Modelling wheat yield responses to soil and climate variability at the regional scale

We present a study on the impact of soil and climatic variability on the yi eld of winter wheat in the Herault-Libron-Orb Valley in southern France. Th e study was based on the use of a crop simulation model (Euro-ACCESS), run at 63 individual sites throughout the study area, for the current climate ( 1976 to 1984) and for potential future changes in temperature and precipita tion (2047 to 2054). Three climate scenarios were selected to represent low , mid and high changes, although significant winter wheat yield decreases w ere only observed for the climate scenario with the largest change. In gene ral, the influence of climate change on yields was small (less than 0.1 t h a(-1) over the whole simulation period), but strong inter-annual variation was found, which is typical of the Mediterranean climate. Soil variability within the study region was the most important source of spatial variabilit y for the simulated yields, and the soil available water capacity was ident ified as a good indicator of yield change for large climatic change. Soil v ariability was important in this study because of the small size of the stu dy region and because of the strong influence of water limitation on crop g rowth in Mediterranean areas. Statistical relationships were established be tween crop yields, yield changes and the soil available water capacity. The se relationships were used to extrapolate the crop simulation results from individual sites to the whole region using data from soil maps at a scale o f 1:250 000. This modelling exercise demonstrated the importance of explici t consideration of soil as well as climatic variability in crop-climate imp act studies.