Heat and water stress can drastically reduce crop yields, particularly when they co-occur, but their combined effects and the mitigating potential of irrigation have not been simultaneously assessed at the regional scale. We quantified the combined effects of temperature and precipitation on county-level maize and soybean yields from irrigated and rainfed cropping in the USA in 1970–2010, and estimated the yield changes due to expected future changes in temperature and precipitation. We hypothesized that yield reductions would be induced jointly by water and heat stress during the growing season, caused by low total precipitation (P _GS) and high mean temperatures (T _GS) over the whole growing season, or by many consecutive dry days (CDD _GS) and high mean temperature during such dry spells (T _CDD) within the season. Whole growing season (T _GS, P _GS) and intra-seasonal climatic indices (T _CDD, CDD _GS) had comparable explanatory power. Rainfed maize and soybean yielded least under warm and dry conditions over the season, and with longer dry spells and higher dry spell temperature. Yields were lost faster by warming under dry conditions, and by lengthening dry spells under warm conditions. For whole season climatic indices, maize yield loss per degree increase in temperature was larger in wet compared with dry conditions, and the benefit of increased precipitation greater under cooler conditions. The reverse was true for soybean. An increase of 2 C in T _GS and no change in precipitation gave a predicted mean yield reduction across counties of 15.2% for maize and 27.6% for soybean. Irrigation alleviated both water and heat stresses, in maize even reverting the response to changes in temperature, but dependencies on temperature and precipitation remained. We provide carefully parameterized statistical models including interaction terms between temperature and precipitation to improve predictions of climate change effects on crop yield and context-dependent benefits of irrigation.

高温和缺水压力会显着降低作物产量，特别是当它们同时发生时，但尚未在区域范围内同时评估它们的综合影响和灌溉的缓解潜力。我们量化了温度和降水对 1970-2010 年美国灌溉和雨育作物县级玉米和大豆产量的综合影响，并估计了由于未来温度和降水的预期变化而导致的产量变化。我们假设，由于整个生长季节的低总降水量 ( P _GS ) 和高平均温度 ( T _GS ) 或许多连续干旱天数 ( CDD _GS ) 和本季节此类干旱期 ( T _CDD )期间的高平均温度。整个生长季节 ( T _GS , P _GS ) 和季节内气候指数 ( T _CDD , CDD _{GS )}) 具有相当的解释力。雨养玉米和大豆在整个季节在温暖和干燥的条件下产量最低，干旱期更长，旱期温度更高。在干燥条件下变暖和在温暖条件下延长干旱期会使产量损失更快。对于全季气候指数，与干燥条件相比，湿润条件下温度每升高 1 度玉米产量损失更大，而在较冷条件下增加降水的收益更大。大豆的情况正好相反。T _GS增加 2 C降水量没有变化，预计各县玉米产量平均下降 15.2%，大豆平均产量下降 27.6%。灌溉减轻了水和热压力，在玉米中甚至可以恢复对温度变化的响应，但对温度和降水的依赖性仍然存在。我们提供精心参数化的统计模型，包括温度和降水之间的相互作用项，以改进气候变化对作物产量和灌溉的环境相关效益影响的预测。