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Human Mobility and Disaster Resilience:
Human Mobility and Disaster Resilience:
Lessons from Flash Floods and Transportation Systems
Lessons from Flash Floods and Transportation Systems
31 January 2025
Southeast Sao Paulo experienced a flash flood last week which affected 180,000 people. The most impactful videos showed floods sweeping away cars on the streets and crowds stuck in flooded subway systems. When I worked on transportation analysis for emergency events in a military context, I quickly realized how the question of transportation system resiliency is a crucial but often overlooked consideration for emergency management. Population mobility is essential for overall quality of life (access to work and income, shelter, aid) and is tied to many aspects of risk reduction, such as resilient infrastructure planning, emergency warning communications, mobility corridor planning, and emergency transportation operations.
Human Mobility During Environmental Emergencies
Human mobility pattern research is an absolutely fascinating field. The applications are endless and eye-opening in our framing of human influences on other systems through space and time. Modeling human mobility as it relates to infectious or waterborne disease transmission is essential to predicting, controlling, and mitigating the spread of these diseases. Similarly, modeling human behavior during various environmental disasters provides emergency managers effective tools to plan egress/ingress routes, determine where mobility corridor hotspots are located, and anticipate where and when response is most needed. Without this understanding and planning, there is a potential for high concentrations of populations to be exposed to extreme risk during and after an environmental event.
City planners and emergency responders must understand these behavioral patterns in areas susceptible to flash floods, as the temporal scale of the event (risk) is very short, yet the intensity of the event is very high. Reactive response is not sufficient for these events. High-density city planning should be proactive, meaning there should be intentional designs which encourage an adaptation of human mobility corridors around high risk environmental corridors. Even in rural areas where access roads are dispersed and often lack maintenance, preventative planning is essential to maintain corridor connectivity. I once sat in on a county board meeting in Mississippi that discussed a situation where an elderly couple had difficulty getting to hospital appointments six months after a major flood because sections of their road were inaccessible. Imagine what would happen if they experienced a medical emergency and it took over an hour for anyone to reach them because of the lack of transportation infrastructure planning.
I would love to explore the spatiotemporal relationship between human mobility and water mobility in the future. I particularly find short, intense events (like flash floods) extremely interesting as it both challenges current risk communication methods as well as incorporates psychological phenomena such as collective disaster memory. I have listed some resources and articles that explore human mobility during disaster events. I would challenge one point that I noticed throughout most of the articles: there is a focus on increasing “preparedness”. Preparedness is one part of building resilient systems, especially in the short-term; however, I would argue long-term mitigation should start with adaptive designs, taking into consideration the main driver of these events - nature.
Costs of Mobility Loss
Mobility loss not only potentially increases risk of exposure and injury, it also costs people in many ways which affects overall quality of life and access to livelihoods (Sustainable Development Goals 3, Good Health and Well-being, and 8, Decent Work and Economic Growth). The article ““Flood Impacts on Urban Transit and Accessibility—A Case Study of Kinshasa” published by He et al. analyzed the economic impacts of flooding on Kinshasa (Democratic Republic of the Congo). They conclude:
“flood disruptions cause increases in public transit headways, transit rerouting, decreases in travel speeds, which translate into travel delays and loss of job accessibility. This induces substantial economic costs to local commuters – about $1.2 million daily – and hinders the establishment of an integrated citywide labor market.”
Access to basic needs - such as water, food, and income - is essential for human survival. Transportation corridors which lack the integration of environmental considerations as well as human behaviors permeate an environment of injustice and unnecessary human suffering. An investment in resilient infrastructure is an investment in people.
Additional Resources
Sao Paulo under water, Brazil on alert! Subway station flooded, car swept away in the city
BBC. “São Paulo storm brings floods, chaos and lightning.” https://www.bbc.com/news/videos/cdrykzr5038o.
“Brazil - Floods and severe weather in São Paulo City.” ReliefWeb. https://reliefweb.int/report/brazil/brazil-floods-and-severe-weather-sao-paulo-city-noaa-cpc-media-echo-daily-flash-27-january-2025.
Arrighi, C., M. Pregnolato, R.J. Dawson, and F. Castelli. “Preparedness against Mobility Disruption by Floods.” Science of The Total Environment 654 (March 2019): 1010–22. https://doi.org/10.1016/j.scitotenv.2018.11.191.
Han, Su Yeon, Ming-Hsiang Tsou, Elijah Knaap, Sergio Rey, and Guofeng Cao. “How Do Cities Flow in an Emergency? Tracing Human Mobility Patterns during a Natural Disaster with Big Data and Geospatial Data Science.” Urban Science 3, no. 2 (May 6, 2019): 51. https://doi.org/10.3390/urbansci3020051.
He, Yiyi, Stephan Thies, Paolo Avner, and Jun Rentschler. “Flood Impacts on Urban Transit and Accessibility—A Case Study of Kinshasa.” Transportation Research Part D: Transport and Environment 96 (July 2021): 102889. https://doi.org/10.1016/j.trd.2021.102889.
Song, Xuan, Quanshi Zhang, Yoshihide Sekimoto, and Ryosuke Shibasaki. “Prediction of Human Emergency Behavior and Their Mobility Following Large-Scale Disaster.” In Proceedings of the 20th ACM SIGKDD International Conference on Knowledge Discovery and Data Mining, 5–14. New York New York USA: ACM, 2014. https://doi.org/10.1145/2623330.2623628.
Wang, Qi, and John E. Taylor. “Patterns and Limitations of Urban Human Mobility Resilience under the Influence of Multiple Types of Natural Disaster.” Edited by Lidia Adriana Braunstein. PLOS ONE 11, no. 1 (January 28, 2016): e0147299. https://doi.org/10.1371/journal.pone.0147299.
Watson, Grace, and Jeong Eun Ahn. “A Systematic Review: To Increase Transportation Infrastructure Resilience to Flooding Events.” Applied Sciences 12, no. 23 (December 2, 2022): 12331. https://doi.org/10.3390/app122312331.
2024 Floods: A Year in Retrospect
2024 Floods: A Year in Retrospect
January 2025
Severe weather and widespread flooding ravaged communities globally in 2024. Public data from the Emergency Events International Disaster Database indicate 132 flooding events this year, affecting nearly 45.2 million people. The number of people affected by flooding events are comparative to 2023 (170 flood events, 30 million affected).
Unfortunately, we have come to expect these data year after year. So what have we learned from these disasters? And what are we doing about it? Climate change impacts and population growth demands are at the crux of flood risk exposure. Flood events of 2024 provide perspective on opportunities to adjust how we understand the human-water relationship, risk communication, and flood risk management. While there is much to say of these topics and beyond, these initial points of reflection provide an opportunity to expand our conversations around flood event considerations and risk management.
Understanding Exposure: Who and Where.
45.2 million people experienced tragedy from flooding this year. At least 5,419 people died as a result of flooding. Let those numbers sink in. Those are real people who, knowingly or not, were exposed to flood risk and are now living in the wake of flooding destruction. Many disproportionately affected communities are lower income or underserved populations, most of which are forced to live in densely packed areas with high exposure risk. Our current development schemes and policies reinforce this social dynamic, resulting in extremely high annual statistics around flood related impacts, damage, and loss of life.
There is a need to understand not only where flooding events occur, but the demographics of who is impacted and how to reduce their exposure on a larger scale. This ultimately may direct society away from management (primarily levees and dams) and toward adaptation, like the Netherlands’ “Room for the River” program. These changes require extreme levels of financial investment and changes in development planning. However, with flood damage costs ranging between $200-500 billion annually in the U.S. alone, there is room to argue that preventative financial investments to reduce exposure may outweigh annual financial requirements for post-event response.
Additionally, many individuals in high exposure areas do not fully understand the risk associated with potential flooding nor are evacuation plans widely communicated. Risk education and communication is essential to providing individuals with tools to manage their own risk exposure and mitigation.
These are basic considerations for how to look at our understanding of flood risk exposure. There are many facets to this conversation happening in risk management, policy and governance, social justice, sustainable development, and finance sectors. My intent with this blog and with my studies is to highlight these conversations and bodies of research to provide an interdisciplinary lens to water-related risk management.
Changing Climate, Change in Planning.
Climate change is the biggest influence on increasing frequency and severity of storms. Unusually heavy and long-lasting monsoons were among the top ten most destructive storms of 2024. However, “unusual” weather behaviors are becoming more common with changing climate conditions, but our forecasting and current models often do not match reality. There are many studies around restructuring atmospheric forecasting, hydrologic models to match current weather events, and a focus on modeling snowmelt forecasts and behaviors. I am excited to share research integrating machine learning into hydrologic forecasting, remote sensing tools to more accurately identify flood risk areas and modeling, and more research that integrates climate change impacts on forward looking modeling and forecasting.
Sociohydrology: An Interdisciplinary Approach.
Sociohydrology is a young field, but an extremely important interdisciplinary field. Increasing our understanding of human-water interactions and phenomena on a larger spatiotemporal scale, our research can inform policy and decision making, challenge our perception of current water management practices, increase social justice awareness, and integrate SDG long-term planning. The human-water paradigm is shifting and we must heed the call to take a holistic approach to our understanding of this dynamic challenge.
Data gathered from EM-DAT (Emergency Events Database) on 08 Jan 2025. Graphics created in Flourish.
https://www.emdat.be/
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