A powerful storm system that hit the U.S. Northeast on July 9 and 10, 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, causing widespread flash flooding. 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.
Studies by scientists around the world show that the water cycle has been intensifying and will continue to intensify as the planet warms. An international climate assessment I co-authored in 2021 for the Intergovernmental Panel on Climate Change reviewed the research and laid out the details.
It documented an increase in both wet extremes, including more intense rainfall over most regions, and dry extremes, including drying in the Mediterranean, southwestern Australia, southwestern South America, South Africa and western North America. It also shows that both wet and dry extremes will continue to increase with future warming.
Why is the water cycle intensifying?
Water cycles through the environment, moving between the atmosphere, ocean, land and reservoirs of frozen water. It might fall as rain or snow, seep into the ground, run into a waterway, join the ocean, freeze or evaporate back into the atmosphere. In recent decades, there has been an overall increase in the rates of precipitation and evaporation.
A number of factors are intensifying the water cycle, but one of the most important is that warming temperatures raise the upper limit on the amount of moisture in the air. That increases the potential for more rain.