Relative Roles of Large-Scale Orography and Land Surface Processes in the Global Hydroclimate. Part II: Impacts on Hydroclimate over Eurasia

Abstract

A series of simplistic simulations from an AGCM coupled to a simple land surface scheme and water vapor tracers was performed to explore the relative roles of basic factors in land surface conditions, with regard to the seasonal evolution of the hydroclimate over Eurasia. Large-scale orography in Asia and vegetation (further decomposed to soil and vegetation skin) were evaluated, with orography represented in the model by surface altitude, soil represented by water-holding capacity, and vegetation skin represented by surface albedo and roughness. The percentage of global annual precipitation over land (occupying 25.6% of the total surface) was 14.8%, 15.0%, and 21.7% for the mountainless ?bare rock? (i.e., vegetationless) surface, and the bare-rock and vegetated surface, respectively. The result for evaporation was 8.9%, 9.0%, and 16.2%, respectively, showing higher sensitivity to the land surface changes than precipitation. The orography and vegetation (i.e., soil and vegetation skin) showed different impacts on Eurasian hydroclimate on the seasonal and regional scales. Thermodynamical forcings to the atmosphere increased over the continent with the inclusion of both. Large-scale orography in Asia exerted east?west contrast in the surface energy exchange in summer in eastern Eurasia. An increase in extratropical winter precipitation with mountains was also noticed because of the atmospheric vapor transport changes. Impact of soil and vegetation skin was clearly found in the warm season in the extratropics; soil impacts extratropical summer precipitation due to enhanced recycling of water and the resultant increased water supply.