Balancing positive and negative environmental impacts of urban greening considering future climate: A case study in the Paris region, France

Abstract :

Urban greening enhances summer thermal comfort in cities; however, vegetation requires watering and reduces solar gains on buildings, potentially increasing energy consumption for heating. A methodology was developed to investigate whether the positive effects of urban trees on human health offset the increased water and energy consumption impacts.

This method involves four steps:

1. Modelling the urban microclimate based on regional climatic data, accounting for vegetation effects;

2. Evaluating indoor temperatures and possible overheating using building thermal simulation;

3. Deriving the damage of overheating on human health,

4. Performing a life cycle assessment.

This process was applied to a case study on an urban greening project, including renovating an existing social housing building. According to the results, urban greening thanks to trees allows a decrease in outdoor air temperature around 1.7 °C (median value, 1.3 °C and 2.0 °C for 10th and 90th percentile, resp.) and a decrease in indoor temperature around 0.4 °C (median value; 0.25 °C and 0.55 for 10th and 90th percentile, resp.) during the five weeks heat wave period. Some life-cycle environmental impacts were reduced, particularly those related to damage to human health (−12.5 %), with limited impact transfer. The impact reduction due to energy savings from building renovation is higher.

While many cities invest in urban greening projects, the importance of energy renovation is often overlooked. This prioritisation may be questioned, and the analysis presented in this article could serve as a valuable tool in guiding decision-making. By using the same indicator (Disability-Adjusted Life Years, DALY) to express life cycle and overheating-related impacts, this approach enables the integration of mitigation and adaptation in decision-making processes.