Soil evaporation in arid and semi-arid regions is generally moisture-limited. Evaporation in these regions is expected to increase monotonically with increase in precipitation. In contrast, model simulations in a snow-dominated, semi-arid Reynolds Mountain East (RME) watershed point to the existence of an anomalous trend in soil evaporation. Results indicate that soil evaporation in snow-dominated watersheds first increases and then subsequently decreases with increasing precipitation. The anomalous variation is because of two competing evaporation controls: (a) higher soil moisture in wetter years which leads to larger evaporation, and (b) prolonged snow cover period in wetter years which shields the soil from the atmosphere, thus reducing soil evaporation. To further evaluate how the competition is mediated by meteorological and hydrogeological characteristics of the watershed, changes in the trend due to different watershed hydraulic conductivity, vegetation cover, and snowfall area fraction are systematically studied. Results show considerable persistence in the anomalous trend over a wide range of controls. The controlling factors, however, have significant influence both on the magnitude of the WY evaporation and the location of the inflection point in the trend curve.
Wang, R., M. Kumar and D. Marks (2013): Anomalous trend in soil evaporation in semi-arid, snow-dominated watersheds. Advances in Water Resources, 57: 32-40. DOI: http://dx.doi.org/10.1016/j.advwatres.2013.03.004