Impact of the climate change on the crop water deficiency at the regional scale: study case in Bourgogne Franche-Comté, France.

In the Bourgogne Franche-Comté region, climate change will lead to an increase of the field evapotranspiration during the crop cycle and a modification of the rainfall distribution within the year, leading to longer and more intense drought periods in summer. This will increase the crop water requirement, while reducing water availability and accessibility, which could negatively impact agricultural productivity and stability. It is thus necessary to evaluate actual and future water deficiency in a way to develop and implement adapted responses (new farming practices, new crops, water storage…). Based on simulated weather data (rainfall and potential evapotranspiration) integrating the effect of climate change until 2100, soil characteristics (texture and depth) and crop water requirement, we estimate the daily water balance at the scale of the Bourgogne Franche-Comté region, France. We use weather data at an 8*8 square-kilometres grid and soil water capacity is estimated at the soil map unit using the methodology developed by Bruand et al. (2004). This methodology estimates the water capacity of each layer of the soil unit based on their texture class (Aisne triangle) and removing the proportion of gravels and rocks considering that their contribution to water storage is negligible. For the 10 main crops of the region in terms of field area (i.e. grassland, winter wheat, winter barley, winter oilseed rape, spring barley, maize, soybean, sunflower, winter peas and spring peas), we calculate the water balance using the methodology developed by Jacquart and Choisnel (1995) at the scale of the intersection between the weather grid and the soil map unit in a way to represent homogeneous pedoclimatic territories. The soil water capacity is thus divided in two reservoirs with no horizontal transfer. Water from the first reservoir (40% of the soil water capacity) is easily accessible to the crop while water from the second reservoir is less and less accessible as the reservoir is emptied. At a daily step, the meeting of the crop water requirement is estimated regarding the water available in the soil reservoirs and the rainfalls. This study enables to estimate the actual water deficiency of the main crops and its potential increase due to climate change. We can thus identify crops that could not be cropped anymore without irrigation in some area and estimate the water required if we want to keep these crops in the future. These results are also important to evaluate if it is possible to developed new practices or water storage in response to the effects of climate change. Our approach allows as well to evaluate and anticipate the possibility to implement new crops requiring less water, avoiding the drought periods or able to access more water in the soil. These results will allow the agricultural sector to develop outlets for these new crops.