Climate Change’s Effect on Supply and Demand in the Upper Basin

UNIVERSITY OF DENVER WATER LAW REVIEW ANNUAL SYMPOSIUM 2013: ADDRESSING SUPPLY AND DEMAND IMBALANCES IN THE COLORADO RIVER BASIN

Denver, Colorado   April 12, 2013

Climate Change’s Effect on Supply and Demand in the Upper Basin

As part of their annual symposium, the University of Denver Water Law Review hosted a number of presenters focused on the imbalances in supply and demand in the Colorado River Basin.  Brad Udall spoke on the role of climate change in affecting supply and demand in the Colorado River Basin.  Brad Udall is the Executive Director of the Getches-Wilkinson Center for Natural Resources, Energy, and the Environment at the University of Colorado School of Law.  He was the lead author of the Water Sector chapter of the Global Climate Change Impacts in the United States Report and the Western Water Assessment Climate Change in Colorado Report.

Udall began his keynote address by outlining the basics of the water cycle and the role of climate change in the water cycle.  Udall explained the water cycle is the mechanism the earth uses to move heat from hot areas to cooler areas.  A warmer climate leads to more water vapor in the atmosphere.  The warmer climate generally translates to more evaporation and precipitation on a global basis, but regional imbalances still occur.  Udall explained, as the climate warms, wet places will become wetter, and dry places will become drier.

Next, Udall spoke on the impact of Hadley cells.  Hadley cells develop when evaporation at the equator rises into the atmosphere and moves toward the poles.  In the subtropics, the water evaporation cools and sinks creating a return flow back towards the equator.  Hadley cells fuel the growth of the world’s major deserts around the subtropical latitudes at 30 degrees north and south of the equator.  Udall believes Hadley cells will proliferate because of climate change and, as a result, the major deserts will continue to grow in size.

Udall then explored climate change’s impact on the supply of the Colorado River.  Udall focused on the recently completed Colorado River Basin Supply and Demand Study (“Basin Study”), which projected possible future flows at Lee’s Ferry.  The models in the Basin Study took some aspects of climate change into consideration.  In seventy-five percent of the fifty-year models in the Basin Study, the projected flows at Lee’s Ferry declined.  The median result of the models projected Lee’s Ferry flows would drop nine percent by 2060, with climate change as one of the contributing factors.

Udall also addressed allocation, overuse, and reservoir problems.  According to models he presented, on average by 2060 there would be a four percent annual increase in Colorado River Basin demand due to climate change.  These models did not include the increase in energy demand as a result of population growth in the Basin.  Lake Mead, which provides water to the Lower Basin, currently has a net deficit of 1.4 million acre-feet per year.  Currently, the Lower Basin covers this deficit with unused Upper Basin flows.  The Lower Basin will need to address this current deficit as the demand in the Upper Basin increases.  As demand in the Upper Basin increases, there will likely be calls on the Lee’s Ferry and shortages.

Finally, Udall discussed the level of uncertainty involved in science and climate change policy.  Udall contended a lack of certainty does not provide grounds for not taking action.  Scientists can only calibrate global climate models imprecisely because the time horizon on these models is usually 100 years into the future.  Udall emphasized that possible futures exist outside the models and there is no rational way to rank the myriad of models in use; however, Udall still believes in taking action to combat climate change.  Udall also stressed the high level of uncertainty involved when scientists reduce a global climate model to a specific region.  Ultimately, Udall wants to better integrate the efforts of scientists producing the models with the decision-makers using them because the models, even though imprecise, provide a good starting point for people active in the climate change forum.