First Name:
Elena
Last Name:
Cristiano
Type of BP
Technical solution
Typology of Non- Conventional Water Resources (NCWR) What kind of NCWR do you deal with ?:
Rainwater (RW)
What is the collection area (m2)?:
96 m² (Two twin modules of 48 m² each).
What is the material of the collection area?
Rainfall falls directly on the CAM GR surface (plants and soil)
What is the average annual rainfall (mm)?:
Average volume water harvested per year : 10-20 m3 Depending on the tank management the volume can vary (full system):
-Emptying every day: 20 m3 per year
-Emptying once a week: 10 m3 per year
-Emptying every day: 20 m3 per year
-Emptying once a week: 10 m3 per year
What is the material of the storage tank?:
Plastic
What is the storage area of the collected rainwater (m3)?:
The storage capacity of harvested rainwater is 0.7 m3 (2 tanks of 0.35 m3)
Number of population concerned by the reuse
150
What are the challenges raised by your Best Practice?
Environmental pollution, Move towards zero discharge at local level, Vulnerability to climate Change
How could you describe your Best Practice?
The intensive green roof at the University of Cagliari covers a total area of 96 m², arranged in two twin modules of 48 m² each, and was originally constructed in 1980 at the entrance of the Faculty of Engineering.
The system features a 30 cm soil layer classified as sand, supporting spontaneous CAM vegetation (Agave americana), which thrives without irrigation or regular maintenance. This vegetation and substrate layer collects and retains rainwater, effectively reducing and delaying runoff peaks, and contributes to urban flood mitigation. Any excess water is conveyed to two storage tanks, each with a capacity of 350 L, where it is stored for subsequent reuse in irrigating both the surrounding green areas and the green roof itself, thereby enhancing the system’s hydrological performance while reducing potable water demand and improving overall water resource efficiency. Since 2016, the roof has been equipped with continuous monitoring instrumentation, including rainfall and outflow gauges recording at 5-minute intervals, providing high-resolution data on retention dynamics. These measurements support ecohydrological modelling and inform climate change adaptation strategies, demonstrating the long-term environmental and hydrological value of intensive green roof systems in Mediterranean urban contexts.
The system features a 30 cm soil layer classified as sand, supporting spontaneous CAM vegetation (Agave americana), which thrives without irrigation or regular maintenance. This vegetation and substrate layer collects and retains rainwater, effectively reducing and delaying runoff peaks, and contributes to urban flood mitigation. Any excess water is conveyed to two storage tanks, each with a capacity of 350 L, where it is stored for subsequent reuse in irrigating both the surrounding green areas and the green roof itself, thereby enhancing the system’s hydrological performance while reducing potable water demand and improving overall water resource efficiency. Since 2016, the roof has been equipped with continuous monitoring instrumentation, including rainfall and outflow gauges recording at 5-minute intervals, providing high-resolution data on retention dynamics. These measurements support ecohydrological modelling and inform climate change adaptation strategies, demonstrating the long-term environmental and hydrological value of intensive green roof systems in Mediterranean urban contexts.
Please describe your Best Practice in 5 keywords?
CAM green roof;, Flood mitigation;, Urban development;, Resilient city; Hydrological model;
Please provide any links to useful documentations (including website)presenting your Best Practice
In which area has your Best Practice been implemented ?
Urban area, Other (Please specify below)
Other area
Dense Urban
Best Practice location implementation (Country)
Italy
Localisation
POINT (9.11052189302 39.228627219025)
Who are the beneficiaries and/or the target group of your Best Practice ?
Local Population, Municipalities, Other (Please specify below)
Other beneficiaries
University community, including staff, students, attendees, etc
f the Best Practice has been implemented within a partnership, who were your partners ?
University of Cagliari is the only partner involved
Have you involved stakeholders?
No
What are the obstacles to implementation of Best Practice ?
Other (Please specify below)
Other obstacles
Cagliari's green roof faced no major obstacles. Built in 1980 with CAM vegetation, its stable structure allowed a smooth 2016 retrofit with monitoring sensors, presenting no construction, maintenance, or operational barriers .
Did you receive funding for the research and development of the proposed BP?
Yes
Please indicate the source of funding
National funding
What difficulties you have faced to access the funding ?
Highly competitive funding calls.
Has your Best Practice been validated/upscaled?
For the intensive CAM green roof at the University of Cagliari, the Best Practice has been validated but not physically upscaled.
The roof’s hydrological performance has been confirmed through field monitoring between 2016 and 2019, during which rainfall and outflow were continuously measured. These data were used to calibrate the EHSM ecohydrological model (Viola et al., 2017), demonstrating the system’s retention capacity and effectiveness in reducing runoff peaks.
Although the system has not been implemented at a larger scale, its potential for upscaling has been evaluated. Scenario analyses conducted by Cristiano et al. (2023), assessed the costs and benefits of widespread green roof deployment in urban areas worldwide, highlighting the contribution such installations could make to stormwater management, urban flood mitigation, and climate adaptation.
In summary, the practice is scientifically validated through monitoring and modelling, while large-scale implementation remains a potential future step supported by research-based assessments.
Cristiano, E., Urru, S., Farris, S., Ruggiu, D., Deidda, R., & Viola, F. (2020). Analysis of potential benefits on flood mitigation of a CAM green roof in Mediterranean urban areas. Building and Environment, 183, 107179.
Cristiano, E., Farris, S., Deidda, R., & Viola, F. (2023). How much green roofs and rainwater harvesting systems can contribute to urban flood mitigation? Urban Water Journal, 20(2), 140-157.
Viola, F., Hellies, M., & Deidda, R. (2017). Retention performance of green roofs in representative climates worldwide. Journal of Hydrology, 553, 763-772.
The roof’s hydrological performance has been confirmed through field monitoring between 2016 and 2019, during which rainfall and outflow were continuously measured. These data were used to calibrate the EHSM ecohydrological model (Viola et al., 2017), demonstrating the system’s retention capacity and effectiveness in reducing runoff peaks.
Although the system has not been implemented at a larger scale, its potential for upscaling has been evaluated. Scenario analyses conducted by Cristiano et al. (2023), assessed the costs and benefits of widespread green roof deployment in urban areas worldwide, highlighting the contribution such installations could make to stormwater management, urban flood mitigation, and climate adaptation.
In summary, the practice is scientifically validated through monitoring and modelling, while large-scale implementation remains a potential future step supported by research-based assessments.
Cristiano, E., Urru, S., Farris, S., Ruggiu, D., Deidda, R., & Viola, F. (2020). Analysis of potential benefits on flood mitigation of a CAM green roof in Mediterranean urban areas. Building and Environment, 183, 107179.
Cristiano, E., Farris, S., Deidda, R., & Viola, F. (2023). How much green roofs and rainwater harvesting systems can contribute to urban flood mitigation? Urban Water Journal, 20(2), 140-157.
Viola, F., Hellies, M., & Deidda, R. (2017). Retention performance of green roofs in representative climates worldwide. Journal of Hydrology, 553, 763-772.
Is there the potential to exploit/outscale the Best Practice?
Yes, the intensive CAM green roof at the University of Cagliari has strong potential for replication and upscaling. Its modular and simple design, based on a 30 cm sandy soil layer and low-maintenance CAM vegetation (Agave americana), allows it to be easily reproduced on other roofs without extensive technical modifications. The system’s ability to collect and retain rainfall, reduce runoff peaks, and convey excess water to storage tanks makes it suitable for urban-scale deployment, particularly in Mediterranean climates or cities seeking climate-resilient stormwater management solutions.
Large-scale adoption could enhance urban flood mitigation, support biodiversity, and contribute to climate adaptation strategies, demonstrating the broader applicability of this intensive green roof model in diverse urban environments.
Large-scale adoption could enhance urban flood mitigation, support biodiversity, and contribute to climate adaptation strategies, demonstrating the broader applicability of this intensive green roof model in diverse urban environments.
Do you have or know any platform of sharing Best Practice that you would like to link to this inventory platform?
No
Does your Best Practice contribute to an innovation? If so, please provide a short description of the innovative component
Yes, the Best Practice includes an innovative component. The innovation of the intensive CAM green roof at the University of Cagliari lies in its scientific validation and monitoring of hydrological performance in a Mediterranean context.
Specifically, this green roof represents the first rigorous assessment of the flood-mitigation capacity of spontaneous CAM vegetation (Agave americana), addressing a research gap on how CAM compare with conventional C3 vegetation in terms of rainwater retention and runoff reduction.
In addition, the system is equipped with continuous high-resolution monitoring, recording rainfall at 0.2 mm resolution and outflow every 5 minutes, providing detailed quantitative data on hydrological performance. This monitoring was implemented on a zero-maintenance, self-sustaining system, demonstrating that CAM vegetation can deliver long-term retention benefits without irrigation or ongoing maintenance. Finally, the roof serves as a benchmark for future blue-green infrastructure, such as the CAM Polder Roof prototype with integrated water tanks, linking ecological sustainability with stormwater.
Specifically, this green roof represents the first rigorous assessment of the flood-mitigation capacity of spontaneous CAM vegetation (Agave americana), addressing a research gap on how CAM compare with conventional C3 vegetation in terms of rainwater retention and runoff reduction.
In addition, the system is equipped with continuous high-resolution monitoring, recording rainfall at 0.2 mm resolution and outflow every 5 minutes, providing detailed quantitative data on hydrological performance. This monitoring was implemented on a zero-maintenance, self-sustaining system, demonstrating that CAM vegetation can deliver long-term retention benefits without irrigation or ongoing maintenance. Finally, the roof serves as a benchmark for future blue-green infrastructure, such as the CAM Polder Roof prototype with integrated water tanks, linking ecological sustainability with stormwater.
What technolog(ies) and/or tool(s) has(ve) been used for your Best Practice ?
Kalyx-RG rain gauge (UM-780-700 by Environmental Measurements Limited - EML);, EHSM: Ecohydrological Streamflow Model;, CAM: Crassulacean Acid Metabolism.
Please indicate the TRL associated with your Best Practice
TRL9 : Actual system proven in operational environment (competitivemanufacturing in the case of key enabling technologies)
Flow rate (m3/day)
0.20
Flow rate
Inflow based on average annual rainfall: 0,2 m3/d Inflow based on average rainfall event intensity: 0.19-0.76 m3/d
What is the necessary area to implement your Best Practice (m2) ?
96.00
What is the necessary area to implement your BP ?
two twin modules of 48 m² each
Comment : Salinity
NA
Comment : Suspended solids SS
NA
Comment : COD
NA
Comment : BOD5
NA
Comment : Phosphorus content
NA
NA
Pathogens
NA
Flow rate (m3/day) of treated NCW
0.20
Flow rate of treated NCW
NA
Efficiency (BOD5 % Removal)
NA
Comment : Efficiency (COD % Removal):
NA
Efficiency (SS % Removal):
NA
Efficiency (Salinity % Removal)
NA
Comment : Other (% Removal)
NA
What is the impact on the beneficiaries of your Best Practice ?:
The intensive CAM green roof at the University of Cagliari delivers multiple benefits to its beneficiaries by integrating stormwater management, ecological, and energy-related functions.
• Urban flood risk reduction: The system significantly mitigates peak runoff during extreme rainfall events, with an Index of Retention for extreme events (IOR95) of 0.38, contributing to resilient urban drainage systems.
• Enhanced urban resilience: By retaining and slowly releasing rainwater, the roof reduces pressure on the drainage network, supporting cities in adapting to climate variability and extreme weather.
• Improved quality of life: The vegetated roof enhances urban aesthetics, supports biodiversity, and contributes to air quality improvement, creating a more pleasant and healthier environment for building users and the surrounding community.
• Energy savings: Through latent heat flux and evaporative cooling, the roof helps regulate indoor temperatures, potentially reducing energy demand for air conditioning.
Overall, the system provides hydrological, ecological, and energy-related co-benefits, demonstrating how a low-maintenance green roof can simultaneously improve urban sustainability, resilience, and quality of life.
• Urban flood risk reduction: The system significantly mitigates peak runoff during extreme rainfall events, with an Index of Retention for extreme events (IOR95) of 0.38, contributing to resilient urban drainage systems.
• Enhanced urban resilience: By retaining and slowly releasing rainwater, the roof reduces pressure on the drainage network, supporting cities in adapting to climate variability and extreme weather.
• Improved quality of life: The vegetated roof enhances urban aesthetics, supports biodiversity, and contributes to air quality improvement, creating a more pleasant and healthier environment for building users and the surrounding community.
• Energy savings: Through latent heat flux and evaporative cooling, the roof helps regulate indoor temperatures, potentially reducing energy demand for air conditioning.
Overall, the system provides hydrological, ecological, and energy-related co-benefits, demonstrating how a low-maintenance green roof can simultaneously improve urban sustainability, resilience, and quality of life.
Total Cost (€):
0.00
Comment : Total Cost:
Average installation costs (commercially available): 250 €/m2. (our prototype was installed in the 80’s, we did not pay for it)
Comment : O&M Cost:
No maintenance costs
Capital Cost
Not available
Comment : Average Energy consumption:
No energy consumed
Garden Irrigation
Not sold
Price of treated NCW
Not sold
How your Best Practice is economically feasible ?
The intensive CAM green roof at the University of Cagliari is economically feasible due to its minimal operational costs and low retrofit investment.
Key factors include:
Zero maintenance costs: The spontaneous CAM vegetation (Agave americana) is drought-resistant and self-sustaining, requiring no irrigation or routine care. In contrast, an equivalent green roof planted with conventional C3 species would need approximately 72 m³ of water per year, corresponding to a savings of around €108/year at a water cost of €1.5/m³.
Low retrofit costs: The only significant investment for system enhancement was the installation of hydrological monitoring sensors in 2016, without major structural modifications.
The monitoring system relies on scientific projects.
Key factors include:
Zero maintenance costs: The spontaneous CAM vegetation (Agave americana) is drought-resistant and self-sustaining, requiring no irrigation or routine care. In contrast, an equivalent green roof planted with conventional C3 species would need approximately 72 m³ of water per year, corresponding to a savings of around €108/year at a water cost of €1.5/m³.
Low retrofit costs: The only significant investment for system enhancement was the installation of hydrological monitoring sensors in 2016, without major structural modifications.
The monitoring system relies on scientific projects.
Is your Best Practice economically viable ?
8
Is your Best Practice environmentally sustainable ?
10
If there was a sustainability assessment carried out, what are the result of this assessment ?
No sustainability assessment was undertaken.
Number of jobs created &/or preserved
4.00
Comment : Number of jobs created &/or preserved
3-4 researcher positions during several projects
Please indicate the other various social impact of your Best Practice :
Preservation of living environment, Improvment of health conditions, Sustaining natural ecosystems
To which Sustainable Development Goals (SDGs) your Best Practice contributes?
SDG6: Clean Water and Sanitation, SDG7: Affordable and Clean Energy, SDG11: Sustainable Cities and Communities, SDG13: Climate Action
The intensive CAM green roof at the University of Cagliari has provided several valuable lessons from its design, implementation, and long-term monitoring. The spontaneous CAM vegetation (Agave americana) has proven highly effective in Mediterranean climates, achieving a retention Index (IOR) of 0.52 without irrigation or regular maintenance. While conventional C3 vegetation can reach slightly higher retention (IOR ≈ 0.71), it requires substantial watering and ongoing care, demonstrating that CAM species offer a low-maintenance, cost-effective alternative for urban green roofs.
Continuous high-resolution monitoring of rainfall and outflow, combined with calibration of the EHSM ecohydrological model, has been essential to validate system performance. The monitoring revealed that antecedent soil moisture strongly influences retention during extreme rainfall events: dry substrate maximizes retention, whereas saturated conditions reduce available storage. This highlights the importance of considering initial soil moisture and operational strategies when designing or evaluating green roofs for stormwater management.
The roof has also demonstrated long-term viability as a self-sustaining system, with its combination of deep sandy substrate and CAM vegetation enabling effective water retention and regulation over decades, without the need for irrigation. Beyond hydrological performance, the roof provides ecological and aesthetic benefits, making it a multifunctional urban infrastructure.
Finally, the University of Cagliari CAM green roof serves as a benchmark for future innovations, such as the CAM PolderRoof, which integrates water reuse tanks while maintaining low-maintenance vegetation and high stormwater retention, showing the potential for scaling and replication in urban Mediterranean environments.
Continuous high-resolution monitoring of rainfall and outflow, combined with calibration of the EHSM ecohydrological model, has been essential to validate system performance. The monitoring revealed that antecedent soil moisture strongly influences retention during extreme rainfall events: dry substrate maximizes retention, whereas saturated conditions reduce available storage. This highlights the importance of considering initial soil moisture and operational strategies when designing or evaluating green roofs for stormwater management.
The roof has also demonstrated long-term viability as a self-sustaining system, with its combination of deep sandy substrate and CAM vegetation enabling effective water retention and regulation over decades, without the need for irrigation. Beyond hydrological performance, the roof provides ecological and aesthetic benefits, making it a multifunctional urban infrastructure.
Finally, the University of Cagliari CAM green roof serves as a benchmark for future innovations, such as the CAM PolderRoof, which integrates water reuse tanks while maintaining low-maintenance vegetation and high stormwater retention, showing the potential for scaling and replication in urban Mediterranean environments.
Have you any recommendation to add?
To promote the wider adoption of green roofs, policy measures should combine financial incentives, public engagement, and regulatory integration. Providing subsidies, grants, or tax incentives, especially for installations on public buildings, can create demonstration sites that encourage broader uptake. At the same time, awareness and communication campaigns are essential to inform citizens, planners, and decision-makers about the multiple benefits of green roofs, including stormwater management, urban heat mitigation, energy savings, and biodiversity support. Finally, integrating green roofs into urban planning regulations and climate adaptation strategies ensures that their installation is systematically considered in both new constructions and retrofits. By aligning financial, social, and regulatory measures, cities can accelerate replication and upscaling, maximizing the environmental, hydrological, and social impacts of green roofs.
Please indicate the acronyms of used &/or developed technologies/Tools:
Nature based process, Soil infiltration, Sustainable Drainage Systems, Evaporation, Others