Are the North American deserts expanding? Some climate signals from groundwater storage conditions

The areal average underground water storage in a natural catchment is directly manifested by the low flow or baseflow features from that catchment. Accordingly, an analysis was conducted of the annual lowest flows of twelve prototype near-pristine river basins with long streamflow records and minimal confounding human activities in four deserts of North America, namely the hot Chihuahua, Sonora, and Mojave deserts and the cold Great Basin desert. Except possibly for those in the Sonora Desert, the analysis has revealed no evidence that these few remaining pristine watersheds have undergone consistent or significant negative terrestrial water storage trends over the past century in their riparian aquifers and therefore no evidence of any increase in their aridity. Thus, if groundwater conditions in these deserts have been deteriorating, this suggests that it is likely attributable to human activities rather than to climate change. The situation in the Sonora Desert is unclear, on account of remaining questions regarding human impact. The reliability of the methodology is further probed by comparing the shorter term groundwater changes in all four deserts with well-known concurrent sea surface temperature changes in the Pacific Ocean; the groundwater storage changes appear to be related, albeit weakly, to the El Nino-Southern Oscillation and to the Pacific Decadal Oscillation; in the three hot deserts, the El Nino-Southern Oscillation effect decreases with eastward distance from the Pacific Ocean, but not that of the Pacific Decadal Oscillation. Copyright (C) 2011 John Wiley & Sons, Ltd.