Creation Of Drought Index For Winter Wheat Based On Effective Soil Moisture And Evapotranspiration On The North China Plain

Timely and effectively monitoring agricultural droughts for winter wheat production is crucial for water resource management,drought mitigation and even national food security on the North China Plain.The key scientific problem are that the crop water requirement(CWR)too dependent on the default parameters in the estimation process,which leads to low accuracy and the agricultural drought index does not take the water budget into account perfectly.On the basis of optimizing the CWR parameterization process,two agricultural drought indices,i.e.the univariate soil moisture and evapotranspiration index(USMEI)and bivariate soil moisture and evapotranspiration index(BSMEI)were developed to reflect water stress for winter wheat based on the effective soil moisture(ESM)and CWR,which were evaluated with agro-hydrological model,disaster records,winter wheat yield at the county level and site scale.The conclusions are as follows:(1)Affected by the weather conditions and latitude,the model of shortwave radiation-the values of coefficients a and b of Angstrom model are below and above the default values recommended by Food and Agriculture Organization of the United Nations(FAO).The coefficient a decreased from northwest to southeast on the North China Plain and increased over time,while the coefficient b was completely opposite to the coefficient a.(2)Based on the calibration scheme recommended by FAO,the crop coefficient of winter wheat at the initial showed large spatiotemporal variability due to the strong influence of precipitation and irrigation.However,the crop coefficients of winter wheat at the mid-season and end of the late season were larger than the default values recommended by FAO,of which the inter-annual variation was small.(3)The optimized scheme of CWR ensures that the agricultural hydrological model SWAP(Soil Water Atmosphere Plant)can effectively simulate soil moisture and winter wheat yield at site scale on the North China Plain.On this basis,regression analysis was carried out by taking the yield difference of winter wheat as a reference.Results showed that the difference of accumulated difference between ESM and CWR in winter wheat growth season can reflect the water stress of winter wheat.(4)The new drought index USMEI(time scale is 8 days)combined ESM and CWR from the perspective of water supply and demand and climatology is suitable for agricultural drought monitoring of winter wheat on the North China Plain at both site and regional scales.Typically,the monitoring capability of USMEI is the best for winter wheat in autumn and winter(October-January).Moreover,USMEI has a strong correlation with winter wheat meteorological yield at the county scale.