Drought Prospects in California for the New 2017 Water Year – October 1, 2016

This blog post has been superseded by more recent storms this water year.  See the January 2017 Tails of California’s Drought.  This older post remains of some retrospective significance in how slow and fast drought conditions can change – Jay Lund

By Jay Lund

Happy New Water Year 2017!

Hopefully everyone has recovered from their celebrations.

The 2016 drought year is over.  It was milder year than the four previous drought years.  The great wet hope of the “Godzilla” El Nino did not end the drought, but brought only near average precipitation.

Going into the new water year, California remains in a drought.

Here are some highlights of current conditions, with links from the California Department of Water Resources’ California Data Exchange Center (CDEC) at http://cdec.water.ca.gov.

Reservoir and Groundwater Storage Conditions

Major reservoirs in California begin this new water year about 3.3 maf lower than long-term average surface storage on September 30.  Groundwater is likely to be recovering in the northern parts of California, but is probably continuing to drop in large parts of the southern Central Valley which are still receiving less water than expected, and are subject to overdraft even in non-drought years.  Cumulative drought groundwater overdraft probably now exceeds 12 maf. (Alas, California does not maintain estimates on long-term groundwater balances, but this will come someday.)

Total water storage is probably depleted 15-20 maf from pre-drought conditions.  Soil moisture in much of the Sierras and Central California remains in drought conditions (due to both unusually high temperatures and lower precipitation).  Like groundwater, conditions of forests and native fishes are severely depressed and are likely to see substantial drought impacts for years after hydrologic conditions improve.

But this seemingly bad situation is substantially better than in October 2015.

Many reservoirs are in pretty good shape in terms of overall storage, certainly compared with October 2015.  Shasta, Oroville, New Don Pedro, and many other sizable reservoirs are entering the new water year with near-average storage levels.  Shasta levels must now be viewed more cautiously, however, because of heightened concerns for operational disruptions due to depressed populations of endangered winter run salmon.  Most surface storage depletions (current storage relative to their historical average) remain in reservoirs at New Melones (tributary to the San Joaquin River, 800 taf depletion), Trinity (in the north, 700 taf depletion), San Luis (which relies on Delta exports to fill, 450 taf depletion), and Oroville (550 taf) and Folsom (250 taf depletion), which were depleted somewhat to make up for reduced releases from Shasta due to temperature concerns.   Lake Cachuma, which serves the Santa Barbara region is also nearly exhausted with only 14 taf remaining and a drought depletion of 135 taf.


Figure 1. Major reservoir storage in California at end of 2016 water year

Ecosystem Conditions

Fish – Native fish populations in California are largely down during the drought, with some down by frightening percentages, such as winter run salmon.  These populations effects will likely require years of effort to recover and make management of future drought years more important.

Waterfowl – Duck populations improved considerably in 2016 from 2015, which were about 25% below the long term average.

Forests – The accumulated effects of drought and warmer temperatures are likely to leave forests susceptible to diseases, pests, and further drought conditions.  There is little that water managers can do to affect drought impacts to forests, although this might be one of the drought’s biggest and most long-lasting effects.

Native ecosystems in good shape should allow more flexibility for agricultural and urban water supply operations.  Alas, this is not the case.  Ecosystem storage, so to speak, is severely depleted.

Will the 2017 Water Year Be Dry?

Statistics from about 100 years of historical records show not a lot of correlation of unimpaired runoff between years.


Figure 2. Scatter plot of Water Year runoff for Sacramento River since 1921

When digested by quintiles, Table 1, only slightly more insight is gained.  Very dry years seem more likely to beget another very dry year and not a very wet year.  And both very dry and middling years have a slight, and probably not statistically significant, chance of producing another drier runoff year. Some of these effects might be residual due to the new water year beginning with drier soil moisture and groundwater conditions than average. (Note, this quintile (20%) water year classification differs from the DWR water year classification which includes a weighting of the previous year’s runoff, and so has a built in higher correlation.)


Table 1. Probabilities of wet and dry conditions from historical data

Thoughts for the coming drought year

Welcome to California water, where anything can happen.

It is best to be prepare for another drought year (and prepare for floods as well).

Even if precipitation is average, there will still be residual storage depletion and ecosystem effects from the previous dry years.  These effects will be harder to manage if the coming year continues to be much warmer than average.  Except for some ecosystem and rural community conditions, which remain quite serious, there is no reason for panic. (Panic is often counterproductive – urgency would be appropriate.)

Many farmers in the southern Central Valley will still feel the effects of water scarcity, even if the hydrologic drought ends, as ending overdraft and greater environmental demands and restrictions for the Delta and San Joaquin River impinge on historical water delivery expectations.  They have a long-term problem worsened by the drought.  Farmers in the Sacramento Valley face some years of disruptions in the timing of water deliveries due to temperature problems for winter run salmon.

In any event, and especially if 2016-2017 is dry, there is urgency to make progress on state, federal, regional, and local water management.  Groundwater, water conservation, water markets, and the Delta remain urgent management concerns, which will interact and require a common state water accounting system sooner rather than later.

And El Nino? The great wet hope will continue, but one should probably consider the historical correlation of El Nino with northern California runoff, below, and dissipate less time with speculative predictions and invest more time on moving California forward with its difficult water problems.


Figure 3. El Nino index versus Sacramento Valley runoff (maf) for the last 50 years.

2016 Water Year Precipitation

Precipitation totals for the ending water year were average-ish historically, and great compared with the previous two years, but made worse due to continued high temperatures.  Below are the final cumulative plots for the 2015-2016 water year, with some comparative companionship.

sanjoaquin2016 northsierra2016 tulare2016

Here are some web sites to watch in the coming water year.

Reservoir levels:








http://cdec.water.ca.gov/cgi-progs/products/PLOT_ESI.pdf – Sacramento Valley

http://cdec.water.ca.gov/cgi-progs/products/PLOT_FSI.pdf – San Joaquin Valley

http://cdec.water.ca.gov/cgi-progs/products/PLOT_TSI.pdf – Tulare Basin

Jay Lund is Director of the UC Davis Center for Watershed Sciences and Professor of Civil and Environmental Engineering at UC Davis. 

Further reading

LOIS HENRY: The backstory of a water scare you never knew about, Bakersfield.com, April 13, 2016.

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7 Responses to Drought Prospects in California for the New 2017 Water Year – October 1, 2016

  1. Steve Macaulay says:

    Jay — Greetings from a fellow pluviophile. Rain is forecast the next 4 days here in Snohomish, where drought seems a fading memory. But even here, it will be back.

    • jaylund says:

      Great to hear from the Pacific Northwet. We experienced abrupt climate change when we moved from Seattle to Davis 30 years ago. Each part of the country has different types of drought. Droughts for most of California last for several years, because California’s water systems dampen the annual 6-month droughts that would be devastating in the eastern US. So far, urban and irrigation demands in the Pacific Northwest are small enough that they last mostly a few months, until the winter. PNW hydropower and ecosystem droughts can be longer.

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  4. Margaret Davenport says:

    Want more info on grape growing regions, especially the North Coast.

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