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

Authors: Green, Timothy; BATES, B.C. - CSIRO; CHARLES, S.P. - CSIRO; FLEMING, P.M. - CSIRO

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2007
Publication Date: 8/23/2007
Citation: Green, T.R., Bates, B., Charles, S., Fleming, P. 2007. A physically based method for simulating effects of CO2-altered climates on groundwater recharge. Vadose Zone Journal 2007; 6: 597-609.

Interpretive Summary: Increased concentrations of atmospheric CO2 will alter regional rainfall and potential evapotranspiration regimes that drive groundwater recharge. Improved methods are needed for assessing the potential sensitivities of the soil-water-vegetation system to climate change. This study includes methods for generating climates and simulating soil-water and vegetation dynamics in response to current and double-CO2 climate sequences. Simulated climates come 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 realisations of the cross-correlated daily climate variables. A numerical simulator of infiltration, variably saturated flow and evapotranspiration produced temporal distributions of groundwater recharge rates for various soil-vegetation environments. The methods were applied to two climatic zones in Australia: subtropical (North Stradbroke Island, Queensland) and mediterranean (Swan Coastal Plain, Western Australia) having summer- and winter-dominated rainfall regimes, respectively. For the simulated mediterranean climate change (14% rainfall increase), changes in mean recharge values ranged from a 34% reduction to an increase of 119%, while subtropical climate change (37% rainfall increase) caused increases from 74% to over 500%. Changes in mean recharge rate, inter-annual variability and temporal persistence were related to the soil and vegetation characteristics. In these simulations, groundwater recharge values were affected by the dynamic growth and dieback 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. Such sensitivities require further exploration.

Technical Abstract: Increased concentrations of atmospheric carbon-dioxide (CO2) will alter regional rainfall and potential evapotranspiration regimes that drive groundwater recharge. Improved methods are needed for assessing the potential sensitivities of the soil-water-vegetation system to climate change. This study includes methods for generating climates and simulating soil-water and vegetation dynamics in response to current and double-CO2 climate sequences. The methods were applied to two climatic zones in Australia: subtropical (North Stradbroke Island, Queensland) and mediterranean (Swan Coastal Plain, Western Australia) having summer- and winter-dominated rainfall regimes, respectively. For the simulated mediterranean climate change (14% rainfall increase), changes in mean recharge values ranged from a 34% reduction to an increase of 119%, while subtropical climate change (37% rainfall increase) caused increases from 74% to over 500%. In these simulations, groundwater recharge values were affected by the dynamic growth and dieback 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. Such sensitivities require further exploration to improve predictions of climate change impacts on groundwater resources.