Visualization: How the Drought is Shrinking California’s Reservoirs

Includes interactive visualization

Data source: California Department of Water Resources

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

Most of these reservoirs typically fill up during the wet winter months and are slowly depleted over the course of the summer and fall (with some exceptions for reservoirs mainly used for agriculture and power generation that 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 although last month’s storms helped soften the blow, in the grand scheme, they were — ahem — just a drop in the bucket.

The visualization above, created by Bay Area web developer Victor Powell, shows fluctuations since 2010 in California’s 30-largest reservoirs. As of mid-March, many are at strikingly low storage levels (although some are much fuller than they were just a month ago), leaving water agencies throughout the state scrambling for options as a long, dry summer approaches.

The grey border marks each reservoir’s maximum capacity, while the blue shows fluctuating storage levels over time. All reservoirs are scaled relative to each others maximum storage capacity by area (with the largest — Shasta Lake — at 30 pixels). Click on each reservoir to graphically see its change in capacity over the designated time period. You can also view these changing percentages by mousing over the reservoir pop-out to the left of the graph. Use the slider at top to select specific times.

Source code and data is open source and available here.

Resources for finding out where your water comes from (in California)

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

  • 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.

    • 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. .