Thermal and hydraulic behavior of substrates for extensive green roofs in mediterranean urban area

The rapid increase in sealed surface in urban area have contributed to the alteration of climatic conditions. The use of vegetation integrated with buildings and other forms of vegetation provides a sustainable solution to these problems, bringing numerous benefits, including the decrease of CO₂ emissions consequent to reduction of electricity consumption to regulate the temperature comfort inside buildings and the reduction of surface runoff into urban sewage systems. The main objective of this work was to study the thermal and hydraulic behavior of vegetated and not-vegetated extensive green roofs. For the purpose, two green roof plots were installed on the roof of the building of the Faculty of Agriculture at the University of Palermo. The experiment was carried out in the spring-summer season of 2025. Meteorological data were acquired through a weather station installed on the roof and substrate temperature and volumetric water content were monitored by Teros 12^® capacitive probes (Meter Group GmbH) embedded into the green roof plots. Drainage was collected into tanks equipped with ultrasonic transducers for automatic acquisition of water level measurements. A commercial substrate (TMT, Harpo VerdePensile s.r.l) was used with expanded clay as drainage layer. Water retention and hydraulic conductivity function were determined from the laboratory measurements carried out with the evaporation method (Schindler, 1980) using HYPROP apparatus (Meter Group GmbH). Substrate thermal conductivity function parameters were determined according to the Chung and Horton model (1987) on data acquired through the THERMOLINK (Meter Group GmbH). Thermal and hydraulic processes that occur on the roof were then simulated considering both 2D and 3D flow domain by the Hydrus 2D/3D software. Comparison between simulated and measured data during either rainfall events and inter-rainfall periods allowed to highlight the role that vegetation plays on the thermo-hydrological processes and support the use of HYDRUS as a predictive tool in green infrastructure planning and management.

References

Chung, S., Horton, R., 1987. Soil heat and water flow with a partial surface mulch. Water Resources Research 23, 2175–2186. https://doi.org/10.1029/WR023i012p02175

Schindler, U., 1980. Ein Schnellverfahren zur Messung der Wasserleitfähigkeit im teilgesättigten Boden an Stechzylinderproben. Archiv für Acker- und Pflanzenbau und Bodenkunde 24 (1): 1-7.