Evaluation of Groundwater Responses to Short-Term Climate Fluctuations in the Central Great Basin

The mission of the Southern Nevada Water Authority (SNWA) is to manage regional water resources and develop solutions to ensure adequate future water availability.  One aspect of that undertaking entails portfolio diversification by obtaining additional groundwater supplies, while maintaining a commitment to sustainable use of water- and environmental resources.  Toward that commitment, in 2008 SNWA began an investigation to estimate the first-order impacts of climate variability and future climate change on groundwater resources in the central Great Basin over a planning horizon of 50 to 100 years.  For the region, the investigation: (1) studied historic climate changes and droughts; (2) tested downscaling methodologies; (3) applied downscaled global climate model (GCM) predictions; (4) determined drought frequencies and magnitudes from dendrochronologies; and (5) examined the influence of historical short-term climate fluctuations on groundwater levels.

Screening over 9,000 wells from the U.S.G.S. National Water Information System database ultimately produced about 20 hydrographs suitable for comparison to precipitation records.  However, because each well has a unique construction and hydrologic response, the comparison required devising a metric independent of these factors: the range fraction.  This metric scales between 0 and 1 and ratios the height of a water level above minimum against the maximum observed potentiometric variation.  Graphical resemblance to regional precipitation averages failed to reject an initial hypothesis that potentiometric changes largely mirrored precipitation.  Lag times between wet or dry intervals and valley-floor potentiometric responses varied from about 1 to 4 years, and averaged about 2 years.  Maximum valley-floor water level changes were typically between 1 and 2 feet.  With appropriate simplifying assumptions, these results can be combined with dendrochronologic and GCM results to estimate groundwater response to different drought and future temperature-precipitation scenarios.