Effects of ENSO on Autumn Rainfall in Central Vietnam

Abstract

28 years (1980–2007) of station and gridded reanalysis data were used to investigate the effects of El Niño/Southern Oscillation (ENSO) on autumn rainfall in the Extended Central Vietnam (ECV) region. Results show that, under El Niño conditions, autumn rainfall in Central Vietnam is reduced by about 10 to 30%. This reduction seems to be caused by a weakening of the North East monsoon circulation, which appears to be linked to an anomalous anticyclonic vortex and a positive sea level pressure anomaly over the East Sea. In addition, the disappearance of a secondary moisture source over the southern region of the East Sea also favors the reduction in rainfall over this region. Conversely, during La Niña, the total autumn rainfall in the ECV region increases by about 9 to 19%. The strengthening of the North East monsoon, with a cyclonic wind anomaly over the East Sea, helps to increase the moisture supply to the area by about 10 to 20%, resulting in enhanced rainfall in the ECV. It is also found that the La Niña conditions do not only cause an increase in rainfall, but also change the temporal distribution of the monthly rainfall over the region, with more rainfall in the latter months of the year.

Influence of the Pacific and Indian Ocean climate drivers on the rainfall in Vietnam

“…And in autumn, the rainfall is much higher than that of winter season with expected coefficient of +18.48 for the contrast between the two seasons. In Central Vietnam, autumn is the season when maximum monthly rainfall occurs and is significantly controlled by cold surges and tropical cyclones (Vu et al, 2015).…”

“…Analysis of rainfall in Vietnam has been conducted by various studies in recent years. Many of these studies (Chen et al, ; Yen et al, ; Vu et al, ) have focused on the central region of Vietnam where heavy rainfall frequently occurs during the autumn period between 11° and 19° latitude as distinct from tropical South East Asia which is about 10° below. In contrast, Southern and Northern Vietnam have maximum rainfall in summer.…”

“…This means that Central Vietnam is drier (wetter) when the SSTs over the NINO3.4 region is warmer (colder). Vu et al (2015) also used station and gridded APHRODITE data to study the autumn rainfall (September-October-November, SON) over Central Vietnam. They found that under El Niño condition, the rainfall is reduced by about 10-30% and during La Niña condition rainfall is enhanced by 9-19%.…”

“…Previous rainfall studies as mentioned above focused on a particular season of interest (e.g., autumn) and the effect of only one climate driver, ENSO, on the rainfall at sites in Vietnam Yen et al, 2011;Nguyen et al, 2014b;Vu et al, 2015). In a study of the relationship between rainfall pattern in Central Highlands and SST patterns in the Indian and Pacific Oceans during the rainy season (April-November), Nguyen et al (2007) have found that, except for May, there is a correlation of rainfall with these SST changes from April to November in Pacific or Indian Ocean or both.…”

Analysing flood fatalities in Vietnam using national disaster database and tree-based methods

“…Flooding is caused by rising water level in rivers during storms or heavy rains or by typhoons in coastal areas. The rainy season or storm season lasts from May to October in the Northern part, from June to December in the Central, and from July to December in the South (Vu et al, 2015). Many inhabitants live along rivers and coasts, and 5 their livelihoods depend heavily on the natural environment.…”