Modelling plant canopy effects on annual variability of evapotranspiration and heat fluxes for a semi-arid grassland on the southern periphery of the Eurasian cryosphere in Mongolia

The ability to predict vegetation cover effects on thermal/water regimes can enhance our understanding of canopy controls on evapotranspiration. The Simultaneous Heat and Water (SHAW) model is a detailed process model of heat and water movement in a snow-residue-soil system. This paper describes provisions added to the SHAW model for vegetation cover and simulation of heat and water transfer through the soil-plant-air continuum. The model was applied to four full years (May 2003-April 2007) of data collected on sparse grassland at Nalaikh in north-eastern Mongolia. Simulated soil temperature and radiation components agreed reasonably well with measured values. The absolute differences between simulated and measured soil temperatures were larger at both the surface layer and deeper layer, but relatively smaller in the layer from 0.8 to 2.4 m. Radiation components were mimicked by the SHAW model with model efficiency (ME) reaching 0.93-0.72. Latent and sensible heat fluxes were simulated well with MEs of 0.93 and 0.87, respectively. The vegetation control on evapotranspiration was investigated by sensitivity experiments of model performance with changing leaf area index (LAI) values but constant of other variables. The results suggest that annual evapotranspiration ranged from 16 to -22% in response to extremes of doubled and zero LAI. Copyright (C) 2010 John Wiley & Sons, Ltd.