Looking through the May 23rd Merced Board of
Supervisors agenda, we found the following item:
We thought it was excessive after the terrific rain and
snow fall of the winter, but the US Geological Survey
enlightened us about the glacial pace at which
groundwater aquifers refill after a drought. That must be
particularly true here where the almond boom created a well-drilling boom. -- blj
California Water Science Center
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Is the drought over?
Updated April 24, 2017
After more than five years of drought in California, water year 2017 has seen above-average precipitation and snowpack, inspiring many to ask, "is the drought over?" On April 7, 2017, Gov. Jerry Brown issued Executive Order B-40-17, officially ending the drought state of emergency in all California counties except Fresno, Kings, Tulare, and Tuolumne. Hydrologically, however, the answer to this question requires consideration of California's three primary sources of water: surface water, snowpack, and groundwater.
Surface Water: Precipitation in water year 2017 has filled the majority of California's major reservoirs to above-historic average levels. Likewise, as the USGS streamgage network shows, flows in the majority of the streams have been at or above average for most of the last 4 months. This indicates that most of California's rivers, creeks, lakes and reservoirs are in good condition.
Snowpack: On average, the Sierra Nevada snowpack supplies about 30 percent of California's water needs as it melts in the spring and summer. A series of back-to-back atmospheric river storms blanketed the Sierra Nevada in January and February 2017. As of April 24, 2017, statewide snow accumulation data indicate that snowpack in the Northern, Central, and Southern Sierra is 190% of normal for this date.
Groundwater: Groundwater aquifers recover much more slowly than surface water and are limited, amoung other things, by how much and how fast water can recharge. Unlike surface water, which can recover during a few days of heavy precipitation, groundwater aquifer recovery often takes years or decades. Groundwater systems are also relied upon more heavily during times of drought. In addition, in many areas of the state, groundwater systems have been depleted for long periods - even between droughts - that they have not recovered from. Excessive, long-term groundwater over-use resulting in groundwater depletion can cause subsidence and permanent loss of groundwater storage as well as water quality degradation and seawater intrusion. These long-term impacts on groundwater have not been remedied by the recent weather. If recovery is possible, it will likely take several to many years to accomplish. Executive Order B-40-17, which ends the drought state of emergency in most of California, stresses the importance of emergency drinking water projects that will help address diminished groundwater supplies.
The long-term outlook for California’s drought can be better assessed in the months ahead. On April 1, the California Department of Water Resources conducted its annual snowpack measurement. This benchmark is important because it provides a comprehensive examination of the snowpack’s water content. Typically, April 1st marks the start of significant snowmelt, producing runoff that recharges reservoirs and groundwater systems slowly throughout the ensuing months. Unless there is excessive heat – which has been the case for the last three years – this slower runoff provides significant usable supply for the year, and can enhance the aquifer-recharge process. On April 1, 2017, DWR measured the snowpack to be 164 percent of average for the date, and determined the snowpack water content to be 183 percent of average. This measurement likely signifies that runoff in Water Year 2017 will be above average, particularly in comparison to recent drought years. However, the rate at which that runoff occurs is particularly sensitive to temperature. A rapid rise in temperatures may cause snowpack to melt too quickly, contributing to excessive runoff in a short period of time; which could lead to flooding. A slow, steady rise in spring and summer temperatures is ideal from a water supply perspective because the snowpack will melt slowly, allowing for optimal replenishment of aquifers and reservoirs.
When compared with historical, long-term data, analysis of surface-water runoff data now being collected by the USGS streamgage network will also help scientists better understand the effects that winter storms of 2017 have had upon California’s drought conditions. Runoff is an important component in maintaining healthy waterways and ecosystems and also contributes to groundwater replenishment through groundwater surface-water interactions. The USGS California Water Science Center – along with cooperating local, state, and federal agencies - continues to collect long-term data that are needed to assess the effects of climate variability on water resources.
While the drought state of emergency is officially over in most of California, the hydrologic effects of the drought will take years to recover. Dedicated science from the U.S. Geological Survey and its cooperators will help California understand the long-term effects the recent drought has had upon California's hydrologic framework.
· On January 17, 2014 California State Governor, Jerry Brown, declared a drought state of emergency. On April 17, 2017, Brown issued Executive Order B-40-17, officially ending the drought state of emergency in all California counties except Fresno, Kings, Tulare, and Tuolumne.
· As of April 18, 2017, the National Drought Mitigation Center estimates approximately 10.3 million people in California are currently affected by the drought.
· California's response to its ongoing drought has been guided by a series of executive orders issued by Governor Brown, the most recent officially ending the drought in most of California, but stressing the importance of emergency drinking water projects that will help address diminished groundwater supplies.
· The time period of January 2016 - December 2016 has been the 3rd warmest on record for California. California saw 2014 as the warmest year on record.
· The latest National Weather Service Climate Prediction Center seasonal drought outlook, valid for April 20 - July 31, 2017, shows drought in areas of southern and Central Coastal California likely to persist throughout those dates. The 1-month precipitation outlook for May 2017, issued April 20, 2017, suggests average precipitation for most of California, and above average precipitation for parts of northern California.
- Snowpack, through runoff, provides about one-third of the water used by California's cities and farms. The snowpack at the beginning of April is crucial because this is when the snowpack is normally at its peak and begins to melt into streams and reservoirs.
- On April 1, 2017, the California Department of Water Resources measured regional snowpack at 164% of normal for this date, and snowpack water content to be 183% normal for this date.
- As of April 24, 2017, statewide snow accumulation data indicate that snowpack in the Northern, Central, and Southern Sierra is 190% of normal for this date.