SNF - Wind driven rain impact of urban microclimate

Wind-driven rain (WDR) refers to rain droplets, driven by the wind, impacting on surfaces in the built environment, leading to wetting and drying processes affecting buildings and the urban microclimate. The proper understanding and management of WDR in the built environment as water source is required since evaporative cooling from urban surfaces wetted by rain is seen as one of the future avenues for mitigating urban heat island effects and heat waves, which are expected to increase due to climate change. A second reason is that WDR is a main agent of deterioration of building materials and, as such when climate change leads to more extreme weather events such as heavy rain, it is expected that building damage risks will increase in the coming decades. The study of WDR in the urban environment includes the study of a rich pallet of surface and contact phenomena, at short and longer time scale and governed by a wide range of physical processes. These phenomena involve spreading, splashing, rolling or bouncing, coalescence of droplets, hemiwicking on the surface, absorption in a porous medium, evaporation, film forming and runoff under gravity.

The research proposed in this project aims at an accurate understanding of the impact of WDR on the urban microclimate and thermal comfort, modeling wetting and drying processes at the droplet and the urban environment scales. To do so, an urban microclimate model will be developed including WDR, which is validated by well-designed experiments and can be used as a tool to analyze the effect of evaporative cooling as mitigation measure to improve the urban microclimate and thermal comfort. Highlight of this model is that it incorporates film forming and runoff, taking into account all relevant droplet physics of multiple impacting droplets as well as the influence of heat and mass exchange at the liquid-air interphase. The research will be performed by two PhDs including experimental investigations, modeling, validation and application cases. PhD A: discrete approach of wetting and drying processes for multiple rain droplets impacting on urban surfaces leading to an accurate modeling of the WDR load. PhD B: analysis of wetting and drying processes in the built environment and their impact on the urban microclimate and thermal comfort, leading to a detailed study of evaporative cooling at neighborhood scale using a validated WDR-urban microclimate model.