California is in deep, deep trouble when it comes to heat, drought, wildfires and water resources. The state is on track to have, by far, its warmest year on record, and the combination of heat and record dry weather has put the majority of the state in the most severe drought conditions on the scale.
As of Aug. 14, 82% of the state was in "extreme" to "exceptional" drought, which are the two worst categories on the U.S. Drought Monitor.
One way of putting the current drought into historical context is through a metric known as the "Standardized Precipitation and Evapotranspiration Index," or SPEI. This index captures both the combined impacts of the lack of rainfall and warmer than average temperatures, since more moisture evaporates from soils and plants as temperatures increase.
Using this index, the National Weather Service forecast office in Hanford, California, which is in the north-central part of the state, plotted the SPEI for the state of California, going all the way back to the beginning of reliable instrument records in 1895. What they found was that the ongoing drought beat the benchmark drought that occurred in 1958-59, for the worst reading on the SPEI scale.
To put it another way, this drought is the worst in California since 1895, based on this index.
Drought index shows combined impact of warm temps & lack of rain, current #CADrought worst on record. pic.twitter.com/elFeEOUa02— NWS Hanford (@NWSHanford) August 14, 2014
Other metrics also show that this is the worst, or one of the worst, droughts to hit the state since instrument records began, and evidence from tree rings and other so-called climate "proxies" show that you'd have to go back a few hundred years in order to find an event of comparable intensity.
The drought is having major economic impacts on the agricultural sector in California. The state is the biggest agricultural state in the country, with $45 billion in annual revenue. A study published in July found that the drought will cost California farmers $1.5 billion in 2014, with total statewide costs of $2.2 billion.
The drought has caused the largest water loss in state history, with a whopping 6.6 million acre-feet of surface water disappearing. This works out to 2.2 trillion gallons -- enough to fill 60 million average-sized swimming pools. The drought is causing the "greatest absolute reduction in water availability for California agriculture ever seen," the study, by the University of California at Davis, found.
Farmers are making up for some of this lost water by pumping as much groundwater as they can tap into, which will diminish the state's ability to withstand future droughts. Unlike surface reservoirs, groundwater can take hundreds to thousands of years to recharge after being depleted, depending on surface soil composition and other factors.