Extreme weather disasters are costing the country billions of dollars in damages each year. A new study from Stanford shows that over the past three decades, the U.S. has seen nearly $75 billion in damage from floods fueled by the climate crisis.
The research, published in the journal Proceedings of the National Academy of Sciences on Monday, pulled monthly, state-level flood damage cost estimates from the Spatial Hazard Events and Losses Database for the U.S. from the years 1988 to 2017. That dataset—which is maintained by Arizona State University—showed that the country saw $199 billion in damages from rainfall-driven floods over that period, and that costs have steadily increased over time.
The authors then obtained data on changing rainfall patterns for each state from the PRISM Climate Group as well as other state-level socioeconomic data from the Census Bureau. Noah Diffenbaugh, the Stanford researcher who led the study, said this let the researchers control for other factors that could impact damage like increases in home values and development in floodplains. Other research has shown that climate change is increasing the frequency and intensity of heavy downpours because a warmer atmosphere can hold more water.
Using the data and knowledge, the researchers created a model to determine how much of damage has been fueled by the climate crisis specifically. They also used their model to conduct a counterfactual analysis, calculating how much disasters would have cost if the U.S. had seen no changes in extreme precipitation.
The researchers’ findings suggest that 36% of the damages caused throughout the 29-year period were driven by climate change. Though some U.S. regions, like the Southeast and Gulf Coast, have been more impacted by heavy rainfall than others, they observed a clear nationwide trend of higher costs during months where there was more extreme rainfall. Just a small percentage of the most extreme events drove the majority of the damage.
“The top 10% wettest precipitation events account for around 70% of flooding costs in the U.S.,” Diffenbaugh said.
The researchers’ model only looked at damages from rainfall itself, not coastal flooding due to rising seas and storm surge. But now that the researchers have developed a model to isolate cost increases due to climatic changes, it can be applied to coastal flood damage, as well as wildfires and other weather disasters.
Daniel Swain, a climate scientist at the Institute of the Environment and Sustainability at the University of California, Los Angeles who was not involved in the study, said that model could be useful to dispel myths about what’s driving increased losses.
“In some circles, there have been arguments that, well, losses are increasing because we’re just building more stuff and putting more stuff in harm’s way, so things are becoming more expensive because we have a higher propensity to build structures in places that are vulnerable,” he said. Those circles include the likes of climate policy researcher Roger Pielke Jr., who has testified about climate change on Capitol Hill. Swain said that it is “true to an extent, but this model isolates climate just the contribution to these losses from the physical hazard itself changing.”
As the climate changes, damages are likely to increase even more. But that also means if we take steps to reduce our greenhouse gas emissions and curb the climate crisis, we could lower those losses. Diffenbaugh said that since so much decision-making about what climate actions to undertake are based on cost-benefit analysis, a model like this could play an important role.
“To accurately evaluate the cost-benefit of different actions, we need to be able to evaluate not only the cost of taking action but also the benefit, and with climate change, a lot of those benefits are avoided damages,” he said.
It may seem crass to look at the economic cost of damages rather than the threat to human life. But Swain said that the framework could help push the U.S. to reduce emissions and invest in adaptation to flooding, which will be needed due to climate change already locked in place even if emissions fell to zero tomorrow.
“For better or for worse, we think about things, you know, about disasters often in terms of the kinds of financial costs or losses that they incur. That’s something the government cares about, something industry cares about, something insurers care about,” he said. “This is a tangible way of measuring the consequences, and we need that.”