In the United States, more people die each year in flash floods than in tornadoes, hurricanes or lightning.
It’s a reminder from the National Weather Service (NWS) after sudden heavy downpours flooded Las Vegas on Thursday night, sending water gushing into casinos and city buses, as well as stranded cars and leaving people citizens and tourists rushing.
Kentucky and the wider Appalachian region also suffered flood-related deaths this week, mostly due to rising water levels in streams and rivers, after a spell of wet weather. The Kentucky governor said at least 16 people had died, including children, a toll he expected to rise as rain continued to fall.
But as the situation in Vegas shows, a place doesn’t have to be near a body of water to be hit by a sudden, dangerous downpour. Flash floods can hit areas where development and concrete cannot absorb excess flash rainfall, and aging infrastructure struggles to drain water in real time.
Flash flooding is typical in the Southwestern United States during the monsoon season, when a seasonal change in winds draws moisture into the area, which can bring more downpours and thunderstorms. But an exceptionally dry year so far means bare ground can also be as hard as concrete in some places, allowing for restricted absorption.
So what exactly is a flash flood? Are there actions to protect against it?
And is the impact that the CL00 related to fossil fuels
does climate change have on the intensification of extreme weather events that extend to flash floods?
According to the NWS, a flash flood is flooding caused by heavy or excessive rainfall over a short period of time, usually less than six hours. Flash floods are usually characterized by raging torrents after heavy rains that tear through riverbeds, city streets or mountain canyons, sweeping away everything in front of them. They can occur within minutes or hours of excessive rainfall.
They can also occur even when there is no rain, such as after a levee or dam breaks, or after a sudden release of water from debris or an ice jam. And the inability of some municipal storm drains to keep up with water discharge can make the situation worse.
Sometimes flash floods and rising water from rivers and streams can devastate an area at the same time. In 2017, after the highly dangerous and costly Hurricane Harvey swamped coastal areas, it stalled in southern Texas for days as a debilitating hurricane that caused catastrophic flooding and river flooding, according to the NWS archives.
And in 2021’s Hurricane Ida, the NWS office in New York declared its first-ever round of flash flood emergencies in the region, an alert level reserved for “extremely rare situations when a severe threat for human life and catastrophic damage from lightning a flood is happening or will happen soon,” he said at the time.
One of the biggest differences between flash floods and general floods is that flash floods can be more dangerous than people realize. Even a few inches of water can have a current that knocks people over. Just a few meters can float a car. Nighttime flash floods are particularly dangerous, as unknown depths are disguised, simply looking like wet surfaces.
The Red Cross has some tips for flood and flash flood safety, such as getting out of your vehicle and moving to higher ground if you get stuck on a flooded road.
But perhaps most worryingly, flash floods are expected to increase as there are more extreme rainfall events brought on by climate change, meteorologists and climatologists say. This is because warmer temperatures increase evaporation, which puts more moisture into the atmosphere which is then released as rain or snow.
Cities need to spend more of their infrastructure budget on fortifying storm sewers. And they might think of relying on nature to fight nature.
The Natural Resources Defense Council argues that populated areas, in particular, need to think about permeable pavement and rainwater harvesting (instead of just allowing too slow runoff), green roofs, rain gardens and planting additional trees. Learn more about the NRDC.
Traditional flooding is also on the increase. Parts of the western United States are hit by long-lasting drought, but also by times of high flood risk. Earlier this year, the Yellowstone River shattered its previous record and reached its highest recorded water levels since monitoring began nearly 100 years ago, impacting the beloved national park.
Research has documented that this increase in extreme precipitation is already happening, not just in areas like Yellowstone, but around the world,” says Frances Davenport, atmospheric science researcher at Colorado State University.
“That the world has seen multiple record floods in recent years – including catastrophic floods in Australia, Western Europe, India and China – is no coincidence,” Davenport said in a commentary. “Climate change makes record extreme rainfall more likely.”
And, yes, it’s not an either/or scenario. The impact of climate change on the intensification of heat and drought leads to forest fires that destroy natural barriers. This increases the potential for dangerous mudslides with flooding.
In fact, climate change can present multiple challenges, some seemingly at odds with others.
Back in Nevada, some social media commenters were sympathetic to the night Vegas experienced, given the danger to the bustling gambling and retirement destination. But they welcomed rain which could help replenish a low and sinking Lake Mead.
More Living with climate change:
Yellowstone Flood Alert: Is Your Home Properly Insured?
Why you and your wallet have to get used to heat waves
Extreme Heat: 5 Power Outage Risks Facing the Entire US, Not Just Texas