California Drought 2015: What's Causing It and What Climate Shift May Break It

California is still in the midst of a long-term drought. It has impacted water sources across the state as rivers dry up and lakes recede. In fact, it recently caused San Jose's Guadalupe River to run dry. But what is causing this drought in the first place? That's a good question.

On January 17, 2014, the California State Governor declared a drought state of emergency. Unfortunately, conditions didn't  improve. In the spring of 2015, the statewide content of the Sierra snowpack was at five percent of average for the time. Those levels were lower than any other year in records going all the way back to 1950. It seemed as if California was in the midst of a historic drought.

But how historic was it? California's 2014 Water Year, which ended on Sept. 30, 2014, was the third driest in 119 years of record. It was also the warmest year on record for the state. In addition, officials recently announced that California's "rain debt" is currently worth an entire year's worth of precipitation and statewide, California's major reservoirs are just at 33 percent of capacity.

But when did this drought begin and what caused it specifically? The drought started in 2011 when a high-pressure system, called La Niña, parked itself off of the West Coast. It rerouted storms that were headed toward the western United States, which deprived California of precipitation. It also diverted cold air that normally absorbed heat from the ocean, creating a type of warm "blob."

The ocean plays a huge role in climate. Ocean currents bring warm or cold water to the surface, which impacts winds, precipitation and other weather facts. California, for example, largely relies on clouds and fog that rolls off of the sea, drenching forests and lands in moisture. It also relies on the snowpack that is created through the winter.

The California drought, in this case, may actually be exacerbated by a massive "blob" of warm water that's 300 feet deep and 1,000 miles across right off of its coast. The blob is part of a complex system, but likely may have made California's drought worse.

The blob is between two and seven degrees Fahrenheit warmer than normal for that part of the Pacific. It actually helps warm up the air passing over the ocean to the land, which makes the air less likely to produce snowfall.

This severe drought, and this warm blob of water, is partly what prompted the NOAA to create the Drought Task Force, which investigated the causes of the dry spell in California. They found that the drought was primarily due to natural climate variability. With that said, California temperatures have been rising and record high temperatures during the drought were most likely due to human-induced climate change.

Most of California is in a severe drought or worse, currently. Yet this drought could break with the help of El Niño, a climate system that's now 80 percent likely of being present through the end of 2015. This system could cause wetter conditions in the winter for California, which may help the state replenish its snowpack and gain back some of the water that it's lost over this historic drought period.

To find out more about the drought in California and other areas of the U.S., visit the United States Drought Monitor's website.

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