Long-term changes in rainfall and tropical cyclone activity over South and Southeast Asia

H G Takahashi

doi:10.5194/adgeo-30-17-2011

Abstract

Abstract. Long-term changes in rainfall and associated tropical cyclone (TC) activity in transition seasons between the wet and dry seasons in South and Southeast Asia, namely boreal spring and fall, were examined, using gridded rainfall, TC tracks, and reanalysis datasets, the focus of discussion being the long-term changes in coastal regions. It was found that long-term changes in rainfall during the transition seasons in South and Southeast Asia were closely associated with those in TC activity over the north Indian Ocean and South China Sea. Rainfall in May increased in the last 40 years over and around Myanmar, which indicates an earlier monsoon onset over the western Indochina Peninsula. Rainfall over and around northern Vietnam also increased in the last 40 years during October, which is known as the monsoon retreat period. These increases were associated with the long-term changes in TC activity. Furthermore, although linear trends have been previously suggested, monotonically increasing or decreasing trends in these long-term changes were not found over the last 60 years.

Highlights

Long-term changes in rainfall are a major issue of climate change and could influence global circulation, through tropical latent heating, as well as agriculture and human health
Takahashi et al (2009) found that the long-term decrease in rainfall over the Indochina Peninsula was most significant along the eastern coast of Vietnam, where rainfall is strongly affected by tropical cyclone (TC) activity
Because the rainfall in seasonal transition periods between wet and dry seasons is associated with TC activity over South and Southeast Asia, this study focused on these periods

Summary

Introduction

Long-term changes in rainfall are a major issue of climate change and could influence global circulation, through tropical latent heating, as well as agriculture and human health. Many studies have discussed long-term changes in rainfall in the last 100 years over tropical monsoon Asia. Rainfall over South and Southeast Asia is strongly affected by tropical cyclone (TC) activity over the north Indian Ocean and western north Pacific/South China Sea. For example, Singh et al (2000) showed that the frequency of TCs over the north Indian Ocean has increased in May and November and weakened in September over the last 100 years, which was likely to affect long-term changes in rainfall. Takahashi and Yasunari (2008) and Takahashi et al (2009) analyzed observational data and proposed that the long-term decrease in September rainfall over Indochina in the second half of the twentieth century, which was found by Kanae et al (2001), could be explained by the weakening of TC activity over the South China Sea and Philippine Sea regions in September. Takahashi et al (2009) found that the long-term decrease in rainfall over the Indochina Peninsula was most significant along the eastern coast of Vietnam, where rainfall is strongly affected by TC activity. Takahashi and Yasunari (2008) estimated the contribution of TCs including typhoons, tropical storms, tropical depressions, westward-moving intraseasonal disturbances, and residual lows to the total rainfall amount, finding that 70% of the rainfall was associated with TC activity

Results

Discussion

Conclusion