Modeling Evapotranspiration In a Semi-Arid Mountain Ecosystem Integrating HYDRUS-1D and Weather Data.

The main source of fresh water in the western US is derived from snowmelt in mountain ecosystems, which often become water-limited late in the summer. Evapotranspiration (ET) is the major water loss process between land and atmosphere in these ecosystems. Although there are a number of ET measurement approaches including soil- and plant-weighing lysimeters, soil water budget, sap flow, growth chambers, chemical tracers, etc., limited information and monitoring capabilities are available for montain vegetation. To better understand this process, ET was modeled during the growing season using measured environmental parameters to estimate vegetation water use. The T.W. Daniel Experimental Forest has advanced instrumentation allowing long-term study of energy inputs from weather and hydrology.The site has four majorvegetation types including spruce/fir, grass/forb, sagebrush, and aspen. The HYDRUS-1D numerical model was used to simulate soil evaporation and plant root water uptake (transpiration)from these four dominant vegetation typesin theDaniel Forest using the environmental data as fitting parameters.A water stress coefficient curve foreach vegetation type was estimated and plotted for the growing season between snowmelt-out and September 30.Modeled water use responses for these vegetation species provide improved evapotranspiration estimates for land surface and climate modeling efforts in mountains of the Western US.