Downstream Dissipation of Storm Flow Heat Pulses: A Case Study and its Landscape-Level Implications

Storms in urban areas route heat and other pollutants from impervious surfaces, via drainage networks, into streams with well-described negative consequences on physical structure and biological integrity. We used heat pulses associated with urban storms as a tracer for pavement-derived stormwater inputs, providing a conservative estimate of the frequency with which these pollutants are transported into and through protected stream reaches. Our study was conducted within a 1.5-km reach in Durham, North Carolina, whose headwaters begin in suburban stormwater pipes before flowing through 1 km of protected, 100-year-old forest. We recorded heat-pulse magnitudes and distances travelled downstream, analyzing how they varied with storm and antecedent flow conditions. We found heat pulses >1°C traveled more than 1 km downstream of urban inputs in 11 storms over one year. This best-case management scenario of a reach within a protected forest shows that urban impacts can travel far downstream of inputs. Air temperature and flow intensity controlled heat-pulse magnitude, while heat-pulse size, mean flow, and total precipitation controlled dissipation distance. As temperatures and sudden storms intensify with climate change, heat-pulse magnitude and dissipation distance will likely increase. Streams in urbanized landscapes, such as Durham municipality, where 98.9% of streams are within 1 downstream km of stormwater outfalls, will be increasingly impacted by urban stormwaters.

Duke Scholars

Author Emily S. Bernhardt Biology

Author Brian McGlynn Earth and Climate Sciences

Author Dean L. Urban Environmental Social Systems