Tucson Standard

In the face of a changing climate, flood monitoring has become a critical area of study with the potential to significantly impact communities worldwide. The U.S. experienced a particularly intense flooding season in spring 2024, with various regions grappling with unprecedented water levels.

Beth Tellman, an assistant professor in the University of Arizona School of Geography, Development, and Environment in the College of Social and Behavioral Sciences, uses satellite imagery to improve understanding of where floods have occurred and are currently happening. She also employs machine learning models to develop datasets for flood monitoring. Her work aims to improve assessments of populations vulnerable to flood exposure and aid in understanding interactions between land cover, climate change, and floods.

Tellman spoke to University of Arizona News about how flood maps are created and how satellite monitoring helps translate people's flood experiences into maps for policymakers.

Q: What are your current projects related to flooding?

A: "One important focus of our projects is on improving algorithms to detect water and floods from satellite images. Some of that work is NASA-funded and has applied aspects within NASA itself. For example, one of the most used satellite sensors in flood monitoring is the VIIRS, or Visible Infrared Imaging Radiometer Suite, which is a NASA-funded project. VIIRS captures one to two images per day everywhere on Earth. This makes it useful for monitoring floods on a global scale.

We are also working with applied data and algorithms in real-world situations. Currently, we are partnering with community-based organizations in the Rio Grande Valley, Texas, building a satellite-based flood database. The database is not just based on our algorithms in the lab and the satellite data. Rather, we are retraining our algorithms with data and experiences from our partners and the people. We also have a major applied project partnering with the Government of Bangladesh for doing flood monitoring with satellites.

My newest project is about trying to create a U.S. flood database to understand how urban development influences new flood patterns. I was awarded an NSF CAREER Award for this project, which involves tracking urban development. If someone builds flood control infrastructure, they often will register that with FEMA or the Federal Emergency Management Agency to remove their property from the regulatory flood plain to either increase property value or reduce insurance costs. We are building a spatial history of where urban development has changed the FEMA regulatory flood plain in the U.S. to see if that's really decreasing flooding or if that's just moving floodwaters downstream to other communities. So we're using satellite imagery together with government records of urban development in flood plains to try and see if there is any flood inequality in the U.S."

Q: How do you map floods?

A: "There are pretty good government records in the U.S. on where floods have happened. The NCEI (National Centers for Environmental Information) has a great storm events database, for instance. There are thousands of flood events that are recorded; typically county governments send those details in so we generally know where a flood has happened on a county scale. We can then pull all satellite imagery for that county and map all the floods we see in those images.

On a global scale, we use a flood inventory we've been using for a long time called the Colorado Flood Observatory. They basically have an Excel spreadsheet of major global floods that appeared in media since they've been keeping this up since the 1980s."

Q: What are the implications of these flood maps for the public and policymakers?

A: "Our satellite images have helped translate people's flood experiences into a map of their entire area that they can then give to a policymaker or government official... In my NSF CAREER project, we mapped about 100 events in the U.S., but I'm working on building a very comprehensive map that would be helpful for understanding flood history."

Q: What are some challenges in flood predictions?

A: "Our research doesn't entail any flood prediction, only observation... For example, riverine flooding results from water overflowing riverbanks; coastal flooding comes from storm surge or hurricanes; pluvial flooding impacts most cities due to direct rainfall pounding surfaces – this type is particularly hard to predict."

Q: There have been several floods in the U.S over recent months; could you offer some perspective on that?

A: "We've experienced some major flooding this spring... There's also prediction for record numbers of hurricanes this summer... With warm ocean temperatures last year contributing huge storms and pluvial flooding across urban cities."

---