Friday, June 23, 2017

Climate Change Altering Droughts, Impacts Across U.S.

The U.S. Drought Monitor in July 2012 at the height of the nationwide drought. (Credit: U.S. Drought Monitor) Click to Enlarge.
As a major drought devastated the West and Midwest beginning in 2012, farmers racked up billions of dollars in crop losses, and water managers grappled with possible water shortages for millions of people as reservoirs dried up in the heat.

That drought is now gone.  But scientists have found that the dry spell showed unusual wild extremes of wetness and warmth — indicators that climate change may be altering the typical characteristics of drought across the U.S., according to a new National Oceanic and Atmospheric Administration study published in the Bulletin of the American Meteorological Society.

The stakes are high.  Extreme drought across the U.S. has contributed to tens of thousands of job losses, unpredictable and often extreme rainfall, and devastating wildfires that have left behind many millions of charred acres of land and billions of dollars in property losses.

Study author Richard Heim, Jr., a researcher at the National Centers for Environmental Information at NOAA, compared a nationwide series of dry spells beginning in 1998 to two other devastating droughts in the 1930s and 1950s, including the Dust Bowl.

He said one of the most unique features of the drought as it spread across the country in 2012 was that some parts of the country were outright soggy while others dried up in the sun. Compared to two earlier dry spells, a recent series of droughts beginning in 1998 saw the largest area of the U.S. with normal or above-normal precipitation.

“The main thing is the 1998-2014 drought episode is the warmest of the three major drought episodes.  It’s also the wettest,” Heim said.  “A huge chunk of the country is in drought (during that period) and other chunks are really wet.”

Warmer temperatures over the past 30 years and more frequent regional dry spells since 1998 are changing the water cycle, posing challenges for urban and agricultural areas throughout the country.

“When broken down by region, the 1998-2014 episode had more days with precipitation than the other two episodes for all regions except the southern plains and Lower Mississippi Valley,” the study says.

During that time, the Northeast and Midwest, which saw their own dry spells, received the most rain and snowfall, while much of the West dried out, the study says.

2012 was a critical year for drought in the U.S.  Several ongoing regional droughts “merged” to create a massive nationwide drought leaving more than 60 percent of the country suffering severe levels of drought or worse.

Today, about 7 percent of the continental U.S. is in drought considered severe or worse, down from 22 percent in early January and 31 percent last November.

Research shows that when dry spells occur, climate change is likely to make them drier than they would otherwise be because warmer temperatures increase evaporation.  It also means that when storms hit, more precipitation is likely to fall as rain than snow, shrinking the snowpack that’s important to storing water for cities and farmers to use during the dry season.

A Climate Central analysis shows that since 1949, 68 percent of weather stations between 2,000 feet and 5,000 feet in elevation in 42 states have seen a lower percentage of winter precipitation falling as snow.

Read more at Climate Change Altering Droughts, Impacts Across U.S.

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