Colorado River

A scenario of 20% reduction in annual Colorado River flow by 2057 due to climate change results in a near tenfold increase in the probability of annual reservoir depletion by 2057. Flexibility in current management practices could mitigate some of the increased risk due to climate change-induced reductions in flows.

Water managers and their stakeholders are now considering how the reliability of water supplies might be affected if drought conditions become more frequent (Fulp 2005). The US Secretary of the Interior, in consultation with the Basin states and other stakeholders, developed an interim plan for managing Lake Powell and Lake Mead, particularly for drought and low reservoir conditions, through 2026. One major emerging concern is how climate change might impact water availability. Water managers and their stakeholders are now considering how the reliability of the water supply would be threatened if recent decreased precipitation and water runoff is the new norm (Fulp, 2005).

Balaji Rajagopalan and colleagues (2009) assessed how both population growth and a changing climate might tax the Colorado water supply. They quantified the annual risk to the water supply for the 50-year period 2008-2057 under a suite of demands – such as urban growth and various management alternatives – based on assumptions about known historical climate variability and projected reductions in stream flow due to climate change. They considered two scenarios of climate change that are within the range of current projections: a linear reduction in annual average flow of 10% and 20% over the 50-year period.

Five alternatives were considered, each consisting of two components: a demand component and shortage criteria in operating the reservoir. The alternatives highlight the sensitivity of risk to various combinations of demand or shortage policy. The demand component includes reductions that range from 2.5% (alternative A) to 8% (alternative E) of the projected demand by 2057, and the reservoir levels at which deliveries are first curtailed range from 36% (alternative A) to 50% (alternative E) of full reservoir capacity.

Projected growth-driven demand overlaid with historical climate variability results in only a low probability of annual reservoir depletion through 2057 (<5%). In contrast, a 20% reduction in average annual Colorado river stream flow due to climate change by 2057 results in a near tenfold increase in the probability of annual reservoir depletion by 2057 (~51%). Rajagopalan and colleagues (2009) suggest, however, that flexibility in current management practices – including reducing 1) water demand by 2.5-8% of the projected demand (by 2057) and 2) reservoir levels at which deliveries are first curtailed from 36-50% – could mitigate some of the increased risk due to climate change-induced reductions in flows.

References: