Heat stress will more strongly affect global wheat yields than drought stress under 21st century climate change

Abstract:

Climate change is likely to intensify and cause more frequent droughts, leading to deleterious effects on crop productivity. Although the Palmer Drought Severity Index (PDSI) was primarily developed for agricultural drought evaluation, it does not directly account for water availability effects on crop development and yield. Here, we propose a crop Yield Drought Severity Index (YDSI) to evaluate yield performance and response to drought under climate change. Our goal is to improve understanding and prediction of crop drought responses as a function of spatial and temporal climate variability, crop and soil properties, crop management, and atmospheric CO₂ concentrations. We developed and analyzed the YDSI for wheat using ecosys, a mechanistic crop model, evaluated against observed global rainfed wheat yields over ten years at 3,767 sites (r² = 0.78) and five CO₂ enrichment experimental study sites (r² = 0.67 - 0.98). We found that plant physiological responses to CO₂ increase drought tolerance by reducing transpiration and thus improving water and nitrogen use efficiency. The amount of irrigation required to maximize wheat yields decreased 60% by the end of the 21^st century under RCP8.5 compared to the present. A modeled advance of anthesis date of 5 days per 1 with current varieties resulted in reduced grain numbers and yields. Overall, we project that the risk of heat stress will increase more rapidly than that of water stress, requiring more focus on the development of heat-resistant wheat cultivars.