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The Rainfall Map That Can Tell You If Your Home Is Doomed

Giving every American access to flood-risk modeling could upend the way homeowners think.


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a family in the back of a truck, in front of a house, in a flood

Residents of Spring, Texas wait to be rescued from rising floodwaters following Hurricane Harvey on Aug. 28, 2017. Photographer: Luke Sharrett/Bloomberg

What would happen if we all had clear information about current and future flood risks to our properties?

First Street Foundation wants to answer that question. The climate and tech non-profit is building up-to-date flood maps to estimate what could happen to homes and businesses in an era of rising sea levels and more frequent, stronger storms. The New York-based foundation says the free-to-use maps are based mostly on open source data and will eventually be granular enough to cover every property in the U.S.

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Estimated New York City flood areas in a category 3 hurricane. Source: Floodiq.com

Through its recently announced Flood Lab project the foundation is now partnering with researchers from eight top universities—including the Massachusetts Institute of Technology, Johns Hopkins University, and the University of Pennsylvania’s Wharton School—to analyze the data for broader social and financial impacts.

First Street’s Executive Director Matthew Eby predicts the move will not only affect home prices but also municipal bonds and mortgage-backed securities linked to real estate in risk-prone areas. We asked him to elaborate. (The following interview has been edited for clarity.)

Bloomberg Green: Why are these tools and projects necessary?

Matthew Eby: We started by asking how do we make the changing environment relevant to people. You hear a lot about what is going to happen in [the year] 2100, but it is hard to understand how it relates to you now as an individual. We quickly realized that flooding accounted for two-thirds of the billion-dollar national disasters that NOAA [the National Oceanic and Atmospheric Administration] has been tracking since 1980. 

And what does flooding actually impact most for people? Their most valuable asset. Their home. Yet there is no possible way for individuals to understand their current or future flood risk. If you look at FEMA flood maps they are meant to price insurance—not to help you understand your home’s personal risk. And people were left with no other tools or data to understand what is a growing risk.

BG: What does it really mean to bring map flood risk down to the individual homes?

ME: We have very high-resolution data that includes where water falls when it is raining and where it flows through the elevation. So it is a precision model that is very granular. But we will also share with users our level of uncertainty. We will then be able to say not only do you have, for example, a 1% risk of flooding right now, but we will also be able to give you the risk over the lifetime of the house.

More importantly, we will be able to explain this in layman terms. What does a 1% risk of flooding mean for how often your basement will fill with water, versus the likelihood of a catastrophic event that will drive you from your home? How will this change in 10 years? That will all be there.

BG: So why bring in academics?

ME: There are fundamental questions related to flood risk analysis that drive billions if not trillions in our economy that academics have not been able not study, because they have not had access to the fundamental underlying data. There are a few for-profit firms that have it but they don’t share it and they don't share their methodology.

The whole point of of Flood Lab is we are unlocking that information and giving it to academics to do the research and analysis so we can answer basic questions: about how flood risk should affect municipal bond ratings, or Fannie and Freddie, and many other highly critical policy questions. Many of these academics directly inform public policy with their research.

BG: Transparency won’t be good for everybody. How about people and towns whose flood risk has gone up?

ME: We are hoping that this information will unlock resilience planning and adaptation planning. If you find out your house has a higher risk of flooding than you thought, there are actions you can take. You can raise your house, or work with your town on shared infrastructure or lobby your local politician about climate change. Operating without this data, because we fear it may impact certain homes, means the risks and the consequences will only be exacerbated in the future.

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This post originally appeared on Bloomberg and was published January 23, 2020. This article is republished here with permission.

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