Urban hydrological change and green roofs as source - control measures for stormwater management

Urbanization modifies the natural hydrological cycle by increasing impervious surfaces, reducing infiltration and accelerating stormwater runoff. In dense urban areas, rooftops form a substantial part of impervious cover and contribute directly to the hydraulic load on drainage systems during rainfall events. Green roofs provide a source-control measure that can partially restore retention, detention and evapotranspiration processes at the building scale. This paper discusses the hydrological role of green roofs in the context of urban hydrological change and stormwater management. It focuses on the mechanisms by which green roofs intercept rainfall, store water in vegetation and substrate layers, delay runoff generation and attenuate peak discharge. Particular attention is given to rainfall depth and intensity, antecedent moisture conditions, substrate properties, vegetation cover and detention response. The paper emphasizes that green roofs should not be assessed only through average retention values, because their performance varies with rainfall characteristics and initial substrate conditions. Instead, they should be considered as dynamic decentralized elements of urban stormwater control. This perspective supports their integration into drainage strategies aimed at reducing runoff peaks, relieving drainage infrastructure and improving the resilience of built-up areas under changing rainfall conditions, while supporting more adaptive responses to future hydrological stress in cities.