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Thematic Report – March 2018 - Rohingya Crisis: Cyclones background

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Organisations working on the Rohingya response are preparing for the cyclone season. This brief provides background on cyclones in Bangladesh and an overview of their impact, to put the emergency preparedness planning into a wider perspective. The 2018 cyclone seasons will be different from those in the past. The influx of over 650,000 refugees residing in temporary shelters and who are not included in national preparedness and early warning mechanisms creates a significantly different level of vulnerability.

• Cyclones make landfall in Bangladesh almost every year. There are two cyclone seasons;
May–April and October–November.

• Between 1877–2017, Bangladesh was hit by 154 cyclones, including 53 severe cyclonic storms, 43 cyclonic storms, and 68 tropical depressions. At least 17 hit Cox’s Bazar (Khan & Damen; World Bank 2010).

• The effects of climate change may be making the country more cyclone prone, with an annual increase of 0.05 cyclones per year between 1985–2009 (WFP & HKI 07/2015).

• Cyclone mortality has decreased. Over time fewer people have died as a result of cyclones as Bangladesh has focused on resilience-building, preparedness and early warning measures.

• In 1991 cyclone Gorky killed 139,000 people in Cox’s Bazar and Chittagong (Saha 2017).
Fewer than 25 people have been killed in each cyclone since 2015. However, cyclones in the last three years have been much less severe than the cyclones the country has experienced in the past.

• It is difficult to make direct comparisons between cyclones because, in addition to differing severity, the impact of a cyclone is determined by time of day, location and tide level.

• Cyclones are characterised by high winds, rains and storm surges. Storm surges are the difference between water level under the influence of a disturbance (storm tide) and the normal level that would have been reached in the absence of the disturbance.

• Protection against storm surges is provided by coastal embankments.

• Storm surges can last in duration from a few minutes to a few days and may cause inundation, the scale of which is dependent on the size of the waves (ACAPS SDR 2014; ADPC 1991, Bangladesh Disaster Management Reference Handbook 06/2017; World Bank 2010).

• Storm surges are the main cause of death during a cyclone (ACAPS SDR 2014). During severe cyclones, storm surges can reach up to 8 metres. The average tidal range in the Bay of Bengal is about 3.5–4 metres. The height of the storm surge is dependent on the intensity of the cyclonic winds, high/low tides and the meteorological tide (such as lunar high tide).

• Storm surges on average reach the following heights and distance inland, although this can be impacted by high or low tides at the time of a cyclone