Precipitation and evapotranspiration partitioning on the Three-River Source Region: A comparison between water balance and energy balance models

Study Region: Three-River Source Region, Qinghai-Tibetan Plateau, China. Study Focus: Evapotranspiration (ET) is often the largest loss of water from grassland ecosystems and consists of two constituents: evaporation (E) and transpiration (T), but it is very difficult to separate E and T. In this study, we used an energy balance model (Shuttleworth-Wallace) and a water balance model (SOILWAT2) to estimate the water budget variables over a 10-year period (2007–2016) in a degraded alpine meadow in the Three-River Source Region on the Qinghai-Tibetan Plateau. New Hydrological Insights for the Region: The models produced contrasting patterns of precipitation and ET partitioning at the study site. Precipitation partitioning by SW2 resulted in substantial fluxes of both ET and deep drainage, while ET estimated by SW consumed almost all precipitation. ET was partitioned by the models into different annual E and T fluxes as well as different monthly and annual T/ET. Our study site located in an important water source region suggests that its water balance would contribute to drainage which aligns better with SW2 results. The surprising discrepancies between the models in the partitioning of precipitation into T, E, and deep drainage, however, is limiting our understanding and management of the degraded site and will require future work to reconcile.