More and more people are affected by floods

ÜFloods on rivers and coastal regions are among the most common and devastating natural disasters worldwide. People lose their belongings and their lives in the floods. The damage sometimes runs into the billions. The most recent floods in North Rhine-Westphalia and Rhineland-Palatinate show what effects floods can also have in temperate zones. Climate researchers expect that extreme weather events will become more frequent in the course of global warming, and with them the number of flood events – to the dismay of the population living in flood-prone areas.

A recent study by American researchers, those in the magazine Nature has appeared, shows that more and more people worldwide are living in regions threatened by flooding and are therefore directly threatened by flood events. Beth Tellman of the Earth Institute at Columbia University in New York and her colleagues write that the proportion of the world population in these areas has increased by an estimated 34.1 percent (86 million people) since the turn of the millennium. That is ten times as many people as previously thought. And the trend will increase even further due to migration and population growth until 2030, the researchers believe.

In their study, the Tellman researchers evaluated more than 12,700 satellite images and used them to create 913 maps of floodplains in 169 countries. The data come from American satellite observations from 2000 to 2018. For each flood event, the researchers estimated the flooded area and the number of people living there with the aid of geographic data sets of the population density.

Only some of the floods were recorded

The analysis showed that a total of between 255 and 290 million people worldwide were affected by floods during the study period. The flooded area was about 2.23 million square kilometers. The most frequent flood events occurred in Asia (398, of which 52 in China and 85 in India), in North and South America (223, of which 98 in the USA) in Africa (143), Europe (92) and Oceania (57). Most of the floods were caused by heavy rain, tropical storms and the associated flooding, but also by ice and snow melt and dam breaks.

However, the researchers admit that only the largest flood events were recorded. Minor floods are in the database, the Global Flood Database, not included. Tellman and her colleagues cite the limited resolution of the satellite observations of 250 meters as the reason.

For 57 countries, including North America, Central Asia and Central Africa, the researchers working with Tellman are forecasting a significant increase in the proportion of the population exposed to floods in the coming years. The reasons they give include the increasing sealing of the soil and climate change. In addition, the population is growing rapidly in some regions, particularly in areas at risk of flooding.

In an article accompanying the study, which is also published in Nature Brenden Jongman, Head of Environmental Disaster Risk Management at the World Bank, comments on the researchers’ method: These have mapped an unprecedented number of validated events, including various types of floods that had not been taken into account in previous analyzes. These include dam bursts, local precipitation events and snowmelt: “The increase in the percentage of people affected by flooding by the authors is ten times higher than in previous estimates,” writes Jongman.

Despite the gloomy trend, the study also said something positive: “The ability to deal with floods and to react to them has increased over time.” Jongman names many factors that both prevent floods and cushion their effects could.

This includes investments in flood protection, drainage infrastructure and early warning systems together with improved building standards, programs to support people affected by floods and, finally, a reinforced policy to implement risk-oriented land use planning. However, the measures would also have to be implemented.

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