PHILADELPHIA, PA, February 11, 2025

A SALURBAL-Climate paper published recently in Nature Cities sheds light on large inequities in flood exposure within 276 cities in eight Latin American countries. The research, led by Josiah Kephart PhD, MPH, an assistant professor at the Drexel University Urban Health Collaborative, and a team of investigators from Latin America, is the first of its kind to examine neighborhood-level social determinants of flood exposure in Latin America, finding that residents of neighborhoods with the lowest education levels experienced, on average, 4.3 times more flooding than the ones with higher education.

• Of the 228.3 million residents included in the study, 38.1 million people —  17% —  lived in neighborhoods that flooded at least once between 2000 and 2018.
• In eight out of ten (80%)  of the 276 cities included in the study, neighborhoods with lower educational attainment were much more likely to experience flooding than neighborhoods with higher educational attainment. These differences were most extreme in smaller cities.
• One in four residents of the lowest education neighborhoods were exposed to flooding, compared to one in 20 residents of the highest educated ones.

An aerial view shows a flooded city center after people were evacuated from Porto Alegre, in Rio Grande do Sul state, Brazil, May 5 2024. Foto: Ricardo Stuckert / PR CC BY-SA 2.0¹

A warmer planet is driving more frequent and intense extreme weather events, including floods.  Rising sea levels, faster snowmelt, and heavy rains are producing an alarming increase in climate-related flooding. Between 2000 and 2015, the global population affected by floods grew by 58-86 million² and floods are now the most frequently occurring climate-related disaster. In Latin America, 80% of the population lives in highly unequal urban areas, where inadequate infrastructure often poses an additional flood risk.

Researchers from the Climate Change and Urban Health in Latin America (SALURBAL-Climate) Project reviewed almost 20 years of data, from 2000 to 2018, examining flooding across 45,000 neighborhoods in 276 cities in Argentina, Brazil, Chile, Colombia, Costa Rica, Guatemala, Mexico, and Panama. These cities are home to 228 million residents. In total, 117 floods were included in the study (large-scale floods often affect many cities), which leveraged daily flood data from the Global Flood Database and social, environmental, and health characteristics compiled and harmonized by the SALURBAL Project. The authors then analyzed the associations between city- and neighborhood-level characteristics with flooding. Specifically,  they looked at differences in neighborhood educational attainment, population density, and greenness.  

Across the cities included in the study, over 38 million people (nearly 17%) lived in neighborhoods that flooded at least once between 2000 and 2018. When comparing across all neighborhoods included in the study, residents of neighborhoods with the lowest educational attainment were on average over four times (4.3) more likely to inhabit areas that have previously flooded, as compared to residents of the ones with higher education. Across the distribution of 44,698 study neighborhoods, 24.0% of the neighborhoods with the lowest educational attainment were situated in flooded areas, whereas only 5.6% of residents of the highest educational neighborhoods resided in flood-affected areas.

Fig. 2: Percentage of total residents experiencing flooding in their neighborhoods.

There were some differences in the size of inequities in flood exposures across cities. Of the 276 cities examined, eight in ten (80%) demonstrated inequities in flood exposure within the city based on neighborhood educational attainment. This pattern was consistent across all countries in the region, although Mexican cities were the most likely to demonstrate this disparity (86.4% of Mexican cities).   

“These findings serve as a harsh confirmation that poorer populations are living in areas that are many times more vulnerable to floods and other climate-related risks,” says lead author Josiah Kephart, PhD, associate professor at Drexel University’s Dornsife School of Public Health. “While this study doesn’t tell us whether floods make neighborhoods worse-off, or whether folks who have fewer resources end up in flood-prone neighborhoods, the message is clear that policymakers must give careful attention to poorer neighborhoods that may be both at higher risk for flooding and have less infrastructure to be able to cope with the effects of flooding.”

The research identified other characteristics of neighborhoods that were more likely to flood: across the region,  neighborhoods that had experienced floods tended to be less dense, greener, coastal, and peripheral to city centers. “These results highlight yet again the large and inequitable impact of climate change in the large and growing areas of lower- and middle-income countries and the need for urgent action------,” says Ana V Diez Roux, one of the Principal Investigators of the SALURBAL-Climate project and a senior author of the study.  

The study clearly documents large inequities in flood exposure within Latin American cities that closely mirror social disparities. These findings underscore the importance of prioritizing the needs and perspectives of socially marginalized communities in environmental risk management and climate adaptation policies.

“Although the study was not designed to tell us why we observed these disparities, the neighborhoods that suffered from flooding were likely the most devalued, with lower housing prices, and therefore available to low-income populations,” says Nelson da Cruz Gouveia, SALURBAL-Climate Co-Investigator, Head Professor at the University of São Paulo and a co-author of the study. “Rapid and unplanned urbanization, common in Latin American cities, often results in the occupation of unsuitable urban areas, with inadequate or completely absent infrastructure, and consequently, with lower value on the real estate market.” 

Adaptation policies will require a shift not only in urban authorities’ decisions and policy-making processes but also in municipal and national budget allocation. A transition from reactive emergency responses to proactive mitigation and adaptation measures can help prevent not only the economic impacts of flooding but also adverse health effects, displacement, and human losses.

Read the full study: https://www.nature.com/articles/s44284-025-00203-3

This research was supported by the Wellcome Trust 227810/Z/23/Z, AVDR/OLS.

Contact: Carolina Rendón - cr3283@drexel.edu

Climate Change and Urban Health in Latin America (“SALURBAL-Climate”) is a five-year project (2023-2028) that addresses a critical need for evidence linking climate change to health impacts across Latin America.

¹This image was originally posted to Flickr by Lula Oficial at https://flickr.com/photos/157736962@N05/53700500641. It was reviewed on 8 May 2024 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-sa-2.0.

² Tellman, B. et al. Satellite imaging reveals increased proportion of population exposed to floods. Nature 596, 80-86 (2021). https://doi.org:10.1038/s41586-021-03695-w