Attribution of typhoon-induced torrential precipitation in Central Vietnam, October 2020

Linh N Luu,Sarah Kew,Kien Ba Truong,Thang Van Vu,Sjoukje Philip,Paolo Scussolini,Gerard Van Der Schrier,Khiem Van Mai,Geert Jan Van Oldenborgh,Robert Vautard,Friederike Otto,Mugni Hadi Hariadi,Maarten K Van Aalst

doi:10.1007/s10584-021-03261-3

Abstract

In October 2020, Central Vietnam was struck by heavy rain resulting from a sequence of 5 tropical depressions and typhoons. The immense amount of water led to extensive flooding and landslides that killed more than 200 people, injured more than 500 people, and caused direct damages valued at approximately 1.2 billion USD. Here, we quantify how the intensity of the precipitation leading to such exceptional impacts is attributable to anthropogenic climate change. First, we define the event as the regional maximum of annual maximum 15-day average rainfall (Rx15day). We then analyse the trend in Rx15day over Central Vietnam from the observations and simulations in the PRIMAVERA and CORDEX-CORE ensembles, which pass our evaluation tests, by applying the generalised extreme value (GEV) distribution in which location and scale parameters exponentially covary with increasing global temperatures. Combining these observations and model results, we find that the 2020 event, occurring about once every 80 years (at least 17 years), has not changed in either probability of occurrence (a factor 1.0, ranging from 0.4 to 2.4) or intensity (0%, ranging from −8 to +8%) in the present climate in comparison with early-industrial climate. This implies that the effect of human-induced climate change contributing to this persistent extreme rainfall event is small compared to natural variability. However, given the scale of damage of this hazard, our results underline that more investment in disaster risk reduction for this type of rainfall-induced flood hazard is of importance, even independent of the effect of anthropogenic climate change. Moreover, as both observations and model simulations will be extended with the passage of time, we encourage more climate change impact investigations on the extreme in the future that help adaptation and mitigation plans and raise awareness in the country.

Highlights

1.1 Characterisation of the cyclonic events of October 2020In October 2020, Vietnam was greatly affected by several persistent heavy precipitation events occurring sequentially during the month
Massive quantities of moisture brought by the easterly winds were uplifted upon meeting the high topography of the Truongson mountain range, which lies along the boundary between Vietnam and Laos (Fig. 1a), leading to heavy rainfall lasting until 9 October
In order to verify the ability of models to properly simulate seasonal rainfall, we compute the annual cycle of rainfall averaged across all 40 stations for observations and all grid points for models over Central Vietnam for 7 models that pass the previous evaluation. We find that those simulations are able to reproduce the observed peak of the rainy season for Central Vietnam in the autumn, coinciding with the active season of typhoons and tropical depressions

Summary

Introduction

1.1 Characterisation of the cyclonic events of October 2020In October 2020, Vietnam was greatly affected by several persistent heavy precipitation events occurring sequentially during the month. Massive quantities of moisture brought by the easterly winds were uplifted upon meeting the high topography of the Truongson mountain range, which lies along the boundary between Vietnam and Laos (Fig. 1a), leading to heavy rainfall lasting until 9 October. Typhoon Linfa struck the coast of Vietnam on 11 October around 16° N (Fig. 2b). This typhoon produced heavy rainfall along its westward path over Vietnam until the 13th of October. During this event, a few stations observed rainfall in excess of 550 mm in a day, with a peak of 629 mm/day at the Namdong station on 10 October (Fig. 1b)

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