Coastal town flooding upon compound rainfall-wave overtopping-storm surge during extreme tropical cyclones in Hong Kong

Abstract This study examines the implications of recent advances in global climate modelling for simulating storm surges. Following the ERA-Interim (0.75° × 0.75°) global climate reanalysis, in 2018 the European Centre for Medium-range Weather Forecasts released its successor, the ERA5 (0.25° × 0.25°) reanalysis. Using the Global Tide and Surge Model, we analyse eight historical storm surge events driven by tropical—and extra-tropical cyclones. For these events we extract wind fields from the two reanalysis datasets and compare these against satellite-based wind field observations from the Advanced SCATterometer. The root mean squared errors in tropical cyclone wind speed reduce by 58% in ERA5, compared to ERA-Interim, indicating that the mean sea-level pressure and corresponding strong 10-m winds in tropical cyclones greatly improved from ERA-Interim to ERA5. For four of the eight historical events we validate the modelled storm surge heights with tide gauge observations. For Hurricane Irma, the modelled surge height increases from 0.88 m with ERA-Interim to 2.68 m with ERA5, compared to an observed surge height of 2.64 m. We also examine how future advances in climate modelling can potentially further improve global storm surge modelling by comparing the results for ERA-Interim and ERA5 against the operational Integrated Forecasting System (0.125° × 0.125°). We find that a further increase in model resolution results in a better representation of the wind fields and associated storm surges, especially for small size tropical cyclones. Overall, our results show that recent advances in global climate modelling have the potential to increase the accuracy of early-warning systems and coastal flood hazard assessments at the global scale.

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Reconstruction of the track and a simulation of the storm surge associated with the calamitous typhoon affecting the Pearl River Estuary in September 1874

Climate of the Past ◽

10.5194/cp-16-51-2020 ◽

2020 ◽

Vol 16 (1) ◽

pp. 51-64

Author(s):

Hing Yim Mok ◽

Wing Hong Lui ◽

Dick Shum Lau ◽

Wang Chun Woo

Keyword(s):

Hong Kong ◽

South China Sea ◽

Storm Surge ◽

South China ◽

River Estuary ◽

Pearl River Estuary ◽

The South China Sea ◽

Pearl River ◽

The Pearl River Estuary ◽

The Pearl River

Abstract. A typhoon struck the Pearl River Estuary in September 1874 (“Typhoon 1874”), causing extensive damage and claiming thousands of lives in the region during its passage. Like many other historical typhoons, the deadliest impact of the typhoon was its associated storm surge. In this paper, a possible track of the typhoon was reconstructed through an analysis of the historical qualitative and quantitative weather observations in the Philippines, the northern part of the South China Sea, Hong Kong, Macao, and Guangdong recorded in various historical documents. The magnitudes of the associated storm surges and storm tides in Hong Kong and Macao were also quantitatively estimated using storm surge model and analogue astronomical tides based on the reconstructed track. The results indicated that the typhoon could have crossed the Luzon Strait from the western North Pacific and moved across the northeastern part of the South China Sea to strike the Pearl River Estuary more or less as a super typhoon in the early morning on 23 September 1874. The typhoon passed about 60 km south–southwest of Hong Kong and made landfall in Macao, bringing maximum storm tides of around 4.9 m above the Hong Kong Chart Datum (http://www.geodetic.gov.hk/smo/gsi/Data/pdf/explanatorynotes.pdf, last access: 3 January 2020) at the Victoria Harbour in Hong Kong and around 5.4 m above the Macao Chart Datum (https://mosref.dscc.gov.mo/Help/ref/Macaucoord_2009_web_EN_v201702.pdf, last access: 3 January 2020) at Porto Interior (inner harbour) in Macao. Both the maximum storm tide (4.88 m above the Hong Kong Chart Datum) and maximum storm surge (2.83 m) brought by Typhoon 1874 at the Victoria Harbour estimated in this study are higher than all the existing records since the establishment of the Hong Kong Observatory in 1883, including the recent records set by super typhoon Mangkhut on 16 September 2018.

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Coastal Resilience Against Storm Surge from Tropical Cyclones

Atmosphere ◽

10.3390/atmos11070725 ◽

2020 ◽

Vol 11 (7) ◽

pp. 725

Author(s):

Robert Mendelsohn ◽

Liang Zheng

Keyword(s):

United States ◽

Probability Distribution ◽

Tropical Cyclones ◽

Storm Surge ◽

Urban Areas ◽

Storm Surges ◽

The United States ◽

Atlantic Seaboard ◽

Order Of Magnitude ◽

Coastal Resilience

It is well known that seawalls are effective at stopping common storm surges in urban areas. This paper examines whether seawalls should be built to withstand the storm surge from a major tropical cyclone. We estimate the extra cost of building the wall tall enough to stop such surges and the extra flood benefit of this additional height. We estimate the surge probability distribution from six tidal stations spread along the Atlantic seaboard of the United States. We then measure how valuable the vulnerable buildings behind a 100 m wall must be to justify such a tall wall at each site. Combining information about the probability distribution of storm surge, the average elevation of protected buildings, and the damage rate at each building, we find that the value of protected buildings behind this 100 m wall must be in the hundreds of millions to justify the wall. We also examine the additional flood benefit and cost of protecting a km2 of land in nearby cities at each site. The density of buildings in coastal cities in the United States are generally more than an order of magnitude too low to justify seawalls this high. Seawalls are effective, but not at stopping the surge damage from major tropical cyclones.

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Storm surge hazard in Hong Kong under global climate changes

10.5353/th_b4673369 ◽

2011 ◽

Author(s):

Hon-sing Leung

Keyword(s):

Hong Kong ◽

Storm Surge ◽

Climate Changes ◽

Global Climate ◽

Global Climate Changes

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Coastal risk assessments due to hybrid disasters in Korea

10.5194/egusphere-egu2020-13590 ◽

2020 ◽

Author(s):

Tae-Soon Kang ◽

Hyeong-Min Oh ◽

Soon-Mi Hwang ◽

Ho-Kyun Kim ◽

Kwang-Young Jeong

Keyword(s):

Climate Change ◽

Risk Assessment ◽

Storm Surge ◽

Risk Index ◽

Coastal Areas ◽

Observation Data ◽

Blue Color ◽

Wave Overtopping ◽

Coastal Risk Assessment ◽

Coastal Risk

Korean coasts are exposed to high risks such as storm surge, storm-induced high waves and wave overtopping. Also, localized heavy rainfall events have occurred frequently due to climate change, too. Especially, since coastal urban areas depend heavily on pump and pipe systems, extreme rainfalls that exceed the design capacity of drainage facility result in increasing inland flood damage. Nevertheless, the population in Korea is concentrated in the coastal areas and the value and density of coastal utilization are increasing. In this study, the risk of hybrid disasters in the coastal areas was assessed for safe utilization and value enhancement of coastal areas. The framework of the coastal risk assessment has been adopted from the concept of climate change vulnerability of the IPCC(2001). Coastal Risk Index(CRI) in this study was defined as a function of Exposure and Sensitivity exclude Adaptive Capacity using GIS-based DBs. Indicators of Exposure consisted of a storm surge, storm-induced high waves, wave overtopping and rainfalls. Indicators of Sensitivity consisted of human(population density), property(buildings and roads), and geography(inundation area). All these indicators were gathered from government agencies, numerical model experiments(ADCIRC, unSWAN, FLOW3D and XP-SWMM model), and field surveys(Drone & Lidar survey). And then spatial analysis was performed by using a GIS program after passing the quality control and analyzed data were standardized and classified 4 grades; Attention(blue color), Caution(yellow color), Warning(orange color) and Danger(red color). This frame of risk assessment was first applied to Marine City, Haeundae in Busan, Korea which was heavily damaged by the typhoon CHABA in 2018. According to the assessment results, it was confirmed that the results were in good agreement with the observation data and damage range. At present, the study area of risk assessment is expanding to other areas. The results of coastal risk assessment are used as reference indicators to identify and prevent the cause of coastal disasters, establish countermeasures, determine the development or management of coastal areas based on GIS, thus will contribute to effective and safe coastal management.

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The Global Long-term Effects of Storm Surge Damages on Human Settlements

10.5194/egusphere-egu2020-21564 ◽

2020 ◽

Author(s):

Sven Kunze

Keyword(s):

Economic Impact ◽

Tropical Cyclones ◽

Storm Surge ◽

Local Population ◽

Developed Countries ◽

Sub Saharan Africa ◽

Positive Trend ◽

Long Term Effects ◽

Human Settlements ◽

Combining Data

The influence of natural conditions on human settlements are immense. While a friendly and calm environment can lead to prosperity and growth, a hostile one with frequent natural disasters can result in stagnation, collapse, and even death. Tropical cyclones, as an unpredictable and recurring disastrous events, pose a considerable threat to prosperous development of human societies. The IPCC estimates that globally around 250 million people are vulnerable to storm surge events every year. If the threat is too large, a natural adaptation strategy would seem to move away to less dangerous places. It thus can be considered puzzling that there is a positive trend of moving to coastal flooding zones in Sub-Saharan Africa, North America and Asia, and this is projected to continue in the future. Additionally, climate change may increase the local exposure to storm surge by rising sea levels and changing intensity of tropical cyclones.Given this worrisome development, a systematic analysis of the relationship between settlement structures and tropical cyclones is called for. In this paper we analyze whether people relocate from hazardous areas impacted by tropical cyclones. Importantly, the greatest threat from a tropical cyclone is generally due to the accompanying storm surge. But, because storm surge levels are hard to model, as of date no global (economic) impact study has attempted to model or used historic storm surge data to estimate the economic impact of tropical storms. Rather most studies only focus on wind damages, while other also include rain damages. Within this paper, we are closing this gap by explicitly modeling historic storm surge data worldwide from 1850-2015 and linking this to local population settlement.&#160;By combining data on bathymetry, tidal cycles, weather conditions, and &#160;pressure drop models for the tropical cyclones we are able to estimate spatial storm surge data at a resolution of 5 arc minutes. This data then allows us, in a first step, to analyze its systematic impact on historical geo-referenced population and settlement structure data at a spatial scale of 5 arc minutes. We are able to show some interesting population patterns in response to tropical cyclones. Contrary to many empirical studies, we find that people do settle away from hazardous areas. This effect is especially large for low elevation coastal zones, while for non low elevation coastal areas we find no effect. The same pattern can be found for developing and developed countries, but the shrinking of the population is 39 percent larger in developing countries.&#160;

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