Re: [asa] IPCC on Colorado River Basin

From: George Cooper <>
Date: Tue Apr 15 2008 - 13:29:23 EDT

While at an expo in Vegas last month, there was excitement and arguments over a newly discovered aquifer to the North that will augment the runoff shortage. The extent of this aquifer was not known to my cab driver. :)

Rich Blinne <> wrote:
  The IPCC just released a new report on climate change and water. Here's what they said about the Colorado River Basin:

  The Colorado River supplies much of the water needs of seven U.S. states, two Mexican states, and 34 Native American tribes (Pulwarty et al, 2005). These represent a population of 25 million inhabitants with a projection of 38 million by the year 2020. Over the past 100 years the area affected by severe or extreme climatological drought in the United States has averaged around 14% each year with the having been as high as 65% in 1934. Westward expansion of population and economic activities, and concurrent responses to drought events, have resulted in significant structural adaptations, including hundreds of reservoirs, irrigation projects, and groundwater withdrawals, being developed in semi-arid environments. As widely documented, allocation of Colorado River water to basin states occurred during the wettest period (1905-1925) in over 400 years. Recently, the Western United States has experienced sustained drought, with 30-40% of the region under severe drought since
 1999, with the lowest five-year period of Colorado River flow on record occurring from 2000-2004. At the same time the states of the U.S. Southwest are experiencing some of the most rapid growth in the country with attendant social, economic and environmental demands on water resources with associated legal conflicts (Pulwarty et al., 2005).

Only a small portion of the full Colorado Basin area (about 15%) supplies most (85%) of its flow. Estimates show that with increased climatic warming and evaporation concurrent runoff decreases would be up to 30% through the 21st century (Milly et al, 2005). Under such conditions, together with projected withdrawals, Colorado River Compact requirements may only be met 60 to 75 percent of the time by 2025 (Christensen et al. 2004). Some studies estimate that by 2050, the average moisture conditions in the Southwestern U.S. could rival conditions observed in the 1950s. These changes could occur as a consequence of increased temperatures (through increased sublimation, evaporation and soil moisture reduction), even if precipitation levels remain fairly constant. Some researchers argue that these assessments, because of model choice, may actually underestimate future declines.

Most scenarios of Colorado River flow at Lees Ferry (which separates the Upper from the Lower Basin) indicate that within 20 years, discharge may be insufficient to meet current consumptive water resource demands. The recent experience illustrates that "critical" conditions already exist in the Basin (Pulwarty et al 2005). Climate variability and change together within increasing development pressures will result in drought impacts that are beyond the institutional experience in the region and exacerbate conflicts among water users. [emphasis mine]
The drought is not all that severe right now. But, it appears that we need to continue our diligence in conserving water in the Mountain West. One of the problems is that the laws concerning water rights were drafted during the 400-year wet period referenced above.

Rich Blinne
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Received on Tue Apr 15 13:31:19 2008

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