Abstract
The application of Global Climate Model (GCM) output to a hydrologic model allows for comparisons between simulated recent and future conditions and provides insight into the dynamics of hydrology as it may be affected by climate change. A previously developed numerical model of the Suwannee River Basin, Florida, USA, was modified and calibrated to represent transient conditions. A simulation of recent conditions was developed for the 372-month period 1970-2000 and was compared with a simulation of future conditions for a similar-length period 2039-2069, which uses downscaled GCM data. The MODFLOW groundwater-simulation code was used in both of these simulations, and two different MODFLOW boundary condition “packages” (River and Streamflow-Routing Packages) were used to represent interactions between surface-water and groundwater features. The hydrologic fluxes between the atmosphere and landscape for the simulation of future conditions were developed from dynamically downscaled precipitation and evapotranspiration (ET) data generated by the Community Climate System Model (CCSM). The downscaled precipitation data were interpolated for the Suwannee River model grid, and the downscaled ET data were used to develop potential ET and were interpolated to the grid. The future period has higher simulated rainfall (10.8 percent) and ET (4.5 percent) than the recent period. The higher future rainfall causes simulated groundwater levels to rise in areas where they are deep and have little ET in either the recent or future case. However, in areas where groundwater levels were originally near the surface, the greater future ET causes groundwater levels to become lower despite the higher projected rainfall. The general implication is that unsaturated zone depth could be more spatially uniform in the future and vegetation that requires a range of conditions (substantially wetter or drier than average) could be detrimentally affected. This vegetation would include wetland species, especially in areas inland from the coast.
Highlights
Global Climate Models (GCMs) are important tools for simulating historical climate and projecting future climate, including precipitation [1]
The application of Global Climate Model (GCM) output to a hydrologic model allows for comparisons between simulated recent and future conditions and provides insight into the dynamics of hydrology as it may be affected by climate change
This study demonstrates how downscaled GCM data can be combined with a groundwater flow model to gain insight into potential effects of climate change
Summary
Global Climate Models (GCMs) are important tools for simulating historical climate and projecting future climate, including precipitation [1]. The downscaling method can be statistical or dynamic, and both methods have varying degrees of uncertainty. Comparisons of several models over the conterminous United States indicate that root-mean square errors of precipitation predictions differ by less than 0.1 mm/day between statistical and dynamic methods [2]. Analyses of uncertainty in statistical downscaling methods indicate significant variations between stochastic and regression-based techniques [3]. Dynamic downscaling involves embedding a smaller-scale regional climate model within the GCM [4]. This approach resolves atmospheric processes on a smaller scale and with physically consistent processes, but is computationally intensive and sensitive to uncertainties in the GCM-derived boundary conditions
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