Assessing drought vulnerability using soil moisture-based water use efficiency measurements obtained from multi-sensor satellite data in Northeast Asia dryland regions

Advanced Very High Resolution Radiometer (AVHRR) Normalized-Difference Vegetation Index (NDVI) and soil moisture data from the Special Sensor Microwave Imager (SSM/I) were utilized to derive Soil Moisture Use Efficiency (SMUE). SMUE, serving here as a proxy for the commonly used Water Use Efficiency (WUE), was used to evaluate drought vulnerability (i.e., the degree of drought stress and sensitivity) in the Northeast Asia drylands for the period of 1987-2006. SMUE was defined as the ratio of June-August NDVI accumulation (NDVIacc) to average soil moisture (SMavg). This ratio was utilized to derive two additional indices representing drought stress (DSI) and sensitivity (DVI). We confined our vulnerability analyses to low NDVI regions because the determination of SSM/I soil moisture is unreliable in areas with high biomass. Both DSI and DVI identified high drought vulnerability in regions of the eastern Kazakhstan grasslands, western portions of the Hexi Corridor in the mid-north of China, the Gobi region, and the southwestern Mongolia grasslands. The identified vulnerable regions covered most of regions with land-degradation expansions or increased sand storm occurrence reported from previous individual studies. This study demonstrated the applicability of our SMUE-based vulnerability indices for identifying drought vulnerability across wide geographic regions.