As flash flood risks rise, protecting Americans in a warming climate only gets harder

Keeping people safe in a warming climate only gets harder. Intensifying rainfall and deadly flash floods across the country are just the latest examples.

Communities from Missouri to Virginia are coping with horrific loss and only beginning to assess the recent flood damages. Resources to help them are already stretched thin. Support agencies and their staffs are constantly challenged to do more with less. The costs of climate change keep climbing, and the pressure to protect people and property never lets up.

Science can’t offer easy solutions, and virtually none in the near-term, but it can help us prepare for the future and understand the risks we’ll face. Flash flooding is a big one, and research shows we can expect it to become more common, and to reach more places widely thought to be out of harm’s way.

That’s because rainfall is intensifying in many parts of the United States. In some places, the amount that once fell in a day now falls in a few hours. More than ever when it rains, it pours.

This is what is expected to happen in a warming climate, because a warmer atmosphere can hold more water – 4 percent more for every 1-degree Fahrenheit degree increase in temperature. Global average temperature has risen by more than 2 degrees Fahrenheit with more than half of that increase coming since 1970.

More water in the atmosphere boosts the odds of big rains. Weather stations east of the Mississippi across Tennessee, Kentucky, West Virginia and Virginia now record at least 10 percent more water per hour of rainfall than they did in the 1970s. In Louisville, the increase is 24 percent. In Huntington, W.Va., it’s 28 percent.

These calculations are based on the widely used Simple Precipitation Intensity index, which divides the total rainfall recorded in a given period — a year in this case — by the number of timeslots in which measurable rain fell. Out of 150 weather stations where hourly data were available, 120 showed at least a 5 percent increase in rainfall intensity since 1970.

That doesn’t mean the stations recorded more rain overall, just heavier rain when it fell. Even across the West in areas where precipitation has trended downward, the rain has been coming down harder on wet days in many cities.

It’s worth pointing out that the U.S. has been a world leader in weather data collection for decades. Records gathered from National Weather Service stations around the country let us analyze data and develop public safety policies with scientific confidence. And while not every storm or flood is the product of climate change, the trends are clear.

The rainfall intensity trends add up to rising flood risks for millions of Americans — many in communities that have rarely, if ever, experienced flash floods. In those that have, intensifying rain means the water can rise faster and higher than in the past. These are serious challenges for the agencies and officials working to protect people, because places that were once safe are increasingly vulnerable.

We are not helpless against the forces of climate change, though.

Governments and companies can slow the rates of change by cutting emissions that add to the thickening blanket of greenhouse gasses wrapped around our planet. That would slow warming and stem the rise in related impact — like rainfall intensity — which could buy more time for planners and local authorities to build defenses, modify homes, shore up infrastructure and redevelop communities toward safer ground. These steps aren’t just for future generations — they can protect residents facing these dangers today.

More immediately, strengthening warning systems and procedures, teaching people how to prepare for flash flooding — especially when it’s an unfamiliar threat — as well as investing in first responders and agencies that lead recovery efforts can also help communities address these growing risks.

Responding to intensifying rain and flash flooding will only get harder and more expensive — just as responding to the rest of the risks related to climate change will. But as disasters keep piling up from coast to coast, more Americans are recognizing that it’s the price of a warming world, and they’ve been paying it for decades.

Jen Brady is lead data analyst at Climate Central, identifying significant trends, patterns and notable climate events. Brady previously worked at the Environmental Protection Agency (EPA) evaluating the climate change impacts of waste and contaminated land management.