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  • Mapping floods in Bangladesh caused by Cyclone Amphan to support humanitarian response
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Mapping floods in Bangladesh caused by Cyclone Amphan to support humanitarian response

Source(s):  International Centre for Integrated Mountain Development (ICIMOD)

By Kabir Uddin and Mir Matin

Cyclone Amphan made landfall in Bangladesh and East India on 20 May 2020. The massive tropical cyclone resulted in the loss of at least 96 lives and caused extensive damage to infrastructure. To make matters worse, communities in the southwest coastal districts of Bangladesh are now facing floods from the subsequent heavy rains and tidal surges while also struggling to adhere to social distancing norms during the ongoing COVID-19 pandemic. The flooding is interrupting the return to normal life for millions of people who were relocated to community shelters (despite fears of an outbreak of COVID-19) after the cyclone struck.

Flood mapping for response

At the moment, humanitarian agencies and the Government of Bangladesh are conducting impact assessments to prepare an effective response strategy and useful to the assessment process are flood inundation maps. Our teams have used synthetic-aperture radar (SAR) satellite remote sensing to provide near real-time inundation maps for supporting flood response, such as during the 2019 Bangladesh floods.

The flood inundation maps for Bangladesh we developed in response to the cyclone are based on analysis of satellite imagery from the Copernicus Sentinel-1 satellite and Sentinel Asia. These maps provide a synoptic overview of the extent of inundation caused by the floods. They can aid disaster management agencies in prioritizing relief and rescue activities in the worst affected areas. To distinguish between perennial waterbodies and the flooding caused by Cyclone Amphan, an image from 16 May was used as the base situation while another from 22 May was used for assessing the flooding situation (see Figures 1 and 2).

Pre/post flooding: Sentinel-1 imageries from 16 May 2020 and 22 May 2020

Figure 1. Pre/post flooding: Sentinel-1 imageries from 16 May 2020 and 22 May 2020 provide a synoptic overview of the extent of the floods due to the catastrophic Cyclone Amphan. The blue sections indicate flood-inundated areas and perennial water bodies. (Source: Copernicus Open Access Hub/Sentinel-1)   

An RGB representation (VH on 16 May as a red band, VH on 22 May as a green band, and VH/VV on 22 May as a blue band) of Sentinel-1

Figure 2. An RGB representation (VH on 16 May as a red band, VH on 22 May as a green band, and VH/VV on 22 May as a blue band) of Sentinel-1 imagery indicates that the red areas are inundated by stormwater, blue areas indicate pre-existing waterbodies (before the cyclone), and yellowish-green areas are other land areas. (Source: Copernicus Open Access Hub/ Sentinel-1)

Inundation situation

Most of the flooding happened in three districts: Satkhira, Khulna, and Bagerhat. Some flooding also happened in parts of Gopalganj and Barisal. District-wise inundation areas are shown in Figure 3 and Table 1.

Sentinel-1 based flood inundation map on 22 May 2020 for the Cyclone Amphan affected area

Figure 3. Sentinel-1 based flood inundation map on 22 May 2020 for the Cyclone Amphan affected area. (Source: ICIMOD/Sentinel-1)

Table 1. Area of sub-districts inundated by Cyclone Amphan (Source: ICIMOD/Sentinel-1)

District

Sub-district

Total area (ha)

Flood-inundated area (ha)

Perennial waterbodies (ha)

Other land (ha)

Bagerhat

Bagerhat S.

26,863

5,129

161

21,573

Bagerhat

Kachua

11,580

1,727

4

9,848

Bagerhat

Morrelganj

42,033

13,355

119

28,482

Bagerhat

Rampal

31,497

15,128

270

16,087

Barisal

Bakerganj

35,633

7,345

407

27,882

Barisal

Barisal S.

24,336

2,641

852

20,842

Bhola

Burhanuddin

26,652

3,464

187

23,001

Bhola

Tazumuddin

6,722

2,373

55

4,292

Borgona

Betagi

16,509

2,534

118

13,845

Gopalgonj

Kotalipara

36,369

4,207

275

31,887

Gopalgonj

Tungipara

16,601

4,017

345

12,239

Jessore

Chaugachha

26,651

2,723

387

23,541

Jessore

Sharsha

33,261

4,088

525

28,648

Jhalakati

Jhalakati S.

18,873

2,375

52

16,446

Jhalakati

Kathalia

14,321

2,653

18

11,633

Jhalakati

Nalchity

22,266

3,864

119

18,284

Jhalakati

Rajapur

15,226

4,511

13

10,702

Jhenaidah

Jhenaidaha S.

46,090

4,872

150

41,067

Khulna

Dumuria

45,332

5,103

2,698

37,531

Khulna

Paikgachha

35,129

19,199

868

14,959

Lakshmipur

Ramgati

35,845

3,881

4,544

23,297

Patuakhali

Bauphal

43,483

6,621

383

36,437

Patuakhali

Mirzaganj

14,699

2,248

51

12,390

Pirojpur

Bhandaria

15,542

3,402

37

12,081

Pirojpur

Kawkhali

8,961

2,681

5

6,274

Pirojpur

Mathbaria

33,432

6,286

110

27,036

Pirojpur

Nazirpur

22,026

3,946

281

17,800

Pirojpur

Pirojpur S.

25,275

6,067

203

18,988

Shatkhira

Assasuni

27,395

9,736

129

17,498

Shatkhira

Debhata

17,197

8,709

73

8,390

Shatkhira

Kaliganj

44,164

17,854

198

26,113

Shatkhira

Satkhira S.

37,120

6,329

1,530

29,245

Shatkhira

Shyamnagar

153,921

20,790

2,308

130,823

Shatkhira

Tala

33,233

4,613

1,750

26,870

*Inundated areas estimated on the basis of the 22 May Sentinel 1 images; can vary on other days (Source: ICIMOD/Sentinel-1)



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  • Publication date 27 May 2020

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