Tuesday, July 23, 2019

How Global Warming has Increased Precipitation in the U.S.

The period from January to May of this year was the wettest 12 months period on record in the United States. This is part of a wider trend which has seen substantial increases in rainfall in the eastern part of the country. Climate Central reports that rainfall in the Eastern US is now between 29 and 55 percent heavier than it used to be. According to NOAA annual precipitation has increased by about 7 percent across the contiguous US during the past Century.

Flooding was commonplace this year but it was not that long ago that multi-year droughts were plaguing Central and Eastern US. This is exactly the kind of extremes that can be expected from a warmer world.

We have seen flooding in the Midwest, the High Plains, and the South. In March Midwestern states experienced devastating flooding along the Missouri River and its tributaries in Nebraska, Missouri, South Dakota, Iowa, and Kansas. At the end of May into the month of June heavy rain in Iowa, Illinois, and Missouri caused sites on Mississippi River to record a top-five crest. At least three people are known to have died in Iowa and Nebraska. On July 8th there was intense flooding in Washington DC and this was followed by a storm and flooding in New Orleans.

More heat means more evaporation and this is related to more precipitation. Atmospheric moisture increases by 6-8 percent for every degree (Celsius) of warming.  Soil moisture in much of the eastern United States was above the 99th percentile this spring and when the ground can no longer absorb water flooding is often the result. However, more moisture does not always mean that soils hold more moisture as rising temperatures increase the rate at which soils dry. Floods in the US have caused at least 3 billion in damages this spring and eroded valuable top soil.

To help mitigate against flooding we need nature-based solutions including natural barriers like mangrove swamps, forests and wetlands. First and foremost we need to reduce greenhouse gas emissions that will minimize warming and reduce the amount of moisture that evaporates and ends up in the atmosphere.

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