From The Glen Canyon Institute (David Wegner):
The 2017–2018 runoff from the Upper Colorado River Basin into Lake Powell is history and it turned out to be on the short side coming in at 42% of normal. The six major tributaries that feed the waters of Lake Powell are currently running anywhere from 5% to 36% of normal. The result is that the levels of both Lake Powell and Lake Mead continue to drop and the risk of a shortage call in 2019 or 2020 is increasing daily.
Some would argue that this is exactly why the reservoirs were built and are so important — to help the region get through droughts. That logic is predicated on the assumption that we are in a drought and not a significant shift in the overall climate, weather, and hydrologic conditions. Droughts are short term events that have a start and an end point. What we are in now, with near unanimous concurrence from scientists across the United States, is a long term shift in the nature, amount, shape and mobilization of the runoff in the Upper Colorado River Basin. A new baseline centered on the concept of aridification of the American Southwest requires a more long-term strategic approach.
So what does this mean to the potential for a shortage call on the Colorado River?
First, some background. The management of the Colorado River is accomplished through the delicate act of balancing the Law of the River with available reservoir storage and actual runoff. Up until 2000–2002 there had always been adequate supply to meet the demand in both the Upper and Lower Colorado River basins. In fact in most years there was more water available then needed and extra water (surplus) was available to the states and water users. In 2001 the Secretary of the Interior, Bruce Babbitt, signed guidelines on how the three lower basin states could use surplus Colorado River water. How quickly times changed.
In 2002, without any fanfare or marching bands, Colorado System Demand surpassed available water supply. In 2002 the basin states realized that shortages in the future were possible. They also realized that with normal levels of inflow and release a structural deficit of over a million acre feet per year would continue to drive the reservoir elevations down. These facts prompted the basin states, at the urging of Secretary of Interior, to establish criteria for avoiding a shortage call — the result was the 2007 Shortage Criteria. Renegotiation on the 2007 Shortage Criteria are due to begin in 2020.
The 2007 Shortage Criteria set the elevations where action is required in both reservoirs Powell and Mead. The basin states and Reclamation developed a formula and set of decision points for when, the quantity, and how water would be moved from Lake Powell to Lake Mead.
1,075′ and its implications
There are three Lake Mead elevation trigger points (1,075, 1,050 and 1,025 feet) with the 1025 ft. elevation requiring mandatory consultation to identify and implement additional actions to keep Lake Mead functioning. As Lake Mead continues to fall more severe restrictions are implemented for the Lower Basin states and Mexico. The first of these elevation trigger points is when Lake Mead hits elevation 1,075 ft or lower on January 1st. Passing 1,075 on January 1 opens the door for the federal government to exert more control over management of the Lower Colorado River. Something the states do not want to have happen.
In order to avoid the issues of federal direction of Colorado River management the seven states have been working to develop Drought Contingency Plans to supplement the 2007 Shortage Criteria. The intent of the Drought Contingency Plans is to avert shortage declarations and to voluntarily share any cuts in water releases from Lake Mead. The problem is that while some additional water can be squeezed from conservation and efficiency, the large volumes of water needed to make up for the continual decline in supply simply are not readily available. What is required is a rethinking of how we live with the available water supply in the Colorado River Basin.