How the Drought is Shrinking California’s Reservoirs [Visualization]

Data source: California Department of Water Resources

This created for The Lowdown by Bay Area web developer Victor Powell, shows fluctuations since 2010 in California’s 30-largest reservoirs. As of July 30, many are at strikingly low levels — even in light of typically bone dry summer conditions — leaving water agencies throughout the state scrambling for options, and beginning to impose water-use restrictions and penalties.

On the map, the grey border marks each reservoir’s maximum capacity, while the blue shows fluctuating storage levels over time. All reservoirs are scaled relative to maximum storage capacity by area (with the largest — Shasta Lake — at 30 pixels). Click on each reservoir to see the change in capacity over the designated time period. Changing percentages can be viewed by hovering over the reservoir pop-out to the left of the graph. Use the slider at top to select specific times. The source code and data set is available here.

California is peppered with a vast collection of dams and reservoirs, providing water — and in some cases power — to cities and farms throughout the state.

Most of the state’s reservoirs typically fill up during the wet winter months and get slowly depleted over the course of the summer and fall (although reservoirs used mainly for agriculture and power generation follow scattered release schedules).

But these aren’t typical times for California: following several below-normal years of snowfall and rain, 2013 clocked in as the state’s driest year on record. And the winter months of 2014 provided little relief, leaving the state bracing for drought conditions into the foreseeable future.

For more on where your water (in California) comes from …


Victor Powell is a Berkeley-based web developer, specializing in data visualization. He runs the consultancy Setosa.
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  • Frank MacLeod

    Do a little research and check your data. While the storage in Lake Isabella, in Kern County, is WAY down it isn’t because of drought. The lake levels have been reduced by the Army Corps of Engineers because an earthquake study showed that one of the dams might be unsafe in an earthquake. They have been studying it to death without any movement on repairs or modifications. Meanwhile, downstream urban and agricultural users of the normally stored water have been without for over five years.

    • http://blogs.kqed.org/howdwegethere Matthew Green, KQED

      Hi Frank: Thanks for your comment. Please note, however, that we never claimed that water levels in every single reservoir featured here have been reduced as a result of drought. While most indeed have, some, including Lake Isabella, have experienced fluctuations due to other factors. .

  • Brian Kreitzer

    I have been keeping up with the drought conditions in the state. The data visualization aspect of the article is quiet powerful. I use to drive by the San Luis Reservoir every 4-6 weeks in my travels between Nor and SoCal. It is humbling and sad to watch the water line retreat to its current level and if that sight alone does not touch the hearts of residential, commercial, and governmental bodies, then we are not paying enough attention. Thank you for the article.