Abstract
It is vital to robustly estimate the risks posed by extreme sea levels, especially in tropical regions where cyclones can generate large storm surges and observations are too limited in time and space to deliver reliable analyses. To address this limitation for the South China Sea region, we force a hydrodynamic model with a new synthetic database representing 10,000 years of past/present and future tropical cyclone activity, to investigate climate change impacts on extreme sea levels forced by storm surges (± tides). We show that, as stronger and more numerous tropical cyclones likely pass through this region over the next 30 years, both the spatial extent and severity of storm surge hazard increases. While extreme storm surge events in this location become generally a more frequent occurrence in the future, larger storm surges around Vietnam and China coastlines are projected to regionally amplify this hazard. This threatens low-lying, densely-populated areas such as the Red and Mekong River deltas, while sections of the Cambodian and Thai coastline face previously unseen storm surge hazards. These future hazards strongly signal that coastal flood management and adaptation in these areas should be reviewed for their resilience against future extreme sea levels.
Highlights
It is vital to robustly estimate the risks posed by extreme sea levels, especially in tropical regions where cyclones can generate large storm surges and observations are too limited in time and space to deliver reliable analyses
We identified all cyclone events in IBTrACS for the Western North Pacific (WNP) region and for the period 1970 to 2020, which: (1) made land fall along the coast of Vietnam; (2) have matching measured sea level data at a tide gauge close to the land fall location; and (3) capture the storm surge in the measured records for that event
The STORM database shows a decrease in frequency of tropical cyclone (TC) globally, including in the WNP region, but 295 we found in the area of our smaller model domain, all four future STORM datasets show an increase in TC frequency
Summary
The warming of the Earth’s seas as a result of anthropogenic climate change represents a pressing challenge to humanity. Because of projected sea-level rise, between 2.5% and 4.1% of the world’s population is estimated to 35 be at risk of 1% Annual Exceedance Probability (AEP; 1:100 year) coastal flooding by 2100, under the mean SSP5-8.5 scenarios and assuming no coastal flood defences (Kirezci et al, 2020) This is an increase of 52% compared to the coastal populations affected by this hazard today. Despite the gravity of the issue, the two most recent reports of the Intergovernmental Panel on Climate Change (IPCC) underscore that there is currently ‘low confidence’ in our ability to predict how storm surges may contribute to changes in future sea level extremes (Wong et al, 2014; Fox-Kemper et al, 2021) This deep uncertainty arises from the significant challenge of predicting changes in tropical and mid-latitude cyclone activity at a regional scale, and because of the small number of storm surge studies available at the time of the last IPCC Assessment Review. Analysing extreme storm surge behaviour, and estimating storm surge hazard, ideally requires long (>100 years) temporal records, which do not exist in most tropical regions (Irish et al, 2011)
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