Implications to aquifer storage from climate-driven shifts in
water-balance partitioning: Indiana, Midwest USA
Abstract
Documented trends in the timing and intensity of precipitation events
have been met with associated hydrologic changes in water-balance
partitioning. Changes in land use, initiation and length of the growing
season and associated irrigation practices, timing of autumn leaf
senescence, snow accumulation and melt, flooding, and drought all affect
the hydrological processes of infiltration, evapotranspiration, and
runoff. This study is an investigation of trends in groundwater recharge
over space and time in the temperate climate of the Midwest USA. It
tests the hypothesis that increasingly intense precipitation events
resulting in extreme runoff events might be short-circuiting processes
of infiltration and groundwater recharge by lowering the residence time
of water in upland landscapes, while increasing infiltration in lowlands
and riparian corridors. The climate-driven changes in precipitation
events can be more easily linked to the documented increasing stream
discharge trends than trends in groundwater levels. In this ongoing
study, multiple methods were utilized to calculate annual and monthly,
or seasonal, potential aquifer recharge amounts and trends in
unconsolidated aquifers in Indiana and surrounding watersheds. Because
observation wells in Indiana are sparsely distributed, estimates of
groundwater recharge for selected wells were used for calibration and
validation of a 40-year spatially continuous water balance (U.S.
Geological Survey Soil Water Balance v 2.0, SWB2) model that solved for
potential groundwater recharge (net infiltration) at a daily time step
and was analyzed at annual and monthly intervals. Using estimates of
annual net infiltration from the SWB2 model, 40-year temporal trends
calculated on space-time cubes suggest that over 50% of the model
domain is experiencing statistically significant increases (p
< 0.006) in potential groundwater recharge. Trend analyses of
unconfined water levels from 1980-2019 were conducted, finding that
water levels in 8 (out of 9) climate divisions in the state are
increasing (rising) in 6 of the 8 climate divisions. The distribution of
increasing water tables reflects the same spatial distribution as the
annual estimates of recharge generated by the SWB2 model.