Ocean Temperatures Linked to Drought in West

It rained so hard over a recent weekend that I thought my garden was going to wash away. Fortunately my freshly planted seeds decided to stay put, and everything is turning green in my part of the world.

by James Laughlin

It rained so hard over a recent weekend that I thought my garden was going to wash away. Fortunately my freshly planted seeds decided to stay put, and everything is turning green in my part of the world.

That's not the case in some portions of the Western United States, according to reports I've read.

"From the brittle hillsides of southern California to the drying fields of Idaho, a relentless drought is worsening across most of the West, water supplies are dwindling, and the threat of wildfires is rising," proclaimed a recent article from the Associated Press.

In a report on April 6, the Drought Monitor, sponsored by the National Drought Mitigation Center, warned of "exceptional" drought conditions in portions of Idaho and Montana — exceptional being it's worst drought category. Extreme drought conditions were reported in states along the Rocky Mountain range and extending out into western Kansas and Nebraska.

The U.S. Natural Resources Conservation Service said there's a potential for water restrictions and widespread crop and pasture losses in central Nevada, southern Idaho, most of south-central Montana and eastern and southwestern Utah. Arizona is facing its worst drought on record.

It won't help water utilities make ends meet, but recent research by the USGS may help in planning and understanding droughts in the United States.

Large-scale, long-lasting droughts have been linked to warmer than normal sea surface temperatures in the North Atlantic Ocean, and not just cooling in the tropical Pacific, according to a USGS study published in the Proceedings of the National Academy of Sciences.

The study found a statistical link between the patterns of U.S. droughts during the last century to multi-decade variations in North Pacific and North Atlantic sea surface temperatures.

The U.S. climate of the last century was marked by three prolonged continental-scale wet spells (1905-1930, the 1940s, and 1976-1995) and three dry spells (the 1930's, 1950s-60s, and 1996-2004). Although researchers have for some time believed that large and sustained shifts in U.S. precipitation are linked with the natural variability of sea surface temperatures, the mechanisms are not well understood and cannot yet be used to help predict the likelihood of droughts.

These sea surface temperature variations are called the Pacific Decadal Oscillation, or PDO, and the Atlantic Multidecadal Oscillation, or AMO. Both oscillations can have positive and negative swings. Currently, a "positive" oscillation has resulted in warm temperatures across the North Atlantic Ocean.

The same warming conditions were seen over the North Atlantic in the 1930s, 50s, and since 1995. In contrast, wet conditions prevail over most of the country during North Atlantic cooling (negative AMO). The researchers found that cool waters in the central North Pacific are associated with drought in the Northern Rockies and Pacific Northwest, whereas warm waters in the central North Pacific are generally associated with drought in the Southwest and central Plains.

The researchers said that the best hope for predicting long-term droughts seems to lie with identifying precursor states in oceanic climate that could lead to drought. The authors noted that persistent and widespread droughts can potentially compromise crop and livestock production, revenues from outdoor recreation and tourism, international and interstate water agreements, sustained urban growth, management of wildland fires, and even conservation efforts nationwide.

James Laughlin, Editor

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