How abrupt changes in surface temperature impacts water cycle over France? The case study of winter bread wheat area.

Since 1980s over western Europe, warming trend intensifies strongly, consistent with climate simulations including anthropogenic forcing. As a result of this warming tendency, a shift is detected in France in maximum and minimum air temperature, delimiting two different climatic periods: 1959–1987 and 1988–2021. Along with this abrupt warming, a trend towards stagnation of crop yields is observed since the 1990s. Bread wheat yields are particularly affected. The impact of climate hazard and agro-climatic risk on the evolution of bread wheat yields is a major issue for agricultural sector, including insurance companies. This work aims at analyzing how surface warming shift impacted water balance over main French bread wheat production basins. The SIM (Safran-Isba-Modcou) dataset with an 8km spatial resolution grid of reanalyzed surface meteorological observations at daily time step from 1959 to 2021 offers the opportunity to address the complexity of processes leading to changes in local water cycle. Water balance is computed on main bread wheat production basins using a two-reservoirs model, SIM climate data and crop agronomic parameters as inputs. Our results suggest that the abrupt shift in air temperature in France in 1987/1988 had a strong influence on the water cycle variables evolution. Along with the increase of water demand and soil drying, water balance is modified on the post-shift period, with various spatial patterns between main production basins. Harsher hydric stress events alter the crop growth cycle. The evolution of climate hazard linked to water balance leads to changes in agro-climatic risk, identified as one of the main factor affecting the evolution of bread wheat yields. Such conclusions suggest that, with both mean and variability changes in water balance state, probability to overcome risk threshold increases. This is of major concern for our partners and may lead to adaptation process from managers.