by Jay Lund and Andrew L. Rypel

Floods and droughts are not opposites and can occur simultaneously. This occurs often in California and is especially well-illustrated this year.

Floods, droughts, and water scarcity are different. Floods are too much water at a place and time, and we would often pay to reduce the water present at that location and moment. Droughts and water scarcity represent too little water at a place and time, meaning we would often pay to increase its availability. We highlight these differences because people tend to view such conditions through an unrealistic zero-sum lens. This essay uses this year’s experience to examine how floods, drought, and water scarcity differ, can occur in the same year, and how droughts might end, but leave legacies.

This California drought is largely over. Even though there is another month left in California’s wet season, the 2020-2022 California drought is largely over. Precipitation in all major basins of California exceeds averages for the entire water year. Snowpacks are well above April 1 averages (usually about the maximum for the year). Most reservoirs have more than average volumes stored for this time of year, and many are in flood operations. Only a few very large reservoirs (relative to their average inflows) remain below historical averages (such as Trinity at 50% and New Melones at 90% of their averages).

Precipitation has been especially high in central California, which somehow attracted more atmospheric rivers than northern California this year. The San Joaquin and Tulare basin precipitation indices exceeded annual averages in early March and late February, compared with just a few days ago for the Sacramento Valley’s Northern Sierra index. This will be a wet year, with Central California basins sometimes exceeding 2x average annual precipitation. Lake Tulare is forming once again.

Soil moisture is abundantly replenished, snowpack is abundant, reservoir storage is almost completely replenished. That leaves groundwater.

This drought has a long tail. Groundwater will take longer to recover in much of California. In the southern Central Valley, many basins did not recover from the additional pumping of the 2012-2016 drought before the 2020-2022 drought, when further depletion occurred.

SGMA will require reduced agricultural acreage even following wet years needed to replenish and repay additional groundwater pumped during the drought. There is great interest in taking advantage of a major groundwater recharge opportunity, given the massive snowpack. This last week, CA state agencies gathered for a webinar and Q&A to discuss ways to utilize the Governor’s recent executive order seeking to expand groundwater recharge opportunities. Yet despite increased management, access to clean and abundant groundwater will continue to be problematic. There may be lingering effects of the drought on shallow rural household and community wells. There will also be ecosystem effects connected to reduced groundwater tables. Some of California’s unique coldwater fish fauna need coldwater upland stream habitats that are supplied, at least in part, by groundwater. These habitats may have been reduced in their footprint during the drought. Similarly, forests classically struggle through droughts, and there were a number of old growth stands that perished during this drought.

Floods occurred amid water scarcity. 2023 has produced unusual flooding. In the December and March storms, major river flooding was averted because of initially low reservoir levels and the efficacy operation of major flood control structures. Yet on the thousands of miles of smaller streams and tributaries, several levee breaks flooded the homes of several thousand people, mostly poorer communities it seems, and led to the deaths of several people. Most of these occurred on the Cosumnes R., Pajaro Valley, Planada, and most recently during re-flooding of Lake Tulare’s historic lakebed.

Most flooded areas affected poorer communities with less ability to provide or advocate for flood protection. While even well-built levees can fail and there is, as yet, no comprehensive public post-mortem of these failures, it is likely these failed levees emanated from under-investments in infrastructure. In some cases, local shenanigans seem to have caused levee failure (Henry 2023). Later this year, the large snowpack and small flood channel capacities on San Joaquin River tributaries will pose some additional flooding risk from snow melt.

Despite this being a wet water year statewide, it also will be a year of water scarcity, arising from a chronic shortage of water/excesses in water demands. Water is usually scarce in most of California, meaning that people would pay to have additional water available. The degree of water scarcity varies with location and time. Scarcity is greater in drier years, and in regions with more water demands. In wet years, water will remain scarce because people are still willing to pay for water. Increasingly, some of this value for water is to replenish aquifers to both comply with the Sustainable Groundwater Management Act (ending overdraft) and to prepare for future droughts – even in wet years.

Water scarcity is essentially permanent in California, given our high and diverse water demands for agricultural, environmental, and urban water use relative to the usually drier amounts of water available. Efforts to capture additional water for surface water reservoirs and groundwater are conceptually attractive, but are now usually uneconomical, as their capital and other costs usually exceed what water users would be willing to pay. This applies as well to the ongoing mania for capturing floods for aquifer recharge (aka “Flood-MAR”, left). Even good ideas have practical, economic, and environmental limits. We should do more Flood-MAR, but it can only supply ≤20% of the state’s shortages in supply (Alam et al. 2020).

Chronic water shortages. California relies on groundwater overdraft for about 2 million acre-ft/year of its water use. This, plus reductions of water availability from climate change and more modest increases in environmental flows for rivers, mean fallowing 1-2 million acres of irrigated land in California is unavoidable, mostly in the southern Central Valley. Retiring land from irrigated agriculture will be the main approach for responding to chronic water shortages. This is difficult for policy-makers to accept, as evidenced by extended disproportionate rhetoric on expanding surface storage and groundwater recharge. New expanded surface storage and aquifer recharge are useful cards, but not nearly enough for a full deck. This problem is important enough that we should play with a full deck.

Much of the American west is suffering from a chronic shortage of water, which worsens during drought years. The Lower Colorado River basin uses about three million acre-ft of water each year than the river’s inflow, which has almost steadily decreased Colorado River reservoir storage each year since 1983 (Lund 2023). In Utah, the Great Salt Lake is shrinking from upstream diversions. Aquifers in Arizona also are being depleted from overuse.

There is a great need to develop a more integrated science-based approaches to adaptive ecosystem management. Ecosystem demands are difficult because they involve interacting water and habitat management over time. This cannot be completely worked out before it needs to be implemented, which will entail unavoidable controversy over time.

Floods, droughts, and ecosystems. Mitigating the impacts from drought on freshwater ecosystems and biodiversity has been a persistent and intractable problem. Despite massive investments in endangered species and aquatic habitats, more California species become listed, or simply go extinct. The clock is running out. The Delta Smelt functionally went extinct during this last drought (above figure). And although efforts abound for captive-bred smelt to thrive again in the San Francisco Estuary, the likelihood of this being truly effective (e.g., regaining high rates of natural reproduction) is low. Most species have essential habitat needs to complete their life-cycle (Sass et al. 2017), and if hatchery-origin fish are stocked onto the same degraded habitats, it is unlikely magic will occur. Parallel stories are unfolding for the Longfin Smelt, and sadly, for California salmon. As recently as the 1960s, annual spawning runs of adult winter-run Chinook salmon numbered 100,000-200,000 fish in the Sacramento River. Recent runs often number in just the 100s of adults. The drought was particularly brutal on winter-run Chinook. The production and survival of juveniles in the Sacramento River during 2022 was the lowest on record. Low numbers of juveniles trace back to low numbers of spawning adults. In addition, there is a thiamine (vitamin B1) deficiency in adults that they pass onto juveniles. If untreated, many juvenile salmon with thiamine deficiency die (Ward and Bell-Tilcock 2022). As for fall-run Chinook salmon (the most robust run of Chinook remaining in California), managers have elected to cancel this year’s fishing season – a devastating blow for the fishing industry. Stitching all the information together, it is clear that lack of water for ecosystems and a deluge of other impacts is generating a “stair-step” shape of ecological decline over time, whereby stocks of native species exit the drought in worse condition than when they entered. In contrast, populations of non-native species – from bass to bivalves – are boosted through the drought, generating an opposite staircase pattern upwards. We carry these ecological trends of drought forward, which only increases the conservation work needed.

Conclusions

California’s water system serves diverse and conflicting purposes and is subject to extraordinary hydrologic variability. It is a great place to study and work on water problems. The 2023 wet season in California illustrates many dilemmas, paradoxes, and challenges of water management with a highly variably hydrology.

1. The 2020 – 2022 California drought is mostly over, but leaves a legacy of depleted groundwater and ecological health. Repayment of drought-depleted groundwater will require additional agricultural fallowing in future years (even wetter years) to comply with SGMA.
2. Floods are not the exact opposite of drought. California can have chronic water scarcity, and even droughts, in years where floods bring substantial damages, and deaths, as seen in 2023.
3. Droughts (and floods) often have long tails after most would declare these events “over”. This is the case for groundwater replenishment reducing and ecosystems following this drought.
4. Native ecosystems and biodiversity evolved under cyclical flood and drought conditions, but many ecosystems are now exposed to chronic drought. Persistent drought has set ecosystems on a trajectory towards assemblages dominated by non-native species. Actual drought just accelerates the transition.
5. There is always a shortage of cheap water. California’s water demands will exceed water supplies in most years, meaning that many will want more water, although most of these will not be willing to pay the costs of providing additional water.
6. Every year, California should be concerned with both droughts and floods, and mindful of over-development of water demands in the face of chronic water scarcity.

Jay Lund is a Professor of Civil and Environmental Engineering at University of California, Davis, and Vice Director at its Center for Watershed Sciences. 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.

Further Reading

Alam, S., M. Gebremichael, R. Li, J. Dozier, and D. Lettenmaier. 2020. Can managed aquifer recharge mitigate the groundwater overdraft in California’s Central Valley? Water Resources Research 56: e2020WR027244.

Lund, J.R., J. Medellin-Azuara, J. Durand, and K. Stone. 2018. Lessons from California’s 2012-2016 Drought. Journal of Water Resources Planning and Management 144: 04018067-1.

Lund, J., A.L. Rypel, and J. Medellin-Azuara. 2021. California’s new drought. https://californiawaterblog.com/2021/03/14/californias-new-drought/

Lund, J. 2023. Resistance is Futile – Agriculture is Key to Fixing Lower Colorado River Water Shortages, https://californiawaterblog.com/2023/02/05/resistance-is-futile-agriculture-is-key-to-fixing-lower-colorado-river-water-shortages/

Moyle, P., K. Börk, J. Durand, T. Hung, and A.L. Rypel. 2019. Futures for Delta Smelt, https://californiawaterblog.com/2019/12/15/futures-for-delta-smelt/

Rypel, A.L. 2021. Do largemouth bass like droughts? https://californiawaterblog.com/2021/05/02/do-largemouth-bass-like-droughts/

Sass, G. G., A. L. Rypel, and J. D. Stafford. 2017. Inland fisheries habitat management: lessons learned from wildlife ecology and a proposal for change. Fisheries 42(4):197-209.

Ward, A.E., and M. Bell-Tilcock. 2022. Spawning of the living dead: understanding how salmon pass thiamine deficiency to their young. https://californiawaterblog.com/2022/10/30/spawning-of-the-living-dead-understanding-how-salmon-pass-thiamine-deficiency-to-their-young/