impacts of trends. We chose to select three challenging issues that deserve attention to address the future of these Mediterranean resources. Our analyses are summarized in figures 2, 3 and 4. The scientific background supporting these figures and the related research proposals are developed hereafter.

Mitigating soil losses

Insert figure 1 here According to the trend scenario, climate change is expected to increase water erosion processes, which will in turn diminish the tonnage of available soil (Figure 2). This loss of soil depth has direct and obvious on-site effects relating to agricultural production including losses of plant nutrients, soil water reserves, and alterations in soil properties [START_REF] Lal | Soil Erosion Impact on Agronomic Productivity and Environment Quality[END_REF]. It also has an off-site effect related to water reservoir siltation. In fact, reservoir siltation represents a major issue for water resource management strategies in the Mediterranean basin, especially in North African and eastern Mediterranean countries (Ayadi et al., 2010). Higher sediment yields (SYs) were reported in this environment than the yields for many other regions across the world [START_REF] Woodward | Patterns of erosion and suspended sediment yield in Mediterranean river basins[END_REF][START_REF] Vanmaercke | Sediment yield in Europe: spatial patterns and scale dependency[END_REF]. In the Mediterranean area, and especially in European Mediterranean countries, the sheet and rill erosion rates that are measured at the plot scale are generally lower than the sediment yields [START_REF] Cerdan | Rates and spatial variations of soil erosion in Europe: a study based on erosion plot data[END_REF][START_REF] Vanmaercke | A comparison of measured catchment sediment yields with measured and predicted hillslope erosion rates in Europe[END_REF]. This finding was explained by the large fraction of rock fragments at the topsoil and by the importance of erosion processes that are not active at the plot scale, such as gully erosion, landslides and riverbank erosion. More generally, gullies and especially badlands were often identified as the primary sources of sediment responsible for reservoir siltation in Mediterranean environments (Heush, 1970;[START_REF] Vente | Predicting catchment sediment yield in Mediterranean environments: the importance of sediment sources and connectivity in Italian drainage basins[END_REF]2008;Poesen et al., 2003;[START_REF] Simmoneaux | Land use and climate change effects on soil erosion in a semi-arid mountainous watershed (High Atlas, Morocco)[END_REF], even if a recent fingerprinting study showed that gully erosion was the predominant sediment source for only 2 of 5 small Tunisian catchments [START_REF] Slimane | Relative contribution of surface and subsurface erosion to reservoir siltation in Tunisia[END_REF]. It is noteworthy that water erosion is considered the most active process that induces soil losses [START_REF] Govers | Scratching the critical zone: the global footprint of agricultural soil erosion[END_REF], which explains why tillage or wind erosion effects are less frequently measured in the Mediterranean context. The expected effect of climate change is two-fold. First, by increasing the intensity of the largest events, an increase in the rainfall intensities or amounts will likely increase water erosion. In this specific Mediterranean context, [START_REF] Luis | A review of daily soil erosion in Western Mediterranean areas[END_REF] showed that the high dependence of soil erosion with the most intense rainfall events because the three highest daily erosive events represented more than 50% of the annual eroded soil. Secondly, increasing droughts may induce decreased vegetation cover, which will have negative effects on soil losses and silting up because vegetation cover is one of the key factors in erosion control [START_REF] Wischmeier | Estimating the soil loss equation's cover and management factor for undisturbed area. In Present and prospective technology for predicting sediment yields and sources[END_REF][START_REF] Morgan | Soil Erosion and Conservation[END_REF]. However, mitigation strategies for counterbalancing this negative trend are possible. Mediterranean civilizations successively developed or improved a large range of Soil and Water Conservation (SWC) techniques to improve water conservation and management, increase agriculture production and reduce soil erosion (Figure 2). These techniques are primarily based on slope correction/water velocity reduction (i.e., bench terraces), increasing the ground cover (i.e., cover crop, mulching, permanent cover using tree/crop associations), and/or soil quality improvement (i.e., amendments). Recently, SWC has been broadened toward sustainable land management or conservation agriculture, fostering less soil disturbance, the retention of crop residue, and continuous ground cover, which have been shown to decrease erosion in comparison with conventional agriculture based on deep tillage [START_REF] Mrabet | Conservation agriculture in dry areas of Morocco[END_REF]. The efficiency of conservation agriculture at improving soil water storage is well-recognized in the Mediterranean basin [START_REF] Mrabet | No-tillage agriculture in West Asia & North Africa[END_REF][START_REF] Moreno F Arrúe | Conservation Agriculture Under Mediterranean Conditions in Spain[END_REF][START_REF] Moussa-Machraoui | Comparative effects of conventional and no-tillage management on some soil properties under Mediterranean semi-arid conditions in north-western Tunisia[END_REF]. Studies that were conducted on inter-row crops such as olive groves (Francia [START_REF] Martínez | Environmental impact from mountainous olive orchards under different soil-management systems (SE Spain)[END_REF][START_REF] Gómez | Soil management effects on runoff, erosion and soil properties in an olive grove of Southern Spain[END_REF] or vineyards (Paroissien et al., 2015) also supported the recommendation for non-inter-row tillage and for maintaining a high inter-row vegetation cover with a cover crop or grass cover. However, all these techniques have been introduced so far with varying degrees of success, depending on the environmental and societal contexts (García-Ruiz, 2013, De Graaf et al., 2013). Maintaining a continuous land cover may for instance have positive impacts on soil protection and negative impacts on production because of water competition in the semi-arid context [START_REF] Marques | Soil conservation beneath grass cover in hillside vineyards under Mediterranean Climatic conditions (Madrid, Spain)[END_REF].

The primary scientific issues that are used to help define adaptation strategies for the Mediterranean area are summarized below. First, there is a need to better understand the spatiotemporal variability of Mediterranean catchment erosion behaviour in terms of sediment sources, active erosion processes and transport efficiency from sediment sources to downstream reservoirs. Promising recent methodological developments are based on the use of fingerprinting techniques or the repetitive acquisition of fine digital elevation models that enable diachronic analysis. European or Mediterranean networking initiatives by scientists and long-term erosion monitored catchments such as the R_Osmed network (https://sites.google.com/site/rosmedsicmed/home/introduction) or COST initiative (http://www.cost.eu/COST_Actions/essem/ES1306) will also help us better understand this variability in relation to the specific role of major/extreme events in catchment sediment yields or in the role of sedimentological connectivity.

A second set of research actions must be dedicated to studies of the past of the Mediterranean basin through a review of the large range of adaptation techniques used in this region and a comparison of their evaluations in terms of soil protection efficiency and acceptability by the farmers as it will be investigated in the forthcoming MASCC project (Mediterranean Agricultural Soils Conservation under global Change). The implementation of these adaptation techniques within spatially explicit numerical models devoted to the Mediterranean environment is also a requirement that can help managers to plan the type, number and location of adaptation techniques to implement within a catchment or a watershed for present and future conditions (Gumière et al., 2014). The last set of necessary actions consists in improving our knowledge of future conditions to anticipate efficient adaptation techniques. Because of the stormy nature of major events in the Mediterranean context, we still need to improve the predictions of sub-daily rainfall characteristic predictions as hourly rainfall intensities. Feedback between climate change and land use change are also critical for adaptation strategy planning, especially in the Mediterranean context, where vegetation cover is a major lever for soil protection.

Avoiding secondary salinization

Insert figure 2 here According to the trend scenario, increasing drought and sea level rise and the spread of irrigation in combination with changes in irrigation techniques are expected to reinforce salinization processes and to deplete soil leaching, which will in turn increase the Na and Cl contents of soils and degrade soil structures (Figure 3). Crop production will be affected when the salinity exceeds the threshold values that depend on each crop's sensitivity during critical stages. Most of the plants suffer yield or biomass production decreases when the soil salinity exceeds 4 ds m -1 , which represents the limit for defining soils with salinity issues. Osmotic stress is the primary process that is involved with effects similar to drought and freezing; plants face difficulties when extracting water from the root zone. Secondary effects are brought on by toxicity from Na and Cl and from deficiencies of other elements such as Ca, K, Zn, etc. All the functions and cycles of a plant can be affected. Another effect comes from the exposure of saline soil to changes in the primary ion on the adsorbed phase to Na + . Afterwards, if the salinity decreases, for instance in the case of remediation, then clay may disperse, ruining the soil structure, hampering drainage and triggering reduction. In landscapes, each upstream area delivers a water supply to downstream ecosystems, and this flow is considered an essential "ecoservice". When salinity increases in the soil of inland fields, leaching may provide salinity to downstream and neighbouring systems through runoff, drainage or underground contamination, fuelling the extension of salinity problems at the landscape scale. In the near future, rising sea levels will increase the salinity pressure on coastal soils and aquifers, but the primary effect is expected from the increase in droughts in Mediterranean countries, which will accentuate irrigation needs. This increase may even be reinforced by the expected needs of agricultural intensifications (see the introduction of this section). For the time being, only a few trials have been performed to simulate increased soil salinity ahead of climatic scenarios in irrigated lands. Preliminary results were obtained [START_REF] De | Prediction of the effects of climate change on the soil salinity of an irrigated area under Mediterranean conditions[END_REF] by modelling the fate of salinity in southern Alicante (Spain), which is cultivated for citrus and legumes. Climate change is creating an enlargement trend in the soil surface that is affected by salinity, from 19% to 34%. Investigators indicate that this effect could be mitigated by a 20% increase in the present irrigation rate. It is feared that salinization issues in the region will reinforce the direct effect of climate change. Furthermore, this trend will be significantly reinforced by the recent evolution of irrigated agriculture techniques. First, groundwater has become increasingly important for irrigation. At present, of the 300 million ha of irrigated land in the world, some 110 million now depend on groundwater, which represents 25% of the total irrigation water (Siebert et al., 2010). The Mediterranean countries are no exception. In North African countries, groundwater has been responsible for the redesign of irrigation frontiers, and it covers over 60% of the total irrigated area, supplying more than 500,000 farms with irrigation water (Kuper et al., 2015). After being perceived as a threat, groundwater gradually became a cherished resource. Salinity issues and solutions also changed in nature because they are not linked to waterlogging problems but are primarily related to the water quality of groundwater. In particular, the depletion of inland groundwater has led farmers to pump from deeper and older geological layers, which are sometimes affected by a natural geological salinity, and in coastal plains, the salinization of aquifers occurs through sea intrusion, threatening some of the most productive irrigated soils. Secondly, the water-saving policies used in several Mediterranean countries largely depend on the generalization of drip irrigation technologies instead of traditional surface irrigation techniques. As a result, the area in Mediterranean countries under drip irrigation has significantly increased in recent years. For example, according to the Moroccan ministry of agriculture [START_REF] Bennouniche | Une innovation technique en train de se faire : le goutte à goutte en pratique au Maroc : acteurs, bricolages et efficiences[END_REF], the area equipped with drip irrigation has increased from less than 100,000 ha in 2000 to 360,000 ha in 2013. The aim of this modernization is to "save water" by increasing the irrigation efficiency according to the phrase, "more crop per drop". However, it is important to note that drip technique benefits related to efficiency will increase with the water volume and can be used at the expense of the proper soil leaching fraction that is required to remove excess salts. The secondary salinization process is partially linked to natural conditions but is also under the control of farmer practices at the field level and water management at the irrigation scheme level, which offers opportunities to undertake mitigation strategies for counterbalancing the above-evoked soil degradation (Figure 3). Secondary salinization depends on the salt budget at the field level as related to farmer irrigation practices, and the leaching processes that they implement depend on farmer perceptions of the problem [START_REF] Bouarfa | Salinity patterns in irrigation systems, a threat to be demystified, a constraint to be managed: Field evidence from Algeria and Tunisia[END_REF]. Salinization is also linked to water management and artificial drainage facilities at a larger scale to avoid waterlogging and the salinization of soils by capillary rise (FAO, 1994). It is thus important to re-engage in research to address secondary salinity issues in a renewable fashion. At present, research efforts in the Mediterranean basin are mostly dedicated to employing effective Integrative Water Resources Management (IWRM) at regional scales (100 km 2 or more), and they mostly consider water volume aspects. Water salinity constrains are often neglected during modelling, which indicates the difficulty in assessing the complexity generated by the behaviour of a particular soil interface under the influence of the individual agricultural practices of irrigation and amendment. The salinity of soil and water should therefore be quantified as a primary constraint to effective IWRM, and it should be considered important for resource volume conservation objectives. In this sense, more research is needed to test the resilience and acceptability of agrosystems with low irrigation rates as general soil salinity problems increase. Another issue is that scientific studies are often solicited for situations in which severe salinity problems have already been identified by the farmers (e.g., obvious soil salinity crusting, and/or dramatic yield decreases). Therefore, because most past studies focused on severe salinization situations, they are likely to present rough representations of the processes that may be inadequate for modelling large time scales with good accuracy. Therefore, the research should focus on ways to identify discrete evidence of early salinization that would allow for under-threshold management and/or accurate modelling of the long-term soil fate with respect to salinity.

Maintaining Soil Carbon stocks

Insert figure 3 here According to the trend scenario, climate change may further diminish the soil organic carbon content of the Mediterranean area (Figure 4). As SOC is also the primary constituent of soil organic matter (SOM), representing approximately 50% of its weight (Pribyl, 2010). Thus, SOC is also often an indicator of soil fertility in environmental services. The loss of SOM and therefore of SOC especially when initial levels are low, as in dryland regions, results in the degradation of soils and their associated agronomic and environmental functions and services [START_REF] Lal | Soil carbon sequestration impacts on global climate change and food security[END_REF]. Figure 4 represents global reported tendencies encountered in the literature, however it should be highlighted that some models and studies predict increasing SOC under certain management practices and predicted climate change conditions, as in Álvaro-Fuentes et al. (2012). Moreover, mineralization depends not only on temperature but also on moisture regime, and, whereas the behaviour of the temperature driver is well established toward an increase, it is less consensual concerning the precipitation regime both in quantity and distribution annually. Therefore, uncertainties are still high as illustrated in the example below Few studies have addressed the impact of future climate change in Mediterranean regions. [START_REF] Hamdi | Short-term temperature dependence of heterotrophic soil respiration after one-month of preincubation at different temperatures[END_REF] designed a study to examine an agricultural soil from northern Tunisia to investigate the effects of temperature variations of up to 50°C on soil respiration and (ii) to test the effect of further organic carbon additions. The results do not support an important increase in soil respiration sensitivity to temperatures ranging from 20-40°C. Only at 50°C, such as during a heat wave, was there a significant increase in the water-soluble carbon, which was likely related to either dead microbial cells or SOC solubilization. Overall, the results indicate a moderate response in the soil respiration to high temperatures, as shown by the Q10 value that was close to 1.7, even from 40°C-50°C, illustrating the need to be cautious when using a mechanistic model such as Roth C based on a Q10 higher than 2. Indeed, a review analysis by [START_REF] Hamdi | Synthesis analysis of the temperature sensitivity of soil respiration from laboratory studies in relation to incubation methods and soil conditions[END_REF] collected and calculated Q10 values from incubations of 253 unique soils from 63 published studies. The authors encountered a large variability of observed temperature sensitivities of SOC dynamics, with a mean value of 2.04 , but with a standard deviation of 1.09 and a median of 1.85. Moreover, the authors showed that this variability is still largely unexplained. Another important aspect of CC is related to water availability. The drying and wetting of Mediterranean soils was shown to stimulate SOM decomposition and carbon dioxide emission. This effect is known as the "Birch effect" [START_REF] Bernoux | The effect of soil drying on humus decomposition and nitrogen availability[END_REF]. [START_REF] Yemadje | Effect of biomass management regimes and wetting-drying cycles on soil carbon mineralization in a Sudano-Sahelian region[END_REF] recently employed a Soudano-sahelian context that was in some ways comparable to Mediterranean climate conditions (annual rainfall from 900-950 mm, but with a long dry period). Soil wetting and mulching were shown to increase soil carbon mineralization, but frequent wetting-drying cycles did not increase the total soil C mineralization [START_REF] Yemadje | Wetting-drying cycles do not increase organic carbon and nitrogen mineralization in soils with straw amendment[END_REF]. But, these last authors also reported that conflicting results for the effect of wetting-drying cycles on C and N mineralization can be found in the literature, with higher or lower, or similar values for C and N mineralization in soils subjected to wetting-drying cycles. In terms of adaptation strategies in combination with the need to fight agricultural soil degradation and organic C depletion, several approaches were proposed and tested in a Mediterranean context, and some of them were widely adopted by stakeholders at the plot or watershed level. The change of land use in a semi-arid area is a strategy in which the major patterns are related to the reduction in long-term fallowing (FAO, 2014). Annual soil cultivation that employs appropriate nutrient management increases the soil C-return (root, stubble,…) because the above and belowground biomass production was increased in comparison with that of the fallow system. The choice of crop species and cultivars is an important key to maximizing the production of crop residues, which are a major resource for organic inputs in Mediterranean croplands. In the cereallivestock system, straw is largely exported out of the plot instead of being incorporated back into the soil. In addition, stubble is intensively grazed primarily to the south of the Mediterranean Sea [START_REF] Ryan | Drylands of the Mediterranean Zone: Biophysical Resources and Cropping Systems[END_REF]. The implementation of crop rotations with plants that allocate more carbon to top and subsoil through a deep root system is an adaptation measure for sinking C. The improvement of rangeland productivity by legume sowing, shrub plantation and integrated livestock are widely used strategies to boost the soil fertility in the arid part of the Mediterranean region. Field studies that were undertaken in Morocco and Tunisia by [START_REF] Mrabet | Total, particulate organic matter, and structural stability of a Calcixeroll soil under different wheat rotations and tillage systems in a semiarid area of Morocco[END_REF] and [START_REF] Jemai | On-farm assessment of tillage impact on the vertical distribution of soil organic carbon and structural soil properties in a semiarid region in Tunisia[END_REF] showed 14% and 28% increases in the SOC from the 0-20 cm soil layer after 11 and 7 years of switching from conventional tillage to conservation agriculture practices, respectively. In Spain, Alvaro-Fuentes et al. (2012) observed a 23% SOC increase in the top 30 cm layer of soil after it was converted to conservation agriculture for 13 years. More generally, the concentrations of organic matter in top-soils of Mediterranean regions were found to increase routinely under no-tillage systems because of the favourable shift in the accumulation and decomposition balance [START_REF] Kassam | Conservation agriculture in the dry Mediterranean climate[END_REF][START_REF] Friedrich | Conservation agriculture in Europe[END_REF]. However, the wide adoption of conservation agriculture among farmers in the Mediterranean regions is still limited. According to [START_REF] Kassam | Conservation agriculture in the dry Mediterranean climate[END_REF], the total Mediterranean cultivated land under conservation agriculture is 1.53 million hectares. Research questions are still focused on refining the expected level of C sequestration attained in the different bioclimatic zones, and also by considering the deeper soil layers from which C losses have been registered under other climatic conditions. However, one of the most important points concerns the adoption and mainstreaming of conservation agriculture, which will have a strong impact on the management of the residues at the landscape and even sub-national level. Residues are also an important source of biomass resources that are made available for livestock. Synergies (other services in the fight against erosion) and trade-offs (biomass competition should then be addressed as well) to find the most appropriate technical solutions for farmers and smallholders whose objectives are yield and income increases. By contrast, the concentrations of organic matter in topsoils from Mediterranean regions routinely increase under no-tillage systems because of the favourable shift in the balance of accumulation and decomposition [START_REF] Kassam | Conservation agriculture in the dry Mediterranean climate[END_REF][START_REF] Friedrich | Conservation agriculture in Europe[END_REF].

Challenging transversal issues for the future of Mediterranean soil resources

Apart from the above-evoked ongoing research on each driver-process-soil capital-ecosystem service chain upon separation, the management of soil resources under global change raises some transversal issues that are detailed here. Towards a reliable change in soil management practices within viable agrosystems Many of the mitigation strategies evoked in the next sections are based on deep changes in agricultural practices. Beyond the successful results obtained on experimental farms, the massive introduction of such strategies within actual Mediterranean agrosystems is still a challenge. For example, the broad adoption of conservation agriculture among farmers in the Mediterranean region is still limited because of possible negative impacts such as the decrease in grazing resources for livestock through the introduction of mulching, or water-stress on agricultural production from the introduction of a permanent vegetation cover. Another aspect is the need for local and national policies that should support actions for, e.g., building up and raising the status of SOC using the adapted programmes and mechanisms with national-wide agricultural strategies such as those within the framework of NAMA. It is now recognized that policies that support sustainable land management practices are focused on both maintaining (preventing loss) and increasing (storing even more) soil organic carbon production for far greater economic, social and environmental impact than the absolute amount of sequestered carbon (Banwart et al., 2014). The introduction of mitigation strategies should be applied in a wider context that considers the whole agrosystem explicitly and its socio-economic environment. An integrated assessment of agricultural systems is therefore required [START_REF] Van Ittersum | Integrated assessment of agricultural systems -A component-based framework for the European Union (SEAMLESS)[END_REF]. Towards site-specific adaptations for preserving the soil resource Beyond the field and farm levels, IAASTD (2009) recommended that the landscape level be considered and that "new cropping patterns adapted to site-specific conditions" be introduced. This approach accounts for the diversity of local contexts (see the first issue in this section) and to admit that "the search for universal truths about causes and remedies for desertification and the appropriate actions to be taken are as diverse as the mosaic of landscape itself" [START_REF] Thornes | Emerging Mosaics[END_REF]. This interpretation is particularly relevant in Mediterranean areas where the complexity of soil patterns (see above) involves a significant diversity of soil properties and soil processes, starting from very small areas such as parcels, farm territories and small watersheds. Significant advances are expected from employing spatial organizations of land uses and soil management practices. These choices will ensure the optimal exploitation of local soil characteristics while providing the best pooled result in terms of soil cover protection at the scale of resource watersheds or irrigation perimeters in which collective management is possible (10-100 km 2 ). An example of current research that is being performed in the Mediterranean area to address these opportunities is the ALMIRA project (Adaptating Landscape Mosaïcs of rainfed Mediterranean Agrosystems for a sustainable management of crop production, water and soil resources). ALMIRA aims to explore the modulation of landscape mosaics to adapt to the Mediterranean Rainfed Agrosystems to Climate Change. For that purpose, ALMIRA proposes to design, implement and test a new Integrated Assessment Modelling approach that explicitly i) includes innovations and actions in prospective scenarios for landscape evolutions, and ii) addresses landscape mosaics and processes of interest from the agricultural field to the resource governance catchment.

Towards a high resolution for mapping Mediterranean soil properties

A systematic soil survey of the Mediterranean basin using the most updated technology and scientific knowledge is still lacking for a site-specific adaptation of local mitigation strategies and should be one of the priority actions in the near future. The specifications of this survey may follow those of the new Digital Soil Map of the world as targeted by the GlobalSoilMap project [START_REF] Sanchez | Digital Soil Map of the World[END_REF]Arrouays et al, 2014a). This targeted global soil map is expected to provide quantitative estimates of major soil properties with associated uncertainties at the nodes of a 90 m x 90 m grid covering the planet and for a set of fixed soil depth intervals ranging from 0 to 2 metres. This new soil map is expected to be largely available through free-access web portals. Researchers (Arrouays et al, 2014b) have suggested the rapid production of a first version of the global soil map by applying largely tested Digital Soil Mapping (DSM) techniques [START_REF] Mcbratney | On digital soil mapping[END_REF], Lagacherie et al., 2007) to existing spatial datasets. These datasets include the input of globally available landscape parameters (e.g., DTM, digital maps of land use, and multispectral remote sensing) and legacy soil data (measured soil profiles, soil maps) that are available in existing soil databases. Interest in the above-evoked Digital Soil Mapping approach for producing the new soil map of the world was tested in various parts of the world including Mediterranean areas such as the Cap Bon Region in northern Tunisia [START_REF] Ciampalini | Documenting GlobalSoilMap.net grid cells from legacy measured soil profile and global available covariates in Northern Tunisia[END_REF] and the Languedoc-Roussillon Region in southern France [START_REF] Vaysse | Evaluating Digital Soil Mapping approaches for mapping GlobalSoilMap soil properties from legacy data in Languedoc-Roussillon (France)[END_REF]. In this latter experiment, successful predictions captured more than 50% of the variability in the mapped soil properties and provided realistic estimates of the prediction uncertainty where possible (for the pH and OC in Languedoc-Roussillon). However, the sparseness of the legacy soil data that were available in current soil databases hampered the capture of the short-scale soil variations of soil properties within the complex Mediterranean Soil patterns. A priority should be made for the densification of these soil data by i) increasing the retrieval of legacy-measured soil profiles, ii) using soil sensing techniques such as Vis-NIR hyperspectral imagery (Lagacherie & Gomez, 2013) or iii) reviving the field collection of soil data following optimized sampling [START_REF] Brus | Sampling for validation of digital soil mapping[END_REF]. These required efforts for collecting soil data will likely not fully remove the uncertainty on the soil property predictions, considering the short scale of variations of Mediterranean soils. However the expected progresses brought by GlobalSoilMapi.e. increasing the spatial resolution of soil predictions, providing quantitative estimations and providing explicit values of expected uncertainty -may greatly help for site-specific decision making.

Conclusions

The Mediterranean soil resource is a highly specific research object with regards to i) its remarkable characteristics as caused by a unique combination of natural and anthropogenic soil-forming factors and ii) the extent of the expected climate and societal changes that are expected to affect this resource in this region of the world. In this context, the preservation of Mediterranean soil resources encompasses three crucial challenges: mitigating soil losses, avoiding soil salinization and maintaining carbon stocks. For each of these challenges, there are specific studies to continue or initiate to try to gain a better understanding of the soil processes driving the trend evolutions in Mediterranean soil resources and the mitigation strategies that should be applied to preserve these resources. The effective application of these mitigation strategies also implies progress in the integrated assessment of the Mediterranean agrosystems and in the design of site-specific adaptations to global change. A significant contribution of soil scientists to this task will be to provide improved information on fine-scale Mediterranean soil patterns through advanced Digital Soil mapping techniques. Finally, this paper has underscored the urgent need to deepen Mediterranean cooperation with regards to soil research and to enrich the exchange and sharing of technologies, resources, experiences and knowledge. Bibliography Alvaro-Fuentes J, Joaquin Morell F, Plaza-Bonilla D, Luis Arrue J, Cantero-Martinez C 2012.

Modelling tillage and nitrogen fertilization effects on soil organic carbon dynamics. Forum, vol. 38, no. 4, pp. 282-295, 2014Forum, vol. 38, no. 4, pp. 282-295, .doi: 10.1111/1477-8947.12054 Visconti F , de Paz J M, Rubio J L, and Sánchez, J. 2011 SALTIRSOIL: A simulation model for the mid to long-term prediction of soil salinity in irrigated agriculture. Soil Use &Management, vol. 27, no. 4, pp. 523-537. doi: 10.1111/j.1475-2743[START_REF] Mrabet | No-tillage agriculture in West Asia & North Africa[END_REF].00356.x thank you for the revision. Our Guest Editor Wolfgang Ludwig now recommends acceptance of the paper and I agree about the scientific content.

Thank you both for acknowledging that the scientific content is OK.

However, you seem to have ignored my advice from the previous decision letter which was "In addition, I suggest to delete the abstract and write a fresh one.

Remember that an abstract should not be part of the introduction -it should rather deliver as many of the findings and conclusions as possible."

Indeed, I am quite serious about this. An abstract, and also the title, are the parts of any publication that are read by most people, and their information content is very important. To say that some authors did this or that does not belong into an abstract. So I would like to repeat this request, and also expand it to provide me with a more specific title that precisely speaks to the content of your paper. Note there is also no such thing in English as "Global Changes".

The abstract has been deeply reworked for matching your advice. There is no more direct reference to authors and we provide a more precise description of our finding. The title of the paper was modified too for giving more precise details on the paper.

Going through the paper, I also notice that there are minor changes needed: you cannot use "GC" as an acronym, spell out global change if you mean that, but not in plural.

GC were replaced by « global change » and the 's' were deleted Some references still lack doi-numbers.

We added 6 more doi to our reference list. 57% of our reference are now documented with a doi. In spite of our efforts, we did not find any doi for the remaining references. Looking at the five most recent REEC papers published as open access papers (on 2017 May18th), we observed that the ratio of documented doi was between 5% and 72% (between 56% and 72% if we only consider « non social science » papers). Our paper match therefore what has been achieved in REEC recent papers.

Finally, I did not earlier pay much attention to the figures. They definitely need to be designed properly. At the moment they are rather tables with some arrows and it is not at all clear to me what they are supposed to represent. Please use an appropriate drawing software to prepare these figures -the publisher has now facilities to offer for doing this in your place. The figures have been modified for not looking like tables. This allowed to better represent the status of the « mitigation strategies » that have been discussed by the reviewers in earlier versions.

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  The Mediterranean Basin is the land region surrounding the Mediterranean sea that has a 57 Mediterranean climate, with mild, rainy winters and hot, dry summers. It is the largest of the 58 world's five Mediterranean climate regions (2,085,292 km 2 ). It stretches west to east from Portugal 59 to Syria and north to south from northern Italy to Morocco and surrounds the Mediterranean Sea, 60 including parts of Spain, France, the Balkan states, Greece, Turkey, Syria, Lebanon, Israel, 61 Palestine Authority, Jordan, Egypt, Libya, Tunisia and Algeria as well as five thousand islands that 62 are scattered around the Mediterranean Sea 63

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  Soil & Tillage Research 120 : 32-39. doi: 10.1016/j.still.2012.01.009. Arrouays, D., McBratney, A.B., Minasny, B., Hempel, J.W., Heuvelink, G.B.M., MacMillan, R.A., Hartemink, A.E., Lagacherie, P., McKenzie, N.J., 2014a. The GlobalSoilMap project specifications, in: Arrouays, D., McKenzie, N.J., Hempel, J.W., Richer-de-Forges, A.C., McBratney, A.B. (Eds.), GlobalSoilMap : Basis of the Global Spatial Soil Information System.. CRC Press-Taylor & Francis Group, Boca Raton, USA, pp. 9-12. Singh M, Thomas R J, Drechsel P, and. Noble A D, Economics of salt-induced land degradation and restoration, Nat. Resour.

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