Analysis: Proposed state investments inadequate to address increase in catastrophic flood risk

The Governor Newsom’s May Revise Budget provides an additional $115 million in investments in flood risk reduction, including:

• $75 million to support local flood control projects
• $40 million for the San Joaquin Floodplain restoration

This is in addition to the $202 million proposed by the Governor in January to reduce flood risk in urban areas, the Delta region and the Central Valley. However, the total investment of $317 million in the May Revise is only a third of the $1 billion proposed by the California Senate for last year’s budget (FY 2022-23) (Des Jardins 2022a, 2022b).

We’re not counting the $175 million for emergency flood response and recovery related to the 2023 storms and snowmelt, since it mostly won’t address long term needs for flood risk reduction. This funding for emergency response is over half of the additional $290 million allocated for flooding in the May Revise Budget.

The inconvenient truth is that state and federal investments in flood risk reduction are utterly failing to keep up with the nonlinear increase in flood risk due to climate change. European researchers looked at changes in daily rainfall records and found that the frequency has “started to deviate significantly and increasingly from that of a stationary climate” since about 1990 (Robinson et. al. 2021).

The European researchers also found statistically significant increases in rainfall records in several regions, while finding that “[s]ubtropical dry regions like the western US, southern Africa (and to a lesser extent the Mediterranean and Australia) have seen lower increases in rainfall records than wet regions in the tropics and mid-latitudes.”

Robinson et. al. (2021): Deviation of observed daily-rainfall records from those expected in a stationary climate (in %), aggregated for SREX regions and averaged between 1980 and 2016. Regions with statistically significant deviations from a stationary climate are highlighted with bold frames. (cc 4.0 license)

Climate dynamics researcher Cristi Proistescu tweeted an insightful analysis of order statistics and concluded “We may not know *where* the next record precip will hit. But we know it will hit most places.”

One example was the extreme precipitation in South Florida in April. European climate scientist Erich Fischer, a lead author of IPCC AR6 and a researcher on climate and weather extremes, tweeted these observations

Seemingly a “black swan event” that is simply off the chart, its occurrence reveals the limitations of focusing on relatively short observational records to estimate worst-case events.https://t.co/N1y3k32WVV

— Erich Fischer (@erichfischer) April 13, 2023

There are large efforts towards this goal and promising first results within the @XaidaProject and through the @MetOffice_Sci UNSEEN approach developed by @ClimateVikki et al. Come see the results in our session @EuroGeosciences https://t.co/2uCrv1gGeY

— Erich Fischer (@erichfischer) April 13, 2023

In sum, although California is a dry region at mid-latitudes, it is still at risk of the same kinds of nonlinear increases in extreme rainfall as have been seen across the globe.

For over a decade, climate scientists have recommended that California do “stress tests” for climate-change amplified extreme flood events. In 2015, the Climate Change Technical Advisory Group recommended developing scenarios (CCTAG, 2015):

A framework that can accommodate an evolving state of knowledge of important processes and a changing landscape for the development and adoption of adaptation measures involves stress tests.

Stress tests are a way to characterize the range of climate-change extremes and both develop scenario-based analyses that consider how the state as a whole would be likely to perform if an extreme drought or flood occurred, and suggest ways to increase resilience to these events (Stern et al. 2013). Stress tests focus on identifying weaknesses and breaking points to the water system that stem from different facets of extreme events. They can help to (1) provide plausible estimates of high-impact, possibly unprecedented events utilizing climate modeling; (2) detect crucial thresholds for specific sectors and society as a whole beyond which environmental or social stability would be endangered; (3) integrate climate indicators and social consequences to assess the probability of exceeding risk thresholds; and (4) suggest new adaptation pathways to stay within bounds of tolerable risk levels (Swart et al. 2013).

However, the CCTAG’s recommendations for developing scenarios of climate change amplified extreme flood events have only begun to be implemented as part of the second phase of the ARkStorm 2.0 project, led by climate scientist Daniel Swain (UCLA 2022). And the vulnerability studies done by the US Geological Survey for the historical ARkStorm 1.0 scenario have yet to be incorporated into state or regional emergency flood response planning. (Wein 2016, Plumlee 2016, Porter 2011.)

The 2023 flooding in the Tulare basin has shown the enormous gaps in California’s regional flood preparedness, even for events that are known to occur more than once every 50 years (Des Jardins 2023). We all need to stop hand-waving and take a hard look at escalating risks to critical infrastructure and vulnerable communities. And consider difficult decisions that might need to be made about routing floodwaters that are greater than the existing flood system capacity.

This blog post was updated on May 13.

Further Reading

CCTAG, Lynn E (Chair), Schwarz A, Anderson J, Correa M, O’Daly W. 2015. Perspectives and Guidance for Climate Change Analysis. Climate Change Technical Advisory Group.

Des Jardins D. 2023. Chaos in Tulare County shows need for advance flood planning. California Water Research blog. Mar 21, 2023.

Des Jardins D. 2022a. California’s FY 2022-23 budget invests little in flood risk reduction. California Water Research blog. Jun 21, 2022.

Des Jardins D. 2022b. Budget negotiations could determine the future of California’s Central Valley. California Water Research blog. Jun 21, 2022.

Des Jardins D. 2021. We need to plan for extreme flooding in California. California Water Research blog. Nov 23, 2021.

Met Office. 2023. Predicting extreme weather. [accessed 2023 May 12]

Plumlee GS, Alpers CN, Morman SA, Juan CS. 2016. Anticipating Environmental and Environmental-Health Implications of Extreme Storms: ARkStorm Scenario. Natural Hazards Review. 17(4):A4015003.

Porter K, Wein A, Alpers CN, Baez A, Barnard PL, Carter J, Corsi A, Costner J, Cox D, Das T, et al. 2011. Overview of the ARkStorm scenario. U.S. Geological Survey Open-File Report No.: 2010–1312. [accessed 2023 May 12].

Robinson A, Lehmann J, Barriopedro D, Rahmstorf S, Coumou D. 2021. Increasing heat and rainfall extremes now far outside the historical climate. Clim Atmos Sci. 4(1):1–4.

UCLA. 2022. Climate change makes catastrophic flood twice as likely, study shows. Press release. Aug 12, 2022.

Wein A, Ratliff J, Báez A, Sleeter R. 2016. Regional Analysis of Social Characteristics for Evacuation Resource Planning: ARkStorm Scenario. Natural Hazards Review. 17(4):A4014002.

Xaida. 2021. eXtreme events : Artificial Intelligence for Detection and Attribution. Xaida. [accessed 2023 May 12].