This is a very typical application of modeling being made now for water supply planning. As mentioned in a prior post, the assumption that more incorrect model projections averaged together gives a correct answer is silly. But this is how planners think, and now much of “science” has been infected by this type of thinking, under the cover of using the label “scenario.” The models are impressive, and they are useful research tools….but for future water supply planning the line between science and sophisticated sophistry becomes quickly blurred.

Roy SB, Chen L, Girvetz EH, Maurer EP, Mills WB, Grieb TM. Projecting Water Withdrawal and Supply for Future Decades in the U.S. under Climate Change Scenarios. Environ Sci Technol. 2012 Jan 12.

The sustainability of water resources in future decades is likely to be affected by increases in water demand due to population growth, increases in power generation, and climate change. This study presents water withdrawal projections in the United States (US) in 2050 as a result of projected population increases and power generation at the county level, as well as the availability of local renewable water supplies. The growth scenario assumes the per capita water use rate for municipal withdrawals to remain at 2005 levels, and the water use rates for new thermoelectric plants at levels in modern closed-loop cooling systems. In projecting renewable water supply in future years, median projected monthly precipitation and temperature by sixteen climate models were used to derive available precipitation in 2050 (averaged over 2040-2059). Withdrawals and available precipitation were compared to identify regions that use a large fraction of their renewable local water supply. A water supply sustainability risk index that takes into account additional attributes such as susceptibility to drought, growth in water withdrawal, increased need for storage, and groundwater use, was developed to evaluate areas at greater risk. Based on the ranking by the index, high risk areas can be assessed in more mechanistic detail in future work.

Click here for the full paper (fee).