Multi-year evapotranspiration estimates from four common vegetation types in a montane region of the intermountain west

Abstract

Evapotranspiration (ET) is a major component of water balance and is crucial for understanding the hydrological processes, however due to highly heterogeneous distributions of soils and plants, accurate quantification of ET remains a major challenge in montane ecosystems. In this study, water use for four common vegetation communities was numerically modeled using Hydrus-1D over four continuous growing seasons (2009 to 2012), supported by a network of soil water content sensor measurements. Plant species included i) aspen (Populus tremuloides) with understory dominated by grass/forb (rudbeckia occidentalis, Bromus carinatus and Elymus trachycaulu), ii) conifer (Picea engelmannii and Abies lasiocarpa), iii) grass (dominated by B. carinatus and E. trachycaulu, et al.), and iv) sage (Artemisia tridentata). The numerical model simulated water transport within the soil and water loss from soil evaporation and plant transpiration processes. Simulations were compared with temporal and spatial dynamics of soil water content, measured at 0.1 m, 0.25 m and 0.5 m within each of 36 subplots at 30-minute intervals. Numerically simulated ET in the sage/grass meadow was compared with ET determined from a centrally-located eddy covariance tower. The simulations effectively predicted soil moisture and ET of the montane plant communities during summer dry down. Results indicate vegetation type showed no significant difference (<5 %) in ET comparing four growing seasons, except where abnormally wet conditions occurred. Four-year mean cumulative growing season ET estimates for aspen, deep-rooted conifer, shallow rooted conifer, sage, and grass were 43.0, 40.2, 28.7, 28.8 and 26.1 cm, respectively.