Fire, Then Flood? How Some Weather-Related Disaster Types Increase Risk of Others

Over several weeks in July, when as many as five flash floods devastated the town of Ruidoso, New Mexico, the causes were not as obvious as many people might have thought. Because while rainfall during that period was significant, it wasn’t particularly abnormal for July, which is the beginning of the southwest summer monsoon that typically runs through September.

What made these rains different—and devastating—is that they followed the South Fork and Salt wildfires, which scorched the same area in June, incinerating trees and other vegetation that could have helped slow floodwaters and leaving behind burn scars—burnt soil that cannot absorb rainfall, causing more intense runoff.

This is an example of how one disaster can exacerbate the risk of others, an effect known as cascading disasters. The Ruidoso fires and floods also highlight the need to understand how disaster risks are interrelated and why it is important to address those risks as early as possible, especially as the U.S. experiences a higher frequency of billion-dollar disasters over time.

To help advance that understanding, The Pew Charitable Trusts has highlighted four interrelated disaster types—extreme heat, drought, wildfire, and flooding—to identify how increased risk in one can raise the risk of another, and what can be done to break the vicious cycle.

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Extreme Heat

Summer 2023 was the hottest ever—until summer 2024. In fact, August 2024 was the planet’s hottest month since global records began in 1880. These records aren’t driven just by extreme heat waves in a handful of states, but instead by higher temperatures across all 50 states.

This trend has consequences: Heat-related illnesses drove nearly 120,000 emergency department visits throughout the U.S. in 2023. And extreme heat increases the risk of drought by raising what scientists refer to as saturation vapor pressure, or the maximum amount of water vapor that the air can hold. In short, warmer air can capture and hold more water, which in turn means increased rates of evaporation and drier conditions on land.

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Droughts

Over time, increasing saturation vapor pressure can lead to what is called a vapor pressure deficit—which measures how dry the air is near the Earth’s surface. Vapor pressure deficits cause vegetation to accelerate the rate at which moisture is pulled from root systems, which can cause plants to eventually wilt and die, increasing drought severity.

In June and July—particularly before remnants of Hurricane Beryl brought needed rainfall to the South and Midwest—much of the U.S. was experiencing a drought. And droughts can be costly. For example, last year’s drought conditions throughout the Southern and Midwestern U.S. led to nearly $14.5 billion in economic losses, ranking as one of the costliest disasters in 2023. Drought in turn can increase the risk of …

Patrick T. Fallon

Wildfires

Droughts boost wildfire risk because vegetation becomes more flammable as it dries out. And when extreme heat and droughts combine, according to the National Oceanic and Atmospheric Administration (NOAA), the effects can be devastating—including decreased stream flow, dry soils, tree deaths, and potentially “extreme wildfires that spread rapidly, burn with more severity, and are costly to suppress.”

Wildfires in the U.S. are growing larger and more intense because of three main factors: growth in the fuel load, or the burnable vegetation that influences both wildfire risk and intensity; increased development in wildfire-prone landscapes; and an increase of the vapor pressure deficit. Wildfires caused huge economic and human losses in 2023, from Maui to the Great Smoky Mountains, with more than 55,000 individual fires burning over 2.6 million acres throughout the U.S.

And the financial cost for American taxpayers is growing rapidly, with the Congressional Budget Office reporting that federal agencies’ spending on fire suppression has more than tripled since the 1980s, even when adjusted for inflation. Since 2000, wildfires have burned an annual average of 7 million acres throughout the U.S., more than double the annual average of acres burned in the 1990s. As noted above, this increases the risk of a fourth type of disaster.

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Floods

As shown in the Ruidoso disasters, wildfires and the burn scars they leave behind created a condition in which any significant rainfall could lead to flash flooding. As the National Weather Service (NWS) explains, “Rainfall that would normally be absorbed will run off extremely quickly after a wildfire, as burned soil can be as water-repellent as pavement. As a result, much less rainfall is required to produce a flash flood.” The NWS also notes, “If you can look uphill from where you are and see a burnt-out area, you are at risk.”

According to a Pew analysis of NOAA data, in the two decades since 2000, at least one flood has occurred somewhere in the U.S. on eight out of every 10 days, on average. And these events aren’t limited to coastal areas. In fact, riverine and flash flooding, particularly in inland and mountainous states, do more damage each year than hurricanes and other coastal storms.

All levels of government have much work to do to reduce the impact of cascading disasters. A recent study from the National Academies of Sciences, Engineering, and Medicine finds that while many communities have plans for hazards they are historically accustomed to experiencing, they are less likely to plan for multiple events occurring in succession.

Comprehensive approaches to resilience must use forward-looking data and science to identify the root causes of risk and offer proactive measures to reduce both the likelihood of cascading disasters and their compounding impacts on people and nature.

The tragic events in Ruidoso illustrate how important it is for federal, state, and local governments to take urgent action to understand their ever-shifting climate-related disaster risk and to adopt holistic approaches to resilience policy, planning, and projects.

Mathew Sanders leads state-level efforts to plan for and build resilience to current and future climate-related disaster impacts for Pew’s U.S. conservation project.