The world is getting rainier — and no wonder. As the climate warms, the atmosphere can hold and release more moisture, meaning torrential downpours are on the rise around the planet.
“There is a crystal-clear analysis that shows, decade by decade, we have more of these extremes,” said Simon Papalexiou, a professor of civil, geological and environmental engineering at the University of Saskatchewan in Saskatoon, Canada, and the lead author of a new study showing an ominous rise in the frequency of heavy rainstorms.
The new study, published June 3 in the journal Water Resources Research, shows that heavy downpours have become more common since the middle of the last century, when global warming started to intensify.
Rain is an essential part of the world’s weather system, of course. But heavy downpours can devastate communities, disrupt agriculture and contribute to road accidents and other problems. In the past year alone, torrential rain has destroyed crops and delayed the planting of corn and soybeans, costing farmers billions; sent sewage spewing into the streets after Hurricane Florence; and pushed rivers over their banks and into communities, claiming lives and destroying livelihoods in the Great Plains and the Midwest.
“Flash floods, landslides, infrastructure destruction, outbreaks of waterborne disease, water contamination, traffic chaos” are all possible consequences of excessive rain, Papalexiou said. “The list is really large.”
For the new research, Papalexiou and University of Bologna hydrology professor Alberto Montanari analyzed data collected at 8,730 weather stations around the world between 1964 and 2013. The scientists charted the time and intensity of the heaviest downpours in each region, and then compared the results to the patterns they expected to see based on the region’s history.
The analysis showed there were 7 percent more downpours than expected between 2004 and 2013. North America, Europe and Asia led the pack in heavier rain, with about 8.5 percent more downpours during those years than expected.
The heavy rainfalls show no signs of abating even as climate change brings droughts to some parts of the world — and experts say they may intensify.
In 2017, Hurricane Harvey dumped more than 60 inches of rain on parts of Texas — the most ever recorded for a storm in the United States — and led to more than 100 deaths and an estimated $125 billion in property damage. And the National Oceanic and Atmospheric Administration (NOAA) just announced that the year between May 2018 and May 2019 was the rainiest 12-month period on record in the U.S.
Based on his research and on the link between heavy downpours and rising temperatures, the rainy trend is likely to continue, according to Papalexiou. “If global model projections [of climate change] turn out to be true, then definitely we should expect to see more intense and more extreme events, even in places not currently in danger,” he said.
Papalexiou acknowledged that climate forecasting is uncertain business, but said, “The science is there, the facts are there. Something is going on.”
David Easterling, a climate scientist at NOAA's National Climatic Data Center in Asheville, North Carolina, agreed. “If we continue to warm, the 100-year storm may become the 25-year storm,” he said.
Easterling said the new study adds to a growing body of evidence showing increased rainfall around the world. Its key contribution, he said, was its focus on each region’s worst downpours, which captured rainfall trends worldwide instead of just in the wettest parts of the world.
“The bottom line is they’re finding very similar patterns to what a lot of other people have found,” he said. “This study is one more way of defining extreme precipitation and finding that it has increased in the observed record in large parts of the world.”
Papalexiou and Easterling agree that more needs to be done to mitigate the destructive and potentially deadly consequences of heavy rainfall and flooding. Cities need to identify their most flood-prone areas and design accordingly, Papalexiou said, creating buffer zones and restoring natural landscapes like marshes that can absorb floodwaters.
“Water strives to do what it did the last 5 billion years,” he said. “It follows gravity. It wants to meet the sea. If we get in its way, we’re going to have issues.”
With help from the federal government, some states have undertaken new flood protection projects, building flood walls, dams and levees to keep floodwaters at bay. And not a moment too soon, according to Papalexiou.
“We need long-term resilience strategies,” he said. “We can’t wake up tomorrow and decide to fix this issue.”
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