“Water year” 2010 ends next week, making this a good time to take stock of our historic position on the Colorado River. And by a couple of different measures, things are truly historic:
- The latest forecast (and right now forecasting amounts to tiny fractions of in inch) puts Lake Mead’s surface elevation at 1084.14 feet above sea level at midnight Sept. 30, the official end of the water year. That is the lowest end of a water year since 1936, when Mead was being filled for the first time.
- The latest weekly forecasts show Mead dropping below 1083 during the third week in October, which by another measure (lowest surface level at any point in the year) drops below the lowest point of the drought of the 1950s. That’s the point at which we can unambiguously say Mead is the lowest it’s been since they filled it in the 1930s.
- Perhaps more importantly, the surface elevation level translates to an end-of-year storage level of 10.1 million acre feet of water, which is by far the lowest storage level at the end/start of a water year on record. This is the measure that matters the most, and by this measure we’ve been lower than the 1950s levels for a while. (Total storage for a given surface elevation decreases as the lake silts up.)
Click on the image for a bigger version, but it’s pretty easy to see at a glance what’s been happening. Since the late 1990s, the reservoir that supplies water to Las Vegas, LA, San Diego, Phoenix and the vast farm empire of Imperial County has been in decline.
The U.S. Bureau of Reclamation released the latest draft of its 2011 Annual Operation Plan last week, with a preliminary summary of the year just past. In short, it was dry:
Inflow to Lake Powell has been below average in nine of the past eleven water years (2000-2010). Although slightly above average inflows occurred in 2005 and 2008, drought conditions in the Colorado River Basin persist. Provisional calculations of the natural flow for the Colorado River at Lees Ferry, Arizona, show that the average natural flow since water year 2000 (2000-2010 inclusively) is 12.0 maf (14,800 mcm). This is the lowest eleven-year average in over 100 years of record keeping on the Colorado River.
Lake Powell, located upstream, is the collection point for most of the Colorado’s flow. Reduced inflow there means less water to be released for downstream users.
It is important to remember that, despite the drought conditions, releases from Lake Powell have been sufficient during each of those 11 dry years to meet the Upper Colorado Basin states’ legal obligations under the Colorado River Compact. Drought has eliminated the surpluses on which the lower basin had come to depend, in the process laying bare the real problem with Colorado River Management. (see my May post for an explanation of the problem.)
But numbers, schmumbers, right? Via NASA, some pictures that tell the story better than any of my pretty graphs:
(thanks to Tom Yulsman for pointing out the NASA images)