Climate Fact: Persistent Drought in California and the Western U.S.

The year-long drought that covered over half of the United States in 2012 resulted in about 30 billion dollars in damage costs, and the Western drought and heat wave of 2013 is on NOAA’s list of billion dollar weather and climate disasters. Unfortunately, dry conditions in the West are lingering in 2014. A zone of high pressure in the atmosphere off the West Coast – almost four miles high and 2,000 miles long – is blocking storms from bringing precipitation into California, rerouting them to Alaska and portions of western Canada. This ridge of high pressure has been stalled for an incredible 13 months. Scientists aren’t sure why it has been stalled for so long or how much longer it will stick around, but the impacts are clear.

Droughts are among the most expensive natural disasters, harming agriculture, the economy and human health. They also create perfect conditions for wildfires, like the Colby wildfire in Glendora, California. Sparked by campfire embers flying into the dry foothills of the San Gabriel Mountains, the Colby fire caused evacuation of nearly 2,000 residents and burned 1,932 acres as of January 23, 2014.  About half of California’s annual statewide precipitation occurs in December, January and February. December 2013 was drier than normal, making 2013 the driest calendar year since 1895 for the Western region. Since then, drought has expanded throughout the Pacific Northwest and intensified in California because of low precipitation and low snow water equivalent, the amount of water contained within the snowpack. Drought is expected to worsen in the Pacific Northwest through the end of January and persist until the end of April 2014. It will possibly worsen for California, as well – Governor Jerry Brown declared a statewide drought emergency in mid-January.

Scientists have shown that drought is a common and recurrent event in North America by studying the thickness of tree rings, which narrate the story about how climate and hydrology behaved historically. Droughts can be regional or pan-continental, short or multidecadal, and can occur in different climates and seasons. Pan-continental droughts – like the 2012 U.S. drought that covered 61.8 percent of the contiguous U.S. – are less common than single-region droughts, but have occurred in 12 percent of years since the 10th century. No major U.S. region is immune to such droughts. There have also been pan-continental megadroughts lasting several decades, which were most common during the 12th and 13th century.

View NASA’s side-by-side comparison of satellite images of California in January 2013 and January 2014.

Image below: U.S. Drought Monitor for the Western region.


The U.S. Drought Monitor is jointly produced by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the United States Department of Agriculture, and the National Oceanic and Atmospheric Administration. Map courtesy of NDMC-UNL.

(Sources: Cook, B.I, J.E. Smerdon, R. Seager, E.R. Cook. 2014. Pan-Continental Droughts in North America Over the Last Millennium. Journal of Climate 27:383-397; California Department of Water Resources. 2014. Drought Information. Accessed online 23 January 2014. http://www.water.ca.gov/waterconditions/drought/; National Oceanic and Atmospheric Administration. 2014. U.S. Seasonal Drought Outlook. Accessed online 23 January 2014. http://www.cpc.ncep.noaa.gov/products/expert_assessment/sdo_summary.html; National Oceanic and Atmospheric Administration. 2014. State of the Climate: National Overview for the Month of December. Accessed online 23 January 2014. http://www.ncdc.noaa.gov/sotc/national/2013/12; Incident Information System. Soda Fire. Accessed online 23 January 2014. http://inciweb.nwcg.gov/incident/3765/ and Incident Information System. Colby Fire. Accessed online 23 January 2014. http://inciweb.nwcg.gov/incident/3766/; United States Drought Monitor. 2014.  U.S. Drought Monitor: West. Accessed online 23 January 2014. http://droughtmonitor.unl.edu/Home/RegionalDroughtMonitor.aspx?west; San Jose Mercury News. 2014. California Drought: What’s Causing It? Accessed online 23 January 2014. http://www.mercurynews.com/science/ci_24904396/california-drought-whats-causing-it; Overpeck, J.T. 2013. Climate Science: The Challenge of Hot Drought. Nature 503: 350-351)

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