Improving the algorithms for the estimation of wet surface evaporation on the Tibetan Plateau

Abstract

Interception water accounts for 15–50% of precipitation, constituting a vital facet of the hydrological cycle. However, modeling of interception water evaporation over the wet surface of the Tibetan Plateau (TP) is frequently omitted in evapotranspiration models. In this study, a new calculation method for wet surface fraction (F_wet) was introduced to the MOD16-STM evapotranspiration model (Yuan et al. 2021) by reanalyzing the correlation between relative humidity and precipitation responses across the TP region. The new F_wet equation aids in more accurate categorizing wet and dry surface fractions for the TP region. The justification for recalibrating the wet soil resistance for evaporation was also provided. Compared with the MOD16-STM model, optimizations resulted in an increase of R² from 0.45 to 0.76, while RMSE was reduced from 40.1 to 27.1 W m^–2 and MB decreased from –26.2 to 2.3 W m^–2 under wet conditions. The integrated model with the revised wet surface evaporation algorithm exhibited significant performance enhancement‌, ‌particularly through mitigation of wet surface evaporation underestimation‌. The modified algorithm enables improved capture‌ of post-precipitation evapotranspiration variation.