Empa - MAMM

An increasing number of people are living in cities where they are exposed to the specific urban weather and climate conditions. Understanding and predicting these conditions is therefore of growing and major importance for several applications such as: urban heat island (UHI) mitigation, air quality and building energy consumption. Accurately simulating urban weather and climate is however still challenging because of multiple scales of the air flow and various processes (e.g. radiation trapping, evapotranspiration) that coexist in the urban atmosphere. Current urban climate models based on meso-scale models do not model correctly the urban (in-canyon) vegetation.

This research aims to improve the performance of a state-of-the-art urban canopy model (UCM) by accurately representing the impact of urban (in-canyon) vegetation, allowing precise and city-wide high resolution simulations during heat wave events. The improvements include models for the interactions between trees, buildings and the atmosphere at the local (i.e. neighbourhood) scale. Field observations and high-fidelity CFD simulations are used for the model evaluation. The improved UCM is then coupled with the weather and climate model COSMO in order to evaluate the impact of the urban environment on the urban climate. The resulting modelling system is finally used to perform accurate urban climate simulations over the cities of Zurich (European medium sized city, temperate climate) and Singapore (Asian mega city, tropical climate) during heat wave events. Urban heat island mitigation measures based on urban vegetation are assessed.