Projections for April through July runoff to Lake Powell in 2007 remain low. The water supply picture in the Colorado River Basin neither improved nor weakened in May. The May final unregulated inflow forecast for April through July runoff into Lake Powell is 4.0 million acre-feet. This is only 50 percent of average.
May was a month with periods of much above average temperatures with higher than expected inflow. Unregulated inflow to Lake Powell in May 2007 was 1,578,000 acre-feet (69 percent of average). The peak snowmelt-runoff inflow to Lake Powell for 2007 occurred on May 23, 2007 when inflow reached 31,600 cfs. The water surface elevation of Lake Powell increased by 9.3 feet in May 2007.
While inflow was higher than projected in May, the projection for inflow to Lake Powell in June is not so bright. There is very little snowpack remaining in the Upper Colorado River Basin and inflow to Lake Powell in June is projected to be only about 35 percent of average.
Reservoir storage is currently 12.74 million acre-feet, or 52 percent of capacity. The current elevation of Lake Powell (June 6, 2007) is 3,610.1 feet, 89.9 feet from full pool elevation of 3,700 feet. The elevation is now likely near the peak for the year. The elevation of Lake Powell is likely to increase until mid-June and then begin to decline. The projected elevation of Lake Powell on July 1, 2007 is 3,610.4 feet.
Upper Colorado River Basin Drought
The Upper Colorado River Basin is experiencing a protracted multi-year drought. Since 1999, inflow to Lake Powell has been below average in every year except one.
In the summer of 1999, Lake Powell was essentially full with reservoir storage at 23.5 million acre-feet, or 97 percent of capacity. Inflow to Lake Powell in 1999 was 109 percent of average. The manifestation of drought conditions in the Upper Colorado River Basin began in the fall months of 1999. A five year period of extreme drought occurred in water years 2000, 2001, 2002, 2003, and 2004 with unregulated inflow to Lake Powell only 62, 59, 25, 51, and 49 percent of average, respectively. Lake Powell storage decreased through this five-year period, with reservoir storage reaching a low of 8.0 million acre-feet (33 percent of capacity) on April 8, 2005. Drought conditions eased in water year 2005 in the Upper Colorado River Basin. Precipitation was above average in 2005 and unregulated inflow to Lake Powell was 105 percent of average. Lake Powell increased by 2.77 million acre-feet (31 feet in elevation) during water year 2005. But as is often the case, one favorable year does not necessarily end a protracted drought. In 2006, there was a return to drier conditions in the Colorado River Basin. Unregulated inflow to Lake Powell in water year 2006 was only 73 percent of average.
Water year 2007 will be another year of below average inflow. The current projection for spring runoff into Lake Powell is only 50 percent of average. Projected inflow to Lake Powell for the entire 2007 water year is 68 percent of average. With 2007 projected to be a below average inflow year, one sees that over the past 8 years (2000 through 2007, inclusive) inflow to Lake Powell will have been below average in all but one year (2005). Reservoir storage in Lake Powell and Lake Mead has decreased over the past 8 years. Reservoir storage in Lake Powell and Lake Mead is currently 52 and 50 percent of capacity, respectively.
This update courtesy Tom Ryan, Bureau of Reclamation