Can we count on the river flows of the past to predict the future?

Fisherman at Warrior Point at Pyramid Lake

For 96 years of the 20th century [1900-1995], the Truckee River flowed an average of 579,000 acre-feet (at Vista near the Truckee Meadows Waste Water Plant). That average number represents a continuous flow of 800 cubic feet per second (CFS).  Our measurements of flow during the last century, of course, were made after many changes had already taken place in the Truckee River watershed.  A dam was already in place at Lake Tahoe and a large network of ditches, dikes, and diversions from the river were already in place throughout the Truckee Meadows and Washoe Valley.  And the nation’s first reclamation project was constructed between 1905 and 1917.

Today, however, the changes that are occurring to our river may go well beyond ditches, dams, and diversions.  The watershed is seeing an increase in temperature that may be unprecedented in thousands of years.  Higher temperatures will very likely lead to greater evaporation and less snow.  That leads us to ask: What is the chance that we’ll see an average Truckee River flow of 579,000 acre-feet in the  remaining 86 years of the 21st century?

 The Nettie, an expedition boat on the Truckee River, western Nevada, in 1867. Photo: Timothy O'Sullivan

The Nettie, an expedition boat on the Truckee River, western Nevada, in 1867. Photo: Timothy O’Sullivan

Some studies are saying that the entire west – not just the far southwest dependent on the Colorado River – are facing a moderate to serious drop in precipitation coupled with increasing temperatures that may result in streamflows dropping by as much as 25%.Projected Changes in Annual Runoff

What worries many is that the decrease in river flows may have already started.  The Truckee River has already seen 14 years of “abnormal” dry conditions with only 2 years in that time frame seeing above average precipitation.  Drier than average conditions mean that water for Truckee River flows into Pyramid Lake are inadequate to keep up with natural evaporation rates.

Much of the worry about dry conditions has focused on the Colorado River and more recently on California.  In an article in “The Week” (theweek.com) the headline reads “The unprecedented water crisis in the American Southwest”, which focuses on the Colorado River.  Scientists are increasingly sounding the alarm of drying conditions affecting all who depend on the Colorado River.

“We can’t depend on history to project the future anymore,” said Carly Jerla, a geological hydrologist who closely monitors the Colorado. The river’s wet 20th century may have been an anomaly; in the 13 centuries before the 1900s, its flow was actually 15 percent lower. The current drought may also be the product of a wider pattern of climate change, signifying a barren future: Several global-warming studies predict that rising temperatures will reduce the river’s flow by up to 35 percent by 2050.

The articles on the continuing drought focus on the impacts to agriculture and the residents

The Derby Dam diverts Truckee River water from its natural course which goes to Pyramid Lake. Instead water flows into the Truckee Canal to the Carson River.

The Derby Dam diverts Truckee River water from its natural course which goes to Pyramid Lake. Instead water flows into the Truckee Canal to the Carson River.

who reside in the west’s Mega-cities like Las Vegas, Los Angeles, and Phoenix.  But every westerner faces an uncertain future if there is a shift even half as great as 25-35% declines in stream flow.  The Truckee River is critical to the Truckee Meadows and a decline of such proportion would be devastating to the people and wildlife of the entire region.  Can we conserve 35% of all water use?  Agriculture?  Urban?  Industrial? Can natural systems at Lake Tahoe and Pyramid Lake and the length of the Truckee River survive with a smaller fraction of our left-over water?

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About Dennis Ghiglieri

My concern for the Truckee River grew over the years. It started with picking up trash and supporting better water quality. I helped create the "living river"plan with other citizens on the Community Flood Coalition; a plan to reduce flood impacts to infrastructure through river restoration and protection of the floodplain. I understand how critical the Truckee River is to the environment – and economy – of our entire region. I'm hoping that through these pages we can all understand our connection to the Truckee River and why we need to protect it.

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