Quantifying the climatic impacts on rainfall in South China and water discharge in the Pearl River (Zhujiang), China

Abstract

Monthly and annual changes in precipitation in South China during 1990-2011 are examined in this study. As located in the sub-tropical climate zone, the annual rainfall in South China is concentrated in the summer. During the same period of time, an average of 9 tropical cyclones approaching South China each year which also contribute ample of rainfall to South China during the tropical cyclone season (June-September). Since the climatic system is interconnected, so this study attempts to examine the combined effect on inter annual rainfall variations in South China due to El Nino Southern Oscillation (ENSO), tropical cyclones affecting South China and the Asian Monsoon. It is generally agreed that during the El Nino onset years, South China would be more wetter, but with less than average tropical cyclones affecting South China. As such, effects on precipitation in South China caused by these two factors offsetting each other and data indicate there is no consistent trend of either more or less rainfall recorded for the El Nino onset years during 1990-2011. On the other hand, the first half of the year right after the El Nino years are in general more wetter than normal. This can be due to the lagging effect of El Nino events normally happened in the winter time, plus the fact that the strength of winter monsoon during the El Nino years is weak, resulting in more rainfall in the following year. Furthermore, annual changes in precipitation in South China directly affect the surface runoff of the Pearl River and a strong positive correlation between the two variables exists for the period 2000-2011. The +/- 25% annual variations and the seasonal variations of rainfall in South China post a challenge to the water resource management in the Pearl River Delta Region. Therefore dams and reservoirs built along the Pearl River are necessary to store surplus rainwater in order to supply sufficient fresh water to the Pearl River Delta Region during the dry seasons or years. On the other hand, further studies and monitoring programs are recommended to continue assessing and evaluating impacts of dam constructions to the environment and the ecosystem of the Pearl River Delta Region.