Role of Vegetation on the Intensity of East Asian Summer Monsoon

Abstract

This present thesis investigates the role of vegetation over East Asian summer monsoon (EASM). The relationship with the vegetation and monsoon is under active research but these previous studies do not have the consistent processes in climate and monsoon when the vegetation increases. To better understand the intensity change of EASM, the more precise study of the vegetation effects on EASM is needed. In this thesis, the effects of vegetation change on EASM is investigated through observations data and model experiments. In observation, the highest 5 years and lowest 5 years are separated from the East Asian (EA) region averaged LAI which is detrended 29 years. When the vegetation increases over EA region, the precipitation increases significantly over northern Asian regions and Korea. On the contrary, the precipitation decreases over Southern Japan and Eastern sea of China. The increase of vegetation derives the increases of evapotranspiration, decreases of surface temperature, weakening the monsoon circulation, and the anomalous anti-cyclone pattern over Southern China and cyclone pattern over Korea by sinking the westerly upper-level jet. To demonstrate the mechanism of vegetation change and monsoon change in observations, the model sensitivity experiments are conducted. In the present condition, the increased vegetation shows dipole pattern of the precipitation change like observation and it is more remarkable in more increased vegetation experiment. Vegetation change in EA region has a linear relationship with the intensity change of EASM.