Impact of Indochina deforestation on the east Asian summer monsoon

This paper describes a study that investigates the local and remote effects of Indochina deforestation on the east Asian summer monsoon. During the summer months, the peninsula is subject to strong monsoonal flow whose downstream rainfall is of vital importance for China, where a significant fraction of the world's population lives. It is, therefore, extremely important to investigate how the landscape change affects this monsoonal flow, and whether this effect is strong enough to cause notable changes in the regional rainfall. For this reason, a modeling experiment with the International Pacific Research Center regional climate model was carried out. Ensemble simulations with the current vegetation cover in the peninsula and its reforested scenario were performed for the period from 20 April to 31 August 1998. The results of the experiment indicate that deforestation in the peninsula has not only local, but also far-reaching effects on the east Asian summer monsoon. Locally, the effect could be described as increases in wind speed and temperature, and as a decrease in water vapor mixing ratio from the surface up to about 850 mb. Furthermore, the deforestation tends to enhance the rising motions, and, hence, tends to reduce surface pressure and geopotential height up to about 850 mb over the deforested area. The local landscape changes tend to increase rainfall on the downwind side and decrease it on the upwind side. Far-reaching effects in summer include a weakening of the monsoonal flow over east China, near the Tibetan Plateau, and a strengthening over the neighboring seas to the east. These changes yield sandwich-type drier and wetter bands that are elongated along the main flow path of the east Asian summer monsoon. A comparison of the modeled changes with the observed rainfall trends suggests that the deforestation in the Indochina Peninsula could be one of the major factors causing changes in the climate of the region.