Are high-capacity wells mitigating or intensifying climate change effects on stream baseflow in the state of Wisconsin (USA)? A case study 1984–2014

Baseflow is generally cooler in temperature and of better quality than storm flow, and it maintains stream flow during dry periods. Decreases in baseflow levels and increases in stream temperatures lead to decreases in the diversity of aquatic species. Agricultural irrigation was once almost exclusively practiced in the arid western portion of the United States, but in the past few decades, the use of irrigation has accelerated in the humid Great Lakes region of the United States. In Wisconsin, the number of high-capacity wells increased substantially from less than 4000 in 1983 to over 16,000 in 2014. With precipitation generally increasing in the second half of the twentieth century and projected to increase through the twenty-first century in Wisconsin, baseflow would be expected to increase as well. However, there are areas in Wisconsin where baseflow has declined. This study found that as the number of wells withdrawing from the confined aquifer increased, the baseflow tread increased from a declining trend of approximately 15% to an increasing trend of almost 67%. This increase illustrates a mitigating effect to the decreasing trend related to climate variables alone. As the number of wells withdrawing from an unconfined aquifer increases, the already declining baseflow trend intensified from 18% to over 28%, illustrating the contribution high-capacity wells have in basin baseflow decline in areas where aquifers are connected to surface water. This study highlights that environmental stresses are related to baseflow declines across the state of Wisconsin and that the decreases are being mitigated or completely reversed by the addition of groundwater to the surface from below the confining layer.