The 10 most water-sustainable cities have, on average, 160 cloudy days and 93 days of full sun. The 10 least water-sustainable cities are nearly the mirror image: 90 cloudy days and 168 sunny days per year. (For those who like statistics, let’s just say the differences in these averages are highly significant.).
While the bottom five cities for water sustainability (the very sunny Las Vegas, Phoenix, Mesa, Tucson, and L.A.) grew by an average of 37 percent from 1990 to 2000, according to Census data, the five most water-sustainable cities actually lost population, with an average loss of 3 percent.
In fact, of the five most water-sustainable (and cloudy) cities, only Chicago grew. The other four—Cleveland, Milwaukee, Detroit and New Orleans—all lost population.
There are two reasons for concern here.
First, rapidly growing populations threaten to outpace water supplies in many cities. Even in the relatively wet Southeastern United States, recent droughts have revealed that booming populations are straining water supplies in places like North Carolina and Atlanta.
These trends will be worsened by climate change, which is predicted to increase drought risk throughout the United States. And the regions most at-risk for climate-change-induced drought encompass the cities that today have both the lowest water sustainability and rapidly growing populations.
In short, Americans are collectively moving from the places that are best equipped to deal with climate change to those that are least equipped.
The second reason for concern is that supplying water to regions that lack abundant local supplies requires intense manipulation and alteration of rivers. Massive dams store water for diversion into long canals—artificial rivers for cities that lack their own. The result is blocked rivers, decimated populations of salmon and other native fish, and parched deltas and estuaries (where rivers meet the sea).
For example, dams on the Colorado River provide the water to support the rapid growth of cities from San Diego to Las Vegas to Phoenix. But as a result, the Colorado River rarely flows to the sea and its delta has now been reduced to 5 percent of its original size.