27 May 2020 An aerial image of typical flood inundation in Bangladesh. The murky waters reflect flood inundation areas and rural settlements and fields covered by floodwaters. (Photo: Kabir Uddin/ICIMOD) 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 having 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. Flood inundation maps are helpful for such assessments. ICIMOD has worked on using 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. ICIMOD prepared flood inundation maps for Bangladesh by analysing 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). 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) 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 Figure 3. Sentinel-1 based flood inundation map on 22 May 2020 for the Cyclone Amphan affected area. (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) (This piece was first published on the ICIMOD website on 27 May 2020.) Kabir Uddin GIS and Remote Sensing Specialist, Geospatial Solutions Mir Abudul Matin Theme Leader, Geospatial Solutions