Intensifying impacts of compound drought and heatwave events on water use efficiency in U.S. corn and soybean

The increasing frequency and intensity of compound drought and heatwave events pose a severe threat to agricultural water use efficiency (WUE), amplifying risks to global food security and water resource sustainability. While compound extremes can trigger unprecedented disruptions in agricultural water-carbon dynamics compared to single extreme events, their effects on WUE remain poorly understood. To address this gap, this study examines the spatiotemporal variations in U.S. corn and soybean WUE in response to compound drought and heatwave events from 1960 to 2018. Using superposed epoch analysis, we found that compound drought and heatwave events reduced WUE by 14.7% in corn and 11.3% in soybean compared to normal conditions. These compound events also resulted in greater reductions in yield and evapotranspiration than single drought or heatwave events. While the impacts of both single and compound extremes were generally short-lived, with WUE recovering in the following year, long-term trends reveal intensifying effects: compound drought and heatwave events have shown intensified adverse impacts on 37.5% of corn and 46.2% of soybean production areas. This intensification is closely linked to the role of temperature, which was consistently identified as the dominant climatic driver of WUE responses under drought, heatwave, and compound extremes. These findings underscore the urgent need to prioritize compound drought and heatwave events in agricultural impact assessments and develop targeted adaptation strategies to mitigate their intensifying effects on agricultural WUE.