Standardized Soil Moisture Index (SSI)

“SSI is based on the concept of percent of normal precipitation and Palmer Z-index, as well as the statistical construct of SPI. SSI essentially utilizes the z-score to explain how many standard deviations the soil moisture deviates from the historical mean soil moisture, and thus identifies droughts as statistical outliers in the time series



where xSMAP is the soil moisture content from SMAP Level 3 data for a single day, µNLDAS is the mean value of soil moisture content for the corresponding day from NLDAS, and σNLDAS is the standard deviation” (Xu et al., 2018)



Xu, Yaping, Lei Wang, Kenton W. Ross, Cuiling Liu, and Kimberly Berry. 2018. “Standardized Soil Moisture Index for Drought Monitoring Based on Soil Moisture Active Passive Observations and 36 Years of North American Land Data Assimilation System Data: A Case Study in the Southeast United States.” Remote Sensing 10, no. 2 (February): 301.

Related Content


Space technologies for drought monitoring and management

The impacts of climate change are ever more apparent. The frequency and scale of devastation and destruction of weather hazards are on an increasing trend. According to the latest Intergovernmental Panel on Climate Change Report (IPCC, 2021) climate change is intensifying the water cycle. This will cause more intense droughts in many regions. Moreover, water-related extremes impact the quality of life disproportionately strong. Drought accounts for 25% of all losses from weather-related disasters in the United States of America (Hayes et al., 2012).