Surface Soil Moisture Drydown over the Tibetan Plateau from SMAP: Consistency with In Situ Observations, Spatial Patterns and Controls

Soil moisture (SM) mediates land–atmosphere water and energy exchanges and is therefore central to evapotranspiration, drought evolution, and hydroclimate extremes. The SM drydown timescale (τ), typically derived from exponential decay fits following rainfall or snowmelt rewetting, provides a compact measure of near-surface “memory” and drying rate. Despite the availability of microwave satellite SM products, their reliability for drydown characterization over the Tibetan Plateau remains uncertain, and systematic evaluations of drydown events and τ against in situ networks are still limited. Here, we integrate five Tibetan Plateau (TP) soil moisture sensor networks with SMAP to (i) assess consistency in drydown event detection and τ estimation across observation systems and (ii) map TP-wide τ patterns and identify dominant controls using SMAP (2016–2025). SMAP-derived τ is generally smaller than in situ τ, indicating a faster drying signal in the satellite product; this may be attributed to differences in effective sensing depth and spatial representativeness between satellite footprints and point measurements. TP SMAP τ exhibits a pronounced southeast-to-northwest decreasing gradient, with the shortest τ over the arid interior. Partial least squares regression identifies elevation, sand fraction, and vegetation conditions as primary drivers of spatial τ variability. This research provides observational constraints for understanding land-surface hydrological processes and land–atmosphere coupling in alpine regions.