Today the journal Nature Climate Change published results of a groundbreaking paper that explores the changing character of precipitation extremes in California. The eye-opening results indicate that while overall precipitation levels will not change significantly in the next decades, the state has already entered a period of increased extreme precipitation events that will continue to present tremendous challenges to ensuring stable water supplies. My colleague Dr. Geeta Persad, Western States Senior Climate Scientist at UCS, reflects on the meaning of the results below.
The hills on the east side of the San Francisco Bay are a lush, perfect green at this time of year. I drink them in greedily during my daily commute to and from work. Especially because, like any Californian, I know that this greenness will leave with the wet season.
As climate change transforms the water landscape for our state, the greenery feels particularly precious. A new paper out of UCLA’s Institute for Environment and Sustainability today suggests that volatility in California’s water resources is only going to get worse. Its findings drove home for me how much smarter we need to get about managing climate change impacts on water in California.
Climate change is not just a slow and steady trend affecting water conditions in our state. One of the key findings of the paper led by Dr. Daniel Swain, is that “precipitation whiplash” – a rapid transition from very dry conditions to very wet conditions – is likely to increase with climate change.
Why does this matter? This kind of whiplash is exactly what we’ve experienced over the last few years. We’ve transitioned from the worst drought in California’s recorded history to two wet seasons that produced around $1 billion in flood-related damage and repairs. These projections could mean an increase in extreme wildfire risk and weakened, dried-out soil followed by extreme rainfall and runoff events—the perfect storm of ingredients to produce mudslides like the ones that devastated Montecito earlier this year.
Simulations in this new paper also indicate that, between now and 2060, almost the entire state has at least a 66.6% chance of experience a precipitation event like the one that created the 1862 California flood, which transformed the Central Valley into an inland lake. This means that in the next 40 years, our largest urban centers are more likely than not to experience unprecedented flood events that our modern water management systems and infrastructure have never before had to deal with.
Climate change means more than a change in averages
This paper is especially important because it quantifies climate change impacts on California precipitation—like precipitation whiplash and extremes—that really matter for water management. As long as we keep only planning for averages, we won’t be managing many of the catastrophic risks that climate change creates for water management in California.
In Swain and his coauthors’ simulations, the tripling of extreme precipitation risk, sharp increases in precipitation whiplash, and uptick in extreme dry seasons happen even while average precipitation barely changes. Plus, their projections show a strong shortening of the wet winter season and expansion of the dry summer season statewide. That could create a need for more water storage to bridge between the wet and dry seasons, even without a change in the total amount of water we get each year.
We have a very long way to go to adequately plan and build a safe and reliable water system for the reality of how climate change will impact our water resources and infrastructure. Studies like this one and others that have come out over the past several years highlight that we have to fundamentally transform how we think about the role of climate in water management in California. Climate change’s influence on the character of California’s water is complicated, but the more of that complexity we integrate into our decision-making, the more likely we are to develop management strategies that avoid the worst outcomes. Luckily, papers like this one show that we have the science to do so.
Geeta’s reflections highlight the need to accelerate and intensify work that has recently begun in California. We are just at the beginning of figuring out how to manage water for changing climatic conditions. Since 2015, UCS has been highlighting the problems of how our current infrastructure is not built for increased drought and flooding in conjunction with more precipitation falling as rain rather than snow. We also have shown that climate change is highlighting the critical importance of increased groundwater management to meet our needs. The UCLA report’s findings on the increase in extreme events further underscores the urgent need for change.
Our highly-engineered water systems in the western states is built for a seasonal regime that is fast disappearing. It is designed to store melting snowpack in the spring for farms and cities to use in the summer and fall. As in the drought of 2012-2016, we can no longer count on sufficient precipitation and snowpack to store sufficient water in dry years. Furthermore, during the last two wet years we found that our systems were in some cases inadequate to deal with some extreme events, most dramatically demonstrated by the near-failure of Oroville Dam in February 2017.
Rethinking how we build for a new normal of extremes
The need to change how we build and manage water infrastructure is only one example of how we need to think differently about the built environment now that dramatic changes from a warming world are taking hold. Yet few of the people who are responsible for how we build roads, dams, canals, bridges, and buildings know what to do with the science that is emerging. That is why UCS sponsored legislation in 2016, AB 2800 (Quirk) to bring scientists and engineers together to come up with recommendations (due to be released late this summer) on how science can better inform our building decisions.
Global warming is going to necessitate a wholesale re-thinking of how we approach building and maintaining our communities far into the future. Translating science to a form that can be used by engineers and architects is only one facet of the problem, however. It will require we rethink about everything from updating building codes and standards, to improving coordination between local, state, and federal levels of government, to approaching cost/benefit calculations of projects with climate change factors included, to fixing chronic underinvestment in disadvantaged communities so that they can better deal with future challenges.
A future of “whiplash” weather in California is but a microcosm, and a warning for much more uncertain and hazardous conditions as the world gets warmer. We are fortunate that science is improving our ability to forecast these changes, but we need policies and programs to make changes based on what we are learning. Time is very short: this is now a problem of our present, not our future.