Estimating Water Use in a Semi-Arid Montane Ecosystem Using a Soil Moisture Network and Numerical Modeling.

Fresh water supplies in the western US are largely derived from snow melt within montane ecosystems that often become water-limited later in the year. Water use by varied montane ecosystems can impact downstream water supply through diminished soil water storage, which must be replenished prior to stream and ground water recharge. We used field measured water content coupled with HYDRUS-1D numerical modeling to simulate growing season evapotranspiration (ET). Our objectives were to estimate evaporation (E), transpiration (T) and ET from four common semi-arid montane vegetation types (Aspen, Conifer, Grass/Forb and Sagebrush) over a four year period at the instrumented T. W. Daniel Experimental Forest (TWDEF) located in Northern Utah. We estimate the growing-season variation in E, T, and ET fluxes and relate the variability of these to the soil water content (θ) and reference ET (ET₀).  The patterns of E, T and ET were also compared based on vegetation type, calendar year and canopy duration. Results show the timing of the annual peak E, T and ET cycles, which vary among years for each vegetation type. The total annual E, T and ET exhibit no significant difference among years for specific vegetation, but show significant differences between trees (Aspen and Conifer) and non-trees (Sage and Grass/Forb).  Considering the canopy duration affected by snow melt timing, ET exhibits significant difference among years for the same vegetation type.