Rainy season precipitation variation in the Mekong River basin and its relationship to the Indian and East Asian summer monsoons

Ruowen Yang,Shu Gui,Jie Cao,Wei-Kang Zhang,Yun Tao

doi:10.1007/s00382-018-4471-1

Abstract

In this paper, we study the relationship between the covariability of the Indian summer monsoon (ISM) and East Asian summer monsoon (EASM) and the rainy season precipitation anomaly in the Mekong River basin (MRB) using ERA-Interim reanalysis data and precipitation from the Climate Hazards Group Infrared Precipitation station for 1981–2016. The results indicate that the interannual variability of the rainy season precipitation in the MRB is significantly modulated by the ISM and EASM covariability. Herein, the ISM mainly influences the rainy season precipitation west of the MRB, and the EASM mainly influences the rainy season precipitation over the southeastern MRB. When the Bay of Bengal (BOB) and South China Sea (SCS) are dominated by positive anomalies of diabatic heating associated with a stronger ISM and EASM, the anomalous westerly winds in the BOB and significantly anomalous easterly winds in the SCS, which carry more warm-wet air, induce a stronger than normal convergence and upward motion in the MRB. This results in much heavier rainy season precipitation in the MRB. Model runs with a linear baroclinic model confirm the observational analysis results.

Highlights

The Mekong River basin (MRB), one of the most important transboundary rivers in southeast Asia, starts in Tibet, flows from China’s Yunnan Province to Vietnam, and empties into the South China Sea (Fig. 1)
The correlation coefficient associated with the ISMI is 0.253, which did not pass the significance test even at the 90% confidence level, and the correlation coefficient related to the EASMI is 0.294, not passing the significance test at the 95% confidence level
These results suggest that the individual Indian summer monsoon (ISM) or East Asian summer monsoon (EASM) may not significantly regulate the rainy season precipitation in the MRB

Summary

Introduction

The Mekong River basin (MRB), one of the most important transboundary rivers in southeast Asia, starts in Tibet, flows from China’s Yunnan Province to Vietnam, and empties into the South China Sea (Fig. 1). The quantitative relationship between the ISM and EASM covariability, anomalous MRB precipitation during the rainy season and corresponding physical processes remains unclear. This condition motivates us to determine whether there is a significant relationship between the ISM and EASM covariability and the anomalous precipitation over the MRB during the rainy season. 3, the relationship between the rainy season precipitation anomaly in the MRB and the ISM or EASM is investigated, revealing the possible physical processes through which the ISM and EASM covariability influences the interannual variability of the rainy season precipitation in the MRB. 3 and are used to confirm the relationship and associated physical processes revealed in Sect.

Data and method

Observational analysis

Rainy season precipitation anomalies in the MRB

Anomalous circulation patterns

Model results

Summary