Regional climate warming increases occurrence and intensity of winter wheat drought risk

Abstract

During the 1960–2021 period, France experienced two rapid increases in 2m air temperature, in 1987/1988 and 2014/2015. Between the periods 1960–1987 and 1988–2014, this induced significant differences in the mean state of the local water cycle climatic components. Evolving climate hazards linked to the water cycle led to water balance modifications, especially in winter bread wheat fields. This work aims to analyze the resulting changes in agro-climatic risk linked to drought after each abrupt warming. For each grid point of the Safran-Isba-Modcou (SIM) dataset and each year, daily values of Relative Extractible Water ($REW$) under a wheat stress threshold of 40 % are cumulated to obtain a water stress index. For the first time, the modeling of water stress index distributions using Tweedie family distributions allows to disentangle modifications in frequency and intensity of drought events. These display various changes depending on the wheat production basin and the studied period. Overall, the mean water stress index increases in each production basin, with the Nord-Pas-de-Calais and Parisian production basins being particularly impacted by the 1987/1988 abrupt warming. Our results highlight that the modifications of climate hazards lead to harsher hydric stress events over main French wheat production basins. The probability of extreme drought events is rising strongly in several production basins. Changes in agro-climatic risk associated with drought are one of the main factors affecting crop growth cycle and development. As the probability to overcome risk threshold increases, yields may be significantly reduced, leading to increased economic losses. This is of major concern for the agricultural sector, including crop insurers, and underscores the urgent need for adaptation and prevention measures.