Revisiting the contribution of transpiration to global terrestrial evapotranspiration

Even though knowing the contributions of transpiration ( T ), soil and open water evaporation ( E ), and interception ( I ) to terrestrial evapotranspiration ( ET = T + E + I ) is crucial for understanding the hydrological cycle and its connection to ecological processes, the fraction of T is unattainable by traditional measurement techniques over large scales. Previously reported global mean T /( E + T + I ) from multiple independent sources, including satellite‐based estimations, reanalysis, land surface models, and isotopic measurements, varies substantially from 24% to 90%. Here we develop a new ET partitioning algorithm, which combines global evapotranspiration estimates and relationships between leaf area index ( LAI ) and T /( E + T ) for different vegetation types, to upscale a wide range of published site‐scale measurements. We show that transpiration accounts for about 57.2% (with standard deviation ± 6.8%) of global terrestrial ET . Our approach bridges the scale gap between site measurements and global model simulations,and can be simply implemented into current global climate models to improve biological CO 2 flux simulations.