A new agricultural drought index for monitoring the water stress of winter wheat

Timely and effectively monitoring agricultural droughts for winter wheat production is crucial for water resource management, drought mitigation and even national food security. With soil moisture and actual evapotranspiration (ET) products from 2001 to 2018 supplied by the European Centre for Medium-Range Weather Forecasts (ECMWF) and Moderate Resolution Imaging Spectroradiometer (MODIS) data, respectively, 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. Our case study on the North China Plain (NCP) indicated that the USMEI could effectively monitor agricultural drought, especially in autumn and winter from October to January. Furthermore, compared with the evaporative stress index (ESI) and soil moisture anomaly percentage index (SMAPI), the correlations between the USMEI and climatic yields were acceptable at the county level or site scale. However, for the rest of the winter wheat growing season, the ESI and SMAPI performed better than the USMEI. In addition, the BSMEI was not suitable for monitoring droughts for winter wheat because this index overestimated the drought intensity.