Constrained variability of modeled T:ET ratio across biomes

Abstract

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.

Ecohydrological modelling with EcH2O‐iso to quantify forest and grassland effects on water partitioning and flux ages

“…The higher evaporation may be reflected in the low T:ET ratios for the forest and grassland plots which are only 40 and 44%, respectively. This compares with literature values more typically ~70% (e.g., Fatichi & Pappas, ; Good, Noone, & Bowen, ; Schlesinger & Jasechko, ), whereas 58% was reported by Soubie, Heinesch, Granier, Aubinet, and Vincke () for a similar mixed forest in Belgium. Thus, despite the effective use of vegetation data to calibrate the model in terms of biomass production and allocation, the data were insufficiently detailed to avoid this uncertainty in the partitioning of soil evaporation and transpiration.…”

Modelling carbon sources and sinks in terrestrial vegetation

“…Average annual values of litter production in terms of (a) reproductive‐fall (fruits and flowers) and (c) leaf‐fall as function of precipitation as derived from the global database of litterfall mass and litter pool carbon (C) and nutrients (Holland et al ., ). Superimposed onto observations are the simulations with the Tethys–Chloris model at the ecosystem scale for 79 sites world‐wide characterized by different biomes and climates (Fatichi & Pappas, ). Simulated ratios between C reserve, annual net primary productivity ( NPP ) and annual leaf‐fall (subplots (b) and (d), respectively) are also shown as a function of mean annual precipitation.…”

“…Observed values of forest carbon use efficiency ( CUE ) as a function of gross primary production ( GPP ; data from Litton et al ., ; DeLucia et al ., ) compared with simulated values of CUE with the Tethys–Chloris model at ecosystem scale for 79 sites world‐wide characterized by different biomes and climates (Fatichi & Pappas, ). The lack of correlation between CUE and GPP and the spread of observations are comparable for both model results and observations.…”

Ecohydrological dynamics in the Alps: Insights from a modelling analysis of the spatial variability

“…We used the mechanistic ecohydrological model T&C (Fatichi, Ivanov, & Caporali, ; Fatichi & Leuzinger, ; Fatichi & Pappas, ; Manoli, Ivanov, & Fatichi, ; Pappas, Fatichi, & Burlando, ), which simulates the principal processes of the hydrological cycle, such as precipitation interception, transpiration, ground evaporation, infiltration, and surface/subsurface water fluxes, including the lateral transfer of water. It further simulates plant‐related processes, such as photosynthesis, phenology, carbon allocation, and tissue turnover.…”

“…We used vegetation parameterizations derived from previous applications of T&C for sites of the Swiss FluxNet network (Wolf et al, ), which reproduce realistically carbon, water, and energy responses (Fatichi & Pappas, ; Fatichi, Rimkus, Burlando, Bordoy, & Molnar, ; Fatichi, Zeeman, Fuhrer, & Burlando, ). Only discharge data from two sites are available for validating the hydrological response in the Kleine Emme catchment (Table S1).…”