Temperature Surges Caused by Hot Runoff in Urban Watersheds
Abstract
Urbanization and the change it induces in land cover - such as the increase in imperviousness - are well known to raise air temperature in cities. The potential impact of urbanization on the temperature of surface water bodies, on the other hand, is less studied and understood. During and after rainfall, the interaction of cooler precipitation with hot urban pavements leads to hot runoff, and its merger with urban streams can result in an abrupt change in water temperature. This thermal pollution can be detrimental to aquatic ecosystems, and the understanding of this phenomenon is essential to mitigate its negative impacts. In order to identify the frequency and magnitude of such temperature surges, as well as to analyze their relation to land cover, we analyzed data from temperature sensors located at 25 USGS stream gaging stations in the eastern region of the United States. These gages were retained from a larger surveyed sample since they had the required temporal resolution (better than 15 min) and were located in urban watersheds. The identification of surges consisted of first isolating temperature jumps of at least 0.5 ° C in 15 minutes occurring simultaneously with water flow increase, which was used as a surrogate for runoff input. Next, the magnitude of the surges was defined as the difference between the maximum stream temperature (following the runoff event) and the baseline temperature. Applying this procedure, surges as high as 8.6 ° C were observed in Hickey Run, DC, and Moores Run, MD. In general, more than half of the surges were higher than 1 ° C. In some watersheds that rate exceeded 80%, along with over 100 surge events during the summer and spring of 2017 and 2018. The results also demonstrate that development in the watershed is the best predictor of the number of surges (Spearman correlation coefficient equal r = -0.72). Regarding the magnitude of temperature surges, the drainage area is the best predictor ( r = -0.74). Overall, our results highlight the potential for a hydrological urban heat island to develop with higher temperatures in urban surface bodies compared to their rural counterparts, and identify its main physical drivers that are linked to urbanization of land cover.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H41M1890Z
- Keywords:
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- 1803 Anthropogenic effects;
- HYDROLOGY;
- 1833 Hydroclimatology;
- HYDROLOGY;
- 1836 Hydrological cycles and budgets;
- HYDROLOGY;
- 1847 Modeling;
- HYDROLOGY