Heat-Down: Modelling Smarter Integrated Stormwater Management Solutions for Cooling Cities

A project funded by the Swiss National Science Foundation
(Project ID 200021_201029)

There is growing evidence that heat waves are becoming more frequent under climate change. Heat waves associated with higher daytime temperatures and reduced nighttime cooling are exacerbated in urban areas due to highly impervious surfaces, limited air humidity, anthropogenic heat, and reduced ventilation. This presents a threat to public health, increased energy consumption for cooling, reduction in economic productivity, increased heat related damage on infrastructure and a reduction of overall people’s well-being. Also associated with climate change and intensified by the increasing level of urbanization is the challenge of stormwater management. Urban pluvial flooding (or surface flooding) is one phenomena that causes larger damages when compared to other natural hazards. In adapting and minimizing these risks, cities have been adopting blue-green infrastructure solutions (such as green roofs, infiltration basins and rain gardens) and reducing the reliance on grey infrastructure (e.g. building underground reservoirs or pipelines. Blue-green infrastructure in cities, have been demonstrated to mitigate UHI effects. However, with the exception of a few studies, the quantitative potential of these systems on UHI mitigation and its relation to the water requirements has not yet been thoroughly explored.

Heat-Down aim to understand how elements of smart urban stormwater systems in the era of digitalisation and blue-green infrastructure solutions, can contribute to UHI mitigation and improve urban thermal comfort.

Modelled land surface temperatures for the Inner Zurich region in Switzerland using the TARGET Model (preliminary model simulation) at 2pm during the heatwave on 22nd June 2017, how will the availability of stormwater harvesting & implementation of Blue-Green Infrastructure enable local cooling?

The project combines expertise from Switzerland, Australia and The Netherlands on urban stormwater management, urban climatology and Blue-Green Infrastructure planning and, through the development of an integrated model to provide support to urban planners, investigate the potential of smarter stormwater management to enrich the multiple benefits of existing and new ‘green’ and ‘grey’ water infrastructure and practices to:

  • Provide daytime heat mitigation and improved urban thermal comfort to city dwellers
  • Effective harvesting and re-use of stormwater in a manner that no only provides heat mitigation, but also delivers on other benefits such as flood protection, waterway health and biodiversity enrichment
  • Identify strategies that cities can use to adapt to the impending challenges brought about by urbanization and climate change

The Heat-Down project will enable the use of microclimate modelling in an exploratory and spatial planning context, as part of integrated urban water management and future city planning in the digitalization era.

Modelling Approach

The proposed integrated model will be built on top of the UrbanBEATS planning-support system. UrbanBEATS was developed to support the planning of Blue-Green Infrastructure in urban environments and has expanded towards the quantification and assessment of Blue-Green planning strategies (both infrastructure and policies) from a multi-functional perspective. To enable city-wide assessment, we are adapting an existing microclimate modelling approach known as The Air-temperature Response to Green/blue-infrastructure Evaluation Tool (TARGET) (Broadbent et al., 2019). Through the combination of both models, planners and stakeholders can engage in rigorous scenario analysis to explore robust strategies for sustainable and liveable city planning.

Proposed Integrated Modelling Framework illustrating the linkage between Work Packages and the coupling of Total Urban Water Cycle model with stormwater management options, the modified TARGET Model, which constitute the Fast Urban Climate Model (diagram partly adapted from Broadbent et al., 2019) – ET stands for Evapotranspiration, Tac is the street level air temperature, Tb is the air temperature above the urban canopy layer, Tsurf is the surface temperature, RH is the relative humidity, Ta is the reference air temperature.

  • Broadbent, Ashley M., et al. “The Air-temperature Response to Green/blue-infrastructure Evaluation Tool (TARGET v1. 0): an efficient and user-friendly model of city cooling.” Geoscientific Model Development 12.2 (2019): 785-803.

Case Studies

Two unique case studies representing two highly contrasted spatial scales, urban densities, climates and infrastructure will be used to validate the Heat-Down project model developments. The City of Zurich in Switzerland may face a significant increase (up to 3ºC) in day and night temperature, according to climate scenario simulations (Funk et al., 2018). It is the largest city in Switzerland and continues to experience urban expansion; it is located next to a major natural water body (the lake Zurich), which may have a positive impact on reducing UH effects. Recently, the City of Zurich published a plan to mitigate urban heat impacts (Stadt Zurich, 2020), in which different approaches are proposed and preliminarily assessed. In contrast, the second case study, the City of Melbourne (Australia), has ambitious integrated water management and climate adaptation targets that will not be achieved through current practices. Novel approaches that see stormwater as a precious resource are imperative (City of Melbourne, 2017). It
faces hot and relatively dry summer climate, has a separate sewer system suitable for in-sewer stormwater storage and a few unique stormwater management and urban heat mitigation facilities (known as the Innovation Districts).

Proposed case studies for Heat-Down, maps depict green and blue spaces and built environment (Sources: Swiss GIS Data from Kanton of Zurich, Australian GIS Data from data.vic.gov.au, Logos – City of Zurich from stadtzuerich.ch, City of Melbourne from melbourne.vic.gov.au)

The Team

We have an interdisciplinary team across three universities and one industry partner.

João P. Leitão (Project Lead)
Senior Scientist
Urban Water Management (Eawag)
Peter M. Bach
Research Scientist
Urban Water Management (Eawag)
Kerry Nice
Research Fellow
Melbourne School of Design (Melbourne Univ.)
Frans van de Ven
Associate Professor
Civil Engineering and Geosciences (TU Delft)
Cintia Dotto
Senior Sustainability Office (Climate Change)
City of Melbourne