Rapid Modification of Urban Land Surface Temperature During Rainfall

This paper examines runoff dynamics and heat transfer during rainfall over urban surfaces, in particular pavements. A kinematic wave approach is combined with heat storage and transfer schemes to develop a model for pervious and impervious pavements. The resulting framework is a numerical prognostic model that can simulate the temperature fields in the subsurface and runoff layers to capture the rapid cooling of the surface, as well as the thermal pollution advected in the runoff. Extensive field measurements are conducted over several types of experimental pavements in Arizona to probe the physics and then to validate the model. The experimental data and the model results are in good agreement, and their joint analysis elucidates the physics of the rapid heat transfer from the subsurface to the runoff. A demonstrative application of the model over a (hypothetical) parking lot, with impervious or pervious asphalt, is then presented. It illustrates that the rate of ground surface temperature cooling for the impervious pavement is lower than the pervious one (where infiltration is very effective at removing heat). Finally, the analysis of the energy budgets unravels the relative importance of the various physical mechanisms in transferring heat from the subsurface to the runoff and the atmosphere. This transfer is dominated by terms associated with water flux and subsurface heat extraction, while latent, sensible, and radiative heat fluxes are minor contributors. The findings underline the importance of including rainfall-induced cooling in geophysical models that seek to study urban heat islands or urban precipitation modification.