Transpiration and evaporation of grassland using land surface modelling

Partitioning transpiration (T) from evapotranspiration (ET) is a key process for understanding the interaction between land surfaces and the atmosphere. This paper reports daily partitioning results for a grassland over a 10‐year period, obtained using the Community Land Model 3.5 (CLM3.5) land surface model. Hourly forcing data were collected from a long‐term observation system located in the northeast of Japan (http://doi.org/10.24575/0001.198108). To test the model behavior, total ET was validated using eddy correlation measurements combined with the energy balance method. The results were compared with previous research using an isotope approach for partitioning. The results demonstrate that our model can capture the dynamics of ET and its components at this location. Evaporation (E), originating from the ground and canopy, varied inter‐annually, and from 2006 to 2015, average annual E was approximately 285 mm/year from the ground and 45 mm/year from the canopy. Average, T, was approximately 302 mm/year, accounting for approximately 48% of the total ET. Inter‐annual results demonstrate that the water flux transported by vegetation ranges from 17 to 83% during the April–October period. A sensitivity test conducted with forcing data indicates air temperature, incident solar radiation, and longwave radiation exhibited a notable effect on all ET components. Relative humidity exhibited the only negative feedback to both evaporation and transpiration, contrary to the other forcing parameters. Our study reemphasized the effectiveness of CLM3.5 in partitioning T from ET and in understanding the complex interaction between land surfaces and the atmosphere. Results showed that evaporation, originating from bare ground and canopy, varied inter‐annually. From 2006 to 2015, the averages of annual evaporation from the ground were about 284.8 mm/year, and evaporation from canopy was about 45.3 mm/year. The average amount of transpiration was about 302.4 mm/year, which accounted for about 47.8% of the total evapotranspiration. The inter‐annual results showed that the water flux transported by vegetation ranged from 10 to 70%. The single sensitivity test of the forcing data to evaluate the effect on all components of evapotranspiration was conducted, involving air temperature, incident solar radiation, longwave radiation, precipitation, wind speed, and relative humidity. Relative humidity shows the only negative feedback to both evaporation and transpiration, which is