Last updated: May 2025
The project focused on implementing multilayer blue-green roofs in four Italian cities—Cagliari, Palermo, Perugia, and Viterbo—as part of a broader European initiative to address climate change impacts in urban environments (1,3). Spearheaded by a collaboration between multiple Italian universities and the Dutch company Metropolder, the project began in 2019 (1,3). The primary goal is to enhance urban resilience by integrating green infrastructure capable of mitigating climate-related urban hazards such as flooding and heat waves, which are increasingly severe due to climate change and urbanisation (2,3). The multilayer blue-green roofs combine the ecological benefits of traditional green roofs with an added water storage layer, allowing them to retain rainfall and manage runoff effectively (2,3). This dual function helps reduce pluvial flooding and the urban heat island effect, while also improving thermal insulation in buildings (2,3). Each installation was planted with low-maintenance, climate-adapted vegetation, and equipped with sensors to monitor ecohydrological and thermal performance over several years (1,3). These roofs are capable of retaining up to 100% of rainfall from significant events, thereby easing the burden on urban drainage systems and contributing to climate adaptation in Mediterranean cities (2,4).
photo of the green roof project
https://pubmed.ncbi.nlm.nih.gov/37244101/
Overview
Nature-based solution
- Nature on buildings (external)
- Green roofs
- Green walls or facades
Key challenges
- Climate action for adaptation, resilience and mitigation (SDG 13)
- Climate change adaptation
- Environmental quality
- Air quality improvement
- Green space, habitats and biodiversity (SDG 15)
- Green space creation and/or management
- Regeneration, land-use and urban development
- Regulation of built environment
- Water management (SDG 6)
- Stormwater and rainfall management and storage
Principal problems in Functional Urban Area (FUA)
- Climate-Related Hazards
- Urban flooding (stormwater)
- Heat stress & Extreme temperatures
Key priorities
Climate action (adaptation and/or mitigation), Biodiversity (conservation and/or restoration)
Focus
Creation of new green areas, Creation of green roofs and walls
Project objectives
- To maximise the water storage capacity of building roofs while increasing thermal insulation (ref 1)
- Contribute to the creation of innovative, sustainable, and resilient cities (ref 3)
- Improve the air quality, promote biodiversity, and increase the aesthetic value of the overall city (ref 2)
- The aim is to identify the most efficient approach to maximise the benefits of this nature-based solution (ref 4)
- Increase urban biodiversity by attracting various plant and small animal species (ref 3)
Implementation activities
The Polder roof systems include a water retention layer, providing buildings with runoff control similar to green fields. The Smart Flow Control technology integrates sensors that measure rainfall, temperature, water depth, and wind speed. WARREDOC is coordinating the validation of the Polder roof solution by installing four green roofs in Italy (Universities of Perugia, Viterbo, Palermo, and Cagliari), in collaboration with TU Delft, where the first prototype was installed. (ref 1).
In June 2019, a multilayer blue-green roof prototype was installed at the University of Cagliari. This 16 m² roof, with an 8 cm sand-based soil layer and a 10 cm storage layer, is planted with Cactaceae, a vegetation resistant to high temperatures and low water availability. It requires minimal maintenance. Data collected has been used to model ecohydrological and thermal dynamics, focusing on the benefits of flood mitigation and thermal insulation. Results from two years of monitoring are being studied to assess the potential for large-scale urban applications. (ref 2)
Additionally, an ecohydrological model was calibrated based on six months of field data. The model simulates the system's performance under current and future rainfall and temperature scenarios, helping to assess the roof's effectiveness in achieving project goals. (ref 4)
Climate-focused activities
Climate change adaptation:
- Increase urban vegetation cover to reduce urban heat island effect
- Implement green walls or roofs to lower indoor temperature and provide insulation
Main beneficiaries
- Researchers/University
Governance
Management set-up
- Led by non-government actors
Type of initiating organisation
- Researchers/university
Participatory approaches/ community involvement
- The project didn't involve any form of stakeholder participatory activities
Details on the roles of the organisations involved in the project
The WARREDOC Centre of the University for Foreigners of Perugia carries out coordination and supervision activities on both the scientific and technical activities of installing green roofs related to the Italian pilot project involving the University of Tuscia, the University of Viterbo (Unitus), the University of Cagliari (Unica) and the University of Palermo (Unipa). It takes responsibility for Output-line II (Evaluation of the suitability of the experiments in Italy), III (installation of 4 polder roofs in Italian cities) and Output-line VII (monitoring, evaluation and communication of the project). Financing body TU Delft University (Netherlands) ref 1.
Metropolder Company (Netherlands) developed the Polder roof system and Smart Flow Control technology used in the project. The company provides technical support and innovations for the water retention and management aspects of the roofs ref 1,3.
Project implemented in response to ...
... an EU policy or strategy?
Unknown
... a national policy or strategy?
Unknown
... a local policy or strategy?
Unknown
Type of enablers
Unknown
Financing
Total cost
Unknown
Source(s) of funding
- Research organisation / University
Type of funding
- Direct funding (grants, subsidies, or self-financed projects by private entities)
Non-financial contribution
Unknown
Impacts and Monitoring
Environmental impacts
- Climate change
- Lowered local temperature
- Expected lowered local temperature
- Water management and blue areas
- Increased protection against flooding
- Expected increased protection against flooding
Economic impacts
- Unknown
Socio-cultural impacts
- Unknown
Type of reported impacts
Presence of formal monitoring system
Yes
Presence of indicators used in reporting
No evidence in public records
Presence of monitoring/ evaluation reports
Yes
Availability of a web-based monitoring tool
No evidence in public records
Potential risks of implementation and trade-offs
Unknown
References
1.
Università per Stranieri di Perugia (2023). Green roofs for green and sustainable water management. Accessed on September 27, 2024, [Source link];
2.
EGU General Assembly (2024). Retention capacity and thermal properties of a multilayer blue-green roof in Sardinia: two years of monitoring. Accessed on September 27, 2024, [Source link];
3.
Cristiano, Elena, et al. (2022). Multilayer blue-green roofs as nature-based solutions for water and thermal insulation management. Accessed on September 27, 2024, [Source link];
4.
Cristiano et al. (2023). Management strategies for maximizing the ecohydrological benefits of multilayer blue-green roofs in mediterranean urban areas. Accessed on September 27, 2024, [Source link];
5.
Universita di Cagliari ( 2018). Universita di Cagliari, Italy. Accessed on September 27, 2024, [Source link];
6.
www.citypopulation.de (n.d.). Monserrato. Accessed on September 27, 2024, [Source link];
photo of the green roof project
https://iris.unica.it/retrieve/ec158e06-e95f-4373-9b04-fb79e6c37e53/nh0531129.pdf
Information about this nature-based solution was collected as part of the Naturescapes project funded by the European Union under Grant Agreement No 101084341.