Hydrologic Transport of Thermal Energy from Pavement

Abstract

Heat island impacts generated from the built (urban) environs have been recognized for decades as a component of climate change. Increasing imperviousness of the urban environments generates a demonstrable impact on hydrologic cycle, chemical and particulate matter loads in rainfall-runoff, and the thermal parameters of the atmosphere and rainfall-runoff of the built environments. From this broader context, a specific monitoring and modeling study was conducted to examine the dynamic, intra-event thermal transfer between pavement and rainfall-runoff for an asphalt-paved urban source area. Measured results were compared with a series of published models. Event-based hydrologic results illustrated a correlation between peak flow and thermal energy flux as well as between initial pavement temperature and thermal energy flux to runoff. Transfer of energy from the pavement to runoff was primarily a flow-limited process, and cumulative volume was correlated with cumulative thermal energy transfer on a storm event basis. Based on 17 events, only the runoff volume from Tropical Storm Fay (August 21, 2008) was heat-limited (water volume was not correlated to heat flux), resulting in a thermal first-flush. Energy balance components in each model were examined for capability to reproduce measured results. All models performed similarly, but models would benefit by field validation of these components using direct measurement, particularly long wavelength radiation.