by Jay Lund
There was not a “Miracle March” to follow California’s precipitation “Flat-line February.” Instead, we’ve had a “Meh March.”
With the near-end of its wet season, California’s 2020 water year is and will be dry. The Northern Sierra 8-gage Precipitation Index is now about 25 inches, and might increase about 10% more by the end of the water year. This would place the 2020 water year somewhere between the 3% – 7% driest year on record for this index (98 years). Other precipitation and snow statistics for California tell a similar story.
Sacramento Valley runoff for 2020 also will be greatly reduced (see first figure). Other basins in California are similarly dry.
Just how dry is 2020?
On the whole, with about 50% of average precipitation and snowpack, California can expect dry conditions for its forests and upland habitats, particularly later in the summer as soil moisture is depleted. These impacts will be somewhat dampened because recent years have not been terribly dry, so there is more soil moisture and groundwater. Next year could be different.
From Figure 1 above, we can expect about 50% of average stream runoff, maybe a little less. This of course has implications for reservoir inflows, hydropower generation, agricultural and urban water supplies, and aquatic and wetland habitats. Fortunately, most California reservoirs are still pretty full and many groundwater supplies have at least partially recovered from the 2012-2016 drought. So for many water users, the first dry year is not so bad. Still, there will be impacts.
Is the 2020 water year a drought?
Maybe for some, but mostly not yet.
In some pragmatic senses, a drought is a dry event that water users are not prepared for.
For some users and uses, a single dry year is a drought. This includes upland habitats which depend on soil moisture to get through our long dry season, more junior summer and fall water users on streams without reservoirs, rural water users with marginal supplies subject to groundwater depletion, and wetland and aquatic habitats, especially if they lack supplemental water supplies.
Most of California’s human water users have become prepared for dry years and droughts over the last 150 years by adopting a portfolio of infrastructure and actions, including irrigation systems, water storage, groundwater, water trading, and water conservation practices that sustain their activities through California’s annual 6-9 month drought (worse annually than most of the US ever sees). For most major cities and many agricultural areas, these preparations also suffice for most multi-year droughts (Lund et al. 2018).
The difficulties of managing drought increase with a drought’s duration. Most of California, even ecosystems, are adapted to a long single dry season, preceded by a wet season. A dry year extends and reduces water stored for this dry season. Sequential dry years further reduce the water stored in soils, reservoirs, and groundwater for dry-season water demands.
By the third and fourth dry years, ecosystems and human water supply systems go from straining to breaking. In long multi-year droughts, cities can be forced to ration water, farmers must consider sacrificing their most profitable crops, more rural drinking water supplies are left dry by declining groundwater, and salmon runs can no longer rely on stored cold water.
Is 2020 the beginning of a major statewide drought?
Maybe. The plot below shows each year in a 113-year unimpaired Sacramento Valley streamflow record plotted against the previous year’s unimpaired streamflow. There is only a slight tendency for a dry year to be followed by another dry year (a previous post shows this another way). The dryness of the previous year explains less than 1% of how wet the next year will be. So the probability of this dry year being the beginning of several years of drier-than-average conditions is slightly more than 50%.
What should be done?
Prepare for this year to be dry (a certainty) and prepare for next year to be dry (fairly likely).
Preparation is key to reducing the impacts of dry years (Lund et al 2018). Many with dry-year contingency plans will begin their implementation. For those without prepared plans, now is a good time to start making plans and preparations. Active preparations should include:
- Reducing less crucial water uses, particularly where water can be directly or indirectly stored.
- Support and prepare to support wetland and aquatic ecosystems, including and especially the Delta.
- Inventory regional groundwater availability, and think about SGMA consequences of drought.
- Work with your neighbors to prepare.
The various COVID-19 shut-downs and slow-downs are likely to make late preparations more difficult, especially where plans, such as those for the Delta, ecosystems, and groundwater, require coordination among many agencies and entities, now with few and smaller face-to-face meetings and competing with a pandemic for attention and resources.
Pandemic concerns will require managing water and ecosystems amid a drought of attention and resources and viral distractions.
Also prepare for next year to be wet and have flooding, because this can easily happen too.
Welcome to California.
Lund, J., California’s Driest February and Coming Drought?, CaliforniaWaterBlog.com, March 1, 2020
California Department of Water Resources’ California Data Exchange Center (CDEC) web site: http://cdec.water.ca.gov/index.html True California water wonks will enjoy this distraction.
Jay Lund is a Professor of Civil and Environmental Engineering, Geography, and a few other things at the University of California, Davis.