Cooling effect of water-holding pavements made of new materials on water and heat budgets in urban areas

People often suffer from the intense summer heat in Japan. This trend is increasing in urban areas because of the heat island effect and global warming. We evaluated the effect of pavements made of traditional and new materials on water and heat budgets. We expanded the NICE (NIES Integrated Catchment-based Eco-hydrology) model to simulate the water and heat budgets for the various materials and to reproduce the cooling of water-holding pavement (consisting of porous asphalt and water-holding filler made of steel by-products based on a silica compound) by evaporation (NICE-URBAN); the results were compared with those from the simplified empirical model. NICE-URBAN simulated the cooling of water-holding pavement during the intense heat of summer in an urban area more correctly than the empirical model. Because the model estimates that the air temperature above the water-holding pavement is 1–2 °C lower than that above the lawn and 3–5 °C lower than that above the building rooftop, this material has a powerful positive cooling effect in combination with a lawn for a passive cooling effect. The simulation of NICE-URBAN showed that the surface temperature decrease in water-holding pavement is closely related to evaporation from the surface, the water volume of the pavement and the surface reflectance. The procedure used to integrate the model simulation with land use planning to effectively select and use ecosystem service sites is a very powerful approach to create thermally pleasing environments in a megalopolis.