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SPECIAL SECTION: GROUNDWATER RESOURCES ASSESSMENT UNDER THE PRESSURES OF HUMANITY AND CLIMATE CHANGE

Physically Based Simulation of Potential Effects of Carbon Dioxide–Altered Climates on Groundwater Recharge

^a USDA-ARS, Fort Collins, CO 80526
^b CSIRO Land and Water, Floreat, Western Australia 6014, Australia
^c CSIRO Land and Water, Canberra, ACT 2601, Australia (retired)
^* Corresponding author (tim.green{at}ars.usda.gov).

Received 9 July 2006.

Increasing concentrations of atmospheric CO₂ will alter regional rainfall and evapotranspiration regimes that drive groundwater recharge. Improved methods of simulation and analysis are needed for assessing the potential sensitivities of soil–water–vegetation systems to climate change. This study demonstrates methods for generating climates and simulating soil–water and vegetation dynamics in response to current and double CO₂ climate sequences. Climate change scenarios came from dynamic equilibrium (constant CO₂) runs of a general circulation model (GCM). Based on historical climate and GCM output, a stochastic point weather generator produced realizations of the cross-correlated daily climate variables. A numerical model of infiltration, variably saturated flow, and evapotranspiration produced temporal distributions of groundwater recharge rates for various soil–vegetation environments. Climate change scenarios were simulated for two climatic zones in Australia: subtropical (North Stradbroke Island, Queensland) and Mediterranean (Gnangara, Swan Coastal Plain, Western Australia) having summer- and winter-dominated rainfall regimes, respectively. In these simulations, groundwater recharge values were affected by the dynamic growth and senescence of vegetation, as changes in temperature and rainfall regimes affected growth rates and leaf areas. The temperature regime dominated the hydrologic response in the Mediterranean climate, and the rainfall frequency–duration regime dominated in the subtropical climate. For the simulated Mediterranean climate change (14% rainfall increase), changes in mean recharge values ranged from –34% to +119%, while subtropical climate change (37% rainfall increase) caused increases from 74 to > 500%. Changes in mean recharge rate, interannual variability, and temporal persistence were related to the soil and vegetation characteristics. The model was useful for quantifying complex, nonlinear responses to climate change that require further exploration.

Abbreviations: ET, evapotranspiration • GCM, general circulation model • PET, potential evapotranspiration • RCM, regional climate model • SVAT, soil–vegetation–atmosphere transfer • VPD, vapor pressure deficit

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