A lab experiment for optimizing the cooling efficiency and the watering rate of pavement-watering

Abstract

Due to their tendency to absorb heat, urban materials participate in the formation of urban heat islands thus contributing to increased health risks during heat waves. Since 2013, the city of Paris has experimented in situ pavement-watering campaigns as an emergency cooling tool during heat-waves. These studies have highlighted the influence of the materials being watered on the optimal watering strategy to adopt. In this regard, a laboratory experiment was developed to study the thermal behaviour of various urban materials under heat-wave conditions with or without watering. Here, results from watering an asphalt road structure with twelve different rates are presented to fine-tune the process for optimal cooling. The sample undergoes a heat-wave-like 24-hour cycle inside a climate chamber. Two distinct cooling regimes are highlighted versus the watering rate, corresponding to the increase of evaporation with the watering rate until maximum evaporation rate is reached. This aspect was used to maximise the cooling efficiency of the method while minimising the water consumption. Using the surface heat budget, the evaporative cooling flux was also determined. Pavement-watering was found to have a great impact on heat stored in the pavement and released to the atmosphere. Results otherwise compare favourably with field observations.