Flash floods

Tropical Storm Hilary made landfall on Mexico’s Baja peninsula, and its damaging wind and heavy rainfall moved into Southern California on Aug. 20, 2023. For the first time ever, the National Hurricane Center had issued a tropical storm watch for large parts of Southern California. Forecasters warned of a “potentially historic amount of rainfall,” and the governors of California and Nevada declared states of emergency. Hurricane scientist Nick Grondin explained ahead of landfall why the storm, with help from El Niño and a heat dome over much of the country, could bring flash flooding, wind damage and mudslides to the region. How rare are tropical storms in the Southwest? California had only one confirmed tropical storm landfall in the past. It was in September 1939 and called the Long Beach Tropical Storm. It caused about US$2 million dollars in damage in the Los Angeles area – that would be about $44 million today. A hurricane in 1858 came close bu...

Powerful storm systems that hit the U.S. Northeast starting July 9, 2023, dumped close to 10 inches of rain on New York’s Lower Hudson Valley in less than a day and sent mountain rivers spilling over their banks and into towns across Vermont. Vermont Gov. Phil Scott said he hadn’t seen rainfall like it since Hurricane Irene devastated the region in 2011. Extreme water disasters like this have disrupted lives in countries around the world in the past few years, from the Alps and Western Europe to Pakistan, India and Australia, along with several U.S. states in 2022 and 2023. The role of climate change is becoming increasingly evident in these types of deluges. Cars were stranded in floodwater on the campus of the United States Military Academy at West Point, N.Y., on July 10, 2023. U.S. Military Academy via AP Studies by scientists around the world show that the water cycle has been inte...

The extreme flooding and mudslides across California in recent weeks took many drivers by surprise. Sinkholes swallowed cars, highways became fast-moving rivers of water, entire neighborhoods were evacuated. At least 20 people died in the storms, several of them after becoming trapped in cars in rushing water. As I checked the forecasts on my cellphone weather apps during the weeks of storms in early January 2023, I wondered whether people in the midst of the downpours were using similar technology as they decided whether to leave their homes and determined which routes were safest. Did they feel that it was sufficient? I am a hydrologist who sometimes works in remote areas, so interpreting weather data and forecast uncertainty is always part of my planning. As someone who once nearly drowned while crossing a flooded river where I shouldn’t have, I am also acutely conscious of the extreme human vulnerability stemming from not knowing exactly where and when a flood will st...

The year 2022 will be remembered across the U.S. for its devastating flooding and storms – and also for its extreme heat waves and droughts. The nation saw 18 disasters that caused more than US$1 billion in damage each, well above the average. The year started and ended with widespread severe winter storms from Texas to Maine, affecting tens of million of people and causing significant damages. Then, March set the record for the most reported tornadoes in the month – 233. During a period of five weeks over the summer, five 1,000-year rainfall events occurred in St. Louis, eastern Kentucky, southern Illinois, California’s Death Valley and Dallas, causing devastating and sometimes deadly flash floods. Severe flooding in Mississippi knocked out Jackson’s troubled water supply for weeks. A historic flood in Montana, brought on by heavy rain and melting snow, forced large areas of Yellowstone National Park to be evacuated. In the fall, hurricanes Ian and Fio...

The summer of 2022 started with a historic flood in Montana, brought on by heavy rain and melting snow, that tore up roads and caused large areas of Yellowstone National Park to be evacuated. It ended with a record-breaking heat wave in California and much of the West that pushed the power grid to the breaking point, causing blackouts, followed by a tropical storm that set rainfall records in southern California. A typhoon flooded coastal Alaska, and a hurricane hit Puerto Rico with more than 30 inches of rain. In between, wildfires raged through California, Arizona and New Mexico on the background of a megadrought in Southwestern U.S. that has been more severe than anything the region has experienced in at least 1,200 years. Near Albuquerque, New Mexico, a five-mile stretch of the Rio Grande ran dry for the first time in 40 years. Persistent heat waves lingered over many parts of the country, setting temperature records. At the same time, during a period of five weeks between...