Estimation of Climate Change Effects on Water Use Efficiency of Rain-fed Winter Wheat

Investigating the influencing rule of climate change on water use efficiency (WUE) of rain-fed winter wheat can offer scientific reference for agriculture adapting to climate change. Based on yield information and observed soil water data at representative stations, the historical trend of WUE is analyzed. Simulation models for meteorological yield and soil water variation quantity are established, and four different kinds of climate change scenarios, which are outputs by regional climate models of PRECIS and REGCM4.0 are combined to estimate the probable variation trend of WUE in the future years of 2021-2050 for rain-fed wheat. It is validated that in the basic scenario years, simulated yields by the combination of two regional climate models with meteorological yield simulation model are close to actual values, so methods for estimating future yield of wheat is proved feasible. Results by data analyzing shows that the average yield for representative stations varies as a cubic curve during the last 30 years of 1981-2010, and grows faster before the year of 2000. Water consumption of wheat also increases with fluctuating. The average WUE value of rain-fed wheat for representative stations in Gansu, Shanxi and Henan are 13.19 kg·mm^-1·hm^-2, 12.86 kg·mm^-1·hm^-2 and 11.28 kg·mm^-1·hm^-2, respectively. The varying trend of WUE is similar to a quadratic curve, and the maximum value appears in the year of 2003. Estimation results under four different climate change scenarios shows that in 2021-2050, water consumption of winter wheat would increase dramatically, and the increasing amount could reach to 6.2% for all the representative stations and all scenarios averagely. Yields in the future would decrease and some increase, and the variation rate would be 1.4% on average. The value of WUE would decrease 3.8% on average, meanwhile, the variability rate would also decrease. The increase of water consumption would be the main cause for WUE decreasing in the future. From the inter-annual variation during 2021-2050, WUE would show a non-significant trend of increasing under the simulation of PRECIS model, and comparing to the average value of 1981-2010, the decreasing rate of WUE would be more significant under A2 scenario than B2. However, there would be a significant decline trend for WUE simulated by REGCM4.0 model, and under the scenario of RCP8.5, the reduced value of WUE would be higher than that of RCP4.5. Generally speaking, the climate scenario of RCP has even more negative effects on WUE of rain-fed wheat.