Application of a Fine-Scale Modeling Approach to Assess Broad-Scale Changes in Stream Salmonid Habitat in a Changing Climate

Despite abundant research exploring how climate change may affect population demographics of stream fishes (e.g., survival, growth, and relative abundance), tools are needed to provide accurate, fine-scale stream temperature predictions over large spatial extents encompassing multiple fisheries management agencies and jurisdictions. As such, a fine-scale modeling approach based on artificial neural networks was developed to forecast reach-specific thermal conditions under different climate-change scenarios across the Upper Midwest, USA (i.e., Michigan, Minnesota, and Wisconsin). Specifically, models collated landscape and climatic data to predict individual stream temperatures across watersheds and states with relatively high accuracy (r2 = 0.71–0.76). Collectively, models predicted widespread increases in stream temperature across the study region averaging 1.5 °C through 2087, with substantial warming in Wisconsin and Minnesota but moderate warming in Michigan streams. For instance, the extent of warm-transitional (July mean water temperature 19.5–21.0 °C) and warmwater (>21.0 °C) habitats in Wisconsin—currently 40% of stream kilometers—was projected to reach up to 63% in 2042 and 71% in 2087, with concomitant reductions in growth and survival of stream salmonids (e.g., brook charr Salvelinus fontinalis, brown trout Salmo trutta, and rainbow trout Oncorhynchus mykiss). Overall, our modeling approach provides managers with a stream-specific yet spatiotemporally broad tool for predicting the magnitude and distribution of stream warming amid climate change that can be used to prioritize efforts for stream salmonid management and conservation. Such information is critical for developing state and regional climate adaptation strategies for Upper Midwest streams and coordinating thermal habitat management activities (e.g., groundwater conservation and riparian/watershed rehabilitation) among fisheries and aquatic resource agencies and across jurisdictions.