Differences between urban and natural stream temperatures across the eastern United States

Stream temperature is inherently shaped by human activity, often reflecting reduced riparian cover, runoff from impervious surfaces, limited connectivity between groundwater and surface waters, and a host of other sources of water delivery, including stormwater, wastewater, and dam releases.  This is especially true in urbanized areas, where heat exchanges may be additionally altered by urban hydrology, delivering warm pulses of water during heavy storms that locally elevate water temperatures.  While this effect has been documented in several cities, no comprehensive summary of these impacts exists at regional and larger scales.  Our work documents the impact of urbanization on stream temperatures during wet and dry periods in small streams for several cities across the eastern United States.  Our work seeks to benchmark how stream temperature surges during storms and average stream temperatures in more urbanized watersheds differ from nearby forested, less-impacted sites.  We show that the occurrence and magnitude of temperature surges as well as the statistical characteristics of dry-day stream temperature varies with climate and level of imperviousness.  Interestingly, comparisons within and across cities demonstrate the complex responses of stream temperature to urbanization, suggesting that the human imprint on stream temperature signals is highly variable and reflects site specific characteristics rather than regional influences.