The percentage of the global population at risk from flooding has risen by almost a quarter since the year 2000, according to a new study, with migration and a growing number of flood events behind the rapid increase.
And the problem is set to worsen. In future, the authors expect the numbers at risk of flooding to continue to rise.
Indeed, they estimate that by 2030, there will be an extra 25 countries experiencing increasing floods in addition to the 32 being impacted at present.
The information for the study was gathered from the Global Flood Database, a collaboration between Cloud to Street and The Flood Observatory (DFO), with funding from Google Earth Outreach.
Analysis of detailed satellite images was used to document the rise this century, which the researchers suggest is significantly greater than had been predicted by existing flood maps which they claim fail to consider the extent of demographic change.
They cite as an example Hurricane Harvey in Texas in 2017, when they claim that around 80,000 homes were flooded that were not on government risk maps.
In this new study, researchers looked at daily satellite imagery to estimate both the extent of flooding and the number of people exposed to over 900 large flood events between 2000 and 2018.
They found that between 255 and 290 million people were directly affected – and between 2000 and 2015, the number of people living in these flooded locations increased by 58-86 million.
This represents an increase of 20-24% in the proportion of the world population exposed to floods, some 10 times higher than previous estimates.
The increase was not evenly spread throughout the world. Countries with increased flood exposure were mainly in Asia and sub-Saharan Africa.
In European and North American nations, the risk was stable or decreasing.
Around 90% of the flood events observed by the scientists were in South and Southeast Asia, around the basins of major rivers including the Indus, Ganges-Brahmaputra and the Mekong.
One of the questions raised by the research is why people in many countries are moving into flood prone areas rather than away from them, with the suggestion that this continues to be an economic impetus.
While the global population grew by over 18% between 2000 and 2015, in areas of observed flooding, the population increased by 34%.
The authors say that the key drivers of flooding are heavy rainfall, tropical storms or surges and snow and ice melt. Dam breaks represented less than 2% of floods but had the highest increased incidence in terms of population exposed.
The researchers involved in this study are affiliated with the Columbia Earth Institute, University of Arizona, University of Michigan, University of Texas at Austin, University of Colorado, Boulder, INSTAAR, University of Washington, Google, and Science Systems & Applications Inc/Biospheric Sciences Lab, as well as the NASA Goddard Space Flight Center.
The research was published in the journal Nature.
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