Water Resources Engineering (WRE) connects engineering hydrology and hydraulics with global, economic, environmental, and societal issues. Our student Ethan Washburn makes this connection here…
The article Understanding Uncertainties In Future Colorado River Streamflow, by Julie Vano et al. was published in the January 2014 Bulletin of the American Meteorological Society. This article relates to the WRE domain of hydrology and the specific issue of streamflow predictions for the Colorado River. Predictions have been made which estimate decreases in runoff values ranging from 6% to 45%. The authors of this article explored the uncertainties in the methodologies and models upon which the predictions were based. The study compared the following factors used to generate streamflow predictions: number of Global Climate Models (GCMs), number of Regional Climate Models (RCMs), emission scenarios, total number of projections, spatial resolution, downscaling techniques, and Land Surface Models (LSMs). Table 1 from the article summarizes these details for studies used determine Colorado River streamflow estimates (Vano et al., 2014). Figure 1 from the article shows the flow of different approaches used to generate streamflow projections (Vano et al., 2014). The authors identified four sources for the uncertainties of the future predictions of streamflow for the Colorado River. In order of greatest to least importance they are: GCM and emission scenario selection; spatial scale and topographic dependence of the projections; representations of land surface processes; and statistical downscaling methods. Based on this article, there are several factors that go into predicting streamflow and even small changes can result in large differences in predicted values. According to James Jacob’s article, The Sustainability of Water Resources in the Colorado River Basin, there is no significant trend in precipitation in the area for the last 110 years. However, there is an increasing trend in surface temperatures with the most recent 11-year average exceeding previous recorded values (James, 2011). James concludes that models strongly suggest that warmer temperatures will result in a decrease in Colorado River streamflow.
In a broader context, the WRE issue related to the hydrology around the Colorado River has economic and environmental impacts. The Colorado River has two large reservoirs (Lake Mead and Lake Powell) and several small reservoirs which provide water for more than 30 million people in arid regions of the United States and Mexico. The ongoing drought in the area is outside of normal 20th century climate variability, and many fear that a permanent shift to a drier climate is underway (Vano et al., 2014). A reduction in streamflow would result in less water available for the people serviced by the Colorado River Basin. It relates to economics because, a reduction in the water supply could lead to increased water supply costs. There are also significant environmental impacts related to the uncertainties of our models. As our climate becomes increasingly different the historical models become increasingly inaccurate. One area for research is improving these models.

Table 1

 

Figure 1: Approaches to Developing Streamflow Projections

Figure 1: Approaches to Developing Streamflow Projections

References:

Jacobs, J. 2011. The Sustainability of Water Resources in the Colorado River Basin. Winter Issue of The Bridge on Sustainable Water Resources, 41 (4), pp. 6-12. Available at: https://www.nae.edu/File.aspx?id=55285 [Accessed: 8 Apr 2014].

Vano, J. A., Udall, B., Cayan, D. R., Overpeck, J. T., Brekke, L. D., Das, T., Hartmann, H. C., Hidalgo, H. G., Hoerling, M., Mccabe, G. J. and Others. 2014. Understanding Uncertainties In Future Colorado River Streamflow. Bulletin of the American Meteorological Society.

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