Impact of Horizontal Resolution of Topograpy on Surface Water Budget over the Tibetan Plateau and Surrounding Mountain Ranges using 60-km-mesh Global Atmospheric Model

Impact of horizontal resolution of topography on surface water budget over the Tibetan Plateau (TP) and surrounding mountain ranges is investigated with 60-km-mesh global atmospheric model. Numerical experiments are conducted under the same boundary conditions except for topography. Horizontal resolution of topography is changed from 60-km (T_L319) to 560-km (T_L31) mesh. Coarser horizontal resolution of topography leads to warmer surface air temperature owing to lower surface elevation over high-altitude regions with complex terrain such as the TP and surrounding mountain ranges. In spring, in which snow line rises as surface air temperature rises, warmer surface air temperature results in not only higher snow line in the same time but also earlier snow line arrival at the same location. Springtime melting and runoff, therefore, occur earlier, which results in snow-free area increase. Increase of snow-free area leads to increase of surface evaporation, and lower surface albedo causes surface absorbed solar radiation increase. Magnitude of these changes is larger in the western TP than in the eastern TP. Processes related to the changes resulted from the differences of horizontal resolution of topography bear a close resemblance to those involved in elevation dependent warming. Results of this experiment suggest that caution is needed for the impact of horizontal resolution of topography on seasonal cycle of surface water budget when climate models with different horizontal resolution are compared, especially in high-altitude regions with complex terrains.