NOAA, Mantua (2010) NOAA (2010) Modified from McCabe et al., s Dust Bowl. 1950s drought

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1 Interannual to Multidecadal Climate Variability Effects on Sustainable Groundwater for Agriculture Jason Gurdak, PhD Assistant Professor Department of Geosciences San Francisco State University High Plains aquifer Acknowledgements Bret Bruce, USGS, Denver, CO Brian Clark, USGS, Little Rock, AR Kevin Dennehy, USGS, CO Randy Hanson, USGS, San Diego, CA Pete McMahon, USGS, Denver, CO Rheannon Scheiderer, USGS, Little Rock, AR USGS, National Water Quality Assessment (NAWQA) Program USGS, Groundwater Resources Program, Office of Groundwater UNESCO Groundwater Resource Assessment under the Pressures of Humanity and Climate change (GRAPHIC) Natural Climate Forcings El Niño/Southern Oscillation (ENSO): 2 6 year cycle NOAA, 2010 Natural Climate Forcings Pacific Decadal Oscillation (PDO):( ) & year periodicities Mantua (2010) Winter anomalies and atmospheric circulations Atlantic Multidecadal Oscillation (AMO): year periodicities NOAA (2010) NOAA, 2008 Natural Climate Forcings Modified from McCabe et al., 2004 Motivation: Coupling between global climate cycles and hydrogeologic processes is poorly understood. Effects of ENSO, PDO, AMO on Groundwater Resources? Recharge? Nitrate Fate & Transport? 1930s Dust Bowl High Plains Ogallala aquifer Denver Mississippi Embayment Regional aquifer study (MERAS) Memphis 1950s drought

2 Motivation Estimated Withdrawals from Principal Aquifers in the U.S. Maupin and Barber ( ): USGS Circular 1279 Motivation Estimated Withdrawals from Principal Aquifers in the U.S. Maupin and Barber ( ): USGS Circular 1279 Maupin and Barber, 2005 USGS NAWQA Study Design: Source, Transport, and Receptor USGS NAWQA Study Design: Source, Transport, and Receptor 10 year groundwater-quality study Analyzed A l d 180 chemical compounds and physical properties from: domestic (private) wells, - 70 public-supply wells, - 50 irrigation wells, and shallow monitoring wells. focus of talk Gurdak et al., 2009 Vadose Zone Research Network Recharge Rates ( 3 H and Cl ) Controlled by land use and climate Monitoring well McMahon et al., 2006, WRR

3 Conversion of Rangeland to Irrigated Cropland Affects Water Quality Conversion of Rangeland to Irrigated Cropland Affects Water Quality Gurdak et al., 2009 Gurdak et al., 2009 Episodic Recharge Event 2004 second wettest year on record (snow in November and January) Episodic Chemical Mobilization Event Irrigated Irrigated Field Rangeland Field Rangeland before after Hydrologic Time Series GW Levels (1930 Precipitation (1888 GW Pumping (1978 Stream Flow (1924 Stream Quality (1938 GW Quality (1937 Tree Ring (1476 Singular Spectrum Analysis (SSA) Transform from time domain to frequency domain. Relatively Wet Relatively Dry ENSO index (Wolter and Timlin) PDO index (Mantua and Hare) AMO index (Enfield et al.) Modified from Hanson et al., 2004

4 Results: Singular Spectrum Analysis High Plains Aquifer: Variance in GW Levels ENSO PDO AMO Estimate Recharge using Spectral Analyses Hydrologic-Time Series (HTS) Method PDO Affects Recharge Rates & Mechanism t = transit time Lag-Correlation Coefficients = 0.65 to 0.98 t = phase lag yr -1 ) (mm y Rec charge Focused Recharge during +PDO Diffuse Recharge recharge flux north central south water table water table McMahon et al., 2006, Water Resources Research Gurdak et al., 2007, 2008, Vadose Zone Journal MERAS Hydrologic Time-Series Network GW Levels (1935 Stream Flow (1905 Tree Ring (1004 Climate (1863 (US Historical Climate Network) Post-SSA Climate-Cycle Cycle Extrapolation: Autoregressive (AR) model: 2 example precipitation sites Variance / Periodicity 73% / PDO, AMO ENSO index (Wolter and Timlin) PDO index (Mantua and Hare) AMO index (Enfield et al.) 98% / ENSO, PDO, AMO

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6 Motivation: Availability of GW in the MERAS? USGS Groundwater Resources Program Clark et al., In Review, USGS Professional Paper Mississippi River Valley MODFLOW-2005 Model alluvial aquifer Simulated Water-Level Change % loss of 2007 storage. 13 layers. +50, calibration wells. 6,000 mile of streams. < 130 yr life expectancy. Modified from: Clark et al., In Review, USGS Professional Paper Plunging syncline, axis parallel to river. 5 aquifers and 4 confining units. Conclusions: Understanding GW Sustainability Quantifying spatiotemporal p patterns of climate variability and effects on groundwater will be crucial to improve our understanding of resource sustainability. ENSO and PDO important controls on recharge, GW levels, storage, and contaminant transport. Questions Jason Gurdak jgurdak@sfsu.edu web site: Geosciences Department, San Francisco State University Conceptual models of GW systems must consider climate forcings on these timescales. Potential ti predictability over multi-year/decade d timescales. Preferred periods for artificial recharge, agricultural practices, and other best-management t strategies. t Discriminate human impacts from natural variability (not clear how climate change will affect climate cycles). High Plains Ogallala aquifer Mississippi Embayment Regional aquifer