You’ve probably heard about the California drought by now. If you live in California, it’s hard to hear about anything else. Unfortunately, the drought may be even worse than we realize, because the way we often measure water supply doesn’t consider future water availability. By relying on measurements of current reservoir levels, agencies in charge of water distribution are missing an important part of the water supply picture, leaving their customers vulnerable to longer and more severe droughts.
Reservoir levels tell only half the story
One of the main ways that we measure our water supply is by tracking the state’s reservoir levels. As of today, reservoir levels are looking okay in a number of places. For instance, Lake Shasta, Lake Oroville, and Folsom Lake are more than half full. Lake Oroville and Folsom Lake are actually higher that they were at the end of March 2008 (which was also a dry year). But something is very different this year: the snowpack.
Snowpack is the largest water storage system in California, and as a water source we measure snowpack in terms of snow water content levels. As of today, these are looking very, very bad. Snow water content levels are well below the lowest levels ever recorded (in 1976-1977) and this holds true across the state. What this means is that, although the water levels in Lake Oroville and Folsom Lake are higher than during the last drought – there will be extremely little snow melt this spring and summer to refill them.
The problem with this is that many water providers use current reservoir levels to make decisions about water conservation. For instance, back in 2013 the Metropolitan Water District of Southern California announced that because reservoir levels were “high,” it would not reduce water supplies to local water agencies in Southern California or impose mandatory conservation measures. The District argued that it had more than two million acre-feet of water in storage at the end of 2013 (in addition to emergency reserves), should 2014 prove to be a dry year.
Climate change is intensifying drought
As we now know, 2014 was extremely dry and hot (the hottest year on record, in fact). And so far, 2015 isn’t any better.
Now, Metropolitan Water District is in dire straits, having drained its seemingly ample reserves. To make up for the shortfall, the water district is buying water from Sacramento Valley rice farmers—at such high rates that some can make more money selling water than growing rice.
While no one has a crystal ball, droughts are projected to intensify throughout the Western U.S. due to climate change and, according to NASA, we should expect “megadroughts” in the future. Hotter weather will continue to reduce snowpack, so that less snow melt is available in the spring and summer when it’s needed to refill reservoirs.
New tools are needed to forecast water supply
Clearly, new tools are needed to adapt to longer and more severe droughts. One of these tools should be a way to integrate data about snow levels into forecasts of reservoir storage. There is already information that integrates information about climate change impacts on snowpack, for instance the CalAdapt website has decadal projections of snowpack, but these are at a coarse-scale that makes it hard for water managers to downscale to their system. The U.S. Geologic Survey is currently developing modeling tools to characterize hydrologic processes relevant to changing snowpack and snow melt in five southern Sierra basins (Tuolumne, Merced, San Joaquin, King, and Kaweah basins), but more is needed and fast.
In the meantime, urban and agricultural water suppliers must take much more conservative approaches – it is no longer acceptable to plan as though next year will be wet. For instance, water suppliers should consider using only a fraction of available water supply this year in order to ensure some water is carried over to next year. If we don’t get better at forecasting our water supply beyond current reservoir levels, we might just be left high and dry.
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