Study: Floods by climate change caused $75B in damage in 30 years

It’s long been established that warming temperatures cause more frequent and intense precipitation. But placing a dollar value on the contribution of climate change to storm damage has been tricky.

Now, Stanford University researchers have determined that a third of the financial damage caused by flooding in the U.S. over the past three decades — almost $75 billion worth — can be attributed to excess precipitation caused by climate change.

Other studies have calculated the climate change differential in detail for small areas, while others have made rough estimates at the national level, the Stanford team said. Their paper, published today in the journal Proceedings of the National Academy of Sciences, is the first to make such a precise estimate at a large scale.

The publication was the result of a collaboration between Stanford climate scientists and economists aimed at conquering one of the biggest hurdles in attribution studies. To determine how much damage is due to climate change, researchers first must identify and account for all the other factors that may have added to flood damage, such as increased construction and population in flood-prone areas and rise in home values.

Frances Davenport, the report’s lead author and a PHD student at Stanford’s School of Earth, Energy, and Environmental Sciences, said that previous attempts to estimate damage due to climate change on a national scale relied on broad measures such as average precipitation and nationwide flood damage.

The Stanford researchers, by contrast, looked at state-level flood damages on a month-by-month basis, which gave them a more granular view.

In 2017, for example, the U.S. experienced 32.21 inches of rain, 2.27 inches above the long-term average. But 2017 was also the year of Hurricane Harvey, which produced more than 40 inches of rain over just four days on Texas’s Gulf Coast, causing $125 billion in damages. The Stanford researchers’ method allowed them to capture significant regional variations like this that can get lost in more sweeping statistics.

From there, the Stanford researchers compared their findings with models estimating the contribution of climate change to specific increases in precipitation to help them arrive at the relationship between precipitation and damage.

“This counterfactual analysis is similar to computing how many games the Los Angeles Lakers would have won, with and without the addition of LeBron James, holding all other players constant,” said study co-author and economist Marshall Burke.