Global drought monitoring using SMAP soil moisture and effective soil water hydraulic parameters

This study demonstrates an application of remotely sensed soil moisture (θ_RS) from NASA's Soil Moisture Active-Passive satellite level 3 (SMAP L3) data in developing a near real time, global drought monitoring framework at 36 km resolution. A new soil moisture stress index (SMSI) is proposed to calculate the fraction of the maximum plant available water (PAW) in the surface soil profile (0-5cm) by using effective soil water parameters at remote sensing (RS) scale. A piecewise linear curve is fitted to the loss in soil moisture over the retrieval interval ((-Δθ_RS)⁄Δt) and initial soil moisture (θ_RS) to estimate the transition points of soil moisture loss curve (l(θ_RS)),distinguishing the wet, transitional, and dry hydrologic regimes. Multiple temporal aggregations of soil moisture is used as a measure to capture both long- and short- term characteristics of drought. For the purpose of evaluation, the results are compared with the U.S. Drought Monitor (USDM) for the Contiguous U.S. (CONUS) and Normalized Difference Vegetation Index (NDVI) for Brazil. Results indicate promising application of SMSI in real time for drought monitoring across globe.