Technical note: Including non-evaporative fluxes enhances the accuracy of isotope-based soil evaporation estimates

Abstract

Accurately estimating soil water evaporation is essential for quantifying terrestrial water and energy fluxes. Isotope-based methods are useful but often rely on steady-state (SS) soil water storage assumptions or non-steady-state (NSS) models that ignore non-evaporative fluxes (such as infiltration and transpiration), leading to mass balance errors. Here, we introduce a new framework, named ISONEVA (ISOtope based soil water evaporation estimation considers dynamic soil water storage and Non-EVAporative fluxes), adapted from lake evaporation models to account for both evaporative and non-evaporative fluxes in soils under dynamic soil water storage. Validation under virtual and field scenarios demonstrated that ISONEVA improved evaporation estimates by 24.2 %–79.0 % (virtual) and 57.1 %–79.0 % (field) compared to traditional SS and NSS methods. Furthermore, ISONEVA estimated a plausible upper limit of the E/ET ratio (0.15) in the field test, encompassing the observed value (0.126), whereas SS severely underestimated (0.02) and NSS is unable to estimate E/ET. These results highlight the critical role of dynamic soil water storage and non-evaporative fluxes in isotope-based soil water evaporation estimates.