In a study published in August 2021, scientists found that the proportion of the world’s population exposed to floods grew by 20 to 24 percent. Although researchers expected an increase in the number of people living in flood-prone areas, the new estimates were ten times greater than what previous models predicted.
Reviewing 20 years of NASA satellite data, researchers mapped 913 large flood events across 169 countries and compared them with global population data to better understand the impact on people. The team found that from 2000–2015 between 58 and 86 million more people could be found living in floodplains around the world. More than 255 million people were affected at least once by major floods in that period. The increase in exposure includes new human developments and migration, but also the reclassification of some lands in the wake of large flood events and sea level rise. The types of flood events and number of people affected are represented in the map above.
“We need to understand why people are moving into floodplains and what ways we can support flood mitigation,” said lead author Beth Tellman, a geography researcher at the University of Arizona. “I think satellite and Earth observations can be transformative in how we think about building resilience in a world marked by climate change.”
The research, published in Nature and funded in part by NASA and Google Earth Outreach, relied on direct satellite observations from the Moderate-resolution Imaging Spectrometer (MODIS) instruments aboard NASA’s Terra and Aqua satellites. Building off of previous mapping efforts, members of the team built a new Global Flood Database, the world’s largest open library of flood maps. Tellman’s team included researchers from Cloud to Street, NASA, the University of Colorado, the University of Arizona, Columbia University, the University of Washington, the University of Texas, and the University of Michigan.