Impacts of Rainfall Data Aggregation Time on Pluvial Flood Hazard in Urban Watersheds

Abstract

Pluvial floods occur when heavy rainstorms cause the surcharge of the sewer network drainage, representing one of the most impacting natural hazard in urban watersheds. Pluvial flood hazard is usually assessed considering the effect of annual maxima rainfall of short duration, comparable with the typical concentration times of small urban watersheds. However, short duration annual maxima can be affected by an error of underestimation due to the time resolution as well as the aggregation time of the rainfall time series. This study aims at determining the impact of rainfall data aggregation on pluvial flood hazard assessment. Tuscany region (Central Italy) is selected as a case study to perform the assessment of the annual maxima rainfall underestimation error, since the entire region has the same temporal aggregation of rainfall data. Pluvial flood hazard is then evaluated for an urban watershed in the city of Florence (Tuscany) comparing the results obtained using observed (uncorrected) and corrected annual maxima rainfall as meteorological forcing. The results show how the design of rainfall events with a duration of 30 min or shorter is significantly affected by the temporal aggregation, highlighting the importance of correcting annual maxima rainfall for a proper pluvial flood hazard evaluation.

Flood Models: An Exploratory Analysis and Research Trends

“…Due to various factors, the majority of floods can be in different types, such as (i) fluvial floods, mainly by the overflowing of rivers caused by heavy rains or upstream dams [20,21]; (ii) pluvial floods, which occurs in highly saturated or impermeabilized terrain (e.g., urban areas), due to heavy rains even in the summer season by to monsoon winds [22][23][24]; (iii) flash floods, caused by the sudden increase in the intensity of the rains and the influence of groundwater recharge and the release of water stored in dikes or dams (natural or artificial), destroying the natural and anthropogenic environment due to the speed and force of water [25][26][27]; and (iv) coastal floods, generally caused by the action of the wind in the waves of the sea and the seismic movement under it (e.g., tsunami), causing flooding on the coastal edges of the continent [28,29]. These events affect coastal areas, which are the most densely populated and developed places globally, and the most intensely impacted by marine and river flooding [30].…”