Comments On Western Water 2011

Over the last several years, there have been dire predictions for Lake Mead. These include from the Science Daily

Lake Mead, Key Water Source For Southwestern US, Could Be Dry By 2021

which starts with the text

“ScienceDaily (Feb. 12, 2008) — There is a 50 percent chance Lake Mead, a key source of water for millions of people in the southwestern United States, will be dry by 2021 if climate changes as expected and future water usage is not curtailed, according to a pair of researchers at Scripps Institution of Oceanography, UC San Diego.”

with excerpts reading

“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.”

“Barnett said that the researchers chose to go with conservative estimates of the situation in their analysis, though the water shortage is likely to be more dire in reality. The team based its findings on the premise that climate change effects only started in 2007, though most researchers consider human-caused changes in climate to have likely started decades earlier. They also based their river flow on averages over the past 100 years, even though it has dropped in recent decades. Over the past 500 years the average annual flow is even less.”

Another article in the New York Times by Felicity Barringer on September 27 2010  is

Water Use in Southwest Heads for a Day of Reckoning

which includes the text

“LAKE MEAD NATIONAL RECREATION AREA, Nev. — A once-unthinkable day is looming on the Colorado River. Barring a sudden end to the Southwest’s 11-year drought, the distribution of the river’s dwindling bounty is likely to be reordered as early as next year because the flow of water cannot keep pace with the region’s demands.”

and

“But the operating plan also lays out a proposal to prevent Lake Mead from dropping below the trigger point. It allows water managers to send 40 percent more water than usual downstream to Lake Mead from Lake Powell in Utah, the river’s other big reservoir, which now contains about 50 percent more water than Lake Mead.

In that case, the shortage declaration would be avoided and Lake Mead’s levels restored to 1,100 feet or so.

Lake Powell, fed by rain and snowmelt that create the Colorado and tributaries, has risen more than 60 feet from a 2004 low because the upper basin states, Colorado, New Mexico, Wyoming and Utah, do not use their full allocations.”

There is an informative article in the May 2011 issue of the publication Western Water Assessment. Intermountain West Climate Summary that updates us on this issue. It is

The Spring Runoff Roundup: Another Look at ENSO, Dust-On-Snow, Beetles, and Lake Mead by Jeff Lukas, Western Water Assessment. Intermountain West Climate Summary. May 2011. Vol 7 Issue 3

Excerpts read [highlights added]

There were no great expectations for the winter of 2010-11 in the Intermountain West. A merely average snowpack and runoff would have seemed fortunate, given the generally dry conditions of the previous decade, and the strong La Niña conditions tilting the region slightly towards dryness. But a very wet October turned out to be a harbinger for the rest of the winter, and the snow—aside from a dry January— kept falling in all of the high mountains of the region except for southern Colorado. In April, the average initiation dates for the spring melt came and went, as the snowpacks continued to accumulate.

By May 1, snowpack levels in many basins were in uncharted territory, higher than any recorded during the SNOTEL era, since the late 1970s. The Tower site near Steamboat Springs, which on average receives more snow than any other SNOTEL site in the Colorado River basin, reached a record 202″ of snow on the ground at the end of April, containing a record-tying 71″ of water equivalent (Figure 1). Incredibly, as of May 23, the SWE at Tower has increased to 79″. In Utah, all three river basins in the Wasatch region (Bear, Weber, and Provo) had record snowpacks for May 1, all at over 200% of average for the date. On May 23, the Snowbird, Utah SNOTEL was recording 75″ of SWE, which is about 180% of the average SWE for that site, which usually occurs in late April.”
“……..the surface elevation of Lake Mead is expected to rise 32 feet by fall 2011, to over 1115’.”

“While this year’s above-average runoff and the resulting “equalization release” to Lake Mead are surely welcome news for water interests in the Lower Basin, they don’t alter the overall picture of a river system operating very close to the balance between supply and demand, vulnerable to even modest long-term declines in system yield. Even the unusually high inflows projected for Lake Mead this water year would bring it back only to the level of fall 2006, when it was well into the downward trajectory that started in 2000.

“A similar perspective is shown by looking at Upper Basin yield, as measured by water-year natural flow at Lees Ferry. The 2011 water year natural flow was projected to be around 19 MAF as of mid-May, or 4 MAF above the 100-year mean of 15.0 MAF. But the cumulative deficit, relative to that mean, that was racked up during the mostly dry years from 2000 to 2010 is on the order of 33 MAF. We would thus need another seven years in a row as wet as this year’s projected flow to balance the system deficit accumulated during the first decade of the 21st century.

This year’s record (in some locations) snowpack and high forecasted flows might be taken as evidence that the long-term projections of reduced runoff for the Upper Colorado basin are flawed.But those projected lower flows are driven mainly by the expected increase in sublimation and evapotranspiration due to warming basin-wide temperatures. Global climate models have mixed outlooks for precipitation trends for our region, but all indicate that the high interannual and decadal variability in precipitation experienced in the last century will continue. So we can enjoy a wet year when it comes, and know that they will come again but the long-term projections still suggest a decline annual flow in the Colorado River basin.”

This article, while a valuable summary of this past winter’s record precipitation, does not emphasize  the significance to multi-decadal climate predictions because the seasonal predictions made last Fall failed to skillfully predict the actual rain and snowfall amounts and pattern that actually occurred. If the seasonal prediction models do not have this skill, there should be even less confidence in the statement that “the long-term projections still suggest a decline annual flow in the Colorado River basin.”  Their article also does not separate out the fraction of 2000-2010  reduction in Lake Mead levels due to evaporation from the lake surface as contrasted with the extraction for irrigation, urban consumption and other uses.

A better approach, in my view, is to follow the recommendations in our paper

Hossain, F., D. Niyogi, J. Adekoke, G. Kallos, R.A. Pielke Sr., 2011: Making sense of the water resources that will be available for future use. EOS Forum, Vol. 90, No. 17, 26 April 2011, 144-145. Copyright (2011) American Geophysical Union

where we wrote [highlight added]

“We … need a vulnerability assessment approach to evaluate the effect of environmental and societal threats to fresh water. This vulnerability concept requires the determination of the major threats to these resources, not only from climate but also from other social and environmental issues such as the ones described above. After these threats are identified for each resource, the relative risk from natural and human-caused climate variability and longer-term change should be compared with other risks so that the optimal mitigation or adaptation strategy can be adopted. The advantage of this vulnerability strategy, which should be location-specific, is that even if the forecast of water availability due to, say, climate or other threats were deemed to be unfounded years later, the optimal mitigation or adaptation strategy identified from multiple threats should have allowed for this margin of error during planning. In essence, such an approach guarantees a higher chance of success than would a one-dimensional strategy such as one based on projections only from global climate models that are reported in literature [Schneider et al., 2007].”

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