Wearing snowshoes and aviator sunglasses, Gov. Gavin Newsom stood in a field near Lake Tahoe recently and listened to a Department of Water Resources engineer announce the results of California’s April snow survey , which is conducted each year when snow depths in the Sierra Nevada. reach their maximum.
The news was good: The manual survey, conducted by poking blue metal tubes into the ground, had measured 64 inches of snow – 13 percent above average for the location and time of year – virtually guaranteeing that the state would not experience a severe drought this year. summer.
This is the second consecutive year of above-average snowfall and is a huge turnaround from conditions in early 2024, when the statewide snowpack was just a quarter of the historical average.
But despite the cheerful tone, everyone gathered on this field: the governor, the engineers, the director of the DWR who declared that “average is great!” — was probably aware of the long dry years of the recent past and the worrying fact that the future of California’s mountain snowpack looks bleak.
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The relationship between snowfall and climate change is not as simple as it seems at first glance. Although rising temperatures will cause snow to fall as rain, this is partly offset by the fact that precipitation will become more intense overall, as warmer air can hold more water vapor. Parts of Alaska and northern Canada have experienced increased snowfall over the past 40 years; In these frigid regions, the amount of snow is more limited by cold weather, which decreases the amount of moisture in the air.
On the other hand, in areas of the country that are generally close to the “rain/snow line” – that is, places like the Mid-Atlantic where snow is often only at just a few degrees of falling as rain – even a small amount of climate change significantly reduces annual snowfall. It’s certainly no coincidence that last winter was New York’s least snowy season on record, with Central Park receiving just 2.3 inches of snow between October 2022 and March 2023.
On the west coast, another complicating factor is the presence of high mountains. Mountains have a dual effect on snowfall: not only are they colder than adjacent valleys, but they also increase precipitation by forcing moist air to rise and drop its water. As a result, the Sierras can experience blizzards that would be unfathomable in low-lying areas, such as a single storm in late March that dumped more than 10 feet of snow on Sugar Bowl Ski Resort in four days.
The mountains also cause the snow to stay longer than expected. Even in the far reaches of Minnesota’s Northwoods, the snow is mostly gone by late April, but the central Sierra Nevada typically holds snow until early June. The combination of these factors means that mountain snowpack plays a crucial role in regional hydrology, as it acts as a sort of natural reservoir that stores significant amounts of water during winter and spring and releases it during the summer.
With the help of computer models, we can begin to unravel the effects that climate change will have on California’s snowpack over the coming decades. First, as temperatures warm, the rain/snow line will shift to higher elevations, meaning a greater proportion of precipitation will fall as rain. This will be moderately offset by an increase in total precipitation, but climate models suggest the net effect will be a decrease in snowfall everywhere except the highest peaks in the Sierras.
Finally, and perhaps most importantly, warmer temperatures will cause the snowpack to melt more quickly, causing two opposing problems. Increased snowmelt in late winter will increase the risk of devastating flooding as mountain runoff converges with heavy precipitation that only becomes more extreme. And during the summer months, when the state will need more water due to hotter, drier conditions, there will be little or no water left in streams and rivers fed by melting rivers. snows.
To some extent, these problems can be solved by increasing reservoir capacity to replace the “free” storage previously provided by mountain snowpack. But building new reservoirs is a long and expensive process: the Sites Reservoir project in the Sacramento Valley was proposed in the 1950s, abandoned in the 1980s, resurrected in the 1990s and finally funded in 2018 with $816 million. dollars from California’s water bond (still only a fraction of the estimated $4 billion cost).
Once funding is secured for this project, there are still bureaucratic hurdles to overcome.
Work on Sites Reservoir’s nine dams has been repeatedly delayed by fights over environmental reviews and water rights, and even after Governor Newsom used his authority under new amendments to California law on the quality of the environment to speed up the judicial process, at the earliest in seven years. the construction process will begin in 2026.
Remaining patient in carrying out projects like this – projects that will not result in an improvement in the state’s water conditions but simply allow it to keep pace with climate change – requires recognizing that every announcement that the Reservoirs being at 100% capacity may not be a reason to rejoice, but rather a missed opportunity to store even more water.
It also requires that policymakers not lose sight of the general trend toward thinner, more transient snowpack, even after a few good years in a row.
Ned Kleiner is a scientist and disaster modeler at Verisk. He holds a doctorate in atmospheric sciences from Harvard.
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