Urbanization has significantly intensified surface runoff and degraded urban water quality, particularly in developing countries. Rainwater harvesting (RWH) systems represent a sustainable approach to stormwater management by mitigating runoff volumes, reducing dependency on potable water, and addressing diffuse pollution. In Brazil, ceramic-tiled roofs are among the most prevalent in residential areas; however, their hydrological behavior and pollutant wash-off dynamics remain underexplored.
This study aims to evaluate both quantitative and qualitative runoff parameters for a conventional ceramic-tiled roof under real-world rainfall conditions. A pilot roof with a 25° slope was monitored across 38 rainfall events. Hydrological performance was assessed using two methods: the SCS-Curve Number (CN) model and direct estimation of the runoff coefficient (C). The results showed high runoff generation, with an average C of 0.89 (median 0.93), strongly influenced by rainfall depth. The average CN was 99.5. Out of 712 mm of cumulative rainfall, only 7% was retained.
Water quality was evaluated during 26 events through two complementary analyses. First, runoff samples were collected every 17 minutes during the first hour of each event. Kruskal–Wallis tests revealed significant temporal variation in electrical conductivity (EC), suggesting early mobilization of dissolved pollutants. Second, the occurrence of first flush was assessed by fitting a first-order exponential decay model to pollutant concentrations. Events with R² > 0.90 were classified as first flush occurrences for EC and total organic carbon (TOC).
These findings emphasize the substantial runoff potential of ceramic-tiled roofs and the dynamic nature of early pollutant wash-off. This study highlights the importance of site-specific hydrological and water quality calibration to improve urban drainage modeling. Future work will focus on extending these models to optimize RWH system design and pollutant retention strategies, promoting more efficient and resilient urban water management in subtropical environments.
