Influence of space-time rainfall variability on urban runoff

In small urban catchments a very high space-time rainfall resolution is needed in order to obtain with sufficient accuracy the flash flood forecasting as well as the monitoring of sewer systems. The errors in hyetograph input due to different spatial resolution are amplified by hydrological losses and flow processes so that they may produce some relevant errors in runoff volumes and peak discharges. In this paper we deal with a field investigation, carried out during an eight-year period on an urban test catchment located in the outskirts of Rome. This watershed drains a residential area and for its geomorphological and environmental characteristics, it can represent a typical situation in the Italian urban context. To link the precipitation measurements to the discharge ones a rainfall-runoff model is calibrated by the use of data with high spatial and temporal resolution; the results are shown in the paper.