Constrained variability of modeled T:ET ratio across biomes

A large variability (35-90%) in the ratio of transpiration to total evapotranspiration (referred here as T: ET) across biomes or even at the global scale has been documented by a number of studies carried out with different methodologies. Previous empirical results also suggest that T: ET does not covary with mean precipitation and has a positive dependence on leaf area index (LAI). Here we use a mechanistic ecohydrological model, with a refined process-based description of evaporation from the soil surface, to investigate the variability of T: ET across biomes. Numerical results reveal a more constrained range and higher mean of T: ET (70 +/- 9%, mean +/- standard deviation) when compared to observation-based estimates. T: ET is confirmed to be independent from mean precipitation, while it is found to be correlated with LAI seasonally but uncorrelated across multiple sites. Larger LAI increases evaporation from interception but diminishes ground evaporation with the two effects largely compensating each other. These results offer mechanistic model-based evidence to the ongoing research about the patterns of T: ET and the factors influencing its magnitude across biomes.