Wisconsin's Role in Great Lakes Restoration - American Water ...

Climate Variability and Groundwater Recharge in Southwest Wisconsin
Madeline B. Gotkowitz, Wisconsin Geological and Natural History Survey, Madison, WI
Doug R. Joachim, Dept. of Civil and Environmental Engineering, UW – Madison, Madison, WI
Steven J. Vavrus, Gaylord Nelson Institute of Environmental Study, UW- Madison, Madison,
WI
Steven P. Loheide lI, Dept. of Civil and Environmental Engineering, UW – Madison, Madison,
WI
Kenneth R. Bradbury, Wisconsin Geological and Natural History Survey, Madison, WI
Record precipitation in 2007 and 2008 contributed to widespread groundwater flooding near
Spring Green, WI, and caused over $17 million in economic losses. About $8.5 million will be
invested in the area to mitigate such flooding and high water table conditions. We assessed
the utility of flood mitigation efforts by simulating future changes to recharge and water table
elevation. In this evaluation, eight statistically-downscaled global circulation models (GCMs)
predict daily values of precipitation, temperature, and relative humidity. These provide the
basis for the soil water balance model, which produces daily estimates of runoff and
infiltration. Infiltration is applied as recharge to the water table in a transient groundwater
model of the region. Model simulations from 1981-2000 provide a base case for comparison
to predictions from future periods of 2046-2065 and 2081-2100.
Results show that while recharge may decrease on average, the variability in annual recharge
may lead to occasional years of high groundwater levels. Under the base case, annual
recharge averages 14.1 inches across the model domain. Despite a general increase in
precipitation during both future climate periods of 2.3 inches, simulated average annual
groundwater recharge decreases 0.6 inches by 2065 and decreases an additional 1.5 inches
by 2100. The simulated decrease in average recharge is driven by increasing annual
temperatures and a resulting increase in simulated evapotranspiration. However, this set of
eight GCMs leads to a broad range in annual recharge, with the range in recharge varying
from no change from the base case to a decrease of over 7.5 inches per year. High
groundwater levels may indeed become more common despite drier conditions overall, as
suggested by a positively skewed frequency distribution of annual recharge. These results
suggest that preserving current land use in Spring Green may require implementation of the
proposed mitigation efforts.
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