Urban green spaces, including green roofs (GRs), are vital infrastructure for climate resilience, retaining water in city landscapes and supporting ecohydrological processes. Quantifying the hydrologic performance of GRs in the urban environment for future climate scenarios is the original contribution of this research developed within the URCA! project. For this purpose, a continuous modelling approach is undertaken to evaluate the hydrological performance of GRs expressed by means of the runoff volume and peak flow reduction at the event scale for long data series (at least 20 years). To investigate the prediction of GRs performance in future climates, a simple methodological approach is proposed, using monthly projection factors for the definition of future rainfall and temperature time series, and transferring the system parametrization of the current model to the future one. The proposed approach is tested for experimental GR sites in Genoa and Rende, located in Northern and Southern Italy, respectively. Referring to both the Genoa and Rende experimental sites, simulation results are analysed to demonstrate how the GR performance varies with respect to rainfall event characteristics, including total depth, maximum rainfall intensity and ADWP for current and future scenarios.

Reference evapotranspiration sensitivity to climatic variables in Genoa, Italy. Komal*, A. Palla Department of Civil Chemical and Environmental Engineering, University of Genova, Montallegro 1, Genoa, Italy*Corresponding author email: komal.jabeen@edu.unige.itTo develop nature-based solutions for sustainable urban water management, it is important to understand the effect of climatic variables over Reference Evapotranspiration (ET0). The aim of this study is to observe the effect of variation in independent meteorological variables in estimation of ET0 through Penman Montieth Equation for a green roof experimental site located in Genoa, Italy. Sensitivity of ET0 along the year is investigated by using relative changes in the dependent variable (ET0 in mm/day) against relative changes in the following independent variables: maximum temperature (Tmax in °C), solar radiation (Rs in MJ/m²/day), wind velocity (U in m/s), maximum relative humidity (RHmax in %) while keeping all other dependent variables constant. Reference evapotranspiration at daily scale was assessed by the Penman–Monteith equation according to the guidelines given in FAO irrigation and drainage paper 56. A dimensionless sensitivity coefficient, SCX for each independent variable, X, is defined as follows:where the subscripts Base refers to the observed set of dependent variables while the subscript X refers to the subset including the modified dependent variable. The modified variables are built according to a matrix of 40 values characterized by a 5% increase.In the daily analysis, the SC average values for T, Rs and U are positive while for RHmax is negative. According to the results, FAO-56 is highly sensitive to the value of Rs as confirmed by the average value of SC equal to 0.3147) that means every 5% increase in Rs would result in 31.47% rise in the rate of ET0 on average annually. Average value of SC for Tmax was 0.1641, for RH max was -0.0951 and for U was found to be 0.2063. SC values were ranked as Rs > U > T max > RHmax but this impact of increase or decrease does not work identically all through the year since all the SC coefficients show seasonality. In particular, for summer season the sensitivity of ET0 is higher for Rs and Tmax as the intensity and duration of incoming solar radiation is high while the effect of windspeed is negligible in summer, contrary in winter season, ET0 is negatively affected by Rs and Tmax. follows the pattern of but it varies in magnitude. The effect of wind is quite noticeable in winter when windspeed is generally higher in Genoa with respect to temperature and solar radiation becoming the ET0 driving factor. As Genoa is a coastal city and the climate is mainly humid, the effect of maximum relative humidity is almost constant all through the year. This study can serve as a baseline to understand the sensitivity of FAO Penman equation across different urban zones of Italy and consequently to understand the hydrologic performance nature-based solution under climate change.

Nature-based solutions (NBS) restore green spaces and natural hydrological cycle reducing runoff generation, promoting infiltration or exfiltration and evapotranspiration (ET). ET governs much of hydrological and microclimatic functioning of urban NBS, yet it remains inconsistently measured, modelled and reported accross the literature. This review critically evaluates ET measurement and modelling in green roofs (GR), while positioning them within the broader urban NBS context. This structured narrative review synthesizes 104 studies published between 1948 and 2026, identified through database search and complementary reference-based search, critically evaluate ET modelling approaches, observational evidence, data requirements, and uncertainty implications in urban NBS. Based on this review, priority research needs include long-term multi-site observational datasets, standardised ET measurement protocols, and climate-adaptive modelling frameworks capable of supporting reliable NBS design and performance assessment under future climatic conditions.