Tropical Cyclone produced rainfall trends in Vietnam and their relationship with the North Pacific (NP) pattern during 1979 – 2021

This study investigated long-term changes of tropical cyclones (TCs) activity and rainfall produced by TCs, hereafter TC-rainfall, over Vietnam in the period of 1979-2021. Furthermore, it is investigated how rainfall changes are influenced by the North Pacific (NP) pattern.

First, it was found that TC activity has not changed significantly in its frequency, and its related rainfall including TC and tropical depression (TDs) produced rainfall, hereafter TCTD-rainfall over entire Vietnam. On the other hand, significant increasing trend of TC activity (XX per 10 year), TC-rainfall (65 mm per 10 year), TCTD-rainfall (75 mm per 10 year), and total rainfall (440 mm per 10 year) is found in North Vietnam in the period of 1979-2021. However, TC, TD activity, TC-rainfall and TCTD-rainfall did not show any significant trends in Central and South Vietnam. Second, decadal and inter-decadal variation of rainfall in North Vietnam are significantly correlated with the North Pacific (NP) pattern during autumn season (October-December). Negative (positive) phases of the NP is characterized by a low (high) sea level pressure (SLP) located over the northern North Pacific Ocean and anomalously warm (cold) sea surface temperature (SST) over central and eastern tropical Pacific, resulting in to less (more) TCs activity and rainfall events over the South China Sea and Vietnam. In summary, it is found that rainfall produced by TCTD exhibits significantly increasing trend in North Vietnam, as well as total rainfall and the NP pattern plays an active role in altering rainfall anomalies in North Vietnam in the decadal and inter-decadal timescales.