Georgia averages 50 inches (127 cm) of rain a year. Arizona averages 13 (30 cm). Which is more likely to suffer water shortages? I’m fascinated by the non-trivial nature of the answer.

The problems of both lakes Lanier and Mead have been well chronicled. At Lanier in 2007, we were within three months of Atlanta running out of water. On Lake Mead, we’re – well, we’re all running around like our hair’s on fire, but we’ve got more than a three month supply sitting in our ginormous reservoirs. You can run the numbers and see some dire scenarios on the dry site of the range of probability, but our hair is substantially less flammable than Atlanta’s.

Lake Lanier

To refresh the important details, Atlanta’s hair-on-fire moment came after what was very much a garden-variety drought, nothing at all out of the normal envelope of climate variability. We’ve made it through a drought far more significant here in the Colorado River Basin in terms of depth and duration, much farther out of the normal range of variability (11 driest years on record, etc.), and yet all the Colorado’s users have gotten their full allocation every year during the drought.

There are two reasons for this. One is a system that was engineered with very large storage as a buffer against multi-year droughts. The second is an interlocking network of institutional arrangements for the distribution of that water that have been used to sort out arguments over how to administer things as the big reservoirs dropped.

The southeastern United States lacks both. Which is a very circuitous introduction to an interesting news release out of the University of South Carolina this week:

Water scarcity in the western United States has long been an issue of concern. Now, researchers studying freshwater sustainability in the U.S. have found the Southeast, with the exception of Florida, does not have enough water capacity to meet its future needs either.

“For more than a century, the Southwest has been the focus of long-running legal disputes over water resources, but the Southeast is now becoming a more contentious region for water use,” said Dr. Will Graf, a geographer in the University of South Carolina’s College of Arts and Sciences.

Graf was part of the team that did the recent “Cadillac Desert” empirical reconstruction in PNAS. While the southwest, Divas of the Arid, got all the attention, Graf and colleagues point out implications for the southeast as well:

“It turns out that the Southeast has a relatively small margin of water surplus for the future,” said Graf.

And we’ve got the institutional and engineering framework in place to try to work out our problems. The southeast is still down near the bottom of that learning curve.