Evapotranspiration partitioning using an optimality-based ecohydrological model in a semiarid shrubland

Partitioning of evapotranspiration (ET) into biological component transpiration (T) and non-biological component evaporation (E) is crucial in understanding the impact of environmental change on ecosystems and water resources. However, direct measurement of transpiration is still challenging. In this paper, an optimality-based ecohydrological model named Vegetation Optimality Model (VOM) is applied for ET partitioning. The results show that VOM model can reasonably simulate ET and ET components in a semiarid shrubland. Overall, the ratio of transpiration to evapotranspiration is 49% for the whole period. Evaporation and plant transpiration mainly occur in monsoon following the precipitation events. Evaporation responds immediately to precipitation events, while transpiration shows a lagged response of several days to those events. Different years demonstrate different patterns of T/ET ratio dynamic in monsoon. Some of the years show a low T/ET ratio at the beginning of monsoon and slowly increased T/ET ratio. Other years show a high level of T/ET ratio for the whole monsoon. We find out that spring precipitation, especially the size of the precipitation, has a significant influence on the T/ET ratio in monsoon.