The rise of extreme rain
Thursday, September 14, 2017
Warm air can carry more water than cool air. You may understand this fact intuitively even if you don’t realize it. The greater moisture of warm air explains why your skin doesn’t get as dry in the summer and why the forests of the sweltering Amazon get a lot more precipitation than northern Canada’s forests.
About 40 years ago, the earth’s surface temperatures began to break out of their recent historical range and just kept climbing.
Not coincidentally, the number of storms with extreme rainfall began to increase around the same time. They’re up more than a third since the early 1980s, according to research by Kenneth Kunkel of the North Carolina Institute for Climate Studies.
Kunkel’s threshold for an “extreme” rainstorm varies by region, depending on how much rain a place typically receives. It’s a count of storms that would ordinarily occur only once every several years — the sort of storms that stretch a community’s capacity to cope.
The main reason these storms seem to be more frequent is global warming. Gabriel Vecchi, a Princeton researcher, compares warmer air to a bigger bucket: It can carry more water from oceans and then dump that water on land.
Regular readers know that I think it’s a mistake to shy away from talking about the connection between climate change and weather. Yes, the connection can be complicated. Even as most places get more rain, for example, some dry places have suffered more droughts.
Yet human beings should be able to deal with complexity. There is overwhelming evidence that climate change is altering the weather. Irma and Harvey weren’t caused by climate change, but they almost certainly would not have been so powerful if the air and the seas fueling them hadn’t been so warm.
And the rise of extreme rainstorms isn’t limited to hurricanes. “Heavy precipitation events in most parts of the United States have increased,” says the latest draft of the National Climate Assessment, written by scientists who are careful not to overclaim. “There is strong evidence,” it continues, “that increased water vapor resulting from higher temperatures is the primary cause.”
The weather around us is changing. The changes are already doing damage, and they will accelerate as the planet warms.
Just look at Florida. Irma, thank goodness, made a late turn and caused less damage than feared. Yet Florida faces problems much bigger than any one storm. The increased rain is falling into seas swollen by melted ice caps. Florida is also the country’s flattest state, barely above sea level. As a result, floods and severe “king tides” have become more common.
The city of Hallandale Beach has closed drinking wells, inundated by saltwater, as Elizabeth Kolbert has reported. In 2013, Miami Beach elected a mayor who promised to deal with floods; he ran a campaign ad that showed him getting ready to commute by kayak. In nearby Coral Gables, as Bloomberg’s Christopher Flavelle recently wrote, the mayor worries about boats ramming into the bridges because of rising canals.
Welcome to the era of extreme rain. We can continue to pretend it’s all a coincidence and watch the consequences mount. Or we can start to do something about it — by using less of the dirty energy that’s changing the climate and by preparing for a future that’s guaranteed to be hotter and rainier.
David Leonhardt is a columnist for the New York Times