By Jay Lund, Andrew L. Rypel, and Josue Medellin-Azuara

As March begins to drag on with little precipitation in the forecast and few weeks left in California’s traditional wet season, we are in another dry year. This is California’s second dry year in a row since the 2012-2016 drought.  Statistically, California has the most drought and flood years per average year than anywhere in the US.  This statistical fact seems to becoming increasingly extreme, as predicted by many climate change models.

As Californians have adapted to drought over the last 150 years, drought damages and losses have changed.  Traditional drought water supply losses to cities and agriculture have fallen tremendously, as a percent of urban and agricultural economies.  The 2012-2016 five-year drought had total direct damages of about $10 billion statewide, without direct loss of life (Lund et al 2018).  For a state economy exceeding $2 trillion/year, drought impacts were often large locally, but statewide water shortage impacts were less than 0.09% of the state’s economy.  Traditional drought impacts are important, but are manageable if managed well (we sometimes have trouble with this).

Yet, wildfires in the four following years worsened considerably from the drought-related deaths of over a hundred million forest trees and other factors.  These wildfires caused a record of over $55 billion in direct property losses and 175 direct deaths, with many weeks of widespread air pollution with still larger and more widespread economic and health impacts, including estimates of more than 1,000 additional deaths.  Additional health impacts from these events are likely chronic and poorly understood (such as increased risk of cancer and lung damage from particulate inhalation). The drought was not responsible for all these wildfire impacts, but probably some substantial share of them.

Arguably, the 2012-2016 drought’s impacts occurred mostly after the drought ended.  And most economic and health drought impacts were to people who suffered no water shortages.

California’s new drought, with higher temperatures and greater resulting wildfire and air pollution impacts, and perhaps other untold ecological and human health impacts, is a new aspect and era for drought in California.  Wildfire-related air pollution affects almost everyone in California, even the majority who don’t see traditional water shortages – but do see often-delayed drought-related shortages of safe air to breathe.

State of this drought today. Today, northern California has about 52% of average precipitation for this time of year.  Snowpack levels are at 62% of average, but this is less important because California’s reservoirs are only 57% of long term average total storage.

Some of California’s major reservoirs are as low in this second year of drought as they were in the third and fourth years of the 2012-2016 drought.  Today, storage in Shasta reservoir is 2.28 million acre feet. Since 2012, only 2014 had a lower storage at this time of the year (at 1.94 million acre feet). These conditions pose major challenges for endangered fishes like winter-run Chinook salmon that have extended freshwater rearing periods during the summer. If temperatures are as warm as the last drought, we might see problems supplying cold water for young winter-run salmon below Shasta dam, a problem which killed more than 90% of this salmon run in 2014 and 2015.

High drought temperatures seem likely again, as temperatures have been high for recent years, including the previous drought.  In the last drought, higher temperatures were responsible for about 25-30% of the drought’s total moisture deficit, which increased tree mortality in forests.  Higher temperatures also make it harder to maintain cold water for salmon and other species.  Less cold water is available, and it warms faster as it travels downstream.  Increasing temperatures have been noted as a major challenge for the embattled delta smelt, which is near extinction.  Its close threatened relative, longfin smelt, also is sensitive to temperature (Yanagitsuru et al. 2021). We have barely begun to understand, detail, or try to manage the more complex effects of warm droughts, especially for ecosystems.

Groundwater Redux and Future

The biggest traditional drought impacts are likely to occur from increased agricultural groundwater pumping to partially compensate for reduced surface water supplies: 

• Many rural community and household wells will be left dry or become contaminated as deeper wells pull nitrate contamination deeper (Stone and Gailey 2019). 
• Some environmental surface flows will be drawn underground by lower aquifer levels.
• Additional land subsidence will reduce capacities for surface canals and floodways.
• Accumulated overdraft from additional drought years and the years elapsing during this drought will make achieving SGMA groundwater sustainability objectives harder without additional reductions in agricultural acreages in deeply overdrafted basins.  (The magical magnitudes of water espoused from Flood-MAR will become still less plausible, even though plausible amounts remain useful.  Droughts often test our assumptions.)

The Delta

The Delta is always a pivotal weak point in California’s water system.  Managers are always very attentive to Delta management and its drought challenges.  Much will depend on details we don’t know yet about this drought.  A few things to watch:

• Reduced water supplies from the Delta are certain in the drought, but the exact amount of reductions won’t become clear for some time.
• Warmer temperatures and lower Delta channel flows seem to have accelerated the spread of invasive aquatic plants during the last drought.  This might well happen again.  These same conditions also could increase harmful algal blooms, with both water quality and potential public health impacts, and are being studied by a variety of agency and independent scientists.
• Delta salinity barriers are likely under continued severe conditions. 
• Struggles for native Delta fishes remains a perennial issue which peaks in times of drought.  Will this be the true end of Delta Smelt?

Other usual, but still important, impacts

• California’s hydropower generation, usually about 15% of state electricity production, will fall.
• Continued shifts in forest and rangeland ecosystems can be expected.
• Agricultural water shortages, and resulting unemployment and financial stress to irrigation districts.
• Local urban water shortages, and financial stress to water utilities from reduced water sales and perhaps to poorer water customers
• Water markets – prices up
• Water right curtailments – seem likely, with details becoming clearer in the months ahead.

Drought in California is always an old story and a new one.  Alas, we probably will need the N-95 masks episodically after the pandemic to combat drought impacts in the coming years.

Some data sources

Here are some data-rich sites useful for folks who want to follow the drought.  The main overall go-to data site is DWR’s excellent CDEC,  https://cdec.water.ca.gov/index.html – Bon apetit!

Precipitation:  https://cdec.water.ca.gov/snow_rain.html

Snowpack:  https://cdec.water.ca.gov/snowapp/sweq.action

Reservoir levels:

A nice table of major reservoir storages throughout California, produced at the end of each month. https://cdec.water.ca.gov/reportapp/javareports?name=STORAGE

A nice table comparing major reservoir levels for this time over the last few years, including the previous drought.  https://www.spk-wc.usace.army.mil/fcgi-bin/average.py?report=sc7ls

Jay Lund and Andrew Rypel are professors and Co-Directors of the Center for Watershed Sciences at the University of California – Davis.  Josue Medellin-Azuara is a professor at the University of California – Merced.

Happy Pi Day! (3/14)

Further reading

Durand JR, Bombardelli F, Fleenor WE, Henneberry Y, Herman J, Jeffres C, Leinfelder–Miles M, Lund JR, Lusardi R, Manfree AD, et al. 2020. Drought and the Sacramento-San Joaquin Delta, 2012–2016: Environmental Review and Lessons. San Franc Estuary Watershed Sci. 18(2). doi:10.15447/sfews.2020v18iss2art2. https://escholarship.org/uc/item/6hq949t6.

Lund J, Medellin-Azuara J, Durand J, Stone K. 2018. Lessons from California’s 2012–2016 Drought. J Water Resour Plan Manag. 144(10):04018067. doi:10.1061/(ASCE)WR.1943-5452.0000984.

Stone, K. and R. Gailey (2020), “Economic Tradeoffs in Groundwater Management During Drought,” CaliforniaWaterBlog.com, June 10, 1919.

Ullrich, P.A., et al. (2018), “California’s Drought of the Future: A Midcentury Recreation of the Exceptional Conditions of 2012–2017”, Earths Future. 2018 Nov; 6(11): 1568–1587.

Woodhouse, C. A., Pederson, G. T., Morino, K., McAfee, S. A., and McCabe, G. J. (2016), Increasing influence of air temperature on upper Colorado River streamflow, Geophys. Res. Lett., 43, 2174– 2181, doi:10.1002/2015GL067613.

Yanagitsuru, Y., et al. (2021), “Effects of temperature on hatching and growth performance of embryos and yolk-sac larvae of a threatened estuarine fish: Longfin smelt (Spirinchus thaleichthys),” Aquaculture, Vol. 537.