Reconstruction of a Storm Map and New Approach in the Definition of Categories of the Extreme Rainfall, Northeastern Sicily

Abstract

Abstract:After more than 350 mm of rainfall fell in a few hours on 22 November 2011, thousands of landslides and floods were induced in two main zones of Northeastern Sicily. The total rainfall has been reconstructed integrating available rain gauge data with Tropical Rainfall Measuring Mission (TRMM) satellite data from NASA (National Aeronautics and Space Administration); the landslide distribution in the field has confirmed the pattern of rainfall accumulated on 22 November 2011. Precipitation maxima of 1, 3, 6, 12, and 24 h was recognized as the hazardous events, which marks the evidence of a changing climate, with a shift toward more intense rainfalls in recent times. To investigate the sequence of the annual maxima, the historical time series have been transformed in the Standard normal distribution, from the cumulative probability of the GEV (Generalized Extreme Value) distribution. Following a similar definition of the Standard Precipitation Index (SPI), the transformation of the historical data in the standardized values allows the definition of categories of hourly maxima in term of extreme, severe, moderate, or mild. This transformation allows to eliminate the asymmetry of the time series, so that trends and fluctuations have been highlighted by the progressive accumulation of data (Rescaled Adjust Partial Sum). This statistical approach allows the improvement of the interpretability of the hydrological extreme events, and could also be used in other cases.

Communicating Hydrological Hazard-Prone Areas in Italy With Geospatial Probability Maps

“…The rainstorm are therefore considerably higher than the rest of Europe as the mean erosivity density in Italy is 2.02 MJ ha −1 h −1 , compared to 0.92 MJ ha −1 h −1 in Europe. In addition, although Northern Italy is particularly stormy, extreme rain events are also common in Central and Southern Italy (Fiorillo et al, 2016). This manifest the fact that, as we move from south to the driest hydro-climatic areas, the storm rainfall intensities remain high.…”

“…Wood areas are in green color. Fiorillo et al, 2016;Candela and Aronica, 2017). On the other hand, from the specific analysis of the extreme rainfall occurred in Sicily, it emerges that precipitations are nearly always associated with particularly intense storm (Caccamo et al, 2016).…”

Multiple Effects of Intense Meteorological Events in the Benevento Province, Southern Italy

“…The statistical characteristics of annual maxima were investigated by processing the actual data using two distinct procedures. In the first step, each ordered time series was fitted by a distribution function to find the probability of all theoretical values; the second step transformed the resultant probabilities into the Z values of the standard normal distribution [31].…”

“…The cumulative probability found by the GEV frequency distribution (Equation (1)) was then transformed in the Z value of the standard normal distribution. The result of this transformation is a symmetric series with a zero mean and a standard deviation equal to 1 [31].…”

“…Figure 6a shows the GEV function found by Equation (1) for annual rainfall maxima in 6 h; the actual data are plotted by the Weibull formula (Equation (2)). The cumulative probability calculated by the GEV frequency distribution (Equation (1)) was transformed into the Z value of the standard normal distribution (Figure 6b), resulting in a symmetric series with a zero mean and a standard deviation equal to 1 [31]. Because the transformation into the standard normal distribution provides dimensionless values, it allows for a direct comparison between time series of different durations (1, 3, 6, 12, and 24 h).…”