INVESTIGATING THE BEHAVIOR OF URBAN STREAM TEMPERATURES DURING SUMMER STORMS IN ATLANTA, GA

Urban stream temperature regimes exhibit distinct differences in baseflow temperature and thermal response to precipitation events as compared to natural streams. While responses of urban stream temperatures at baseflow have been well documented in the literature, the thermal response associated with storm flow is less understood. Rapid rises and falls in stream water temperature after summer rainstorms, termed a ‘heat pulse,’ have been observed in urban streams in several studies. We investigated how catchment size, imperviousness in close proximity to the watershed outlet, and whole watershed imperviousness influences the magnitude and frequency of heat pulses coincident with summer storms at thirty two sites in the Atlanta, GA metropolitan area. We examined fifteen-minute stream temperature and discharge data from May to August for six years (2014-2019), extracting the timing and magnitude of heat pulses across all sites. These responses were compared with estimates of imperviousness using the National Land Cover Database. All sites experienced a wide range in heat pulse frequency (zero to over 100 pulses during one summer) and magnitude (up to 5 °C change over 15 minutes). Our preliminary results highlight that impervious cover alone is not explanatory of the number or magnitude of heat pulses. Smaller catchments (>5 km2) tend to have more pulses than larger catchments, but size does not organize the mean pulse magnitude or the maximum pulse. Our results increase our understanding of the responses of stream temperatures in urban areas, of critical importance to maintaining healthy waterways as urbanization continues to increase worldwide.