Threats to Colorado River Water Supply

National Park Service

Photo: National Park Service

The Colorado River supplies water to approximately 27  million people in seven states and irrigates more than three million acres of farmland. In Southern California alone, it supplies 18 million Metropolitan Water District customers with 40 percent of their water.

So last year, when a study out of Scripps Institution of Oceanography reported that there’s a 50 percent chance that the Colorado River’s largest reservoir (and the largest reservoir in the United States), Lake Mead, will be dry by 2021, the news generated a lot of buzz.

But a new study out from the University of Colorado Boulder finds that despite a 10-year drought in the Colorado River system, the odds of draining the river’s delivery system before 2026 are pretty slim — below 10% in any given year.  Researchers say this is primarily due to the massive reservoir storage capacity along the Colorado — more than 60 million acre feet, which includes Lake Mead.  The reservoir system of the Colorado is currently at 59 percent of capacity, according to the study.

But the scientists predict that by mid-century, the Colorado could become less reliable unless water-management strategies change.

The researchers found that if climate change causes a 10 percent reduction in the Colorado River’s average stream flow as some recent studies predict ([PDF]), the chances of fully depleting the system’s reservoirs will exceed 25 percent by 2057.  If there is a 20 percent reduction in stream flow, the chances of deleption rise to 50 percent.

“On average, drying caused by climate change would increase the risk of fully depleting reservoir storage by nearly ten times more than the risk we expect from population pressures alone,” said lead study author Balaji Rajagopalan in a press release about the study.

The authors of the study conclude that the magnitude of the risk will depend not just on the amount of drying the region experiences, but also the types of water management and conservation strategies that are implemented in the near future.

For the last decade, California’s annual use of Colorado River water has varied from 4.5 to 5.2 million acre feet.

Photo by Adrian Fogg

Photo: Adrian Fogg

Cities, Farmers, Ski Resorts Sweat Out the Snowpack

“Better late than never”is about all you can say if you’re keeping a wary eye on the Sierra snowpack. Winter finally arrived in the Lake Tahoe region, just in time for Christmas skiers–but maybe not in time for water consumers looking ahead to next summer.

As of Christmas Day, the three key reservoirs in northern California were all at less than half of their “normal” levels for this time of year; Shasta (47%), Oroville (45%) and Folsom (44%). Oroville, a critical link in the State Water Project, was at just 22% of its total capacity.

With the winter’s first hands-on Sierra snow survey coming up next week, Elissa Lynn, Sr. Meteorologist for DWR tells me that readings from the network of automated snow sensors indicate that we’re about 15% of the way toward a full “normal” season (as measured on April 1st). That means we have a lot of catching up to do.

Ski resorts are already having a lean year and as Tom Knudson writes in today’s Sacramento Bee, some are looking ahead to when climate change might cause this kind of year to become the norm.

Filling Out the Reservoir Picture

At the annual “Watershed Event” fundraiser for the Sacramento River Watershed Program, Elissa Lynn, Sr. Meteorologist for the state Dept. of Water Resources, offered a rundown of where we stand at the start of the official “water season.”

The short version: It’s bleak.

Lake Oroville in September

As I noted last week, Lake Oroville, a key reservoir on the Feather River, stood at 31% of capacity as of midnight on September 30. Readings from the same hour showed the state’s largest reservoir, Shasta Lake, at 30%; Folsom Lake (American River, east of Sacramento) at 28%; and San Luis Reservoir, east of Silicon Valley at 12–yes, twelve percent of capacity.

Capacity figures by themselves can be misleading. We expect reservoirs to be low this time of year, right at the end of the dry season. But as DWR was taking these readings, Oroville, to use one example, was at 49%–less than half–of “normal” for this time of year.

So, much depends on the coming winter. Even with all the advanced tools that forecasters have at their disposal in this first decade of the 21st Century, it’s hard to say how much water we’ll wring out of the skies this winter. Lynn says we’re in a “La Nada” pattern, meaning the Pacific Ocean isn’t giving a strong signal for either El Nino or its opposite, La Nina. The two conditions describe the degree–or lack–of cold water upwelling from the ocean depths, which has a strong influence on California’s precipitation patterns.

But Lynn says the consensus among forecasters is “leaning toward a dry-to-average” winter and average won’t get us there. We’ll need several soggy months to make up for lost water and avoid more severe water restrictions throughout the state next summer.