## Materials
### Data Description  
Daily meteorological data were obtained from JRC-MARSOP [63] and 10-daily fAPAR and NDVI from SPOT VEGETATION (1 km) [69] for the period 10/1998-10/2012. Temperature and solar radiation are at a 25 km grid, while rainfall, PET and AET are at a 0.25\({}^{\circ}\) grid. A cropland mask was retrieved from ESA GlobCover 2009 [70]. The classes used were \"Post-flooding or irrigated croplands (or aquatic)\", \"Rainfed croplands\", \"Mosaic cropland (50%-70%)/vegetation (grassland/shrubland/forest) (20%-50%)\" and \"Mosaic vegetation (grassland/shrubland/forest) (50%-70%)/cropland (20%-50%)\". The soil water holding capacity was retrieved from the European soil map [71] and Digital Soil Map of the World [72] and used in AgroMetShell [73]. AgroMetShell provides a toolbox for agrometeorological crop monitoring and forecasting developed by FAO. This toolbox includes a database with the weather, climate and crop data used to analyse the impact of weather on crops [74]. AgroMetShell also contains crop-specific water balance parameters for different crop growth stages. In this study, we used the meteorological data from JRC-MARSOP and used AgroMetShell to compute the actual evapotranspiration (AET) for every season during the period 1999-2012. The soil types and textures of the different regions show a high suitability for arable agriculture due to the presence of silt (Table 1). The information for the planting dekad and the length of the growing season as required in AgroMetShell were extracted from the MARS database [63] for Belgium and France; and obtained from [68] for Morocco (Table 2). \begin{table}
\begin{tabular}{l l l l l} \hline \hline  & & & **Soil Type** & **Soil Texture** \\ \hline \multirow{4}{*}{Wheat} & \multirow{2}{*}{BE} & Polders & \multicolumn{1}{l}{Caloric Regosols + Caloric Fluvisols} & \multicolumn{1}{l}{Loam + Silt loam} \\  & & Sandy Loam Region & \multicolumn{1}{l}{Dyrtic Podzoluvisols + Orthic Luvisols} & \multicolumn{1}{l}{Sandy loam + Loam} \\ \cline{3-5}  & \multirow{2}{*}{FR} & Eure-et-Loir & \multicolumn{1}{l}{Gleyic Luvisols + Orthic Luvisols} & \multicolumn{1}{l}{Clay Loam + Loam} \\  & & Somme & \multicolumn{1}{l}{Orthic Luvisols} & \multicolumn{1}{l}{Loam} \\ \cline{3-5}  & \multirow{2}{*}{MAR} & El Jadida & \multicolumn{1}{l}{Calic Kastanozems + Vertisols + Eutric Fluvisols} & \multicolumn{1}{l}{Loam + Siltly Clay + Silt Loam} \\  & & El Kelaa & \multicolumn{1}{l}{Eutric Gleysols + Calcic Xerosols} & \multicolumn{1}{l}{Clay Loam + Loam} \\ \hline \multirow{4}{*}{Maize} & \multirow{2}{*}{BE} & Loam Region & \multicolumn{1}{l}{Orthic Luvisol + Dystric Podzoluvisol} & \multicolumn{1}{l}{Loam + Sandy Loam} \\  & & Liege Region & \multicolumn{1}{l}{Stagno-Gleyic Luvisol + Orthic Luvisols +} & \multicolumn{1}{l}{Clay Loam + Loam + Silt} \\  & & & Dystric Cambisol & \multicolumn{1}{l}{Loam} \\ \cline{3-5}  & \multirow{2}{*}{FR} & Ain & \multicolumn{1}{l}{Gleyic Luvisols + Orthic Luvisols + Eutric} & \multicolumn{1}{l}{Clay Loam + Loam + Silt} \\  & & Haut Rhin & \multicolumn{1}{l}{Gleyic Luvisols + Orthic Luvisols} & \multicolumn{1}{l}{Clay Loam + Loam} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The soil types and textures of the study sites. \begin{table}
\begin{tabular}{l l l} \hline \hline  & & **January February March April May June July August September October November December \\ \hline \multirow{4}{*}{Wheat} & \multirow{2}{*}{BE} & Polders & \multirow{2}{*}{BEL} \\  & & Sandy \\  & & Loam \\  & & Region \\ \cline{3-5}  & \multirow{2}{*}{FR} & Eure-et-Loir & \multirow{2}{*}{MARS} \\  & & Somme \\ \cline{3-5}  & & El-Jadida & \\ \cline{3-5}  & & El-Kelas & \\  & & des Senghera & \\ \hline \multirow{4}{*}{Maize} & \multirow{2}{*}{BE} & Loam & \multirow{2}{*}{MARS} \\  & & Region \\ \cline{3-5}  & & Liege & \\ \cline{3-5}  & & Region \\ \cline{3-5}  & & & \\ \cline{3-5 Official crop yield statistics for common wheat and silage maize for the period 1999-2012 were obtained from the national statistical services.