Rainstorms able to induce flash floods in a Mediterranean-climate region (Calabria, southern Italy)

Abstract

Abstract. Heavy rainstorms often induce flash flooding, one of the natural disasters most responsible for damage to manmade infrastructures and loss of lives, also adversely affecting the opportunities for socio-economic development of Mediterranean countries. The frequently dramatic damage of flash floods are often detected, with sufficient accuracy, by post-event surveys, but rainfall causing them are still only roughly characterized. With the aim of improving the understanding of the temporal structure and spatial distribution of heavy rainstorms in the Mediterranean context, a statistical analysis was carried out in Calabria (southern Italy) concerning rainstorms that mainly induced flash floods, but also shallow landslides and debris flows. Thus, a method is proposed -based on the overcoming of heuristically predetermined threshold values of cumulated rainfall, maximum intensity, and kinetic energy of the rainfall event -to select and characterize the rainstorms able to induce flash floods in the Mediterranean-climate countries. Therefore, the obtained (heavy) rainstorms were automatically classified and studied according to their structure in time, localization, and extension. Rainfall-runoff watershed models can consequently benefit from the enhanced identification of design storms, with a realistic time structure integrated with the results of the spatial analysis. A survey of flash flood events recorded in the last decades provides a preliminary validation of the method proposed to identify the heavy rainstorms and synthetically describe their characteristics. The notable size of the employed sample, including data with a very detailed resolution in time that relate to several rain gauges welldistributed throughout the region, gives robustness to the obtained results.

Improvement to the Huff Curve for Design Storms and Urban Flooding Simulations in Guangzhou, China

“…The Huff curve was initially developed by Huff [28] for characterizing temporal rainfall distributions in an area and has been widely applied to describe the hyetograph and to predict the runoff in a watershed [28,[38][39][40][41][42][43]. The Huff curve is a dimensionless hyetograph.…”

Examples of Application of GASAKe for Predicting the Occurrence of Rainfall-Induced Landslides in Southern Italy

“…The Tyrrhenian sector is rainier than the Ionian one (1200-2000 mm vs. 500 mm); nevertheless, the most severe storms occur more frequently on the Ionian side of the region [41]. According to [42], heavy and frequent winter rainfall, caused by cold fronts mainly approaching from NW, and autumn rains, determined by cold air masses from NE, affect the region. In spring, rains show lower intensities than in autumn, while strong convective storms are common at the end of summer.…”

Changes in the occurrence of rainfall-induced landslides in Calabria, southern Italy, in the 20th century

“…Elevation in the region ranges from sea level to 2260 m a.s.l., and morphology is shaped by a tectonic uplift initiated in the Quaternary and that remains active. Allochthonous crystalline rocks, Palaeozoic to Jurassic in age, stacked over carbonate units in the middle Miocene, represent the backbone of the region, with Neogene flysch filling tectonic depressions (Tortorici, 1982;Monaco and Tortorici, 2000). Mean annual rainfall averages 1150 mm in the region, with the Ionian (E) side of the region less rainy than the Tyrrhenian (W) side (Terranova, 2004) (Fig.…”

“…Finally, we discarded from the analysis all the RE with mean rainfall intensity < 10 mm day −1 . The value was selected heuristically, following Terranova and Gariano (2014), to exclude from 1921-1950, 1951-1980, and 1981-2010. the analysis less significant events. The remaining 1466 RE with landslides have durations in the range 1 < D < 32 days (average 7 days), and cumulated event rainfall in the range 10.0 < E < 1504.7 mm (average 202.3 mm) ( Table 1).…”