by Jay Lund, Peter Moyle, and Andrew Rypel

This updates a post from December on the likelihood of California entering a second dry year. Normally, a second dry year brings drought operations for California’s overall water system operations.

Today, it is even likelier that California is entering a multi-year drought.

Precipitation conditions have improved somewhat with a nice atmospheric river this last week, but remain 51% of average for this time of year for the Sacramento Valley. (San Joaquin and Tulare basins are 61% and 47% of historical seasonal average precipitation so far.) Snowpack has improved somewhat with very recent storms, but is about as scarce as the precipitation.

The Sacramento Valley precipitation index today is about 14 inches below average. This translates statistically to about 16 inches of likely precipitation deficit this year (on average). From historical statistics, this averages 7.4 maf or 41% below average Sacramento Valley runoff this water year (on average), solely due to reduced precipitation. The scatter in the plot below gives little hope for a wet year.

The warmer temperatures of recent years, and this year, increase evapotranspiration which returns more precipitation to the atmosphere, leaving less for runoff and aquifer recharge than would have occurred historically. This increases the effective precipitation deficit. Estimates of this effect are substantial, but can vary considerably. So although reduced precipitation might reduce this year’s annual runoff by about 7 maf from average, runoff might be still lower because of depressed groundwater levels from last year’s runoff and more evapotranspiration from higher temperatures.

Reservoir storage conditions have mostly worsened, not refilling as much as usual from last year (which was dry) and the last dry season. Most large surface reservoirs are 50 – 75% of their long-term averages for this time of year. (This is good news for flood management this year, however.)

Groundwater in the Sacramento Valley is in good shape, and much of southern California’s groundwater storage also has refilled. Southern Central Valley groundwater has not recovered entirely from the 2012-2016 drought.

Although there is still some chance that this year could become average, wetter, or even have a major flood, it less likely.

Preparing for an impending drought?

“Plans are nothing, but planning is everything.” – Dwight Eisenhower

Californians should always be prepared for droughts (and floods, and apparently now wildfires). But this year, it looks wise to make more urgent preparations. Many actions below are probably happening, but others might be wishful thinking.

• Farmers and irrigation districts with trees and vines will be making back-up water source arrangements, and consider how much groundwater to use – especially in areas with critical overdraft. Dry years now will increase difficulties of achieving SGMA groundwater objectives.
• Cities will check their stocks, drought conservation and contingency plans, and drought finances (on top of COVID financial impacts on utilities and impoverished customers).
• Wildlife refuges should plan to reduce water needs and arrange for back-up water sources for declining species such as riparian brush rabbits and tricolored blackbirds, resident waterfowl, and other birds. Similarly, managers should be identifying drought water sources for wetlands state-wide.
• Fish managers should be preparing/improving refuges for declining and endangered fishes, such as Suisun Marsh, including implementing the Delta Smelt Resiliency Plan. This includes improving/expanding captive breeding programs.
• Fisheries and water agencies, along with water regulators, should work together in advance to modify flow and habitat operations in California rivers to support struggling fish, especially salmon and steelhead, through even less favorable times. For the Sacramento Valley, implement the Sacramento Valley Salmon Resiliency Strategy and use it as model for drought-oriented strategies in other river systems.  
• Salmon and steelhead hatcheries should prepare for reducing production in response to reduced cold water availability for hatcheries and downstream.
• Delta managers, water project managers, and regulators should be planning now (ideally together) for low inflows and changed water operations in the coming year, including planning and permitting for salinity barriers in the coming years.
• Fish agencies should monitor populations of all 62 California Fish Species of Special Concern and be prepare additional actions to protect populations threatened by drought. We assume such protection already exists for species formally listed as Threatened or Endangered (and we don’t need to lengthen this list).
• Surprises are scenarios we did not expect. We seem to be in an age of surprises, especially the last 12 months. Organizations prepare for surprises by organizing adaptable plans and resources, collecting data, and developing rapid analytical capabilities, training to make flexible and fast decision (with inter-agency communications and exercises), and preparing to dedicate substantial resources rapidly. Surprises are the pop quizzes (or pop final exams) of organizational competence.

Will 2021 being dry make 2022 drier?

The same logic on a dry 2020 making a dry 2021 more likely applies now to prospects for 2022. Precipitation in northern California is poorly correlated across years, historically, as shown by the plot below.  The trend is essentially flat for precipitation.

However, a drier year in runoff tends to reduce the next year’s runoff a bit, as shown in the plot below for runoff.  So next year is likely to have a little less runoff even if we get average precipitation this year. 

Runoff is slightly correlated over time because precipitation accumulating in groundwater is likely to increase flow into streams in the next year, and lack of precipitation accumulating in groundwater tends to reduce streamflows in the next year.

Longer droughts have progressively larger economic, social, and environmental impacts.

We should prepare.

Jay Lund is a professor of civil and environmental engineering and Co-Director of the University of California – Davis Center for Watershed Sciences. Peter Moyle is an Emeritus Distinguished Professor of Wildlife, Fish, and Conservation Biology and an Associate Director of the Center for Watershed Sciences at UC Davis. Andrew Rypel is a professor of Wildlife, Fish, and Conservation Biology and Co-Director of the Center for Watershed Sciences at UC Davis.

Further reading

You can play with these data yourself, cheerfully supplied from DWR’s CDEC: http://cdec.water.ca.gov/reportapp/javareports?name=8STATIONHIST

http://cdec.water.ca.gov/reportapp/javareports?name=WSIHIST

California Department of Fish & Wildlife. 2015.  Fish Species of Special Concern in California.  3rd edition.  Sacramento: California Department of Fish and Wildlife. https://www.wildlife.ca.gov/Conservation/Fishes/Special-Concern

Durand, J., F. Bombardelli, W. Fleenor, Y. Henneberry, J. Herman, C. Jeffres, M. Leinfelder-Miles, J. Lund, R. Lusardi, B. Milligan, A. Manfree, J. Medellín-Azuara, and P. Moyle, “Drought and the Sacramento-San Joaquin Delta, 2012-2016: Environmental Review and Lessons,” San Francisco Estuary and Watershed Science, Vol. 18, Iss. 2, June 2020.

Escriva-Bou, A., J. Lund, J. Medellin-Azuara, and T. Harter “How reliable are Groundwater Sustainability Plans?,” CaliforniaWaterBlog.com, Posted May 10, 2020

Gailey, R., J. Lund, and J. Medellin-Azura, “Domestic well supply reliability during drought: stress testing for groundwater overdraft and estimating economic costs”, Hydrogeology Journal, Vol. 27, No. 4, pp 1159–1182, June 2019.

Klemes, V., 2000: Drought prediction: A hydrological perspective. Common Sense and Other Heresies: Selected Papers on Hydrology and Water Resources Engineering, Canadian Water Resources Association, 163–176

Lennox R.J., D.A. Crook, P. B.  Moyle, D. P. Struthers, and S. J. Cooke 2019. Toward a better understanding of freshwater fish responses to an increasingly drought-stricken world. Reviews in Fish Biology and Fisheries 29:71-92  https://doi.org/10.1007/s11160-018-09545-9.  Open Access.

Lord, B., B. Magnuson-Skeels, A. Tweet, C. Whittington, L. Adams, R. Thayer, and J. Lund, “Drought Water Right Curtailment Analysis for California’s Eel River,” Journal of Water Resources Planning and Management, ASCE, Vol. 144, No. 2: 04017082, February, 2018.

Lund, J. (2020), “Is California Heading for a Multi-Year Drought?,” CaliforniaWaterBlog.com, December 6

Lund, J.R., J. Medellin-Azuara, J. Durand, and K. Stone, “Lessons from California’s 2012-2016 Drought,” J. of Water Resources Planning and Management, Vol 144, No. 10, October 2018.