The recent catastrophic flooding in Connecticut and Long Island, New York serve as a stark reminder of the destructive potential of rapid-onset floods. These events were the result of a perfect storm of meteorological conditions. A stationary frontal boundary combined with a strong low-pressure system blocked in place by Hurricane Ernesto created an ideal environment for sustained heavy rainfall. This phenomenon led to multiple rounds of intense showers and thunderstorms concentrated in the same area, ultimately resulting in devastating flooding.
Unfortunately, this dangerous scenario is expected to happen more frequently. A recent study published in Communications Earth & Environment forecast flash flooding to increase by nearly 8% in the next 75 years with “future flash flood-prone frontiers.” Faced with this increasing weather risk, here are some things you should know about flash floods.
What Are Flash Floods?
Flash floods are a sudden and powerful surge of water. They differ from regular flooding in the speed of onset, duration and impact. Flash floods develop very quickly, often within minutes to a few hours. They are short-lived, lasting from a few hours to a day, depending on the intensity of the rainfall or the source of water. Regular floods develop more slowly and can last for days, weeks or even months, particularly if they are caused by prolonged rainfall, river overflow or sustained storm surges.
This sudden onset is what makes them particularly dangerous, as they leave little time for warning or evacuation. In contrast, regular floods, such as river or coastal floods, develop more slowly, often over several days or even weeks, providing more time for people to prepare and respond.
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Where Do Flash Floods Occur?
Although flash floods can happen almost anywhere, certain spots are particularly vulnerable. Areas with steep terrain, such as mountainous regions, are more prone to flash floods because water flows downhill quickly, concentrating in narrow valleys and low-lying areas. For instance, in 2022, the Appalachian region experienced severe flash flooding due to a combination of heavy rainfall and steep topography. The floods resulted in 39 fatalities and extensive property damage.
Urban areas are also vulnerable to flash flooding. The prevalence of impervious surfaces like roads, parking lots and buildings prevents rainwater from being absorbed into the ground, leading to rapid runoff and overwhelmed drainage systems. This issue is exacerbated by the lack of green spaces that would otherwise absorb and slow down the flow of water.
It's important to note that proximity to large bodies of water is not a prerequisite for flash flooding. Even areas far from rivers or coastlines can experience these sudden and destructive events under the right conditions.
How Strong Are Flash Floods?
The speed and volume of water involved in flash floods give them the power to carry large debris, such as rocks and tree trunks, further amplifying their destructive potential. For instance, during the 2013 flash floods in Colorado, water surged down steep canyons with such intensity that it washed away entire roads and bridges, isolating communities for days. Flash floods are also capable of carving out new channels, altering landscapes permanently.
Are Flash Floods Increasing?
Flash floods have become an increasingly common natural disaster in recent years because climate change exacerbates the risk. As the atmosphere warms, it can hold more moisture, leading to more intense rainfall events. I explain this more in an earlier article in Forbes, with hurricanes adding an additional threat of heavy precipitation. The most recent example is Hurricane Debby, which dumped up to 21 inches of rain in North Carolina.
Studies, such as one published in Natural Hazards in 2021, show that urban expansion combined with extreme weather events significantly increases the likelihood of flash floods.
Are There Signs To Watch For Potential Flash Flooding?
Preparing for flash floods involves a combination of staying informed, planning ahead and taking practical measures to minimize risks. One of the most critical steps is staying informed through weather alerts and understanding the flood risk in your area by checking local flood maps. Knowing whether you live in a flood-prone region, such as near rivers or low-lying areas, can help you take appropriate precautions.
Flash floods leave little time for warning or evacuation. Create an emergency plan that includes clear communication strategies with your family, identifying safe evacuation routes and establishing a meeting point in case you get separated. Equally important is preparing an emergency kit that includes essentials like food, water, medications and important documents, ensuring you have what you need if you need to evacuate quickly.
Reducing Flash Flooding Risks For The Future
As climate change continues to influence weather patterns, it’s increasingly crucial to understand and prepare for flash floods. By staying informed about weather conditions and recognizing the warning signs, communities can better protect themselves against this growing natural hazard.
The increasing frequency and intensity of these events underscore the need for improved urban planning, enhanced drainage systems and greater public awareness to mitigate the potentially devastating impacts of flash floods. Their strength is not only in physical destruction but also in their ability to disrupt entire communities, causing long-term economic damage.
On a promising note, detailed flood modeling and greater computational power may provide more advanced warnings. Improved models reduce computational time from days to hours in large areas, and less than an hour in smaller areas. This will give city officials, emergency crews, the public and businesses more time to prepare and evacuate from these raging waters.
