Evaluating Future Water Resource Risks in the Driftless Midwest from Climate and Land Use Change

Abstract

Assessing the impacts of future changes in rainfall, temperature, and land use on streamflow and nutrient loads is critical for long-term watershed management, particularly in the unglaciated Driftless Area with steep slopes, erodible soils, and karst geology. This study evaluates the Kickapoo watershed in southwestern Wisconsin to examine how projected climate change and cropland expansion may affect hydrology during the mid- (post-2050) and late century (post-2070). Climate projections suggest temperature increase, wetter springs, and drier summers over the century. Annual average streamflow is projected to decline by 5–40% relative to 2000–2020, primarily due to a 5–15% reduction in groundwater discharge. While land use changes from prairie to cropland had a limited additional impact on streamflow, it increased annual average total phosphorus (TP) by 5.67–10.08%, total nitrogen (TN) by 1.08–2.34%, and sediment by 3.11–6.07%, frequently exceeding total maximum daily load (TMDL) thresholds in comparison to the climate change scenario. These findings suggest that although land use changes exacerbate nutrient and sediment pollution, climate change remains the dominant driver of hydrologic alteration in this watershed. Instead, converting 18% (~290 km2) of cropland to grassland could enhance baseflow (0.84–14%), and reduce TP (30–45%), TN (3–5%), sediment (80–90%), and meeting TMDL 90% of the time. These findings underscore the importance of nature-based solutions, such as prairie restoration, supporting adaptive management to reduce nutrient load, sustaining low flows, and strengthening hydrologic resilience, that support key Sustainable Development Goals. This approach offers valuable insights for other unglaciated watersheds globally.