The Most Flood-Prone Counties in America

Millions of Americans are on high alert this week as, what may become the first named tropical storm of the 2026 hurricane season, moves across the Southern United States. In the coming days, heavy rains are forecasted to potentially impact a large swath of the country – from central Texas up through coastal North Carolina and all along the Gulf. According to meteorologists at AccuWeather, downpours could lead to rainfall at rates of up to 3 inches per hour – and an elevated likelihood of deadly flash floods. 

Flash flooding is typically caused by heavy rain that cannot be absorbed as fast as it falls, often due to existing ground saturation levels, heavy development, or soil type. The most vulnerable areas include those along creeks, streams, or rivers, between mountains or steep hills, and even in urban and suburban communities. In these and other high-risk places, a slow moving severe thunderstorm can result in devastating flash floods, which can develop in only a few hours and sweep through population centers with little notice. 

Flash floods are among the deadliest and most destructive natural disasters commonly faced in the United States, and in recent years, major flash flooding events have resulted in hundreds of millions of dollars in damage.

Using data from the National Oceanic and Atmospheric Administration, Climate Crisis 247 identified the U.S. counties most susceptible to flash floods. We reviewed all severe flash flooding incidents between 2016 and 2025, and ranked the counties that have been impacted most often. Supplemental data on damage, fatalities, and specific incidents are as reported by NOAA. 

10. Wake County, North Carolina

• Number of severe flash flooding events, 2016-2025: 63
• Total damage from flash flooding events, 2016-2025: $67,603,000 (1 fatality, 0 injuries)
• Most destructive flash flooding event in county: October 9, 2016 ($65,500,000 in reported damage)
• Most destructive flash flood details: Hurricane Matthew dropped as much as 15 inches of rain, causing flooding along parts of the Neuse, Cape Fear, and Tar river basins.

9. Riverside County, California

• Number of severe flash flooding events, 2016-2025: 67
• Total damage from flash flooding events, 2016-2025: $106,154,000 (1 fatality, 6 injuries)
• Most destructive flash flooding event in county: February 14, 2019 ($102,020,000 in reported damage)
• Most destructive flash flood details: An atmospheric river brought heavy rain to the area, falling at a rate of an inch per hour, flooding parts of San Jacinto Creek, Strawberry Creek, the Santa Margarita River, and tributaries to the Whitewater River.

8. Allegheny County, Pennsylvania

• Number of severe flash flooding events, 2016-2025: 71
• Total damage from flash flooding events, 2016-2025: $14,770,600 (0 fatalities, 0 injuries)
• Most destructive flash flooding event in county: June 20, 2018 ($10,185,000 in reported damage)
• Most destructive flash flood details: Rain fell at a rate 350% above flash flood guidance, causing flooding that damaged homes and prompted more than 60 water rescues.

7. Mohave County, Arizona

• Number of severe flash flooding events, 2016-2025: 85
• Total damage from flash flooding events, 2016-2025: $3,132,000 (3 fatalities, 3 injuries)
• Most destructive flash flooding event in county: September 5, 2025 ($1,084,000 in reported damage)
• Most destructive flash flood details: Scattered thunderstorms brought heavy rain, falling as fast as 3.2 inches an hour. The resulting flash floods damaged roadways, underground water pipes, and other infrastructure.

6. Gila County, Arizona

• Number of severe flash flooding events, 2016-2025: 99
• Total damage from flash flooding events, 2016-2025: $77,488,000 (15 fatalities, 0 injuries)
• Most destructive flash flooding event in county: July 29, 2021 ($40,000,000 in reported damage)
• Most destructive flash flood details: Rainfall at rates of up to 9 inches per hour led to flooding in portions of Pinal Creek, which rose 4.25 feet in a 15 minute period. Flash floods in the area damaged hundreds of homes and resulted in multiple road closures.

5. Coconino County, Arizona

• Number of severe flash flooding events, 2016-2025: 101
• Total damage from flash flooding events, 2016-2025: $12,500,000 (5 fatalities, 4 injuries)
• Most destructive flash flooding event in county: August 22, 2023 ($7,000,000 in reported damage)
• Most destructive flash flood details: As much as 2.5 inches of rain fell in two hours near the southern end of The Grand Canyon National Park — enough water in a short enough time period to flood buildings, homes, cars, and roadways.

4. Pima County, Arizona

• Number of severe flash flooding events, 2016-2025: 111
• Total damage from flash flooding events, 2016-2025: $10,278,500 (5 fatalities, 2 injuries)
• Most destructive flash flooding event in county: July 10, 2018 ($4,000,000 in reported damage)
• Most destructive flash flood details: Severe thunderstorms dropped as much as 3 inches of rain in an area that had already reported several inches only days earlier. Flash flooding caused a Union Pacific train to derail, damaged transportation infrastructure, and resulted in eight swift water rescues.

3. San Bernardino County, California

• Number of severe flash flooding events, 2016-2025: 119
• Total damage from flash flooding events, 2016-2025: $33,382,000 (6 fatalities, 6 injuries)
• Most destructive flash flooding event in county: July 24, 2017 ($8,021,000 in reported damage)
• Most destructive flash flood details: Monsoon rains from a severe thunderstorm caused heavy flooding around the Mojave Desert, damaging or destroying multiple roads and bridges.

2. Yavapai County, Arizona

• Number of severe flash flooding events, 2016-2025: 127
• Total damage from flash flooding events, 2016-2025: $8,000,000 (3 fatalities, 0 injuries)
• Most destructive flash flooding event in county: July 19, 2017 ($7,000,000 in reported damage)
• Most destructive flash flood details: Heavy rain caused flash floods along portions of Big Bug and Grapevine Creeks, both tributaries of the Agua Fria River, which rose nearly 6 feet in under an hour. Floods lead to evacuations and the damage or destruction of more than 100 homes in the community of Mayer.

1. Maricopa County, Arizona

• Number of severe flash flooding events, 2016-2025: 135
• Total damage from flash flooding events, 2016-2025: $28,738,000 (8 fatalities, 3 injuries)
• Most destructive flash flooding event in county: August 14, 2021 ($25,134,000 in reported damage)
• Most destructive flash flood details: Multiple thunderstorms produced rain at rates up to 2 inches per hour over the Sand Tank Wash watershed, resulting in catastrophic flooding in the town of Gila Bend and a state of emergency declaration. Water as high as 6 feet flowed through residential areas, destroying homes, businesses, and vehicles. During the event, at least 30 people who were stranded on rooftops were rescued by the Maricopa County Sheriff’s Office, and two people were killed.