A Novel Synergistic LST-SWIR Index for Evapotranspiration Estimation and Drought Assessment

Accurate mapping of evapotranspiration (ET) via remote sensing is crucial for water resource management, yet it remains challenging in water-limited environments where existing water stress proxies often lack physical robustness or spatiotemporal detail.

We here propose the Temperature-Shortwave Infrared Water Index (TSWI), a synergistic index that directly couples land surface temperature (LST) and shortwave infrared (SWIR) reflectance for ET estimation. TSWI demonstrates strong agreement with in-situ soil moisture and consistency with SMAP and MODIS products. TSWI-based ET estimates perform robustly against flux tower data (R² = 0.64) and water-balance ET (R² = 0.83). Moreover, the standardized TSWI effectively captured the 2022 Yangtze River Basin drought with finer detail than conventional indices. These results demonstrate TSWI as a robust, operational tool for regional ET estimation and drought monitoring, supporting improved water management and early warning systems.