Analysis and implementation of high resolution precipitation data in urban drainage modelling

Urban SIS is a project that develops, demonstrates and puts into production a method to downscale climate and impact indicators to urban scale, realizing a set of Essential Climate Variables over three area of Europe, including Bologna; in particular the precipitation was estimated for 5 non-consecutives years at a spatial resolution of 1x1 km2 and a temporal resolution of 15 min. The database of the area of Bologna contains an amount of data in the order of 10 millions that was managed in this study with RStudio. An analysis of the high resolution precipitation data over the most critical flood prone area of Bologna was performed, selecting a set of critical rainfall events. In the selection were considered the intensities, the cumulated depth and an index of spatial rainfall variability, taken from a firstly in-depth research in the literature regarding the use and the application of high resolution precipitation data in urban drainage modelling. Thanks to HERA, that gently provided the model of the entire urban drainage network of Bologna and the license for the utilization of InfoWorks software, the high resolution precipitation data were implemented into the drainage system. A series of indicators were calculated, in order to quantify the critical surcharge and flooded states of the network. Using the Intensity-Duration-Frequency curves of the area of Bologna, two types of synthetic events were elaborated: one constant over the area and another one with a pyramidal structure, representing the effects of a pour down rainfall event. The comparison between the synthetic events and the selected ones from Urban SIS assesses the direct correlation between the evaluation of the intensity at 1 hour and the indicators of the critical states in the network; the index of spatial rainfall variability has proved to be irrelevant in most of the cases. This study has to be considered valid for the urban drainage system of the area of Bologna