Analyses Of The Spatial And Temporal Variations Of Water Footprint Of Winter Wheat Production In The Guanzhong Region Based On Crop Growth Simulation Model

The water footprint of crop production is usually used as an evaluation index for agricultural water consumption.Traditional research methods heavily rely on statistical yearbook.Especially when estimating crop yield,the statistical grain yields were directly adopted.In statistical yearbooks,crop yields tend to be the weighted averages of total crop yield and sown acreage under both irrigated and non-irrigated conditions.The crop yield data of irrigated areas could be obtained from the administration offices of irrigation districts.Unfortunately,crop yield data were seldom recorded for non-irrigation fields.Therefore,the error of this algorithm would increase with the scale of the region.At the same time,the statistical yearbook data itself will also could be missed completion sometimes.In traditional water footprint researches,crop water consumption was calculated according to the reference crop evapotranspiration（ET）according to the Penman-Monteith equation or the CROPWAT software.Overlooking of crop growth could result in inaccurate reflections of actual water consumption of crops.The yields used traditional water footprint researches were usually historical statistical data,which made the researches only quantitative analyses of crop production water footprint in historical years.Moreover,the traditional method is not able to predict the change of water footprint of crop production under climate change in the future.In this study,the genetic coefficients were estimated first for two representative winter wheat varieties in the Guanzhong Plain and the Weibei Dryland based on winter wheat field experiments conducted in Yangling and Changwu,Shaanxi Province.Physical parameters of soil profile were obtained from the HWSD（Harmonized World Soil Database）database.Irrigation amount and other field management information were obtained from statistical data.Meteorologcal data included the 2001-2015 historical data of 43 weather stations and2021-2051 predicted weather data under the RCP4.5 and RCP8.5 scenarios of 46 weather stations in the Guanzhong region.Then the CERES-Wheat model was used to estimate the water footprint,blue water footprint,and green water footprint of winter wheat production in the Guanzhong region for two periods of 2001-2015 and 2021-2050.The spatial and temporal variations of water footprint,blue water footprint,and green water footprint of winter wheat production in this region were analyzed through spatial visualization and Man-Kendall trend test with R language.Main conclusions were drawn as follows.（1）CERES-Wheat model can accurately simulate the phenological period of winter wheat in Guanzhong region.The RRMSE between simulated and observed values at flowering was 3.7%,and the RRMSE between simulated values and observed values at maturity was 3.2%.Although there were difference of yeild between simulations and historical statistics,but,it was close to the survey data of farmers and the data of trend test report.（2）The spatial distribution of average water footprint of winter wheat production was between 0.4 m³ kg^-1 and 1 m³ kg^-11 from 2001 to 2015 in the Guanzhong region.Lower values distributed in the Guanzhong Plain.The spatial distribution of average green water footprint of winter wheat was between 0.3 m³ kg^-1 and 1 m³ kg^-11 from 2001 to 2015 in the Guanzhong region.Blue water footprint of winter wheat production mainly distributed in the Guanzhong Plain.The spatial distribution was between 0.15 m³ kg^-1 and 0.35 m³ kg^-11 on an average.The ratio between blue water footprint and water footprint was about 30%-50%.Green water footprint of winter wheat production in Weibei Dryland was higher than that in Guanzhong plain.（3）The temporal trend of yeild and water consumption of winter wheat were mainly different from eastern part of Guanzhogn region to western part of Guanzhogn region from2001 to 2015.The increasing trend of yeild and water consumption of winter wheat distributed in the west of Guanzhong region.While,the decreasing trend distributed in eastern part of Guanzhong region.However,the trend was not remarkable.The temporal trend of water footprint of winter wheat production was different from northern part of Guanzhogn region to southern part of Guanzhogn region from 2001 to 2015.The decreasing trend mainly distributed in the eastern part of Guanzhong irrigation.However,there were remarkable difference of composition of the water footprint of winter wheat.The blue water footprint of winter wheat production in Guanzhogn irrigation District was remarkablly decreased.While,there was remarkablly increased trend of green water footprint of winter wheat production in part of Guanzhogn irrigation District.（4）The days of winter wheat growing season of winter wheat might decrease 1.3 day,and the flowering date might advance 1.6 day in most areas of the Weibei Dryland.While in the Guanzhong Plain,the days of growing season might increase.What’s more,the days of growing season under RCP4.5 was more than that under RCP8.5.The yield of winter wheat in most areas of the Guanzhong region would increase 310 kg hm^-22 on an average.（5）Compared with Guanzhong Plain,climate change has more negative effects on Weibei Dryland in terms of phenological phase,yield and water consumption.Compared with historical average,climate change might cause water consumption,water footprint and green water footprint of winter wheat to increase 20.15 mm、0.1-0.2 m³ kg^-1、0.1-0.2 m³ kg^-1,respectively.Climate change might have greater effects in the western part of Guanzhong.