Project title: The Tropical Expansion and its Effects on Summer Droughts and Floods in the Greater Mekong Subregion

 

Funded by Thailand Science Research and Innovation (TSRI, formerly TRF) under collaboration with National Natural Science Foundation of China (NSFC).

 

Period: 3 years (3 December 2018 – 2 December 2022)

 

 

Global climate change causes the expansion of the tropical zone. This project aims to investigate its characteristics in the Greater Mekong Subregion (GMS) and its relationship to floods and droughts in the region. The study comprises five parts. The first part is to analyze the spatial and temporal variations of regional tropical expansion in the GMS. In this part, the three indices namely high cloud cover, brightness temperature and precipitation minus evaporation, were introduced and used to indicate the tropical expansion in the GMS. The results from the three indices show the expansion only in the winter season. The second part is to study the spatial and temporal variations of summer monsoon circulation in the GMS. Indian summer monsoon index (ISMI) calculated from meridional velocities at 850 hPa and 200 hPa was used in this part. There is high correlation between the ISMI and all three tropical expansion indices around the tropics and the edge of the Hadley cell. The third part is to investigate the spatial and temporal variations of droughts and floods in the GMS. The SPI-12 index calculated from precipitation was used as the index. We found that the spatial variation of the SPI over the GMS related to El-Nino and La-Nina years, and the temporal variation related to the expansion of the tropical edge. The fourth part is to distinguish the main processes of the impacts of variability among tropical expansion and summer monsoon circulation on droughts and floods in the GMS. In this part, the forcing field relating to the tropical expansion and summer monsoon were also introduced in terms of sea surface pressure, total ozone column, tropospheric ozone, aerosol optical depth, Southern Oscillation Index and high cloud cover at the equator. In this study, sea surface temperature was pronounced to explain the mechanism of the tropical expansion, which is the aim of the final part to reveal the mechanism for the effect of tropical expansion on the droughts and floods in the GMS.

 

Figure 1 Diagram presenting the mechanism of the tropical expansion

 

This project also helps to build a research team, a Ph.D. student, and a young scientist, who work on regional climate and environment change. The collaboration between Thai-Chinese research teams has been continued.

 

Publications:

-     Chanalert, W., Buntoung, S., Nunez, M., Masiri, I., Nimnuan, P., Choosri, P., Charuchittipan, D., Janjai, S. and Cao, J. (2022). The Greater Mekong Subregion (GMS) and Tropical Expansion: A Regional Study of Convection and Precipitation, Advances in Space Research, 69 (2022), 2443-2549.

-     Wen, D., Cao, J., Zhao, C., Masiri, I. and Buntoung, S. (2021). Interdecadal variation of summer rainfall in the Greater Mekong Subregion and its possible causes. Environmental Research Letters 16. 084064.

-     Gui, S., Yang, R., Cao, J., Tan, S., Janjai, S. and Dong, Z. (2021). The influence of the Atlantic multidecadal oscillation on the interdecadal variability of winter precipitation in the Greater Mekong Subregion. International Journal of Climatology. 41, 5072– 5083. https://doi.org/10.1002/joc.7117.