April 16, 2012
A severe change in the hydrological cycle is expected, and it is expected to hit snow- or ice-dominated areas most severely. This change is expected because of an increase in greenhouse gases. This change at first was expected to increase the amount of potable water but now the dynamics of the changes have been analyzed more closely. We have found out that as temperatures increase less precipitation will fall as snow and snowmelt will occur sooner in early spring and not in the summer or autumn when the water is needed most. The snowmelt and rain will cause an overflow in rivers and causing loss of potable water to the oceans when there are not sufficient reservoirs.
And it is not necessarily changes in precipitation that causes all this because the amount of precipitation generally remains the same. It is the change in temperature that changes the seasonal runoff patterns in these snowmelt-dominated areas because less water falls as snow and more falls as rain, preventing the normal release of water as snowmelt and the quick flowing of rainwater.
The Colorado River of the western United States was determined to be one of the four snowmelt-dominated rivers that also do not have sufficient reservoir capacity to prevent overflow and loss to the ocean. To determine these, first the snowmelt-dominated areas were determined by the ratio of accumulated annual snowfall to annual rainfall and those with R greater than 0.5 were considered snowmelt-dominated. Next, to determine reservoir capacity, the runoff was compared to the reservoir capacity. These determined areas underestimate the area and population affected because populations downstream and other farther areas also depend on the water that comes from snowmelt-dominated areas.
The aspect of the most importance is water supply. In the Western United States, the Colorado River is the most important contributor of water supply. There are no predicted changes in precipitation, only a change in seasonal snowpack and snowmelt, as discussed earlier. The winter snow is expected to decrease and the melting is expected to occur a whole month earlier. On top of that, there is currently not enough reservoir capacity to prevent water loss to the ocean.
The Colorado River, along with the Rio Grande and San Joaquin, supply water to Wyoming, Colorado, New Mexico, Arizona, Nevada, California, Utah, Texas, and parts of Mexico. These rivers, especially the Colorado River, were determined by the Interior Department in 2011 to deplete by 8 to 14 percent over the next 40 years. But in a more optimistic short-term study done in 2009 at the University of Colorado at Boulder, the risk of the Colorado River depleting its reservoirs remains below 10 percent at least through 2026. It was also said as a result of this study that even if the worst drought scenario were to occur, we wouldn’t feel the effects immediately because we have a great storage capacity along the Colorado River, storing almost four times the annual flow of the river. But in between 2026 and 2057, the risk of reservoir depletion increases seven times.
These studies on the Colorado River can comfort us because we know we are relatively safe until 2026, but 2026 is approaching fast and we cannot get comfortable. Large scale changes such as shift in seasonal snowmelt and decreasing amounts of snowfall took decades to develop and will take decades to reverse, if it is even at all possible. The most plausible solution for now is that we must find ways to direct and store this precipitation so we do not lose it to the ocean.
This post was authored by Alejandra Rocha ’12, a senior majoring in Environmental Studies.