Early January was an unusually wild ride of atmospheric rivers. Nine sizable systems produced a train of storms beginning about New Years and lasting for several weeks across almost all of California. After three years of drought, the storms reminded us that California has flood problems similar in magnitude to its drought problems, and that floods and droughts can occur in synchrony. As the dust begins to settle, let’s look at the impacts of these early January floods and examine if the recent three-year drought and its longer-term drought impacts might be ending.
Impact of the Floods
Recent storms have been the proximate cause of about a billion dollars of damage to public infrastructure, private homes and businesses, not all from floods, but also from high winds and landslides. Homes and cars were smashed by downed trees, and roads eroded or washed away by streams and coastal waves. Some piers and harbors were damaged or closed.
More surprising was the number of deaths. Around 20 deaths have been attributed to the storms, about 6 of which were flood-related drownings. Of the thousands of miles of flood levees in California, only two areas seem to have suffered levee failures – a Merced suburb (from a levee failure on Bear Creek) and Wilton (Sacramento County) on the Consumnes River, which had several levee failures. Flooding on major rivers was limited by low storage in most reservoirs, which let them capture large amounts of water rather than discharging it.
For a local reclamation district perspective on the Cosumnes River flooding, see the video below:
Modern flood forecast, warning, and evacuation systems have greatly reduced flooding deaths in the US since the early 1900s. These integrated national, state, and local alert systems appear to have functioned well, although some weaknesses will be evident. A major cause of flood-related drownings nationally is people driving into rising or moving water, erroneously thinking a car can pass safely. Most recent drownings were people in cars. In flood-prone areas, warnings and signage need to improve concerning driving through floodwaters. After more than a decade of levee improvements, no levees failed in protecting major cities. But failures did occur on smaller streams and tributaries. Overall, most of California’s massive network of levees passed the test, but weaknesses should be systematically identified and addressed before the memory of flooding recedes.
Although the increasingly older dam and reservoir spillway infrastructure in California (Rypel et al. 2020) did not fail, it was not thoroughly tested due to most large reservoirs being relatively empty at the start of the year and in the process of filling. In some reservoirs, normal flood reservoir releases were required (as with Folsom), resulting in the usual complaints of ‘water being wasted to the sea’ (Cloern et al. 2017). Yet such episodic high flows are important to ecosystems of California, and its unique biodiversity.
As featured in last week’s blog (Mount et al. 2023), our early January storms might be described as ‘nature’s gift to nature’. Ecologically, these storms have been a bonanza for species and ecosystems that rely on floodplain and wetland habitats. In general, habitat science and management in aquatic ecosystems greatly lags that for terrestrial environments (Sass et al. 2017). In California, access to floodplain habitat for freshwater species is of the highest importance (Opperman et al. 2017). Both the Freemont (Yolo Bypass) and Tisdale Weirs overtopped during recent storms, allowing massive habitat use by our Sacramento River natives. Salmon of several run types were captured in recent surveys of flooded fields along with many native and non-native species. Unfortunately, flooding arrived after some fairly low annual returns of salmon, especially winter-run Chinook salmon. Nonetheless, for the progeny of successful salmon spawners this year, conditions have been optimal so far. And because outmigration survival increases with river flows (Michel et al. 2021), these floods will help buoy Central Valley salmon stocks to some extent following several punishing drought years. There are some active scientific research projects in the floodplains this year that will be informative for learning more about how to manage floods and winter flows for California’s biodiversity. The floods are extremely beneficial for these efforts.
Is the drought over?
There are many ways a drought can be indexed and measured, summarized conceptually in Table 1.
Storms so far this year have done well at replenishing soil moisture, which is good for annual pastures, dryland crops, forests, and shortening the wildfire season, so far. Ample soil moisture also means future storms will produce more runoff to streams, reservoirs, and aquifers. But two and a half months remain in the wet season, and the 2-week forecast is mostly dry.
Water levels in California reservoirs are much improved across the board. Smaller reservoirs have filled and started discharging to make room for managing potential floods. Large reservoirs are refilling now to undo the cumulative impacts of a multiyear drought. This is partly because atmospheric rivers often soak a relatively narrow region with high precipitation, and until recently, most of the fire hose was pointed at the Central Sierra Nevada. With the recent storms, reservoirs are accumulating water. Shasta Lake is filling well at 86% of average for this time of year. Lake Oroville is at 108% of average for this date, having essentially recovered from the drought. However, Trinity Lake is only at 49% of its average for this date. Even major reservoirs can fill fairly quickly from major storms, but it can still be months if storms are smaller. Snow conditions are excellent. Statewide snowpack is currently 141% of the January average and 160% and 119% for the Sacramento and San Joaquin rivers, respectively. More reservoir filling will occur as the accumulated snow melts during spring and early summer. Alternatively, snowpack could grow more with more storms, and in some places, we could have snowmelt floods if the spring is warm.
But many aspects of long and deep droughts end slowly, sometimes over years, and often only after several wet periods. Despite the welcome precipitation, the drought is over only in some facets, but not others. With more storms, many drought impacts will be reduced further.
Table 1. Is the drought over? Which drought?
|Soil moisture storage
|Forests, Unirrigated crops and pasture, reduced runoff for human and ecosystem uses, longer wildfire seasons
|Less water supply for irrigated crops, recreation, cities, hydropower, and cold water for salmon. Empty storage reduces flood risks
|Much better, but still a ways to go. Many reservoirs might fill this year.
|Irrigated crops, well-dependent households, towns, cities, spring and groundwater-dependent wetlands and ecosystems
|A bit better, but perhaps years to go.
|Reduced survival rates of salmon, increased abundance of non-native species, harmful algal blooms, species at risk of extinction
|Quite bad. CA freshwater ecosystems are functionally exposed to chronic, long-term drought every year. Actual droughts impose an additional step in the declining direction.
|· Dead forest trees prolong fire risks for years
· Drawn-down aquifers increase pumping costs and new well costs
· Need to replace drought pumping from aquifers can fallow lands in later wet years
· Depleted fish and bird populations can take years to recover
|Too late, we’ll have these for years to come.
The chronic drought for ecosystems
Ecosystem impacts of droughts have been some of the most stubborn for managers and regulators. California’s aquatic ecosystems have been systematically exposed to long-term chronic drought because of dam building and massive water storage, diversions, and extractions. These are good things for humans, but the debt is real for ecosystems. For some species like the Delta smelt, the end game is now as managers race to release hatchery fish into a fundamentally changed, and apparently hostile, Delta ecosystem. Longfin smelt are tracking closely behind. For other species, like Chinook salmon, the trend is not good. Last ditch actions like two-way trap-and-haul above Shasta are being tried to correct decades of decline. Although there is a tendency to divert as much water as regulations allow during high flows, it is important to recognize that periodic major storms and flooding help support the ecology and geomorphology of our remnant ecosystems, and make them more durable. Flooded bypasses provide a glimpse into a future of green infrastructure that might extend the duration and spatial footprint of flooding. Our flood protection system was designed without ecosystem priorities and with a different understanding of ecological benefits of seasonal flooding. Managed floodplains are a needed feature of our water management system, with many benefits (Torres et al. 2022).
Groundwater recharge is another nature-based solution linked to the multi-decadal drought experienced by ecosystems. California has modest systematic groundwater monitoring, so changes in groundwater stores are difficult to track. In general however, Sacramento basin groundwater has a history of refilling aquifers better and more efficiently than the drier and more overdrafted San Joaquin and Tulare basins. Depleted groundwater in overdrafted basins is likely to extend the drought in these areas and accelerate State Groundwater Management Act (SGMA) actions to reduce pumping. Under SGMA, additional pumping during the drought has increased the overdraft debt that must be repaid by 2040. One potential lesson from this round of storms is the need for faster permitting or pre-event permitting to allow flooding of lands for groundwater recharge. And because increased groundwater recharge ultimately benefits people and ecosystems (especially local streams), this green infrastructure solution could be implemented more nimbly in the future.
The drought is not over, yet. Furthermore, many legacies from the current drought will endure for years. Impacts from recent flooding were intense and expensive, but the state fared mostly okay during the deluge. As usual, native biodiversity continues its stair step pattern of decline from droughts. For groundwater, pumping will need to be further reduced during wet years, just to restore aquifers to 2015 levels needed to comply with SGMA. Nonetheless, at halftime for this wet season, the recent storms have provided hope that the current drought may be ending from multiple perspectives. Another dry year remains plausible, but looks much less likely than it did a month ago. And major floods are now a bit more likely this year.
But as always for California, both floods and droughts are inevitable in the future, and we should prepare.
Andrew L. Rypel is a Professor and the Peter B. Moyle and California Trout Chair of coldwater fish ecology at the University of California, Davis. He is a faculty member in the Department of Wildlife, Fish & Conservation Biology and Director of the Center for Watershed Sciences. Jay Lund is a Professor of Civil and Environmental Engineering at University of California, Davis, and Vice Director at its Center for Watershed Sciences. Carson Jeffres is Field and Lab Director and a Senior Researcher at the Center for Watershed Sciences.