Estimating Net Irrigation Requirements of Winter Wheat across Central-Eastern China under Present and Future Climate Scenarios

Climate change (i.e.,fluctuating precipitation and increasing temperature) is extremely likely to challenge water systems through an increased water demand, potentially impacting water use for irrigation. In China, over 40% of wheat planting areas need to be irrigated to ensure crop yield, especially in semiarid and semihumid regions. To quantitatively simulate the effects of climate change on the net irrigation requirements (NIR) for winter wheat across central-eastern China, we use historical observations to drive a crop-specific water balance model with crop-specific potential evapotranspiration (ETc) and effective precipitation (Pe) and then apply it to future climate scenarios. Specifically, the future climatic variables are based on three concentration pathway (RCP2.6, RCP4.5, and RCP8.5, respectively) scenarios of a general circulation model (GCM) from phase five of the Coupled Model Intercomparison Project (CMIP5). The results show that at the mean annual scale, during the last few decades, high ETc and NIR values have mainly been distributed at the junction of Hebei, Henan, and Shandong Provinces. The days of the growing period (DGP) and Pe values are high in the northwest and southern areas of the study region. The historical values of DGP, ETc, Pe, and NIR are characterized by significant downward trends, accounting for 91.8, 49.5, 29.9, and 26.8% of all stations, respectively. For the future period, DGP, ETc, and NIR will likely decline in most regions. In comparison with the baseline period, the average change rates of NIR in the three scenarios are -11.3, -16.8, and -23.9% in the 2020s, 2050s, and 2080s, respectively. Moreover, the future NIR will increase in Hebei Province, Shanxi Province, and northern Jiangsu Province.