Sensitivity Experiments On Impacts Of Large-scale Land Use And Land Cover Change On Surface Energy, Hydrology Balance And Regional Climate Over East Asia

Using the NCAR Community Land Model (CLM4.0) and Community Atmosphere Model (CAM4.0), the numerical experiments of potential vegetation and current vegetation distribution were carried out. Through the comparison of experiment results, the possible influence of the land-use and land cover change on surface energy balance, water cycle and regional climate over East Asia has been discussed. The main conclusions are as follows:(1) Significant differences of LAI and albedo among various lying surfaces leaded to different effects on radiation. The shortwave radiation was the main factor of the net radiation change. Over all the selected lying surfaces, the maximum of net shortwave radiation appeared in winter and the minimum in summer. The maximum of net long-wave radiation over bare and grass appeared in summer, but in winter over tree and crop. The largest monthly fluctuation range of the net radiation was over grass. The overall trend of the sensible heat flux was increased first and then decreased. The rank of the latent heat flux (from high to low) was tree, crop, grass and bare ground, and the largest monthly fluctuation amplitude of the latent heat flux was over crop. The peak value of latent heat flux was higher than that of sensible heat flux in summer. There were significant changes of the monthly change of transpiration over tree and crop, but weak change over grass. And the evaporation was increasing with the vegetation growing. The change of canopy transpiration was consistent with the change of canopy evaporation. The surface soil moistures over crop and tree were obviously larger than that over grass and bare ground. And the largest monthly fluctuation amplitude of the surface soil moisture was over grass.(2) The land cover change performed as the forest degradation and the rapid increasing in cropland made global net shortwave radiation decreased, and the area was corresponding well to the area where albedo changed. The albedo increases (decreases) caused the shortwave radiation deceased (increased), leading to the sensible heat flux decreased (increased). The land cover change effects on global evapotranspiration were weak. But the impact of land cover change on regional scale climate cannot be ignored, and the climate effects were different owing to the different regions. The albedo was the main factor to influence radiation budget in Ease Asia and Northern America, but the climate effects were characterized of obvious wet and dry seasons through the year in India and South America. In dry seasons, the energy change was mainly caused by increasing albedo, leading to sensible heat flux decreased. But in wet seasons, canopy transpiration was decreased because of deforestation, and resulted to ET and latent heat flux decreased.(3) Current LUC featured by rapid forest degradation and increasing cropland significantly alters the land surface characteristics, leading to increase of surface albedo in all seasons over East Asia, which in turn changes the surface energy balance and hydrological cycles over this region. In addition, impacts of large-scale LUC on the general circulation over East Asia are also detected. Current LUC tends to cause evidently stronger winter monsoon circulation and slightly enhanced summer monsoon. No evident changes of air temperature induced by LUC was found, but more (less) spring precipitation happens in the north (south) of East Asia under the impacts of LUC.