Rainfall depth-duration-frequency curves for short-duration precipitation events in Sicily (Italy)

The design criteria of the hydraulic infrastructures, including, for instance, those for flood defense, urban drainage systems, reservoirs spillways and bridges, are based on the coupled analysis of the magnitude of rainfall events for a fixed duration and their estimated annual exceedance probability. The well-known rainfall depth-duration-frequency (DDF) curves, typically derived from the analysis of long historical annual maxima data series, synthesize the relationships between rainfall depth, duration and exceedance probability which is usually expressed as a return period. The time-resolution of rainfall data typically available for the construction of DDF curves and provided by gauges having large sample size, is hourly or coarser; this has allowed the definition of statistically consistent and reliable curves, suitable for rainfall duration hourly or longer, while, for shorter duration, empirical relationships with a high degree of approximation are generally used. Small river basins and plot-size areas with short response time, as well as urban drainage systems, are expected to be particularly vulnerable to sub-hourly intense rainfall events. Many practical applications, design procedures and mathematical models indeed require a finer time-resolution (i.e. sub - hourly). Moreover, in many regions of the world, such as the Sicily (Italy), an intensification of short-duration rainfall events is observed probably in response to the ongoing climate changes. This work proposes an approach for estimating the distribution of sub-hourly extreme rainfalls and extending depth–duration–frequency (DDF) curves derived for duration over the hourly also to sub-hourly durations. The approach is applied in Sicily starting from the coupled analysis of two different databases. The former (OA-ARRA database) contains long series of annual maxima for the fixed duration of 1, 3, 6, 12 and 24 hours for about 250 gauges, while the latter (SIAS database), include 10-minutes rainfall data series for about 100 gauges collected during the last 15 years (from 2003 to now), form which annual maxima time-series for fixed sub-hourly duration are derived. The approach includes a procedure for pairing raingauges, provided from the two databases, according to a distance- and elevation-based criterion and consolidated inference statistical techniques for the coupled analysis of the data-series from the two gauges

Detecting precipitation trend using a multiscale approach based on quantile regression over a Mediterranean area

One of the most relevant and debated topics related to the effects of the climate change is whether intense rainfall events have become more frequent over the last decades. It is a crucial aspect, since an increase in the magnitude and frequency of occurrence of heavy rainfall events could result in a dramatic growth of floods and, in turn, human lives losses and economic damages. Because of its central position in the Mediterranean area, Sicily has been often screened with the aim to capture some trends in precipitation, potentially related to climate change. While Mann-Kendall test has been largely used for the rainfall trend detection, in this work a different procedure is considered. Precipitation trends are here investigated by processing the whole rainfall time-series, provided by the regional agency SIAS at a 10-min resolution, through the quantile regression method by aggregating precipitation across a wide spectrum of durations and considering different quantiles. Results show that many rain gauges are characterized by an increasing trend in sub-hourly precipitation intensity, especially at the highest quantiles, thus suggesting that, from 2002 to 2019, sub-hourly events have become more intense in most of the island. Moreover, by analysing some spatial patterns, it has been revealed that the south and the east of Sicily are more interested in significant increasing rainfall trends, especially at the 10-min duration. Finally, the comparison between the two procedures revealed a stronger reliability of the quantile regression in the trend analysis detection, mainly due to the possibility of investigating the temporal variation of the tails of precipitation distribution

Effetto combinato di cambiamenti climatici ed urbanizzazione sugli estremi di portata

Il termine “cambiamento idrologico” (hydrological change) è spesso utilizzato per sintetizzare quell’insieme di alterazioni della risposta idrologica dei bacini indotte da fattori naturali o antropici. ll ruolo fondamentale di tali alterazioni nel determinare fenomeni di dissesto ha stimolato l’International Association of Hydrological Scienses (IAHS) a dedicare la decade scientifica 2013-2022 (denominata “Phanta Rhei”) ai cambiamenti idrologici e all’analisi dei diversi fattori perturbanti. I cambiamenti climatici e l’urbanizzazione sono fra i fattori antropici perturbanti più influenti e, allo stesso tempo, più diffusi a livello globale. Il cambiamento climatico è stato abbondantemente studiato in passato, con chiare evidenze di trend sugli estremi (es. Burn et al., 2011; Arnone et al., 2013) e con numerosi esempi attestanti i possibili cambiamenti idrologici indotti (es. Wang and Alimohammadi, 2012; Francipane et al., 2015; Chiarelli et al., 2016; Pumo et al. 2016). Molto più recente è l’analisi degli effetti dell’urbanizzazione sulla risposta idrologica dei bacini (es. Salvadore et al., 2015). Il processo di urbanizzazione è associato a una perdita di “superfici permeabili” (suoli naturali), con conseguente impoverimento dei processi d’infiltrazione, alterazione ai sistemi di drenaggio naturale e ai processi di trasferimento (alterazione dei percorsi idrici e delle velocità di deflusso). La valutazione dell’impatto di tali perturbazioni sulle portate di picco durante eventi estremi, può risultare particolarmente utile nel definire e orientare efficaci politiche di pianificazione urbana e gestione di eventi di inondazione, nonché in attività di verifica delle infrastrutture idrauliche esistenti e di progettazione di quelle future. L’obiettivo di questo lavoro è quello di investigare gli effetti dell'interazione delle suddette perturbazioni sugli eventi estremi di deflusso. A tale scopo, è stato ideato un esperimento numerico, applicato ad un piccolo bacino fluviale, che ha permesso di generare e confrontare serie temporali di deflusso orario sotto diversi ipotetici scenari di cambiamento. Gli scenari, generati attraverso l’uso combinato di un modello di cambiamento di uso del suolo opportunamente implementato e di un modello di generazione di serie climatiche già esistente (Fatichi et al., 2011), descrivono situazioni estreme sia in termini di espansione delle aree urbane che in termini di variazioni (aumento o diminuzione) della precipitazione media annua (MAP). Nella creazione degli scenari climatici si è anche tenuto conto di un aumento della temperatura media, e, a parità di MAP, sono state create diverse configurazioni, caratterizzate da diversa frequenza e/o l’intensità media degli eventi di pioggia. La risposta idrologica del bacino ai vari scenari è stata riprodotta mediante il tRIBS (Ivanov et al., 2004), un modello idrologico, fisicamente basato e distribuito, in grado di simulare, con alta risoluzione temporale, anche le diverse componenti di deflusso. I risultati mostrano un’alta sensibilità degli indicatori della risposta idrologica utilizzati alle variazioni delle caratteristiche di pioggia. In termini di deflusso totale, gli effetti dei cambiamenti climatici sembrano essere prevalenti rispetto a quelli indotti dall’espansione urbana, anche se, a una maggiore frazione di suoli impermeabili, corrisponde un chiaro aumento della componente di scorrimento veloce, i cui effetti sul deflusso totale vengono parzialmente smorzati da una simultanea riduzione della componente di deflusso lento e profondo

HDAC inhibitor confers radiosensitivity to prostate stem-like cells

Background: Radiotherapy can be an effective treatment for prostate cancer, but radiorecurrent tumours do develop. Considering prostate cancer heterogeneity, we hypothesised that primitive stem-like cells may constitute the radiation-resistant fraction. Methods: Primary cultures were derived from patients undergoing resection for prostate cancer or benign prostatic hyperplasia. After short-term culture, three populations of cells were sorted, reflecting the prostate epithelial hierarchy, namely stem-like cells (SCs, α2β1integrinhi/CD133+), transit-amplifying (TA, α2β1integrinhi/CD133−) and committed basal (CB, α2β1integrinlo) cells. Radiosensitivity was measured by colony-forming efficiency (CFE) and DNA damage by comet assay and DNA damage foci quantification. Immunofluorescence and flow cytometry were used to measure heterochromatin. The HDAC (histone deacetylase) inhibitor Trichostatin A was used as a radiosensitiser. Results: Stem-like cells had increased CFE post irradiation compared with the more differentiated cells (TA and CB). The SC population sustained fewer lethal double-strand breaks than either TA or CB cells, which correlated with SCs being less proliferative and having increased levels of heterochromatin. Finally, treatment with an HDAC inhibitor sensitised the SCs to radiation. Interpretation: Prostate SCs are more radioresistant than more differentiated cell populations. We suggest that the primitive cells survive radiation therapy and that pre-treatment with HDAC inhibitors may sensitise this resistant fraction

Classification of Extreme Rainfall for a Mediterranean Region by Means of Atmospheric Circulation Patterns and Reanalysis Data

The atmospheric circulation can be recognized as one of the causes of severe rainfall events occurrence. Such events, especially when are characterized by short durations and high intensities, result in flood events in the Mediterranean area. It is very important to understand how these heavy rainfall events, which can be usually identified with convective rainfall, are related to the different types of atmospheric circulation. In order to do this, some weather circulation patterns (WPs), which have been derived for the Europe, have been first connected with the rainfall annual maxima (AMAX) recorded over the Sicily. The analyses allowed to identify those WPs that are more likely to result into the occurrence of the AMAX. Secondly, two ERA-Interim reanalysis indexes have been used to define a criterion to distinguish those AMAX mainly due to a convective component from those more related to a stratiform precipitation, also detecting a transient zone between these two types of events. Finally, the main results have been connected together with the aim to define a set of triggering factors of extreme rainfall events

Weather circulation patterns as precursor of heavy rainfall events: an application to Sicily, Italy

Since the impacts of climate change on the environment have been constantly rising over the last decades, scientists have paid much attention to understanding the effects of this phenomenon. Climate change leads to different kinds of extremes, such as heavy rainfall events, characterized by short duration and high intensity, and drought, which can cause the problem of water scarcity over a certain area. These types of extreme events cause several damages for the affected areas since they can result in loss of human lives and economic damages. In particular, heavy rainfall events, which are often associated with convective precipitation because of their characteristics, may result in flash floods, especially when they hit small catchments with low times of concentration, thus causing economic damages and, more relevantly, human lives losses. The increasing occurrence of heavy rainfall events in many areas of Europe, also in Italy, over the last few years, has contributed to raising the importance of understanding which factors could be recognized as drivers of these events. In this perspective, it is possible to identify in atmospheric circulation one of the causes of severe rainfall events occurrence since some air fluxes, generated from certain schemes of atmospheric circulation, could lead to the accumulation of moisture within a certain volume of the atmosphere, hence to the occurrence of rainfall. Since even the Sicily (Italy) has been experimenting heavy rainfall events and consequent flash floods and urban floods in the last years, this work aims to find out a relationship between some weather circulation patterns, developed by the UK Met Office, and the rainfall Annual MAXima (AMAX) for the Sicily, recorded by the rain gauge network of Autorità di Bacino - Regione Siciliana. The possible connection between AMAX and WPs has been investigated in order to define some specific schemes of atmospheric circulation that are responsible for leading to the occurrence of AMAX in Sicily. In order to do this, a database containing the AMAX of all the available gauges for the Sicily has been used. A distinction between AMAX occurred in summer and winter season and their related WPs has been performed as well, with the goal to understand the possible influence of WPs on the summer and winter AMAX. Furthermore, in order to distinguish convective from stratiform AMAX, some analyses on reanalysis data, namely the CAPE and the Vertical Integral of Divergence of Moisture Flux (VIDMF), have been done

Convective and stratiform precipitation: A PCA-based clustering algorithm for their identification

The increasing occurrence of flood events in some areas of the Southern Mediterranean area (e.g., Sicily), over the last few years, has contributed to raising the importance of characterizing such events and identifying their causes

PRECIPITATION ESTIMATION THROUGH SATELLITE SYSTEM OVER THE MAJOR MEDITERRANEAN ISLANDS

Reliable and accurate precipitation measurement or estimation is crucial for disaster monitoring and water resource management. Nowadays the scientific community expects significant improvements in precipitation monitoring by the continuous technological evolution of satellite-rainfall estimate systems which are able to produce data with global coverage and thus can provide low-cost information even in scarcely populated areas or places where for economic reasons ground measures are missing. The most recent satellite mission is the Global Precipitation Measurement (GPM), which is an international constellation of ten partner satellites, and a source of rainfall estimates at high spatial and temporal resolution (Huffman et al., 2017). In this context, the aim of this study is to test satellite-precipitation GPM-IMERG products against data provided by dense raingauges over the two major islands of Mediterranean Sea, i.e. Sardinia and Sicily. The two islands are characterized by a complex morphology and by small spatial scale and long see-land transition borders. Moreover, they experience different precipitation types, originated by convective and stratiform systems as well as by the interaction of steep orography in the coasts with winds carrying on humid air masses from the Mediterranean Sea. For these reasons, the two islands can be considered as interesting test sites for satellite-precipitation GPM-IMERG product in the European mid-latitude area and in general for complex domains. The GPM-IMERG post real-time “Final” run product (last version V4 released in spring 2017) at 0.1° spatial resolution and half-hour temporal resolution has been selected for the two years period 2015-2016. Evaluation and comparison of the selected product are performed with reference to data provided by the raingauges network of the two islands. Both GPM and raingauges data have been aggregated at hourly time scale, then the raingauges data have been spatially interpolated and resampled at the GPM resolution grid. In order to obtain general information about the performances of estimates related to the entire two islands, features of rainfall spatial distribution and the influence of the aggregation time scale have been investigated using statistical and graphical tools