Date: May 11, 2018
Magazine:
May/June 2018

A series of March and April storms helped California move much closer to a normal year in terms of precipitation and helped keep the dreaded “D-word” out of the conversation for at least another year.

“As of today’s date (April 16), we are still well below average with regard to snow depth,” said Doug Carlson, who is an information officer with the California Department of Water Resources. “We are only a bit over 41 percent of normal.”

He said a very dry February is the major culprit. Often the wettest month of the winter, this year February checked in with only about 15 percent of its normal precipitation. But Carlson said above average rain in March and April, plus a strong reservoir position going into the water year, has helped offset the less than stellar winter. Though the below average snow depth means less reservoir-filling runoff this spring, Carlson said many of the state’s largest reservoir are at or above normal as the rainy season winds down. For example on the April 16th date, the Shasta reservoir in Northern California was at 108 percent of normal while the Don Pedro Reservoir in the Central Valley was sitting at 123 percent of normal. And that same day, Northern California was being pelted with a cold storm that was sure to deliver a late blanketing of the Sierras.

Checking up-to-date data, Carlson said the state was at 84 percent of its average precipitation at its Northern California weather stations, which is where the vast majority of rain falls each year. Southern California was still tracking far below normal, but Carlson said those numbers are not as accurate as the north simply because the southern half of the state is not equipped with as many weather stations because that is not where the rain and snow typically falls and accumulates.

Though the numbers are looking better, Carlson said many are still concerned about the overall trend. From 2012 through 2015, those four years were historically dry. Carlson said some are wondering if the 2016/17 water year was just an outlier and dryer conditions are going to prevail once again. Again, a year that approaches 85 percent of average isn’t a huge concern assuming it is followed by a year that tops average. But, if this below-average year continues a string of below-average years, only interrupted by one rainy year, concerns will be heightened. As a point of reference, the four drought years produced an aggregate rainfall of less than 75 percent of average, which means the average of the previous 50 years.

Again, speaking in averages, about 75 percent of California’s annual statewide precipitation occurs from November through March with 50 percent occurring from December through February. The average precipitation is dependent on a relatively small number of storms. Typically, only a few storms during the winter season can determine if the year will be wet or dry.

The March storms underscored this fact. On March 1, the statewide snow pack was only at 23 percent of the average. By April 1, average snowpack had climbed to 52 percent of average.

In a press release distributed in early April, California Department of Water Resources Director Karla Nemeth expressed exasperation at the state’s weather patterns. “These snowpack results—while better than they were a few weeks ago—still underscore the need for widespread careful and wise use of our water supplies. The only thing predictable about California’s climate is that it’s unpredictable. We need to make our water system more resilient so we’re prepared for the extreme fluctuations in our water system, especially in the face of climate change.”

The snow survey found a snow water equivalent (SWE) of 12.4 inches, or 49 percent of average for this time of year. The snowpack normally provides about a third of the water for California’s farms and communities as it melts in the spring and summer and fills reservoirs and rivers.

Several days later, DWR released a report detailing the water available for aquifer recharge, which was also less than optimistic. The updated analysis of California’s water resources argued that investment, innovation, and infrastructure will be necessary to achieve the state’s goal of sustainable groundwater management. The report provided an estimate of the amount of water available to replenish groundwater basins to help inform development of local groundwater sustainability plans for critically overdrafted basins by January 2020.

“The WAFR (Water Available For Replenishment) report makes it abundantly clear that a diversified water resources portfolio is needed at the local, regional and state levels,” said Director Nemeth. “If California is to simultaneously bring sustainability to its groundwater basins, cope with climate change, and meet future demands, water managers must embrace a comprehensive, innovative approach.”

DWR estimates that 1.5 million acre-feet (MAF) of water may be available to replenish groundwater basins in an average year. With additional investments in programs such as water storage, conservation, recycling, stormwater capture, desalination, and conveyance improvements, more water could be available for replenishment in the future.

Water deliveries from the State Water Project and the federal Central Valley Project have reduced groundwater overdraft in many basins in the state; however, average deliveries have declined in recent years due to drought and regulatory requirements to protect water quality and critical species in the Sacramento-San Joaquin Delta and tributaries. Climate change is expected to further exacerbate these challenges. The WAFR report states that constructing additional storage north and south of the Delta and improving Delta conveyance infrastructure would limit the decline of water project deliveries and provide a more reliable supply of surface water for replenishment and other purposes.

The WAFR report analyzed water supply, demand, and runoff in 10 regions of the state to estimate how much surface water could be available to replenish groundwater basins. It provided a visual depiction of supply and demand in each region, as well as a range of potential water available for replenishment estimates. It is available through DWR.

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