Current irrigation practices in the central United States reduce drought and extreme heat impacts for maize and soybean, but not for wheat

In this study, we assessed the adaptive effects of irrigation on climatic risks for three crops (maize, soybean, and wheat) at the regional scale from 1981 to 2012 in the Central US. Based on yields of 183 counties for maize, 121 for soybean and 101 for wheat, statistical models were developed for irrigated, rainfed and county-level yields. Results show that irrigation has a statistically significant effect on abating detrimental climate impacts, specifically drought and extreme heat, in maize and soybean but not in wheat. On average, irrigation reduces the negative influences of extreme heat by around 7.2% for maize and 5.0% for soybean yields for each additional 10 degree-days above the optimal temperature for each crop. This is approximately two-thirds of the negative effects of extreme heat under rainfed management. The remaining third of the yield reduction is caused by heat damage that cannot be alleviated by irrigation. No significant differences were detected between county yields and irrigated yields for maize and soybean, suggesting that the existing irrigation practices were reasonably efficient. Efforts to mitigate future climate risks for these two crops should focus on improving the heat sensitivity contributing to the yield losses from heat damage. In contrast, the existing irrigation does not improve the resilience of wheat to climate risks. Both increased temperature and drought were critical to wheat production, which was potentially caused by relatively poor irrigation supplies for wheat. Further enhancement of wheat yield may be possible through improved irrigation management.