by Jay R. Lund
October 2024, the first month of the 2025 Water Year, has been dry, the 16th driest October in 103 years of Northern California precipitation records. And the forecast for the next 10 days shows little for most of California.
DWR has a nice map of this (see figure 1 to see some of not much and lots of nothing!).
Does this dry October mean 2025 will be a drought year?
No. In California, unlike humid eastern US, a single dry month does not make a drought; several dry months in the wet season are required.
October is the driest month in California’s nominal wet season, so a dry October is less meaningful for the water year than having dry months in December through March, which are usually our wettest months.
Figure 2 shows how October precipitation is only slightly correlated with precipitation for the remainder of northern California’s wet season (October – March).
Is this dry October a sign of climate change? Not especially. About 15% of all Octobers in the last 103 years have been this dry or even drier for Sacramento Valley precipitation. There is some substantiated thought of rains arriving later to California with climate change, but historically, we often have dry Octobers anyway.
How is the rest of California’s water system doing?
The dry October will tend to extend and deepen soil moisture deficits accumulating from the summer and fall. So a bit more of the first winter storms will go to refilling these voids before creating runoff.
Surface reservoir levels are still in good shape, fortunately. Most reservoirs are exceeding their long-term average October levels, meaning that if 2025 becomes a drought water year, there will be sizable reservoir storage to help buffer major users for a first drought year.
Groundwater recovery
DWR has been improving its information on groundwater in recent years. Most of this is from local and state desperation for organizing data for use in local and state plans and decisions for implementing the Sustainable Groundwater Management Act (SGMA). But organizing California’s great troves of data (relative to most of the world) has many collateral benefits. California Groundwater Live has some impressive, nice maps and some data success. DWR’s general SGMA page has access to the basin plans. For access to raw groundwater data, the SGMA Data Viewer shows promise. The maps on these sites often show some improvements in groundwater levels in the last two wetter years, but not everywhere. Over time DWR likely produce some more digestible and discussable composite groundwater storage or elevation information for major groundwater basins, much as exists for precipitation and snowpack.
Salmon returns
Another driving condition of California’s water system in recent decades are ecosystems. For example, the abundance of returning salmon to different streams seems relevant for seasonal and real-time water operations, especially for fall. Such information, again in more digestible form, would greatly improve casual and policy discussions as well. Alas, here, even more than for groundwater, a mature insightful digest and presentation of monthly-changing conditions seems mostly absent. But we are not entirely bereft.
There are CDFW salmon Trap Counts, but this is more of a data dump than an insightful display of the condition of salmon returns broadly across the state or the Central Valley, and how they are changing with time. DWR also has a site for Feather River counts. CalFish also has some data for a few watersheds. Some local news articles also provide glimpses, such as Siskiyou New’s Shasta and Scott Rivers and Bogus and Jenny Creeks. Probably there are others as well (Please add a comment with a link to the blog post!).
If the system is ever to mature in terms of success in operating and regulating water projects and diversions in real time for ecosystems, we will first need to assemble real time operations data for environmental conditions, as we have for water supply, hydropower, and flood operations. This is a necessary growing pain.
Annually, there is a nice assembly of salmon return data in the Annual GrandTab California Central Valley Chinook Escapement Database Report.
All this is a long-winded way of saying that while I heard that some salmon returns have been very low this fall and other returns have been much higher, there is not a set of assembled data for making general, regional, or basin-specific assessments month to month. These would be useful for local and regional operations, as well as helpful in supporting the kinds of environmental policy discussions that we seem to need seasonally and for the longer future.
Worrisome signs from Los Vaqueros?
California’s hydrologic system has a larger-than-usual human component. In this case, the fall brought an unexpected rejection of the expansion of the Los Vaqueros Reservoir expansion in the Bay Area. The proposed projects had many Bay Area participants, but faces concerns for rising costs, potential fish-related regulations.
Following the earthquakes and droughts of the 1980s and early 90s, most Bay Area water agencies became much more intertied, so they can share water supplies much more easily. This was a major accomplishment. Many opportunities for cooperation among Bay Area water utilities remain. Hopefully past collaborations continue into new (as well as old) areas.
Robert Kelley’s (1989) excellent history of Sacramento Valley flood control highlights the importance of national political trends for local and regional collaborations on water management. The same has been true historically for regional water supply projects (Pisani 1986). In today’s national era of self and identity-centered politics, let us hope that our common good and common interest in effective water and environmental management can temper the sometimes-aggressive non-cooperation of today’s national politics.
Collaborations have greatly improved California’s water system in the last 30 years. Hopefully we are not entering a collaboration drought for local, regional, and statewide water management.
“How dry I am, how wet I’ll be …”?
So overall, a dry October, by itself, does not tell us much. But it reminds us to pay attention and prepare for whatever the water year and the future will throw at us. And hope we can keep collaborations afloat through these turbulent and sometimes selfish times.
Further reading and useful data sources for the wet season
- Kelley, R. (1989), Battling the Inland Sea, UC Press.
- Pisani, D. (1986), From the Family Farm to Agribusiness: The Irrigation Crusade in California and the West, 1850–1931, UC Press.
Some surface water data websites:
- Precipitation: https://cdec.water.ca.gov/snow_rain.html
- Reservoirs: https://cdec.water.ca.gov/reservoir.html
- Floods and flows, real time w forecasts: https://www.cnrfc.noaa.gov/?product=ensPoints
- Army Corps flood reservoirs: https://www.spk-wc.usace.army.mil/plots/california.html
Some groundwater condition websites:
- DWR California Groundwater Live maps and some data access.
- DWR SGMA page mostly basin plans.
- DWR SGMA Data Viewer with access to raw monitoring well data
Some salmon condition websites:
- CDFW Trap Counts https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=203215.
- DWR Feather River counts
- CalFish Butte Creek salmon counts
- So far Shasta and Scott Rivers and Bogus and Jenny Creeks: https://www.siskiyou.news/2024/10/04/2024-salmon-count-update-from-california-department-of-fish-and-wildlife/
- Annual GrandTab California Central Valley Chinook Escapement Database: https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=84381
Jay Lund is an emeritus professor of Civil and Environmental Engineering and Vice-Director of the Center for Watershed Sciences at the University of California – Davis.
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