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Ground-water response to natural climate variability implications for the sustainability of water resources

Congress: 2008
Author(s):

Keyword(s): climate variability, ground water, recharge, sustainability
AbstractClimate change, whether caused by natural variability or human activity, has important implications for the sustainability of global fresh water resources. The sustainability of these water resources likely will be facilitated by the use of ground water, which has some capacity to balance large swings in precipitation and associated increased demands caused by drought and predicted global warming. Although climate change projections consistently predict warming air temperatures across many regions of the globe, projected precipitation changes are more complicated and not consistently predicted among the global circulation models. One reason for these discrepancies in projected precipitation change is that natural climate variability having cycles on interannual to multidecadal timescales are poorly understood and represented in the global circulation models. These natural climate cycles control complex spatiotemporal patterns in precipitation, streamflow, and ground-water recharge. For example, the interaction between interannual and multidecadal climate cycles may control the distribution of precipitation and, in turn, affects water needs for irrigation and recharge to ground water. Because natural climate cycles on interannual to multidecadal timescales can augment or diminish human stresses on ground water, the responses in water levels and ground-water storage can be dramatic when different climate cycles lie coincident in a positive (wet) or negative (dry) phase of variability. Thus, understanding climate cycles on these timescales has particular relevance for management decisions during drought and for water resources close to the limits of sustainability because even marginal changes in supply and demand are of great importance. Therefore, the objective of this study was to quantify the responses in ground water levels of the High Plains aquifer in the United States (US) to spatiotemporal variability of natural climate cycles. With nearly one-third of all ground-water pumping in the US occurring in the High Plains aquifer (450,700 km2), the water resources supplied by this regional aquifer, like many important aquifers worldwide, are susceptible to the affects of human stresses and natural climate variability. Using singular spectrum analysis of long-term hydrologic time series (mid- 1800s to present), the signal of ground-water pumping was removed and natural variations were identified in all tree ring, precipitation, and ground water time series as partially coincident with known climate cycles, such as El Nino/Southern Oscillation (2 to 6 years), North American Monsoon System (6 to 10 years), Pacific Decadal Oscillation (10 to 25 years), and Atlantic Multidecadal Oscillation (50 to 80 years). Climate-varying recharge and water-level fluctuations were most significantly correlated to the Pacific Decadal Oscillation. Estimated climate varying recharge rates (196 to 476 mm yr-1) were considerably larger than previous estimates of diffuse recharge (0.2 to 110 mm yr-1), indicating the importance of preferential flow during recharge to the High Plains aquifer. The results indicate the importance of interdecadal-climate cycles, help elucidate important mechanisms of climate- varying recharge, and may help managers sustain this valuable water resource. These findings support the conclusion that understanding natural climate variability is a necessary step toward predicting ground-water response under climate change and managing the long-term sustainability of water resources.
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