Assessing the performance of satellite soil moisture on agricultural drought monitoring in the North China Plain

Satellite soil moisture (SM) has been increasingly available and the use of SM-based indices has a great potential for agricultural drought monitoring. This study evaluates the performance of two satellite SM products, the Soil Moisture and Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP), on drought detection and assessment in the North China Plain (NCP) over the period of 2015-2018, with a comparison between two SMbased drought indices, Soil Water Deficit Index (SWDI) and Soil Moisture Condition Index (SMCI). Vegetation Condition Index (VCI) and Vegetation Drought Index (VDI) were adopted as the reference indices. Overall, SMAP outperformed SMOS in SM data validation as well as drought detection in the NCP region. A simple bias correction of the satellite SM data was able to improve their performance in characterizing agricultural drought via SM-based indices. Compared with SWDI, SMCI appeared to be the more appropriate index for drought monitoring, by showing a better agreement with both VCI and VDI in terms of drought characteristics (i.e. spatial distribution, drought category and frequency), though both SM-based indices overestimated drought severity to some extent. A simply SM-based drought indicator could be effective when satellite SM was applied for capturing agricultural drought, and a full consideration of longer term satellite data might be necessary.