Impacts of climate change and sea-level rise on cyclonic storm surge floods in Bangladesh Mohammed Fazlul Karim a,Ã , Nobuo Mimura b,1 a CSIRO Davies Laboratory, University Road, Townsville, QLD 4814, Australia b Department Civil and Env. Engineering, Ibaraki University, Hitachi, Ibaraki 316-8511, Japan article info Article history: Received 27 October 2006 Received in revised form 7 May 2008 Accepted 19 May 2008 Keywords: Cyclone Storm surge Flood Climate change Sea-level rise Adaptation Bangladesh abstract This paper describes the impacts of sea surface temperature (SST) rise and sea-level rise (SLR) on cyclonic storm surge flooding in western Bangladesh. A calibrated numerical hydrodynamic model was used to simulate surge wave propagation through the rivers and overland flooding. The model was calibrated with base condition (present climate), and then eight flooding scenarios of plausible future conditions were assessed by considering increased surge heights. Flooded area, flooding depth and surge intrusion length were computed by superimposing the predicted maximum water level information on a digital elevation model (DEM). This analysis showed that for a storm surge under 2 1C SST rise and 0.3 m SLR, flood risk area would be 15.3% greater than the present risk area and depth of flooding would increase by as much as 22.7% within 20 km from the coastline. Within the risk area, the study identified 5690 km 2 land (22% of exposed coast) as a high-risk zone (HRZ) where flooding of depth 1 m or more might occur, and people should move to nearby cyclone shelters during extreme cyclonic events. Predicted area of HRZ is 1.26 times the currently demarcated HRZ. It was estimated that 320 additional shelters are required to accommodate people in the newly identified HRZ. This information would be of value to policy and decision makers for future shelter planning and designing shelter heights. Crown Copyright & 2008 Published by Elsevier Ltd. All rights reserved. 1. Introduction Flooding due to tropical cyclones is one of the most devastating natural hazards in Bangladesh. The coastal region of Bangladesh is particularly vulnerable to cyclonic storm surge floods due to its location in the path of tropical cyclones, wide and shallow continental shelf and the funnelling shape of the coast (Das, 1972). Cyclone-duced storm surges in this region typically originate in the central and southern parts of the Bay of Bengal or in the Andaman Sea. Due to the shallow continental shelf, the surge amplifies to a considerable extent as it approaches land and causes disastrous floods along the coast (Murty et al., 1986). In addition, the coastal areas of Bangladesh comprise low-lying and poorly protected land which supports a large population. All the ingredients for a major cyclone disaster are present and such disasters have occurred several times in the past and claimed hundreds of thousands of lives notably in 1970 and 1991 (Haque, 1997). A brief summary of historic cyclones (wind speeds above 150 km/h) that made landfall along the coast of Bangladesh and caused catastrophe in terms of coastal flooding and human casualties is given in Table 1 . The country is likely to be affected by more intense cyclonic events in the foreseeable future due to climate change and sea-level rise (SLR). This is of great concern, since the location and geography of Bangladesh makes it not only particularly susceptible to the effects of climate change, but also extremely hard to protect. The consequences of climate change lead to an increase in the cyclone-prone area and put a large number of people at risk. However, over the last decade the country’s capacity to deal with cyclones has improved consider- ably with the establishment of a cyclone warning and evacuation system. For example, cyclone Sidr in 2007 claimed far fewer lives (approx. 3500) than the 1970 and 1991 cyclones, which killed at least 500 000 and 138 000 people, respectively. At present, people in the flood risk areas are directed by the forecasting and warning centre to evacuate to refugee shelters. Unfortunately, the capacity of exiting shelters is not adequate to accommodate all the people in the flood risk areas. Moreover, any increase in risk area due to climate change and SLR will increase the required number of shelters. All of the existing cyclone shelters are located in the high-risk zone (HRZ), which is that part of flood risk area where there is a ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/gloenvcha Global Environmental Change 0959-3780/$ - see front matter Crown Copyright & 2008 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.gloenvcha.2008.05.002 Ã Corresponding author. Tel.: +6174753 8580; fax: +6174753 8600. E-mail addresses: Fazlul.Karim@csiro.au (M.F. Karim), mimura@mx.ibaraki.ac.jp (N. Mimura). 1 Tel.: +81294 385169; fax: +81 294 385268. Global Environmental Change 18 (2008) 490– 500