Simulation of Storm Surges Along Myanmar Coast Using a Location Specific Numerical Model

Coastal flooding induced by storm surges associated with tropical cyclones is one of the greatest natural hazards sometimes even surpassing earthquakes. Although the frequency of tropical cyclones in the Indian seas is not high, the coastal region of India, Bangladesh and Myanmar suffer most in terms of life and property caused by the surges. Therefore, a location-specific storm surge prediction model for the coastal regions of Myanmar has been developed to carry out simulations of the 1975 Pathein, 1982 Gwa, 1992 Sandoway and 1994 Sittwe cyclones. The analysis area of the model covers from 8° N to 23° N and 90° E to 100° E. A uniform grid distance of about 9 km is taken along latitudinal and longitudinal directions. The coastal boundaries in the model are represented by orthogonal straight line segments. Using this model, numerical experiments are performed to simulate the storm surge heights associated with past severe cyclonic storms which struck the coastal regions of Myanmar. The model results are in agreement with the limited available surge estimates and observations.     

Storm surge modelling for the Bay of Bengal and Arabian Sea

Most of the countries around the North Indian Ocean are threatened by storm surges associated with severe tropical cyclones. The destruction due to the storm surge flooding is a serious concern along the coastal regions of India, Bangladesh, Myanmar, Pakistan, Sri Lanka, and Oman. Storm surges cause heavy loss of lives and property damage to the coastal structures and losses of agriculture which lead to annual economic losses in these countries. About 300,000 lives were lost in one of the most severe cyclones that hit Bangladesh (then East Pakistan) in November 1970. The Andhra Cyclone devastated part of the eastern coast of India, killing about 10,000 persons in November 1977. More recently, the Chittagong cyclone of April 1991 killed 140,000 people in Bangladesh, and the Orissa coast of India was struck by a severe cyclonic storm in October 1999, killing more than 15,000 people besides enormous loss to the property in the region. These and most of the world’s greatest natural disasters associated with the tropical cyclones have been directly attributed to storm surges. The main objective of this article is to highlight the recent developments in storm surge prediction in the Bay of Bengal and the Arabian Sea.     

Numerical Modelling of Storm Surge in the Head Bay of Bengal Using Location Specific Model

The head Bay of Bengal region, which covers part of Orissa and west Bengal in India as well as Bangladesh, is one of the most vulnerable regions of extreme sea levels associated with severe tropical cyclones which cause extensive damage. There has been extensive loss of life and property due to extreme events in this region. Shallow nature of the Bay, presence of Ganga-Brahmaputra-Meghna deltaic system and high tidal range are responsible for storm surges in this region. In view of this a location specific fine resolution numerical modelis developed for the simulation of storm surges. To represent mostof the islands and rivers in this region a 3km grid resolution is adopted. Several numerical experiments are carried out to compute the storm surges using the wind stress forcings representative of 1974, 1985, 1988, 1989, 1991, 1994 and 1999 cyclones, which crossed this region. The model computed surges are in good agreement with the available observations/estimates.     

Numerical simulation and prediction of storm surges and water levels in Shanghai harbour and its vicinity

A water level model incorporating the nonlinear interactions between tides and storm surges for numerical simulation and prediction use is developed in this paper. Using a conventional two-dimensional nonlinear storm surge model and tide model and associated semi-momentum finite-difference scheme, both the storm surges caused by the tropical cyclones hitting Shanghai and the tides in related regions during the period 1949–1990, are numerically simulated. In simulating storm surges, 16 tropical cyclones with different kinds of tracks are chosen. Meanwhile, to simulate tides, the governing equations for tides, along with 63 prescribed tidal constituents at open sea boundaries are numerically computed. Sixteen associated cases of total water-level simulations comprising joint effects linking surges and tides and one case of real-time prediction have been carried out in 1990 on the basis of computed surges and tides. The total water levels thus obtained in this way give better results than those obtained by the traditional method, i.e. without taking into account, in the model, nonlinear coupling between storm surges and tides.Comparison of the predictions of storm surges and the total water level with the hindcast ones in 1990 showed that a relatively larger error of prediction mainly results from the incorrect forecasting of tropical cyclones but not from the prediction method itself.     

Cyclones and storm surges in Bangladesh: Some mitigative measures

Bangladesh, with its repeated cycle of floods, cyclones, and storm surges, has proved to be one of the most disaster-prone areas of the world. During the years from 1797 to 1991, Bangladesh has been hit by 60 severe cyclones (mostly accompanied by storm surges). This paper gives a brief account of these disasters with particular reference to the wind speed, surge height, loss of life, and damage to crops and properties, etc.In order to protect the coastal areas of Bangladesh from cyclonic storm surges and floods, a major system of embankments was constructed during the 1960s and 1970s, but this is now in need of rehabilitation. The Cyclone Protection Project, which was approved by the World Bank in 1989, would rehabilitate some of the existing embankments, build new embankments, and construct roads. Locally available materials, indigenous technology, and cheap surplus manpower should be used in this project. A variety of fruit trees should be planted along the dikes and roads.To the south-western part of Bangladesh bordering the Bay of Bengal, lies the world's largest single mangrove tract, known as the Sunderban, which covers a total area of 571 500 ha. This mangrove forest is of extreme importance since it provides efficient protection to life and property against cyclones and storm surges. But due to deforestation, the width of the mangrove belt is being rapidly diminished. The author therefore lays emphasis on coastal afforestation.Absolute security against cyclone hazard is probably out of the question, but an effective cyclone warning response can definitely reduce loss of life and damage to property. The author discusses the current conditions for cyclone forecasting and warning in Bangladesh, and then puts forward some proposals for improving the Cyclone Preparedness Programme.     

Mitigation of Flooding and Cyclone Hazard in Orissa, India

Storm surges generated by the strong tangential wind stressesand normal atmospheric pressure gradients at the sea surface due to tropical cyclones (TC'S)have been studied with the goal of detecting any significant and systematic changes due to climatechange. Cyclone and storm surge data for the 19th and 20th centuries for the Bay of Bengalcoast of the state of Orissa in India are available to varying degrees of quality and detail,the data being more scientific since the advent of the India Meteorological Department in 1875.Based on more precise data for the period 1971 to 2000, statistical projections have been madeon the probable intensities of tropical cyclones for various return periods. The super cyclone ofOctober 29, 1999 (SC1999) appears to have a return period of about 50 years. The cyclones of1831, 1885 and possibly the one in 1895 could have been super cyclones. During the 19th century,there were 72 flooding events associated with cyclones, whereas in the 20th century therewere only 56 events. There was no observational evidence to suggest that there was an increaseeither in the frequency or intensity of cyclones or storm surges on the coast of Orissa. However,the impact of cyclones and surges is on the increase due to increase of population and coastalinfrastructure.     

Simulation of physical and socioeconomic factors of vulnerability to cyclones and storm surges using GIS: a case study

The objective of the present study is to simulate the physical and socioeconomic factors of human vulnerability to tropical cyclones and storm surges at the household level in existing and changing status of households. The primary data were collected from a cyclone prone coastal area in Bangladesh, through structured questionnaire and GPS survey, key informants interviews and field observations. In order to simulate the physical and socioeconomic factors geographical information systems based Structured Query Language (SQL) query has been used. The study simulated the physical and socioeconomic factors of human vulnerability to tropical cyclones and storm surges on the basis of collected data through pre-designed SQL query. The study found the number of most vulnerable households under existing conditions and how much it will be afterward of a favourable or adverse change of the factors of vulnerability associated with households. The major findings of the study unveil that the socioeconomic and physical factors of human vulnerability have important function to determine the household’s level of vulnerability to the cyclone induced disaster. It has been demonstrated that the degree of vulnerability of households is changed with its physical and socioeconomic status. This study provides a conceptual model for assessing and simulating vulnerability to other natural hazards like floods, droughts, riverbank erosions and so forth. This study highlights that the households’ intrinsic vulnerable conditions are responsible for its defencelessness to the hazards and the reduction of vulnerability is the first measure of integrated and sustainable disaster management in the coastal Bangladesh.     

A Historical Record of Coastal Floods in Britain: Frequencies and Associated Storm Tracks

This paper examines flood frequencies in three coastal sectors of Britain and analyses the associated storm tracks and their principal pathways. The results indicate that the east coast of Britain has suffered most floods over the last 200 years. The frequencies of flood incidents in the south and southwest coast of Britain have increased, particularly during the 20th century, whereas on the west coast flood frequencies have declined. Three distinctive pathways of storm track are identified, related to flood incidents in each coastal sector. A southern pathway in a corridor along the 55° N parallel is associated with flood incidents recorded on the south and southwest coast, whilst storms that are associated with floods on the west coast concentrate along the 60° N parallel. The relationship between the frequencies of floods and climatic variations needs to be explored further. However, the development of coastal settlements has certainly increased vulnerability, and hence the risk of flood disasters.     

Impact of cyclonic wind field on interaction of surge–wave computations using finite-element and finite-difference models

Both finite-element and finite-difference numerical models are applied to simulate storm surges and associated currents generated by tropical cyclones that struck the coast of Andhra Pradesh, located on the east coast of India. During a cyclone, the total water level at any location on the coast is made up of the storm surge, surge–wind wave interaction and the tide. The advanced circulation two-dimensional depth-integrated (ADCIRC-2DDI) model based on finite-element formulation and the two-dimensional finite-difference model of storm surges developed at IIT Delhi, hereafter referred as IITD storm surge model, are used. These models are driven by astronomical tides at the open ocean boundary and cyclonic asymmetric winds over the surface of the computational domain. Comparison of model simulated sea-surface elevations with coarse and finer spatial resolutions suggests that the grid resolution near the coast is very crucial for accurate determination of the surges in addition to the local bathymetry. The model underpredicts surges, and the peak surge location shifts more to the right of the landfall as the spatial resolution of the model becomes coarser. The numerical experiments also demonstrate that the ADCIRC model is robust over the IITD storm surge model for surge computations as the coastline is better represented in the former.     

A numerical study of storm surges caused by cold-air outbreaks in the Bohai Sea

Storm surges in the Bohai Sea are not only associated with tropical cyclones and extra-tropical cyclones, but also cold-air outbreaks. Cold-air outbreaks attack China from four major tracks, with each track having its own prevailing wind over the Bohai Sea. As the pressure field of cold-air outbreaks can be converted into the surface wind, storm surges can be investigated by the pressure field of cold-air outbreaks entirely. This paper took the different major tracks, pressure field, and high wind period into consideration and constructed 20 scenarios to describe the actual situation of cold-air outbreaks. Based on the results modeled by FVCOM, the influence of various cold-air outbreaks on the maximum surge in the Bohai Sea and the probability of the surge elevation at three typical tide gauges were investigated. Finally, a powerful decision-making tool to estimate storm surges induced by cold-air outbreaks was provided.     

Hydrodynamic Response of Northeastern Gulf of Mexico to Hurricanes

The northeastern Gulf of Mexico in the USA is extremely susceptible to the impacts of tropical cyclones because of its unique geometric and topographic features. Focusing on Hurricanes Ivan (2004) and Katrina (2005), this paper has addressed four scientific questions on this area’s response to hurricanes: (1) How does the shallow, abandoned Mississippi delta contribute to the storm surge? (2) What was the controlling factor that caused the record-high storm surge of Hurricane Katrina? (3) Why are the responses of an estuary to Hurricanes Ivan and Katrina so different from the corresponding surges on the open coast? (4) How would the storm surge differ if Hurricane Katrina had taken a different course? Guided by field observations of winds, waves, water levels, and currents, two state-of-the-art numerical models for storm surges and wind waves have been coupled to hindcast the relevant hydrodynamic conditions, including storm surges, surface waves, and depth-averaged currents. Fairly good agreement between the modeled and measured surge hydrographs was found. The quantitative numerical simulations and simple qualitative analysis have revealed that the record-high storm surge of Hurricane Katrina was caused by the interaction of the surge with the extremely shallow, ancient deltaic lobe of Mississippi River. A hypothetical scenario formed by shifting the path of Hurricane Katrina to the observed path of Hurricane Frederic (1979) resulted in a much smaller surge than that observed in coastal Mississippi and Louisiana. However, this scenario did still result in a high surge near the head of Mobile Bay. One of the important lessons learned from Hurricane Katrina is that the Saffir–Simpson scale should be systematically revised to reflect the topographic and geometric features of a complex, heterogeneous coast, including the possible surge amplification in an estuary or a submerged river delta.     

The Tropical Cyclone Risk in Cairns

Because of its location close to a region of tropical cyclone formation, the city ofCairns is regularly affected by tropical cyclones. Most cyclones occur in the monthsJanuary–March, although some have affected Cairns in December and April. There is a strong year-to-year variation in tropical cyclone numbers in the Cairns region, with twice as many impacts occurring during La Niña conditions than during El Niño. Several case studies are presented of cyclone impacts on Cairns. Rapidly developing cyclones are a particularly difficult forecast problem, as they can strike the city with less than 24 hours warning. Serious inundation from storm surge often occurs some time after landfall at Cairns.     

The impact of climate change on coastal geological disasters in southeastern China

Climate change is presently a major global challenge. As the world??s largest developing country, China is particularly vulnerable to global warming, especially in the rapidly developing coastal regions in the southeast of the country. This paper provides an overview of the impacts of climate change on the nature of geological disasters in the coastal regions of southeastern China. In the context of climate change, processes with the potential for causing geological disasters in this region, including sea-level rise, land subsidence, storm surges, and slope failures, which already have a substantial occurrence history, are all aggravated. All these processes have their own characteristics and relevance to climate change. Sea-level rise together with land subsidence reduces the function of dikes and flood prevention infrastructure in the study areas and makes the region more vulnerable to typhoons, storm surges, floods, and astronomical tidal effects. Storm surges have caused great losses in the study areas and also have contributed to increases in rainstorms. As a result, numerous rainfall-induced slope failures, characterized by focused time concentration, high frequencies, strong ??burstiness,?? and substantial damage, occur in the study areas. To prevent and mitigate such disasters that are accelerated by climate change, and to reduce losses, a series of measures is proposed that may help to achieve sustainable development in coastal southeastern China.     

Storm surges in the Arabian Gulf

The storm surge phenomenon in the Arabian Gulf, including the Strait of Hormuz, is discussed with particular emphasis on the development of mathematical models for prediction purposes. The Gulf is mainly influenced by extra-tropical weather systems, whereas the region south of the Strait of Hormuz is affected by tropical cyclones. The west-to-east directed extra-tropical cyclone tracks and the generally east-to-west directed tropical cyclone tracks converge near the Strait of Hormuz. A meso-scale weather system that deserves special attention in prescribing the meteorological forcing functions is the so-called winter Shamal. A two-dimensional numerical model is developed to study the storm surges in the Arabian Gulf. The results show that the Gulf is subject to major negative and positive storm surges. Strong winds associated with the Shamal system, coupled with atmospheric pressure gradients, topography and tidal effects, can give rise to water level deviations of several meters. Storm surges observed during the period 17–19 January 1973 show that negative values in the 0.5 to 1.0m range were widespread in the Gulf.     

Storm Surges from Extra-Tropical Cyclones

The possible influence of climate change on the tracks of the extra-tropical cyclones as well as storm surges is studied. Two differentdata bases have been used: one for the Great Lakes of North America and the otherfor the German Bight in the North Sea of Europe. For the Great Lakes region,significant east-west and north-south shifts in the tracks of ETC'S with decadal periodicities have been observed. However, there was no trend in the amplitudes of storm surges. The most important result for the Great Lakes is that, depending upon its position relative to the constantly shifting storm tracks, a given location could eitherexperience a major storm surge or could miss out completely.The storm surges in the German Bight in general, and at Cuxhaven in particular, appear to show a slightly increasing trend in the latterpart of the 20th century. However, the most significant result for the German Bightis that the number of storm tides (i.e., multiple peaks in a given storm surge event)definitely has shown an increase in the second half of the 20th century. This increase isinterpreted as due to the influence of meso-scale weather systems embedded in the synoptic scale ETCs.     

Mitigating the effects of storm surges generated by tropical cyclones: A proposal

One of the regions of the globe that is frequently and very significantly affected by storm surges is Bangladesh. These high amplitude water-level oscillations are generated by the meteorological forcing fields due to tropical cyclones in the Bay of Bengal. The tide also plays a significant role in determining the time history of the total water level. Due to the greenhouse warming associated with the increasing levels of carbon dioxide in the atmosphere, it is expected that the frequency and intensity of tropical cyclones in the Bay of Bengal will increase substantially within the next 50 to 100 years. This new breed of tropical cyclones, referred to as hypercanes, will generate storm surges on the coast of Bangladesh which could attain amplitudes of up to 15 m, much greater than the present-day amplitudes of up to 6 m. Various mitigation procedures are discussed and compared.     

Coastal flooding due to synoptic scale,meso-scale and remote forcings

Coastal flooding occurs due to storm surges generated by tropical and extra-tropical cyclones on the globe. The meteorological forcing fields for the generation of storm surges are the tangential surface wind stress on the ocean surface and the normal atmospheric pressure gradients associated with the weather systems. The large scale forcing from the cyclones is referred to as the synoptic scale and storm surge prediction from synoptic scale forcing is well developed and is reasonably satisfactory around the world. However, coastal flooding also occurs from weather systems, with forcing on a meso-scale and also from remote forcing. It is proposed here that the term “Storm surge” be used to only refer to coastal flooding from synoptic scale forcing and the terminology “Rissaga” be used for coastal flooding from meso-scale forcing. For flooding due to remote forcing, a new term “Kallakkadal” is proposed.     

Correction to: Tropical cyclone: expressions for velocity components and stability parameter

Historically, Leyte Gulf in central eastern Philippines has received catastrophic damage due to storm surges, the most recent of which was during Typhoon Haiyan in 2013. A city-level risk assessment was performed on Leyte Gulf through synthetic storm generation, high-resolution ocean modeling, and decision tree analyses. Cyclones were generated through a combination of a Poisson point process and Monte Carlo simulations. Wind and pressure fields generated from the cyclones were used in a storm surge model of Leyte Gulf developed on Delft3D. The output of these simulations was a synthetic record of extreme sea level events, which were used to estimate maximum surge heights for different return periods and to characterize surge-producing storm characteristics using decision tree analyses. The results showed that the area most prone to surges is the Tacloban–Basey area with a 2.8?±?0.3 m surge occurring at a frequency of every 50 years. Nearby Palo area will likely receive a surge of 1.9?±?0.4 m every 50 years while Giporlos–Salcedo area a surge of 1.0?±?0.1 m. The decision tree analysis performed for each of these areas showed that for surges of 3–4 m, high-velocity winds (>?30 m/s) are consistently the main determining factor. For the areas, Tacloban, Basey, and Giporlos–Salcedo, wind speed was also the main determining factor for surge?>?4 m.     

Simulation of water levels and extent of coastal inundation due to a cyclonic storm along the east coast of India

The devastation due to storm surge flooding caused by extreme wind waves generated by the cyclones is a severe apprehension along the coastal regions of India. In order to coexist with nature’s destructive forces in any vulnerable coastal areas, numerical ocean models are considered today as an essential tool to predict the sea level rise and associated inland extent of flooding that could be generated by a cyclonic storm crossing any coastal stretch. For this purpose, the advanced 2D depth-integrated (ADCIRC-2DDI) circulation model based on finite-element formulation is configured for the simulation of surges and water levels along the east coast of India. The model is integrated using wind stress forcing, representative of 1989, 1996, and 2000 cyclones, which crossed different parts of the east coast of India. Using the long-term inventory of cyclone database, synthesized tracks are deduced for vulnerable coastal districts of Tamil Nadu. Return periods are also computed for the intensity and frequency of cyclones for each coastal district. Considering the importance of Kalpakkam region, extreme water levels are computed based on a 50-year return period data, for the generation of storm surges, induced water levels, and extent of inland inundation. Based on experimental evidence, it is advocated that this region could be inundated/affected by a storm with a threshold pressure drop of 66 hpa. Also it is noticed that the horizontal extent of inland inundation ranges between 1 and 1.5 km associated with the peak surge. Another severe cyclonic storm in Tamil Nadu (November 2000 cyclone), which made landfall approximately 20 km south of Cuddalore, has been chosen to simulate surges and water levels. Two severe cyclonic storms that hit Andhra coast during 1989 and 1996, which made landfall near Kavali and Kakinada, respectively, are also considered and computed run-up heights and associated water levels. The simulations exhibit a good agreement with available observations from the different sources on storm surges and associated inundation caused by these respective storms. It is believed that this study would help the coastal authorities to develop a short- and long-term disaster management, mitigation plan, and emergency response in the event of storm surge flooding.     

Numerical storm surge model for India and Pakistan

The northeastern sector of the Arabian Sea, which covers the Gujarat coast of India and western coast of Pakistan, is a region vulnerable to extreme sea levels associated with tropical cyclones (TCs). Although the frequency of tropical cyclones in the Arabian Sea is not high, the coastal regions of India and Pakistan suffer in terms of loss of life and property caused by the surges. In view of this a location-specific fine resolution model is developed for the Gujarat coast of India and adjoining Pakistan coast. The east–west and north–south grid distance is about 3.0 km. Using this model, numerical experiments are carried out to simulate the surges generated by 1999 and 2001 cyclones which struck the Pakistan coast. The model computed surges are in agreement with the available observational estimates.