New Findings on Top Drivers of Urban Flooding in Denver, Colorado
Our recent work connecting spatial rain and geographic data to municipal reports of urban flooding shows us new insights on drivers of urban flooding. Rainfall is not enough to predict a street flood occurrence, information about the geography is important, as well.
Complex variables which drive urban flooding
In our study we used service request reports from the City and County of Denver Department of Transportation and Infrastructure Wastewater Management Division. These service reports are written by any concerned or affected individual who has encountered street flooding spanning 2000-2019 in Denver. In addition, we collected spatial rain data courtesy of the Mile High Flood District Rain Gauge Network and looked at geographic variables from the US Census. We connected service reports to rain events based on time of occurrence and location. We could connect service requests to rain gauges via Thiessen polygons.
Using Thiessen polygons to connect service requests (red) to rain gauges (green) in Denver
Our first attempt of analysis was to find a threshold for rainfall to predict street flooding. But with no strong predictors, we chose to incorporate spatial variables in a linear regression. Our linear regression showed that population density and 5-minute max intensity are both nearly as strong predictors of pluvial flood reports.
This information can be used to improve city flash flood warning systems which currently rely on rainfall depth over a ten-minute time span. Perhaps different alert systems can utilize a 5-minute max intensity for areas of a specific population density.
Our analysis also found that census tracts with higher social vulnerability see higher rates of street flooding. We used the Social Vulnerability Index from the Centers of Disease Control and Prevention (CDC).
A map of Denver highlighting census tract “hotspots” for urban flooding. The tracts with the highest number of flooding incidents are located in the Globeville and Elyria-Swansea neighborhoods
We suggest further work studying better ways to track urban flooding that are more even and regular. Biases and errors may be present by only looking at human-created reports. Urban flooding is predicted to become a serious problem for American cities with aging infrastructure and more intense storms being predicted in the future.
For more information, see the full article: DeSousa, Stacie, Aditi S. Bhaskar, Christa Kelleher, and Ben Livneh. 2024. “Understanding Spatiotemporal Patterns and Drivers of Urban Flooding Using Municipal Reports.” Hydrological Processes 38(12): e70028. doi:10.1002/hyp.70028.