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Cyclones in a Changing Climate: The Case of Bangladesh

 

Susmita Dasgupta1 Mainul Huq2 Zahirul Huq Khan3 Manjur Murshed Zahid Ahmed4 Nandan Mukherjee5 Malik Fida Khan6 Kiran Pandey7 January 2011 Acknowledgements Financial support for this study was provided by the Economics of Adaptation to Climate Change study administered by the Environment Department of the World Bank. Funding for the Economics of Adaptation to Climate Change study has been provided by the governments of the United Kingdom, the Netherlands, and Switzerland. We would like to extend our special thanks to Ms. Maria Sarraf, Dr. Ainun Nishat and Mr. Khawaja Minnatullah for their valuable guidance. We are thankful to Dr. Robert Mendelsohn and participants of the Economics of Adaptation to Climate Change country consultations for their useful comments and suggestions. We are also grateful to Ms. Roufa Khanam for her valuable help with the GIS and Ms. Norma Adams for editorial help. The views expressed here are the authors’, and do not necessarily reflect those of the World Bank, its Executive Directors, or the countries they represent. Corresponding author: Susmita Dasgupta, MC3-308, World Bank, 1818 H Street, N.W., Washington, DC 20433; E-mail: sdasgupta@worldbank.org; telephone: 202-473-2679; fax: 202-522-2714. 1 Lead Environmental Economist, Development Research Group, The World Bank, Washington DC, USA. 2 Development Policy Group, Dhaka, Bangladesh. 3 Director, Institute of Water Modeling, Dhaka, Bangladesh. 4 Senior Specialist, Institute of Water Modeling, Dhaka, Bangladesh. 5 Adaptation Specialist, Climate Change Division, Center for Environmental and Geographic Information Services, Dhaka, Bangladesh. 6 Director, Climate Change Division, Center for Environmental and Geographic Information Services, Dhaka, Bangladesh. 7 Senior Economist, Environment Division, The World Bank, Washington, USA.

Abstract
This paper integrates information on climate change, hydrodynamic models, and geographic overlays to assess the vulnerability of coastal areas in Bangladesh to larger storm surges and sea-level rise by 2050. The approach identifies polders, coastal populations, settlements, infrastructure, and economic activity at risk of inundation, and estimates the damage versus the cost of several adaptation measures. A 27-centimeter sea-level rise and 10 percent intensification of wind speed from global warming suggests the vulnerable zone increases in size by 69 percent given a +3-meter inundation depth and by 14 percent given a +1-meter inundation depth. Estimates indicate investments including strengthening polders, foreshore afforestation, additional multi-purpose cyclone shelters, cyclone-resistant private housing, and further strengthening of the early warning and evacuation system would cost more than $2.4 billion with an annual recurrent cost of more than $50 million. These estimates can serve as a prototype of the adaptation costs to extreme weather events in climate negotiations. Keyword: Bangladesh, Climate Change, Storm Surges, Geographic Overlays, Damage, Adaptation Cost
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1. Introduction Bangladesh is a global hotspot for tropical cyclones.8 Nearly every year, cyclones hit the country’s coastal regions in the early summer (April–May) or late rainy season (October–November). Between 1877 and 1995, Bangladesh was hit by 154 cyclones, including 43 severe cyclonic storms, 43 cyclonic storms, and 68 tropical depressions.9 Since 1995, 5 severe cyclones have hit the country’s coast. On average, a severe cyclone strikes the country every three years (GOB 2009). The country’s topography is extremely low and flat with two-thirds of its land area less than 5 m above sea level. As a result, lives and property in lower-lying coastal districts along the Bay of Bengal are highly vulnerable to inundation from cyclone-induced storm surges10. Cyclone Sidr (November 2007) and Cyclone Aila (May 2009) provide recent examples of devastating storm-surge in Bangladesh. In 2007, Cyclone Sidr, a 10-year return period cyclone with an average wind speed of 223 km per hour resulted in 4,234 casualties and 55,282 injuries (EMDAT –CRED). Livelihoods of 8.9 million people were affected and damages and losses from Cyclone Sidr totaled US$1.67 billion (GoB 2008).11 In 2009, Cyclone Aila, a 1.2 year retrn period cyclone with an average wind speed of 95 lm per hour caused 190 deaths, 7,103 injuries and affected 3.9 million people. The estimated damage of assets from Aila is US$270 million (EMDAT -CRED).12 The scientific evidence indicates that increased sea surface temperature with climate change will intensify cyclone activity and heighten storm surges (IWTC 2006; IPCC 2007; see also
8 The United Nations Development Programme (UNDP) has ranked Bangladesh as the world’s most vulnerable country to tropical cyclones (UNDP 2004) See also Nicholls 2006. 9 Based on the observed maximum sustained surface wind measured at a height of 10 m averaged over 3 minutes, tropical storms are classified as super cyclonic (wind speed over 220 km per hour), very severe cyclonic (119–220 km per hour), severe cyclonic (90–119 km per hour), cyclonic (60–90 km per hour), deep depression (51–59 km per hour), and depression (32–50 km per hour) (IMD 2010). 10 Storm surge refers to the temporary increase, at a particular locality, in the height of the sea due to extreme meteorological conditions: low atmospheric pressure and/or strong winds (IPCC AR4 2007). 11 Comprehensive data on extreme weather-related losses is maintained by the Centre for Research on the Epidemiology of Disasters (CRED) at the School of Public Health of the Université Catholique de Louvain, Brussels. 12 In general, the relative severity of the impacts from natural disasters in Bangladesh has decreased substantially since the 1970s as a result of improved macroeconomic management, increased resilience of the poor, and progress in disaster management and flood protection infrastructure. Yet, recent cyclones Sidr and Aila have demonstrated that storm-surge losses remain colossal in Bangladesh.
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Woodworth and Blackman 2004; Pielke et al. 2005; Woth, Weisse, and von Storch 2006; and Emanuel et al. 2008). 13 Surges will be further elevated by a rising sea level as thermal expansion and ice cap(s) continue to melt (Nicholls et al. 2007; Dasgupta et al. 2011).14 Hence, the effects of climate change, increase in sea surface temperature and sea-level rise, are likely to exacerbate Bangladesh’s vulnerability to cyclones. Larger storm surges threaten greater future destruction, because they will increase the depth of inundation and will move further inland – threatening larger areas than in the past. The destructive impact of storm surges will generally be greater when the surges are accompanied by strong winds and large onshore waves. This scientific evidence points to the need for greater disaster preparedness in Bangladesh. Given the pervasive impacts of climate-related risks on cyclones over time, the government of Bangladesh has highlighted severe cyclones as a significant hazard and ensuring adequate flood protection infrastructure as a “pillar” of the Climate Change Strategy and Action Plan (GoB, 2009). Currently, systematic studies of the cost of climate proofing coastal protective infrastructure are scarce in Bangladesh. To date, most analytical work has been confined to case studies, with relatively limited sets of locations, impacts, and adaptation measures to date (Khalil 1992; Hoque 1992; Ali 1999: Quadir and Iqbal 2008). Yet, the government has already invested over $10 billion (at constant 2007 prices) in flood management embankments and emergency shelters to make the country more climate resilient and less vulnerable to natural disasters.15 This paper aims to fill that knowledge gap by providing itemized estimates of potential damage and the incremental costs of adapting to intensified cyclones and related storm surges out to the year 2050. The itemized cost and damage estimates for future cyclones developed in this paper could help spur the Government of the People’s Republic of Bangladesh to develop adaptation plans now in order to avoid future losses from cyclone-induced flood 13 A sea-surface temperature of 28o C is considered an important threshold for the development of major hurricanes of categories 3, 4 and 5 (Michaels, Knappenberger, and Davis 2005; Knutson and Tuleya 2004). 14 The most recent evidence suggests that sea-level rise could reach 1 meter or more during this century (Rahmstorf 2007; Dasgupta and Meisner 2009), although the likelihood of that magnitude of increase remains uncertain. 15 The government recognizes climate change is an environmental as well as a developmental issue; and is committed to protect the country from its adverse impact and maintain a stable growth path of the country.
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amplification. For the international community, these estimates could serve as a prototype of the adaptation costs to extreme weather events in climate negotiations. In this paper, information on climate change, hydrodynamic models, and geographic overlays are combined to assess the vulnerability of coastal areas in Bangladesh to larger storm surges and sea-level rise by 2050. The approach identifies polders (diked areas), coastal populations, settlements, infrastructure, and economic activity at risk of inundation, and estimates the cost of damage versus the cost of several adaptation measures. A 27-centimeter sea-level rise and 10 percent intensification of wind speed have been considered to approximate climate change from global warming by 2050. At the outset, we acknowledge several limitations in our analysis. This analysis has not addressed the likely problem of salinity intrusion nor has it addressed out-migration from the coastal zone that may be induced by sea level rise and more intense cyclones. We also have not attempted to estimate location-specific probability of 10-year return period cyclones. The remainder of the paper is organized as follows. Section 2 presents the case of storm surges in Bangladesh. Section 3 describes the modeling and simulation to determine the impact of climate change on magnitude of cyclone-induced inundation. Section 4 summarizes the cost of adaptation. Potential damage from a 10-year return period cyclone in Bangladesh by 2050 is presented in Section 5, and Section 6 concludes the paper. 2. Cyclone-induced Storm Surges in Bangladesh Cyclones pose a threat to lives and property in low-lying coastal regions in Bangladesh. Records indicate that the greatest damage during cyclones has resulted from the inundation caused by cyclone-induced storm surges.16 Though time-series records of storm-surge height are scarce, existing literature indicates a 1.5–9 m height range during various severe cyclones. Storm-surge 16 For details on major cyclones that crossed Bangladesh from 1960 to 2009, see Dasgupta et al., Vulnerability of Bangladesh to Cyclones in a Changing Climate: Potential Damages and Adaptation Cost, Appendices 2 and 3. World Bank, Washington, DC (2010).
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heights of 10 m or more have not been uncommon; for example, the 1876 Bakerganj cyclone had a reported surge height of 13.6 m (SMRC 2000). Overall, it has been estimated that Bangladesh is on the receiving end of about two-fifths of the world’s total impact from storm surges (Murty and El-Sabh 1992). The reasons for this disproportionately large impact include the recurvature of tropical cyclones in the Bay of Bengal; the wide, shallow continental shelf, especially in the eastern part of the country;17 the high tidal range;18 the triangular shape at the head of the Bay of Bengal, which helps to funnel sea water pushed by the wind toward the coast, causing further surge amplification; the nearly sea-level geography of the coastal land; and the high-density population and coastal protection system (Ali 1999). Most surge amplifications occur in the Meghna estuarine region. Surges that make landfall during high tide are even more devastating. In general, it has been observed that the frequency of a 10-m high wave (surge plus tide) along Bangladesh coast is about once every 20 years, while a wave with a 7-m height occurs about once in 5 years. In addition, wind-induced waves of up to 3.0 m in height may also occur under unfavorable conditions (MCSP 1993). The IPCC AR4 indicates that future storm surges and related floods in Bangladesh will likely become more severe as future tropical cyclones increase in intensity (IPCC 2007). A study using dynamic, Regional Climate Model (RCM)-driven simulations of current and future climates indicates a significant increase in the frequency of highest storm surges for the Bay of Bengal, despite no substantial change in the frequency of cyclones (Unnikrishnan et al. 2006). Emanuel (2005) projects increased intensity of tropical storms by 2100 for the North Indian Ocean, as measured by the percent change in landfall power using the Model for Interdisciplinary Research on Climate (MIROC) General Circulation Model (World Bank and United Nations 2010). Hence, from a practical perspective vulnerability of Bangladesh to cyclones/ storm surges may increase even more as a result of climate change 17 This wide shelf amplifies the storm surges as the tangential sea-level wind-stress field associated with the tropical cyclone pushes the sea water from the deep water side onto the shelf; being pushed from the south by wind stress, the water has no place to go but upwards, which creates the storm surge. 18 Records indicate 7–8 m high tide in the Sandwip Channel.
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3. Charting a New Course: Methodology and Vulnerable Area and Population Given the large uncertainties about the magnitude and timing of the added risks from climate change in Bangladesh, it is essential to identify the potential damage and costs of adapting the country’s critical infrastructure to intensified storm-surge patterns in a changing climate. This research approach integrates information on climate change, assets at risk, growth projections, and damage/ cost estimates in a four-step process. First, the potential inundation zone and projected depth of inundation caused by cyclonic storm surges were demarcated for a baseline scenario without climate change and one with climate change. Second, the critical populations and infrastructure exposed to the added risk of inundation in a changing climate—the critical impact elements—were identified. Third, the cost of adapting these critical impact elements in order to avoid damage from the added inundation caused by climate change was quantified. Fourth, potential additional damage and loss from a 10-year return period cyclone induced storm surges in a changing (out to 2050) climate was computed. For the baseline without climate change scenario, tracks of the 19 major cyclones that made landfall in Bangladesh from 1960 to 2009 were used, along with their corresponding observed wind and pressure fields (Figure 1).19 The inundation effect of storm surges was assessed using the two-dimensional Bay of Bengal Model, recently upgraded and updated under the Comprehensive Disaster Management Program of Bangladesh (UK DEFRA 2007). The model is based on the MIKE 21 hydrodynamic modeling system, and its domain covers the coastal region of Bangladesh up to Chandpur and the Bay of Bengal up to 16: latitude.20 The resulting inundation map is based on the maximum level of inundation at all grid points of the model. To approximate cyclones and related storm surges in a changing climate, the analysis considered a sea-level rise of 27 cm (UK DEFRA 2007), increased wind speed of 10 percent (Nicholls et al. 2007; World Bank 2010), and landfall during high tide to approximate cyclones in a changing climate by 2050.21 19 Ibid., Appendix 3. 20 See Dasgupta et al., Appendix 1. World Bank, Washington, DC (2010). 21 Scientific evidence to date suggests that the intensity of cyclones in the Bay of Bengal will increase in frequency; thus, the probability of potential landfall during high tide will also rise.
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Figure 1: Risk from major cyclones in 1960–2009 spanned Bangladesh’s entire coastline The scenario with climate change used the tracks of the same 19 historical cyclones and the affected coastal regions to simulate potential tracks out to 2050. The overlapping tracks of the 1974, 1988, 1991, and 2007 cyclone tracks covered the Sunderban coast, southwestern coast (Sunderban to Patuakhali), Bhola and Noakhali coast in the Meghna Estuary, and eastern coast (Shitakunda to Bashkhali); an artificial track was generated to cover the Sandwip coast and parts of the Noakhali and Chittagong coasts in the central part of the Meghna Estuary. Together, these five tracks were used to determine the inundation zones due to climate change–induced storm surges (Figure 2). Figure 2: Five cyclone tracks span Bangladesh’s coastline under the climate change scenario Note: The meteorological parameters of Cyclone Sidr were used to demarcate the Artificial track.
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To determine potential future inundation zones by 2050 under the climate change scenario, the storm surge model was run for the five cyclone tracks (covering the entire coastal area), incorporating a 27-cm rise in sea level, a 10-percent increase in wind speed, and landfall of cyclones during high tide. Based on the simulation results, which accounted for potential intensification of cyclone-induced inundation, maps depicting the extent and depth of inundation for 2050 were generated once again applying the Bay of Bengal model. Results showed that, under the climate change scenario, the vulnerable area would be 55 percent greater than under the baseline scenario, with an additional 2 m of inundation depth (Figure 3). Figure 3: High risk area by 2050 in a changing climate Inundation depth (m) Baseline scenario (km2) Climate change scenario (km2) Change (%) > 1 20,876 23,764 +14 > 3 10,163 17,193 +69 GIS software was used to estimate the population and infrastructure assets exposed to inundation risk from cyclones and associated storm surges by 2050 under the two scenarios. Currently, 8.06 million people in coastal Bangladesh are vulnerable to inundation depths greater than 1 m resulting from cyclonic storm surges. With population growth, that number is
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projected to increase 68 percent by 2050 under the baseline scenario. Without further adaptation measures, the figure would rise to 110 percent by 2050 under the climate change scenario, and the population exposed to inundation depths greater than 3 m would rise by 67 percent (Table 1). Table 1: Vulnerable population estimates for cyclonic storm surges Inundation depth (m) Current 2050 under baseline scenario Change (%) between current and baseline scenario 2050 under climate change scenario Change (%) between baseline and climate change scenarios in 2050 > 1 16.83 28.27 + 68 35.33 + 25 > 3 8.06 13.54 + 68 22.64 + 67 Bangladesh has extensive existing infrastructure—including polders, cyclone shelters, and early warning and evacuation systems—to protect low-lying coastal areas. To identify the infrastructure exposed to added inundation risk, GIS software was used to overlay the best available, spatially-disaggregated data on current assets and activities in the country’s coastal zone, with projected inundation zones for 2050 under the baseline and climate change scenarios.22 For each exposure indicator, estimates were calculated by overlaying the inundation zone with the appropriate exposure-surface data set. For the exposure grid surfaces, three GIS models were built to calculate the exposed value. The exposure indicators, including land surface, agriculture extent, road infrastructure, and railways, were measured in square kilometers or kilometers. Since the values of the pixels in population surfaces represented numbers of people, the exposure was calculated by multiplying the exposure 22 Exposure surface data were collected from the public sources noted in footnote 24.
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surface by the inundation zone and then summing by multiplying grid count and value.23 The exposure estimates of other impact elements were counts. 4. Costing of Adaptation Bangladesh has an extensive infrastructure such as polders, cyclone shelters, early warning and evacuation system to protect coastal regions. Despite the extensive infrastructure Bangladesh has in place to protect coastal residents from cyclonic storm surges and tidal waves, currently 44 of the country’s 123 coastal polders run the risk of overtopping if a severe cyclone hits. As a result, Bangladesh has a current adaptation deficit totals US$2.462 billion (World Bank, 2010). In a changing climate, the greater expanse and depth of the areas inundated will put many more existing structures at risk. By 2050, another 59 coastal polders will be overtopped, and inadequate mangrove forests will mean higher-velocity storm surges. Moreover, the capacity of life-saving cyclone shelters and early warning and evacuation systems will be exceeded. By 2050, the total additional investment needed to cope with a changing climate will total about US$2.4 billion, with an annual recurrent cost of more than US$50 million (Table 2). The costing of adaptation refers to the increased inundation area and depth for a 10-year return cyclone in a changing climate. The subsections that follow itemize the estimated adaptation costs for enhancing the height of coastal polders, increasing afforestation measures to protect sea-facing polders, constructing multipurpose cyclone shelters and cyclone-resistant private housing, and strengthening the early warning and evacuation system. 23 The computation used population density at the thana level.
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Table 2: Total adaptation cost for cyclones and associated storm surges by 2050 Baseline scenario Additional cost with climate change Measure Investment (billion US$) Investment (million US$) Annual recurrent cost (million US$) Polders 2.462 892 18 Foreshore afforestation 75 Multipurpose cyclone shelters 1,200 24 Cyclone-resistant private housing 200 Strengthening of early warning system 39 8 + Total 2.462 2,407 50 + Height enhancement of coastal polders In the 1960s and 1970s, 123 polders, 49 of which are sea-facing, were constructed to protect Bangladesh’s low-lying coastal areas against tidal floods and salinity intrusion.24 This study used GIS software to overlay the best available, spatially-disaggregated data on polders in the country’s vulnerable coastal zone. To identify which polders will likely be overtopped by intensified storm surges in a changing climate and the extent of that overtopping, the study computed differences between the crest level of embankment for each polder and the inundation depths projected for 2050 under the baseline and climate change scenarios. The results indicate that, by 2050, 26 interior polders and 33 sea-facing coastal polders will be overtopped (Figure 4). 24 The Bangladesh Water Development Board maintains an extensive database on coastal polders, including data on their length, location, construction year, and cost.
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Figure 4: In a changing climate, 33 sea-facing and 26 interior polders will likely be overtopped by 2050. The study computed the cost of enhancing the height of the polders identified as likely to be overtopped in a changing climate. The amount of needed earthwork was determined from engineering designs, and the current local prices for earthwork, compaction, and turfing were provided by the Bangladesh Water Development Board.25 The cost of required hard protection of some polder sections was computed using the rate for the highest ranked, locally available technology (i.e., cement concrete blocks with sand filters and geo-textile). The cost of compensating private landowners for the additional land needed to strengthen the bases of the height-enhanced polders in interior or marginal areas was also estimated. Maintenance cost was assumed to represent 2 percent of capital investment. In a changing climate, the adaptation cost (33 sea-facing and 26 interior polders) totals US$892 million (Table 3).26 25 See Dasgupta et al., Vulnerability of Bangladesh to Cyclones in a Changing Climate: Potential Damages and Adaptation Cost, Appendix 4. World Bank, Washington, DC (2010). 26 Ibid., Appendix 5.
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Table 3: Estimated cost of enhancing height of coastal embankments (million US$) Polder type Baseline scenario Additional cost with climate change Interior 317 389 Sea-facing 2,145 503 Afforestation protection of sea-facing polders In the past, foreshore afforestation schemes have proven cost effective in dissipating wave energy and reducing hydraulic load on embankments during storm surges.27 Currently, however, Bangladesh has insufficient foreshore forests. Of the 957-km total length of embankment of 49 sea-facing polders, there are only 60 km of forest belts, much of which is degraded. The Department of Forests and Institute of Water Modeling recommend a minimum of 500-m width mangrove forest to protect sea-facing polders. This study analysis estimated the current length of coastal afforestation between the coastline and polders, using Google Earth and GIS methodology, to compute the gap between the recommended 500-m width mangroves and existing area-specific ones. The results indicate that 897 km length of existing sea polders would require mangrove forests for protection. For the recommended 500-m width protective forest belt, a foreshore area of 448.5 km2 (897 km x 0.5 km) would require afforestation. At the current cost of US$168,000 per km2, the projected cost would total US$75 million. Multipurpose cyclone shelters In Bangladesh, cyclone shelters are critical for protecting human lives and livestock. During Cyclone Sidr in 2007, for example, 15 percent of the affected population took refuge in cyclone 27 Such benefits were evident in Cyclone Sidr (2007) and Cyclone Aila (2009). An in-depth study of the damages and losses from Cyclone Sidr noted that even scattered, unplanned forestation along the foreshore of the embankments substantially reduced the velocity of storm surges (GOB 2008).
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shelters, which were estimated to have saved thousands of lives (Figure 5). Yet many existing cyclone shelters are in dilapidated condition and fail to provide for the special needs of women, people with disabilities, and provision of livestock. Though the need for cyclone shelters is expected to decline if polders are raised sufficiently and properly maintained, shelters will still be needed to protect inhabitants of smaller islands, where polder protection may not be cost effective; people living in areas with projected inundation depths greater than 3 m; and residents living in one-story houses. Current consensus favors multipurpose cyclone shelters with elevated space for livestock and overhead water storage that can also serve as a primary school or office space in non-emergency times. Figure 5: Many of Bangladesh’s emergency cyclone shelters are dilapidated. In 2001, more than 8 million people in coastal Bangladesh were exposed to storm surge–induced inundation depths of more than 3 m. By 2050, that number is expected to rise to more than 13.5 million under the baseline scenario. In a changing climate, another 9 .1 million inhabitants will be exposed to similar inundation risk. Accommodating these additional people
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will require adding 5,702 multipurpose cyclone shelters, at an estimated cost of US$1.2 billion.28 Cyclone-resistant private housing In the past, the housing sector has accounted for a significant portion of cyclone damage. For example, in 2007, it accounted for half of the economic damage caused by Cyclone Sidr (GOB 2008). In coastal regions, houses can be made cyclone-resistant by following suitable designs and building codes. This study analysis, which consulted with local architects and civil engineers, recommends encouraging the construction of brick-built houses with concrete roofs (on stilts, if needed) in accordance with appropriate building codes. These houses could serve as single or multi-family cyclone shelters during storm surges. The subsidized29 construction material and housing credit would require setting up a revolving fund in the amount of US$200 million. Strengthened early warning and evacuation system Bangladesh’s early cyclone warning and evacuation system is vital to saving lives. The overall quality of cyclone and storm surge forecasting has improved in recent years; however, the general consensus is that further improvements are needed. These include the need for greater precision in forecasting, especially with regard to landfall location and location-specific inundation depth; broadcasting of warnings in local dialects; and raising awareness to promote timely and appropriate evacuation.30 The estimated costs of the surveys and mathematical modeling required to improve projections for location-specific inundation, as recommended by the Institute of Water Modelling, total US$8 million. Modernization of the Bangladesh Meteorological Department (setting up additional observatories and upgrading existing ones, establishing radiosonde stations, 28 To estimate the costing of multipurpose cyclone shelters, current cyclone-shelter costs and capacity were collected from World Bank–funded projects. The current cost of a shelter to accommodate 1,600 people is US$214,000. 29 Subsidy systems should always be designed with caution so that misuse of subsidies can be avoided. 30 The study team conducted focus group interviews with experts at the Institute of Water Modelling, Bangladesh Meteorological Department, Red Crescent Society, and residents of recent cyclone-affected areas on their recommendations for strengthening the early warning and evacuation system.
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modernizing workshop and laboratory, and developing training institute facilities) totals US$30 million. Operation and maintenance costs of existing and additional observatories are estimated at US$5 million per year, while the awareness-raising promotion program recommended by the Red Crescent Society totals US$3 million annually. 5. Potential Damage and loss from a 10 year return period cyclone/ storm surges in a Changing Climate by 2010: This section estimates the impact of a 10-year return period cyclone and associated storm surges by 2050. Exposure of critical impact elements using geographical overlays formed the basis for estimating the potential damages and losses for the baseline and climate change scenarios. The assessment also drew on projected annual growth in Bangladesh’s coastal population (1 percent) and GDP (6–8 percent) and the devastation experienced in 2007 resulting from Cyclone Sidr. Based on major cyclone events experienced by Bangladesh from 1876 to 2009, it is estimated that a cyclone like Sidr (with wind speed of 223 km per hour) has a 10-year return period. In calculating damages, the study adjusted for the greater extent of storm-surge inundation (area with an inundation depth of 1 m or more) from Cyclone Sidr, which was 8.7 percent more than the historical average inundation area of a 10-year return cyclone in Bangladesh. It is estimated that in a changing climate future 10-year return period cyclones will cover 43 percent of total vulnerable area, 17 percent more than the current average. All estimates were adjusted for 2009 price levels, in accordance with the 18-percent increase in the GDP deflator in 2007 and 2009. In this analysis, damages refer to the potential complete or partial destruction inflicted on assets, while losses refer to the potential flow of goods and services not provided and increased costs of continuing essential services. The total additional potential damage from a 10-year return period cyclone in a changing climate is estimated at US$2.437 billion, with US$2.123 billion in added potential losses (Table 4).
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Table 4. Additional potential damage and loss from an average cyclone-induced inundation in a changing climate by 2050 Infrastructure/ sector asset Damage estimate (million US$) Loss estimate (million US$) Housing 1,947.3 0.8 Education 9.0 835.4 Agriculture 75.4 1,084.0 Non-agricultural productivity 87.9 52.7 Roads 239.5 150.0 Power 60.2 Coastal protection 17.3 Total 2,436.6 2,122.9 The sections below estimate the potential human casualties and injuries from such a cyclone and their estimated economic damage, and the potential damage to sectors that experienced high monetary damage and losses from Cyclone Sidr in 2007 (housing, education, agriculture, non-agricultural productivity, roads, power, and protective coastal infrastructure). Human casualties and injuries In 2007, storm surge inundation from Cyclone Sidr affected some 3.45 million residents in Bangladesh’s coastal areas. Cyclone shelters saved thousands of lives, yet 3,406 people died and 55,282 more were injured, according to post-disaster assessments. Focus-group interviews with affected residents revealed that a large proportion of the population was reluctant to move to cyclone shelters, even during an emergency. The primary reasons cited for this reluctance were distance from the homestead, difficult access to shelters, unwillingness to
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leave unprotected livestock behind, scarcity of sanitation facilities, lack of user-friendly facilities for women, and overcrowding. Assuming that Bangladesh attains a replacement fertility rate by 2021 and 1-percent average annual growth in coastal population between 2001 and 2050, the total number of people exposed to the risk of storm surge inundation from a 10-year return period cyclone by 2050 is 5.34 million under the baseline scenario and 10.04 million with climate change. Without improved infrastructure protection in a changing climate, extrapolation with the ratios of casualty (0.001) and injury (0.016) to exposure experienced in 2007 indicates a risk by 2050 of 4,637 additional human casualties and 75,268 more injuries. 31 It is enormously difficult to attach a monetary-equivalent value to these risks that can be combined with and compared to the risks of financial damage and loss. The most appropriate measure of the benefit from reduced risk of fatality is the Value of Statistical Life (VSL), which estimates the monetary equivalent of improved well-being for individuals from reduced risk of mortality. In reality, VSL should reflect the context of the risk; for example, the risk of sudden fatality from an accident would differ from that of reduced future life span from long-term pollutant exposure. This analysis used a VSL estimate of Tk. 15.5 million (about US$0.2 million)32 for Bangladesh.33 Multiplying this figure by the expected value of the increased number of lives at risk from a 10-year return period cyclone in a changing climate results in US$1.03 billion of additional economic damage from greater fatality risk. To calculate the economic damages from increased risk of injury, this study adopted a crude lower-bound estimate, based on the World Health Organization figure for cost per outpatient visit at a secondary hospital in Bangladesh ($4.86) (Cropper and Sahin 2009). This yields a total economic damage from increased injury risk of US$0.352 million; however, this estimate does 31 In the baseline scenario, by 2050 a 10-year return period cyclone would cause an estimated 5,274 casualties and 85,609 injuries; under the climate-change scenario, those estimates would rise to 9,911 and 160,877, respectively. 32 US$1 = 70 Bangladesh takas (Tk) in 2009. 33 This estimate was computed by updating the central estimate of the VSL for the United States (US$7.4 million in 2006 dollars) available from the US Environmental Protection Agency with a price adjustment between 2006 and 2008 and a GDP differential between the United States and Bangladesh.
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not include any value of lost production and income from injury or the more subjective losses of well-being resulting from injury or incapacitation. Housing In 2007, the housing sector was hardest hit by Cyclone Sidr. The types of houses damaged were predominantly semi-pucka, kacha, and jhupris.34 Analysis of Bangladesh’s 2001 census data indicates that only 2.23 percent of rural households with an annual income of US$470 per capita (Tk. 2,750 per capita per month) or higher could afford a brick house with a concrete roof (i.e., pucka house). But it is expected that, by 2050, the vast majority (about 98 percent) of households will live in brick houses, suggesting a significant reduction in housing damage but a substantial rise in household asset damage from cyclones over time (BBS 2007). In a changing climate, it is projected that an additional 1.45 million houses (assuming an average family size of 4.89) will be exposed to significant damage from storm surges by 2050. A 10-year return period cyclone, with a larger extent of inundated area, would be expected to damage another 1.6 million houses. The assumed size of a standard house is 400 square feet, with 2,000 square feet of brick wall surface and US$2,143 (Tk. 150,000) of household assets. Assuming that half of all walls and household assets are damaged, replastering of houses would cost US$229 million (at Tk. 10 per square foot) and asset damages about US$1.718 million. Education infrastructure Given that, by 2050, an additional 7.08 million coastal residents would be exposed to storm surges caused by climate change, 456,690 primary school students (2,283 primary schools) and 312,957 secondary school students (2,086 secondary schools) would be at risk. Accounting for the larger extent of inundation area from a 10-year return period cyclone, an additional 4,840 primary and secondary schools would be damaged. A standard school in Bangladesh is about 160 m2 and its contents worth US$2,857 (Tk. 200,000). Assuming that half of the school walls and contents would be damaged during inundation, the estimated damage would total US$8.96 34 Semi-pucka houses have foundations made of earthern plinth or brick and concrete, bamboo-mat walls, and roofs made of CI sheet with timber framing. Kacha houses have foundations made of earthern plinth, bamboo walls made of organic materials, and thatched roofs made of straw and split bamboo. Jhupris houses have ceilings made of various inexpensive materials (e.g., straw, bamboo, grass, leaves, polythene, gunny bags).
19
million, and the cost of making alternative arrangements during the repair of facilities would be US$0.82 million. Agriculture The study analysis computed the potential damage and loss to crop production, livestock, and fisheries. Cereal production was limited to aman (monsoon), aus (pre-monsoon), and boro (post-monsoon) rice. With the expanded area of storm surge inundation expected with climate change, these crops are expected to incur significant damage (Table 5). Table 5. Cost ($US) to enhance height of coastal embankments Polder type Baseline scenario Added cost with climate change Sea-facing 317 million 389 million Interior 2.145 billion 503 million Historical records show that Bangladesh is about twice as likely to be hit by a tropical cyclone in the post-monsoon season than in the pre-monsoon season (67 percent versus 33 percent). The resulting difference in risk exposure for the three major rice crops was accounted for in the damage estimations. Assuming a 2.4-percent annual growth rate for cereal production, observed during 2001–07, a 10-year return period cyclone would damage 50 percent of yield, resulting in US$788.83 million of additional damage caused by climate change by 2050. In 2007, Cyclone Sidr caused damages and losses of US$19.3 million and US$6.7 million to livestock and fisheries, respectively. Assuming annual growth rates of 3 and 6 percent, observed during 2001–07, the additional damage from a 10-year return period cyclone with climate change would total about US$55.62 million and US$66.36 million, respectively. Non-agricultural productivity In 2007, Cyclone Sidr inflicted US$51.4 million in damages to Bangladesh’s non-agricultural productive sectors, with storm-surge inundation covering 558,512 ha. That year, these sectors
20
(including small- and medium-sized enterprises, commerce, and tourism) accounted for more than four-fifths of the country’s GDP (World Bank 2009); by 2050, their share of GDP is likely to grow by another 11 percent.35 In a changing climate, a 10-year return period cyclone is estimated to damage more than 1 million ha, representing an additional potential damage of US$87.9 million. Road infrastructure Past experience suggests that roads are partially damaged when the depth of surge inundation is less than 1 m and fully damaged above 1 m. Assuming a 25-percent growth in the country’s road network from 2005 to 2050, the study analysis indicates that, under the baseline scenario, 3,998 km of roads would be exposed to an inundation depth of less than 1 m and 8,972 km exposed to a depth above 1 m by 2050. With climate change, those figures would rise to 10,466 and 10,553, respectively. Accounting for the larger extent of inundated area from a 10-year return period cyclone, an additional 3,461 km of roads would be partially damaged and 2,205 km fully damaged under the climate change scenario. Based on the post-assessment damages from Cyclone Sidr in 2007, the additional damage to roads, bridges, culverts, and related infrastructure in a changing climate would total US$239.5 million. Power infrastructure Damage from Cyclone Sidr in 2007 to Bangladesh’s coastal power sector totaled US$8.2 million. Given the coastal area’s projected population growth between 2007 and 2050 and projected power consumption in countries with a similar per capita income, Bangladesh’s power infrastructure is expected to increase 5 times and its per capita power consumption 20 times by 2050. Based on the damages from Cyclone Sidr, combined with the projected growth in power infrastructure, potential damages under the baseline scenario would cost US$239.1 million and US$449.3 million under the climate change scenario. The additional inundation damage from a 10-year return period cyclone would total US$60.2 million in a changing climate. 35 Between 2007 and 2050, Bangladesh’s GDP is expected to increase 21.48 times.
21
Protective coastal infrastructure Storm surge overtopping of polder embankments, the key reason for polder damage, causes rapid and deep scours to form on the country-side slope of the embankment; the process rapidly weakens the structure, leading to its collapse. In 2007, Cyclone Sidr caused US$70.3 million in damages to Bangladesh’s coastal polders and related water regulators. A comparison of projected surge heights with heights of existing polder embankments indicates that, by 2050, an additional 15 polders will likely be overtopped by cyclonic storm surges in a changing climate, with an estimated additional US$17.3 million in damages. 6. Conclusion Bangladesh is a cyclone-prone country. Cyclones hit the Bangladesh coast every year, and on average a severe cyclone, with wind speed ranging 90 – 119 km per hour, strikes Bangladesh every three years. Cyclone risk spans the entire coastline of Bangladesh, and the historical evidence highlights the danger associated with cyclone-induced storm surges. The vulnerability of Bangladesh may increase even more as current scientific evidence points towards a probable increase in the frequency of intense tropical cyclones in the Bay of Bengal. At present, systematic studies of storm surge patterns in the future, location-specific potential damage and adaptation alternatives are scarce in Bangladesh; this paper is an attempt to narrow the knowledge gap. This analysis integrates information on climate change, hydrodynamic models, and geographic overlays to assess the vulnerability of coastal areas in Bangladesh to larger storm surges and sea-level rise by 2050; and the study method adopted a four-step process. First, the potential inundation zone and projected depth of inundation caused by cyclonic storm surges were demarcated for a baseline scenario without climate change and one with climate change with hydrodynamic models. Second, the critical populations and infrastructure exposed to the added risk of inundation in a changing climate—the critical impact elements—were identified with GIS overlays. Third, the cost of protecting these critical impact elements in order to avoid damage from the added inundation caused by
22
climate change was quantified. Fourth, potential additional damage and loss from a 10-year return period cyclone in a changing (out to 2050) climate was computed. Estimates indicate that a 27-centimeter sea-level rise and 10 percent intensification of wind speed from global warming is likely to increase the storm surge-induced inundation area (vulnerable coastal zone) in size by 69 percent given a +3-meter inundation depth and by 14 percent given a +1-meter inundation depth by 2050. At present, a 10-year return period cyclone with an average wind speed of 223 km/ hour, as recorded during the Cyclone Sidr, 2007, covers 26% of the vulnerable zone; estimates of this study indicate that a similar cyclone will be more intense with global warming and is likely to cover 43% of the vulnerable zone by 2050 – exposing an additional 9.1 million inhabitants to risk of inundation. The most recent 10-year return period cyclone, Cyclone Sidr caused a financial damage and loss of $1.67 billion in 2007. The projection of damage reported in this paper suggests a 10-year return period cyclone out to 2050 will result in an additional financial damage and loss of $4.560 billion36 in a changing climate. In addition, a conservative estimate of monetized loss from additional deaths and injuries is $1.03 billion. At present, Bangladesh has 123 polders, an early warning & evacuation system and more than 2,400 emergency shelters to protect coastal inhabitants from tidal waves and storm surges. Yet, estimates point out that currently Bangladesh has an adaptation deficit of $2.462 billion. It has been further estimated that in a changing climate by 2050, 59 polders will be overtopped during storm surges and another 5,500 cyclone shelters (each with the capacity of 1,600 people) to safeguard the population will be needed. Estimates also indicate investments including strengthening polders, foreshore afforestation, additional multi-purpose cyclone shelters, cyclone-resistant private housing, and further strengthening of the early warning and evacuation system would cost more than $2.4 billion with an annual recurrent cost of more than $50 million to cope with climate change.37 36 of which damage is $2.437 billion and loss is $2.123 billion. 37 This analysis assumes a framework of appropriate development policies and institutional arrangements within which to make the assessed infrastructure investments. Indeed, sound policies, planning, and institutions are essential to ensure that capital-intensive measures are used in the right circumstances to yield the expected
23
The climate is expected to change gradually; the required investments for adaptation can be made incrementally.38 The itemized adaptation cost estimates provided in this paper can serve as a tool to spur the Government of the People’s Republic of Bangladesh to develop location-specific coastal adaptation plans now to avoid future losses. Ratios of location-specific potential damage39 and adaptation cost can be used to prioritize and sequence investments as resources permit. For the international community, this paper presents a detailed bottom-up methodology to estimate potential damage, adaptation deficit and adaptation cost to intensified storm surges in a changing climate. The approach integrates information on climate change, assets and activities at risk, growth projections, likely damage and cost estimates. Estimates presented in this paper can also serve as a prototype of the adaptation costs to extreme weather events in climate negotiations. benefits. Height enhancement of polders, for example, must be carefully considered since construction is usually followed by the accumulation of physical capital behind the barrier, which is considered “safe.” 38 Embankments must be strengthened beyond their current protective capacity as the added risk of inundation becomes more certain. Similarly, it is critical to develop appropriate design standards commensurate with likely climate risks over the expected lives of assets and update them as new research becomes available. 39 Computation of location-specific damage estimates is subject of future research.
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References: Ali, A. (1999). Climate Change Impacts and Adaptation Assessment in Bangladesh. Climate Research, vol. 12, pp.109-116. Dasgupta S. and C. Meisner. 2009. Climate Change and sea Level Rise: A Review of the Scientific Evidence. Environment Department Paper No. 118. The World Bank. http://imagebank.worldbank.org/servlet/WDSContentServer/IW3P/IB/2009/05/18/000333038_20090518032108/Rendered/PDF/485250REPLACEM1Change0and0Sea0Level.pdf Dasgupta, S., M. Huq, Z. H. Khan, M. M. Z. Ahmed, N. Mukherjee, M. F. Khan, and K. Pandey. 2010. Vulnerability of Bangladesh to Cyclones in a Changing Climate: Potential Damages and Adaptation Cost. Policy Research Working Paper 5280. Washington, DC: World Bank. Dasgupta S., S. Murray, B. Laplante, and D. Wheeler. 2011. Exposure of Developing Countries to Sea-Level rise and Storm Surges. Forthcoming in Climatic Change. Emanuel, K., R. Sundararajan, J. Williams. 2008. Hurricanes and Global warming: Results from Downscaling IPCC AR4 Simulations. Available at ftp://texmex.mit.edu/pub/emanuel/PAPERS/Emanuel_etal_2008.pdf EMDAT- The International Disaster Database. Center for Research on the Epidemiology of Disaster. http://www.emdat.be/database Government of the People’s Republic of Bangladesh (2009): Bangladesh Climate Change Strategy and Action Plan 2009. Government of the People’s Republic of Bangladesh (2008): Cyclone Sidr in Bangladesh: Damage, Loss, and Needs Assessment for Disaster Recovery and Reconstruction. Hoque, M. M. 1992. “Strategies and Measures to Reduce Cyclone Damage.” In Cyclone Disaster Management and Regional/Rural Development Planning: UNCRD-CIRDAP Seminar, Phase III, 27-29 January, 1992, Chittagong, Bangladesh, 25-45. Nagoya, Japan: UNCRD.
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IMD 2010, http://www.imd.gov.in/section/nhac/dynamic/faq/FAQP.htm#q42 (accessed March 15, 2010) International Workshop on Tropical Cyclones (IWTC). 2006. Statement on tropical cyclones and climate change. November, 2006, 13 pp. Available at: http://www.gfdl.noaa.gov/~tk/glob_warm_hurr.html IPCC (2007). Climate Change 2007: Impacts, Adaptation and Vulnerability: Summary for Policymakers. Working Group II Contribution to the Intergovernmental Panel on Climate Change Fourth Assessment Report. IPCC, Geneva. Khalil, G. 1992. Cyclones and Storm Surges in Bangladesh: Some Mitigative Measures. Natural Hazards. Vol. 6, pp 11-24 Knutson, T. R., and R. E. Tuleya. 2004. Impact of CO2-induced Warming on Simulated Hurricane Intensity and Precipitation Sensitivity to the Choice of Climate Model and Convective Parameterization. Journal of Climate 17: 3477-95. Michaels, P. J., P. C. Knappenberger, and R. E. Davis. 2005. Sea-Surface Temperatures and Tropical Cyclones: Breaking the Paradigm. Presented at 15th Conference of Applied Climatology. Available at http://ams.confex.com/ams/15AppClimate/techprogram/paper_94127.htm Multi-purpose Cyclone Shelter Project (MCSP) 1993. Summary Report, Bangladesh University of Engineering and Technology and Bangladesh Institute of Development Studies, Dhaka. Murty, T.S., and El-Sabh, M.I. (1992). Mitigating the Effects of Storm Surges Generated by Tropical Cyclones: A proposal, Natural Hazards 6(3), 251-273. Nicholls, R.J. 2006. Storm Surges in Coastal Areas. Natural Disaster Hot Spots Case Studies. Chapter 3. Margaret Arnold et al. 2006. The World Bank. Nicholls, R.J., S. Hanson, C. Herweijer, N. Patmore, S. Hallegatte, J. Corfee-Morlot, J. Chateau, R. Muir-Wood. 2007. Ranking Port Cities with High Exposure and Vulnerability to Climate Extremes. OECD Environment Directorate, Environment Working Papers No. 1.
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Pielke, R. A., C. Landsea, M. Mayfield, J. Laver, and R. Pasch. 2005. Hurricanes and Global Warming. Bulletin of American Meteorological Society, November, pp.1571-75. Quadir, D. A. and Md. Anwar Iqbal. 2008. Tropical Cyclones: Impacts on Coastal Livelihoods, IUCN Working Paper. Rahmstorf, Stefan. 2007. A semi-empirical approach to projecting future sea-level rise. Science, 315, 368-370. http://www.pik-potsdam.de/~stefan/Publications/Nature/rahmstorf_science_2007.pdf SMRC (2000). The Vulnerability Assessment of the SAARC Coastal Region due to Sea Level Rise: Bangladesh Case. SAARC Meteorological Research Centre, SMRC Publication. UK DEFRA 2007,Investigating the Impact of Relative Sea-Level Rise on Coastal Communities and their Livelihoods in Bangladesh. UNDP, 2004. A Global Report: Reducing Disaster Risk: A Challenge for Development. http://www.undp.org/bcpr Unnikrishnan A.S., R. Kumar, S.E. Fernandez, G.S. Michael and S.K. Patwardhan, 2006. Sea Level Changes along the Indian Coast: Observations and Projections Current Science India, 90: 362-368. Woodworth, P. L., and D. L. Blackman, 2004. Evidence for systematic changes in extreme high waters since the mid-1970s. Journal of Climate 17(6), 1190-97. Woth, K., R. Weisse, and H. von Storch. 2006. Climate change and North Sea storm surge extremes: An ensemble study of storm surge extremes expected in a changed climate projected by four different regional climate models. Ocean Dynamics 56(1): World Bank. 2010, “The Cost to Developing Countries of Adapting to Climate Change; New Methods and Estimates” , Washington DC. World Bank and United Nations, 2010. Natural Hazards and UnNatural Disasters: The Economics of Effective Prevention. http://www.gfdrr.org/gfdrr/nhud-home Accessed January 2011.

 

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