A Process Based Modeling Approach to Assess Temperature Impacts of Riparian Vegetation Management in a Southwestern Wisconsin Trout Stream

ABSTRACT Rising water temperatures driven by climate change threaten culturally and economically important salmonid fisheries throughout the Upper Midwest. Unsuitable thermal regimes degrade the effectiveness of habitat restoration projects in the region, thus strategies for mitigating peak summer stream temperatures are of interest to state and non‐profit fisheries managers. Using a process‐based stream temperature model, this study explores the thermal impact of riparian tree planting and tree removal in a 179 km 2 watershed in the unglaciated Driftless Area of southwestern Wisconsin. By creating hypothetical riparian vegetation scenarios and systematically adding and removing woody vegetation from the banks, we explore the influence of shade and channel geometry on July stream temperatures with an emphasis on salmonid thermal suitability. We used this model to analyze an 18.5 km study reach to identify management areas that have the most potential to buffer downstream water temperatures throughout the summer with added shade. We developed a downstream thermal change (DTC) metric to measure the magnitude and downstream distance of temperature change following stream alterations. The magnitude of stream cooling was mediated by channel width in our scenarios, with more pronounced thermal changes in narrower stream reaches ( p < 0.05). Modeled tree planting scenarios decreased the maximum July maximum weekly average temperature (MWAT) and July maximum weekly maximum temperature (MWMT) within the study reach by 0.52°C and 0.53°C, respectively. This study offers a workflow using free and open‐source modeling tools to determine the thermal impact of restoration and prioritize future management efforts in cold water stream ecosystems.