Jun Niu

Center for Agricultural Water Research in China, China Agricultural University, Beijing 100083, China

State Key Laboratory of Efficient Utilization of Agricultural Water Resources, Beijing 100083, China

National Field Scientific Observation and Research Station on Efficient Water Use of Oasis Agriculture in Wuwei of Gansu Province, Wuwei 733000, China

Key Laboratory of Agricultural Water Saving of the Ministry of Water Resources, Beijing 100083, China

Abstract

Irrigation is the most important water use sector accounting for about 70% of the global freshwater withdrawals and contributing 75% of China’s total grain production. In this study, we quantified the irrigation effects on maize GPP (∆GPP) across China by combining a land surface model and a light-use efficiency model and using satellite-based irrigation water use.

We show that irrigation promoted maize GPP by 492 gC · m^-2 · yr^-1 on average in China. These benefits (∆GPP) were attributed to irrigation effects (water supply, surface cooling) and climate variability based on a machine learning framework (XGB-SHAP). Irrigation water supply and surface cooling explained certain

percentage ∆GPP, the rest being due to temperature-dominated climate interactions with irrigation.

With the climate change driven by persist warming, the irrigation benefits will be substantially reduced for those regions under ongoing heat stress. While for those regions under heat deficits, warming climate plays a beneficial role. Future maize productivity will be greatly threatened by changing climate, considering the prevailing negative trends for the irrigation benefits. Reinforcing anthropogenic activities such as irrigation water management and planting structure adjustment are strongly required to improve crop resilience to climate variability.