Effects of rainfall and catchment scales on hydrological response sensitivity in urban areas

Abstract

Spatial and temporal rainfall variability play an important role in generation of pluvial flooding. In urban areas, this phenomenon has increased in the last decades, due in particular to an intensification of urbanization and imperviousness degree. In fact, population is growing and moving from rural areas to cities, which are becoming more and more urbanized and densely populated. The increase of urbanization and related increase of imperviousness degree, combined with short and intense rainfall events, caused by climate changes, result in a fast hydrological response, with high probability of flooding. Hydrological models can represent the overall flow behaviour but they remain poorly capable of predicting flow peaks, especially in urban areas. In view of this, a better knowledge of the hydrological response of the urban catchment is needed to improve flood prediction and prevent damages caused by pluvial flooding. Due to the high variability of catchment characteristics at small scale, urban runoff processes are particularly sensitive to spatial and temporal variability of rainfall. For this reason, high resolution data are required for accurate runoff estimation. Rainfall is generally measured with rain gauges, which provide accurate measurements in a specific point, but they are not able to fully describe rainfall variability in space. New technologies, such as weather radars, have been used in recent decades to estimate rainfall intensity. Although these instruments provide an indirect measurement of rainfall and require good calibration and error corrections, they can provide rainfall distribution in space and time, which is fundamental to investigate the hydrological response. Rainfall characteristics, such as intensity, total depth, storm velocity and intermittency, strongly affect the hydrological response of the system and it is important to properly characterize them to estimate the runoff. Catchment characteristics, such as drainage area, drainage network, imperviousness degree and slope, and their representation in hydrological models also play an important role in the prediction of hydrological response. At present, combined effects of rainfall and catchment characteristics and scales on urban hydrological response needs further investigations…