CHARACTERIZING THE EFFECTS OF HYDROMETEOROLOGY AND STREAM NETWORKS ON URBAN STREAM TEMPERATURE RESPONSE TO PRECIPITATION

In urban streams, steeply rising storm hydrographs can be accompanied by rapidly changing water temperature, if water being flushed into the stream is significantly different in temperature than pre-event stream water. The objective of this research was to examine network effects and characterize seasonal and event hydrometeorological influences on urban stream temperature responses to precipitation. At seven sites, with watershed areas ranging from 1-150 km², in Winston-Salem, North Carolina, discharge and water temperature were monitored from September 2010 to July 2011. Temperature increases >2 C occurred in all seasons, with high intensity, short duration storms producing the largest increases. A small number of temperature surges (>1°C increase in 15 minutes) were observed and occurred in both winter and summer. For most analyzed storms, the largest temperature increases occurred in small streams, and the sites with the largest drainage areas had temperature increases >0.5 C less frequently than sites with smaller drainage areas. The site with the smallest watershed also frequently reached its peak temperature earlier than other sites. In addition to the magnitude of temperature change in response to precipitation, the duration of a stream’s response may be an ecologically relevant parameter, but there were no spatial patterns within the data nor were hydrometeorological parameters strongly correlated with duration. Quantifying and predicting the duration of stream temperature responses remains a challenge. Our research suggests that urban stream temperature changes in response to precipitation are not limited to summer storms and are most pronounced small watershed scale (<10 km²). Future research should focus on understanding the ecological and biogeochemical effects of such temperature changes and on developing appropriate mitigation strategies.