The Long-Term Performance of a Rainwater Harvesting System Based on a Quasi-Bicentennial Rainfall Time Series

The University of Genova (Italy) maintains a historical meteorological station that has provided daily rainfall measurements over a quasi-bicentennial period since 1833. The daily rainfall series is analyzed here to assess the impact of long-term precipitation trends on the performance of a rainwater harvesting system. The collected rainwater is used for the irrigation of urban green areas. A behavioral model is applied, involving a dedicated procedure to evaluate the actual soil water content available for vegetation and its decay over time. Non-dimensional indicators are obtained to support adaptation strategies and the sustainable design of the required storage tank. Since both irrigation demand and available water storage depend on the amount of rainfall received, fluctuations in daily rainfall and their trend do affect the performance of the system in a non-trivial way. The results demonstrate that the installation of an RWH system for landscape irrigation is a reliable and resilient solution, at least considering the measured rainfall variations of the last 200 years. In the town of Genoa, no specific adaptation seems necessary in terms of the design of the storage tank other than the usual oversizing, typical of engineering design, to account for uncertainties in the hydrological assessment of any RWH system.