The Impacts of Land Degradation on the Summer Climate over East Asia and mechanisms

Abstract:

There were serious land degradations over East Asia during the past several decades and have identified Tibet Plateau (TP), Northwest China (NWC) and Inner Mogonial (IM) were among areas with severe land degradation. The GCMs with a natural vegetation map and a land degradation map were used to assess the possible impact of land cover change on the summer circulation over the East Asia. In the IM land degradation study, it shows the land degradation caused dry conditions in North China and wet conditions in southern China. Because in the desertification area the reduction in evaporation dominants the changes in the local surface energy budget, and the reduction in convective latent heating above the surface layer enhanced sinking motion. In the TP and NWC study, it shows that land cover change from vegetated land to bare ground over TP and NWC decreased radiation absorbed by the surface and leads to weaker surface thermal effects, which lead to lower atmospheric temperature over, as well as weaker vertical ascending motion, low-layer cyclonic, upper level anticyclonic over TP. These changes in circulation cause a decrease in the precipitation in the southeastern TP. In NWC, especially in northern Xinjiang and surrounding areas, less latent heating causes stronger anomalous lower-level anticyclonic circulation and upper-level cyclonic circulation, leading to less summer precipitation and higher surface temperature. Coincidentally, the East Asia summer monsoon circulation was weakened and the precipitation is reduced due to the land degradation over three areas.