Global flooding to surge by 9-49% this century depending on emission cuts: Fathom

Water risk intelligence firm Fathom has released a new report on the projections of global flooding under climate change, noting that the risk will increase between 9% and 49% this century depending on efforts to cut greenhouse gas emissions.

Fathom’s report compares present-day inland and coastal flood risk with a forecast for 2050 and 2100, demonstrating the impact of a pessimistic high emissions scenario SSP5-8.5 with an optimistic low emissions scenario SSP1-2.6, which is only feasible if all global carbon promises are met.

The firm’s report noted that achieving the best-case low emissions scenario, SSP1-2.6, limits the median flood hazard increase to 9% for 2100 compared to 2020 values, with a likely range of 6-29%.

Meanwhile, the pessimistic scenario, SSP5-8.5, will increase flooding by 49% by the end of the century, with a likely range of 7-109%.

“Near-term increases in flood hazard to 2050 are small; 7% under low scenario SSP1-2.6 and 15% in high scenario SSP5-8.5. There is heavy overlap in the range of what is likely by 2050 in both scenarios: -7–26% is the likely range for SSP1-2.6 and -5–43% for SSP5-8.5. After 2050, these ranges start to diverge,” Fathom explained.

The firm’s report also stated that coastal flooding continues to increase in both low and high scenarios due to the lagged response of the ocean to existing warming, adding that even under SSP1-2.6, coastal flooding is projected to increase by 99% by 2100.

“It is important to note that these global averages result from predicted changes in hazard that have large geographical variations. Some places will see their flood risk fall, whilst for others the increases will be many times larger than the global average even under a lower emissions scenario,” said Dr Oliver Wing, Chief Research Officer at Fathom.

As per Fathom’s report, the largest increases in flooding can be found around global coastlines and in tropical Africa and Asia, in addition to relatively large changes to arid North Africa.

However, uncertainty around this is reportedly high, with the most certainty in flood increases existing along the North Atlantic and Indian Ocean coasts, as well as southeastern Asia and the Pacific Islands.

Discussing the research, Fathom said, “Global and continental scale flood inundation models have existed for around a decade and have seen rapid development in terms of their resolution, physics, representation of climate change, and underlying datasets.

“Use cases include estimating the national or global population exposed to floods, the potential value of assets at risk, the cost and benefits of flood defenses, and the impact of climate and socio-economic change on future losses.

“However, most represent only river flooding, with a hydrodynamic approach to coastal flooding thus far ignored – a significant omission.

“Published in Water Resources Research, the study is the highest resolution and most physically robust global flood modeling effort to date and includes the most comprehensive validation of large-domain flood modeling yet published.

“It underpins the latest version of Fathom’s Global Flood Map, addressing a number of key challenges and taking advantage of recent advances in global data generation.”

Founded in 2013, Bristol, UK-based Fathom provides risk management professionals with scientifically robust tools and intelligence to understand the climate’s impact on water risk. The firm was acquired by re/insurance giant Swiss Re in December of 2023.

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