River floodsGrowing risks in flood-prone areas due to economic growth more than climate change

Published 23 December 2015

Worldwide economic losses from river flooding could increase 20-fold by the end of the twenty-first century if no further actions on flood risk reduction are taken. There are two contributors to risks associated with river flooding. Floods’ frequency and severity (both influenced by climate change); and the exposure to floods of people and economic assets (determined by economic activity and human residency in flood-prone areas). Researchers calculate that in many flood-prone regions of the world, more than 70 percent of the increase in flood-related risks over the coming decades can be attributed to economic growth and residency patterns in flood prone areas.

Worldwide economic losses from river flooding could increase 20-fold by the end of the twenty-first century if no further actions on flood risk reduction are taken. Over 70 percent of this increase can be attributed to economic growth in flood prone areas.

Dr. Hessel Winsemius (Deltares) says: “Our conclusions show that besides keeping global warming well below 2 degrees Celsius target, as negotiated during the COP21 meeting to reduce adverse effects of climate change, a lot of future risk can be prevented by spatial planning and flood resilient building in the rapidly growing economies in flood-prone regions.”

How economic growth affects flood risk
The Netherlands Organization for Scientific Research (NWO) reports that river flood risk is, on the one hand, caused by flood events, occurring with a certain frequency and severity; and, on the other hand, by the exposure of people and economy to these events. Whilst the frequency and severity of flood events is impacted by climate change, the exposed people and economy may grow as well, resulting in more assets and economic production located in harm’s way. The Dutch research team specifically paid attention to the fact that economic growth not only causes increase in risk, it also results in a better ability to cope with these events. Therefore, the researchers investigated in particular where economic growth is disproportionally large in flood prone areas and how this affects risk, relative to a country’s Gross Domestic Product.

Dr. Philip Ward (Free University Amsterdam), said: “The study shows that we need to continue developing innovative strategies to reduce risk, not only focusing on climate change, but focusing on all drivers of risk.”

Large increase of flood risk in South-East Asia (factor six)
The patterns are different for individual world regions. Earlier studies already showed that South East Asia will face a large increase in risk due to climate change. This new research shows that climate change impacts are dwarfed by the effects of economic growth in flood-prone regions, and that these two drivers may compound to an increase in economic risk of a factor six in South-East Asia.

This is after correction for the economic growth in the area. In many African countries, when accounting for differences in growth between flood prone and non-flood prone areas, climate change is the main driver of risk increases. In many European basins and in North and South America, impacts of economic growth and climate change compound to relatively small changes in river flood risk.

The Dutch research team was also responsible for the tool Aqueduct Global Flood Analyzer. In this tool, made in collaboration with the World Resources Institute, global river flood risk (until 2030) was made visible for the general public. Aqueduct is now being extended with risk analysis for coastal flooding, and analysis of the feasibility and effectiveness of risk reducing measures.

— Read more in Hessel C. Winsemius et al., “Global drivers of future river flood risk,” Nature Climate Change (21 December 2015) (doi:10.1038/nclimate2893)