Evapotranspiration partitioning over the Tibetan plateau: Spatial-seasonal patterns and possible controls

The ecosystem and hydrological cycles associated with evapotranspiration (ET) may experience varied extremes under different climatic conditions. Understanding the spatial-seasonal patterns of the transpiration-to-evapotranspiration ratio (T/ET) over the Tibetan Plateau (TP) is critical due to their impacts on hydrology, carbon cycling, and water resource management. However, quantifying T/ET ratios in the high and remote TP regions is practically challenging due to difficulties in obtaining measurements and capturing data. In this study, we used new approaches to partition each ET component, and identified the spatial-seasonal T/ET patterns and possible controls at three catchments in different climate zones over the TP. The datasets included water stable isotopes, hydrological records, ground-based climate variables, China Meteorological Forcing Dataset reanalysis (CMFD), MODIS Normalized Difference Vegetation Index (NDVI), and Global Inventory Modeling and Mapping Studies ET. Results showed that: (1) Large proportions of soil evaporation (Esoil, >50 %) occurred with non-isotope fractionation (E2), especially in arid catchment with intensive soil siphonage during infrequent and highly concentrated precipitation events; (2) Large-scale circulations influenced precipitation and NDVI, resulting in spatial T/ET patterns over the TP (increasing from the Westerlies Zone to the Indian Monsoon Zone); (3) Seasonal T/ET patterns were associated with varying vegetation coverages superimposed on large-scale circulations: summer–low, annual-high patterns at Magazangbu or Lhasa catchments with vegetation cover < 50 %, inversely at Naqu catchment (>50 %); (4) Catchment-scale ET partitioning over the TP generally aligned well with global T/ET patterns. The ET partitioning and spatial-seasonal patterns presented here significantly enhance our understanding of ecological and hydrological process and support investigations into T/ET forcing mechanisms across different climate zones of the TP.