Cyclone Amphan inundation forecast: Based on storm surge forecast for 20 May 2020

Situation summary is due to make landfall on 20th May 2020. Heavy rainfall and an extreme storm surge are expected. The cyclone is due to hit low-lying delta regions, exacerbating the impact of potential inundation.

Inundation forecast method This report uses storm surge forecasts produced by HR Wallingford, based on India Meteorological Department cyclone track forecast at 16:00 UTC (19/05/2020 Model Reference time) to drive Fathom inundation model. Maximum tidal height is assumed. Flood defences are not included. This model is subject to significant uncertainties but shows indicative figures.

Summary of potential impacts • ~15 million people exposed to >0.1m flooding across and NE India. • ~9.7 million people in Bangladesh, ~5.3 million in India, ~0.25 million in Myanmar • 4-6m storm surge in some worst hit areas including Bogerhat, , Satkhira. • In Bangladesh for some provinces, >90% of the total population are exposed. • The and Khulna Divisions have the highest forecast exposure (Bangladesh). • Khorya, Bagerhat, Satkhira and Mongla (), >50,000 people at risk from >3m flooding • has highest risk to >1m flooding, reducing significantly for >3m flood depth • Widespread flooding in , , Bagerhat, , Barisal (Bangladesh). Also possible flooding in , nr (Bangladesh). • N8 Road south of Barisal (Bangladesh) likely to flood • The largest total exposed populations at a state/district level are in the state of West (India). • In the South 24 Parganas district >1.5 million people are exposed (India). ~1 million exposed to >1m flooding; ~190,000 to >3m flooding. • Rohingya Refugee Camps at risk from flooding (Camp 25/Alikhali) in Teknaf, Cox’s Bazar (Bangladesh). Also access routes to the camps. • In Myanmar, greatest numbers are exposed to shallow flooding (>0.1m) in Ponnagyun & Rathedaung Township (62,100). In Sittwe (Akyab) Township, 42,600 exposed to 0.1m flooding with 4,700 at risk from >3m flooding.

This is a research product for situational awareness only, coordinated by the UK Department for International Development Research & Evidence Division. It may be disseminated freely. 1

Figure 1: Simulated flood inundation in meters.

Figure 2: Population exposed to flooding > 0.1m by /tehsil. Size of red dot depicts absolute numbers. Coloured shading indicates % of population exposed within each administrative area

This is a research product for situational awareness only, coordinated by the UK Department for International Development Research & Evidence Division. It may be disseminated freely. 2

Table 1: Total population exposed in Bangladesh (Upazila > 150,000).

Division District Upazila Population Population Population Total % Exposed Exposed to Exposed to Population Population to >0.1m >1m of >3m of Exposed to of Flood Flood depth Flood depth 0.1m Flood depth depth Barisal Patuakhali Mirzaganj 412,800 338,000 19,800 442,000 93% Khulna Bagerhat Morrelganj 402,500 387,300 66,000 404,000 100% Khulna Satkhira Shyamnagar 391,800 372,300 138,500 405,000 97% Barisal Patuakhali Patuakhali Sadar 375,400 296,600 20,400 393,000 96% Barisal Barisal 321,800 192,000 8,800 408,000 79% Barisal Pirojpur 286,900 255,900 21,500 295,000 97% Barisal Amtali 259,400 179,800 4,200 322,000 81% Barisal Barguna Barguna Sadar 254,400 165,100 2,900 292,000 87% Barisal Pirojpur Pirojpur Sadar 247,200 227,900 18,900 248,000 100% Barisal Patuakhali Bauphal 245,300 142,000 4,600 370,000 66% Dhaka Narsingdi Sadar 238,300 132,500 15,800 778,000 31% Dhaka Narayanganj Narayanganj Sadar 220,100 58,100 12,800 1,367,000 16% Dhaka Narayanganj Araihazar 186,900 74,600 10,300 519,000 36% Dhaka Munshiganj Munshiganj Sadar 185,200 90,300 9,600 407,000 46% Barisal Jhalokati Rajapur 181,700 169,800 600 185,000 98% Dhaka Narayanganj 173,900 78,700 18,500 509,000 34% Khulna Khulna Koyra 170,100 152,500 53,400 181,000 94% Barisal Bhola Sadar 168,700 77,900 7,900 494,000 34% Barisal Pirojpur Bhandaria 165,900 155,700 9,900 171,000 97% Barisal Pirojpur Nesarabad (Swarupkati) 162,500 64,300 8,200 236,000 69% Khulna Bagerhat Mongla 157,900 135,900 47,100 173,000 91% Barisal Jhalokati Kanthalia 153,200 141,000 2,200 161,000 95%

Table 2: Total population exposed in India (Tehsil > 20,000).

Division District Tehsil Population Population Population Total % Population Exposed Exposed to Exposed to Population Exposed to to >0.1m >1m of Flood >3m of Flood 0.1m Flood of Flood depth depth depth depth West South 24 Parganas n.a. ( 1187) 1,160,500 736,600 29,900 6,217,000 19% Bengal West North 24 Parganas Basirhat 796,400 585,600 25,300 2,630,000 30% Bengal West Purba Medinipur Tamluk 695,900 272,000 12,600 3,110,000 22% Bengal West South 24 Parganas Diamond Harbour 687,000 244,100 11,700 2,702,000 25% Bengal West Haora Uluberiya 629,300 350,600 15,600 2,381,000 26% Bengal West South 24 Parganas n.a. ( 1229) 390,400 263,600 9,600 420,000 93% Bengal West North 24 Parganas n.a. ( 1220) 332,800 260,300 25,600 362,000 92% Bengal Odisha Bhadrak Bhadrak 290,500 105,900 5,300 1,722,000 17% Odisha Kendrapara Kendraparha 129,500 56,400 15,800 1,646,000 8% West Purba Medinipur Kanthi 77,900 20,600 5,400 2,713,000 3% Bengal West Haora Haora 58,500 48,800 33,500 3,153,000 2% Bengal

This is a research product for situational awareness only, coordinated by the UK Department for International Development Research & Evidence Division. It may be disseminated freely. 3

Table 3: Total population exposed in Myanmar (Township > 20,000).

Division District Township Population Population Population Total % Exposed to Exposed to Exposed to Population Population >0.1m of >1m of Flood >3m of Flood Exposed Flood depth depth to 0.1m depth Flood depth Rakhine Buthidaung Ponnagyun & Rathedaung 62100 29500 300 464000 13% Rakhine Sittwe Myebon 49200 32900 2400 209000 23% Rakhine Sittwe Pauktaw 48700 21200 1600 242000 20% Rakhine Buthidaung Sittwe (Akyab) 42600 15400 4700 242000 18% Rakhine Maungtaw Maungdaw 25600 14800 7900 294000 9%

Figure 3: Population exposed to inundation for Durgachak (India) and Patuakhali/Jholokati/Barisal (Bangladesh). Other detailed maps available on request.

This is a research product for situational awareness only, coordinated by the UK Department for International Development Research & Evidence Division. It may be disseminated freely. 4

Figure 4: Population exposed to inundation for Cox’s Bazar (Bangladesh) and North-West Myanmar. Other detailed maps available on request

This is a research product for situational awareness only, coordinated by the UK Department for International Development Research & Evidence Division. It may be disseminated freely. 5

Modelling approach and limitations Cyclone track: India Met Department forecast Storm surge modelling: HR Wallingford Inundation modelling: Fathom/University of Bristol Population data: WorldPop.

The modelling approach applied here uses storm surge water height forecasts to drive a 2-D inundation model. This model is subject to significant uncertainties both in the surge forecasts and in the inundation simulations. This is not an operational product. No evaluation of this approach has been undertaken to date, rather the data represent a best effort given the immediate need for information. Moreover, the simulations are strictly simulating storm surge inundation and do not account for precipitation driven inundation at this stage. There are no flood defences included in the model, likely contributing to over prediction of exposure in areas benefiting from defences, and it has been built using a global terrain dataset MERIT DEM. Although the best available global terrain dataset for flood modelling, this data is subject to large errors (>2m in 40% of cells) and has a spatial resolution of ~90m. Therefore, it is only suitable for exposure and risk analysis at larger scales. The exposure analysis conducted here uses WorldPop data to provide estimates of the total population exposed. These population data are also subject to substantial uncertainties and are only suitable for large scale, aggregated exposure estimates.

Correspondence: Please direct technical enquiries to Dr Andrew Smith ([email protected]). For all other enquiries please contact Dr Rosalind West (r- [email protected]) or Katherine Marsden ([email protected])

This is a research product for situational awareness only, coordinated by the UK Department for International Development Research & Evidence Division. It may be disseminated freely. 6