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Methodological paper: Assessing the impacts of climate change on flood displacement risk

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This report was written and the analysis was designed and conducted by Justin Ginnetti (IDMC), Pui Man Kam (ETH Zurich - Swiss Federal Institute of Technology in Zurich), Gabriela Aznar Siguan (MeteoSwiss - Federal Office of Meteorology and Climatology), Jacob Schewe (PIK - Potsdam Institute for Climate Impact Research), Leonardo Milano (United Nations Office for the Coordination of Humanitarian Affairs - OCHA, Centre for Humanitarian Data).

Geneva 3 December 2019 – As world leaders meet in Madrid this week at the UN Climate Change Conference (COP25), newly published analysis estimates that, by the end of the century, up to 50 million people per year could be at risk of displacement triggered by floods.

Disasters caused by natural hazards displaced 17.2 million people in 2018, and 7 million in the first half of 2019, with Cyclone Fani driving 3.4 million from their homes in May in India and Bangladesh alone. A small proportion of these hazards are geophysical events, such as earthquakes and volcanoes, but nearly 90 per cent of all disaster displacements are weather or climate-related. Floods are responsible for most displacement, triggering over half, followed by storms.

The Internal Displacement Monitoring Centre (IDMC) now estimates that - in a best-case scenario - the risk of displacement associated with floods could at least double, to around 20 million people by 2099. In a worst-case scenario, it says, the risk could increase five-fold.

“Climate displacement poses a huge global challenge. People are being forced from their homes around the world by cyclones, floods, drought and wildfires. We expect even more extreme weather in the future, so it’s imperative that we understand the magnitude of future risk, what’s driving it, and what we can do about it,” said Justin Ginnetti, IDMC’s Head of Data and Analysis.

IDMC undertook this analysis in partnership with leading experts from the Potsdam Institute for Climate Impact Research (PIK), the Swiss Federal Institute of Technology in Zurich (ETH) and the UN Office for the Coordination of Humanitarian Affairs (OCHA). The extent of future flooding was estimated by transforming future precipitation from global climate models into estimated flood depth using hydrological models.

The report shows that the impacts of climate change, such as an increase in global temperatures, will increase both the frequency and intensity of floods. Population growth around the world will further amplify the risk of future displacement. Low income and developing countries will be disproportionately affected. Sub-Saharan Africa, South-East Asia, Oceania and Latin America are most vulnerable to the effects of climate change, and have the highest concentration of people exposed to floods. These regions are also expected to have the highest rate of population growth and urbanisation this century.

Flooding and landslides destroyed hundreds of homes in Freetown, the capital of Sierra Leone, in August 2019. Informal and unregulated urban sprawl and deforestation on the slopes surrounding the city had created additional risk. Unusually heavy rains linked to El Niño triggered nearly 380,000 displacements in Argentina, Bolivia, Brazil, Paraguay and Uruguay in the first months of the year. Deforestation and the construction of hydroelectric dams may have contributed to the severity of flooding.

“Our analysis indicates that, even if governments successfully implement the Paris Agreement to combat climate change and adapt to its effects, flood displacement risk is still likely to double by the end of the 21st Century,” said Justin Ginnetti.

“Urban development planning will be key in shaping future risk, and governments must also invest in life-saving early-action, such as pre-emptive evacuations.”

For interviews please contact:

Frankie Parrish, IDMC
Email: frankie.parrish@idmc.ch
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