(Because heavy precipitation is more variable than average precipitation, trends have to be measured over broader geographical regions.)
The frequency and intensity of heavy precipitation across the country have increased more than average precipitation, according to the most recent National Climate Assessment, with the largest increases seen in the Midwest and Northeast. Map shows changes in 5-year maximum daily precipitation between 19.Source: Climate Science Special Report: Fourth National Climate Assessment That’s where the biggest impacts can be felt. Another way is to look at changes in the heaviest rainfalls and snowstorms. How much it rains or snows, averaged over time, is one way of analyzing changing precipitation patterns. “But climate change is slowly pushing this variability” toward wetter and drier extremes, he said. “There’s variability from year to year,” and even decade to decade, said Andreas Prein, a project scientist at the National Center for Atmospheric Research. Broadly: Wet places get wetter and dry places get drier. But they are largely consistent with predictions from climate models, which expect to see more precipitation overall as the world warms, with big regional differences. It’s not yet clear whether these changes in precipitation are a permanent feature of our warming climate, or whether they reflect long-term weather variability. (Thirty-year averages are often used by scientists to glean big-picture climate trends from temperature and precipitation data that varies substantially year-to-year.) The map above, created using data from the National Oceanic and Atmospheric Administration, shows the Eastern half of the country has gotten more rain, on average, over the last 30 years than it did during the 20th century, while precipitation has decreased in the West. This divide, a wetter East and a drier West, reflects a broader pattern observed in the United States in recent decades. Yet, California and much of the West remained in the deepest drought in at least two decades, the product of a long-term precipitation shortfall and temperatures that are much hotter than usual. Heavy downpours caused devastating flash floods in central Tennessee, tearing apart houses and killing more than 20 people. In New York City, a tropical storm delivered record-breaking rains this weekend. Source: NOAA’s National Centers for Environmental Information
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