short the southwest region of the United States of a half-billion cubic meters (400,000 acre feet) of water per year, 40 percent of the time by 2025. By the later part of this century, those numbers will double. An acre foot of water is typically considered adequate to meet the annual water needs of two households.
The Colorado River system supplies water to tens of millions of people and millions of acres of farmland, and has never experienced a delivery shortage. But if human-caused climate change continues to make the region drier, scheduled deliveries will be missed 60-90 percent of the time by the middle of this century.
The drying trend that exists in the inland region between Coast Mountains and the Rockies continues to spread and is creeping close to home. In the Okanagan, the South East Kelowna Irrigation District announced, that effective immediately, the allotment for metered agricultural users will be reduced 20 per cent in order to get through summer without running out of water.
General manager Toby Pike told Judy Steeves of the Kelowna Capital News, “The runoff from the low snowpack last winter is just not enough to replenish our water supplies going into the irrigation season - it’s critical that we reduce demand to avoid running out of water.”
In March, April and May, the total rainfall was 42.5 millilitres this year. The average for those three months is 87.6 ml. In May, the average precipitation is 39 ml, while this year it was 14.5 ml.
Typically, June has been the wettest month of the year, but this year, the first week has been the continuation of a hot dry spell, however some showers are in the forecast.
Presently the McCulloch Reservoir is estimated to be at 67 per cent of capacity, where normally at this time of year, it would be full and spilling over. It’s level is the lowest in 15 years.
According to manager Brian Jamison, the Westbank Irrigation District is also experiencing record low reservoir levels, and this will be the first year in its history that Lambly (Bear) Lake has not filled. Jamison told the Kelowna Capital News that Neither Lambly nor Tadpole Lake, a higher-elevation, more recent addition to the district’s network of reservoirs, are expected to fill, with Lambly down 48.4 centimetres and Tadpole down 94 cm.
While irrigation districts manage water supplies very carefully, certain trends are beginning to emerge as drought conditions are in full play south of the border.
In the Scripps research paper titled, "Sustainable Water Deliveries from the Colorado River in a Changing Climate," which appeared in the April 20th edition of the Journal Proceedings of the National Academy of Sciences, the forecast looks grim.
The analysis follows a 2008 study in which researchers Tim Barnett and David Pierce found that Lake Mead, the reservoir on the Colorado River created by Hoover Dam, stood a 50-percent chance of going dry in the next 20 years if the climate changed and no effort was being made to preserve a minimum amount of water in the reservoir.
“We were stunned at the magnitude of the problem and how fast it was coming at us,” said Barnett. “Make no mistake, this water problem is not a scientific abstraction, but rather one that will impact each and every one of us that live in the Southwest.”
“It’s likely to mean real changes to how we live and do business in this region,” Pierce added.
The Lake Mead/Lake Powell system includes the stretch of the Colorado River in northern Arizona. Aqueducts carry the water to Las Vegas, Los Angeles, San Diego, and other communities in the Southwest. Currently the system is only at half capacity because of a recent string of dry years, and the research team estimates that the system has already entered an era of deficit.
Barnett and Pierce noted that a number of other studies in recent years have estimated that climate change will lead to reductions in runoff to the Colorado River system. Analysis consistently forecast reductions of between 10 and 30 percent over the next 30 to 50 years, which could affect the water supply for between 12 and 36 million people.
The researchers estimated that there is a 10 percent chance that Lake Mead could be dry by 2014. They further predict that there is a 50 percent chance that reservoir levels will drop too low to allow hydroelectric power generation by 2017.
The researchers add that even if water agencies follow their current drought contingency plans, it might not be enough to counter natural forces, especially if the region enters a period of sustained drought and/or human-induced climate changes occur as currently predicted.
The new study builds on a perspective, that enough water would be retained in the reservoir to supply the city of Las Vegas, and examines what delivery cuts would be required to maintain that level of supply.
"People have talked for at least 30 years about the Colorado being oversubscribed but no one ever put a date on it or an amount. That's what we've done," said Barnett. "Without numbers like this, it's pretty hard for resource managers to know what to do."
Barnett and Pierce also point out that lakes Mead and Powell were built and calibrated to the 20th century, which was one of the wettest in the last 1,200 years. Tree ring records show that typical Colorado River flows were substantially lower, yet 20th Century values are used in most long-term planning of the River. If the Colorado River flow reverts to its long-term average indicated by the tree rings, then currently scheduled water deliveries are even less sustainable.
Barnett and Pierce show that the biggest effects of human-induced climate change will probably be seen during dry, low-delivery years. In most years, they estimate, delivery shortfalls will be small enough to be manageable through conservation and water transfers.
But during dry years there is an increasing chance of substantial shortages.
"Fortunately, we can avoid such big shortfalls if the river's users agree on a way to reduce their average water use," said Pierce. "If we could do that, the system could stay sustainable further into the future than we estimate currently, even if the climate changes."
“Today, we are at or beyond the sustainable limit of the Colorado system. The alternative to reasoned solutions to this coming water crisis is a major societal and economic disruption in the desert southwest; something that will affect each of us living in the region”.
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The US based research was supported under a joint program between UC San Diego and the Lawrence Livermore National Laboratory and by the California Energy Commission. The views expressed here do not necessarily represent the views of the California Energy Commission, its employees, or the state of California.
Don Elzer writes and comments about travel, current affairs and the natural world. He is the Director of the Wildcraft Forest Ecomuseum and is the editor of The Monster Guide which can be found at www.themonsterguide.com
He can also be reached by email at: treks@uniserve.com
