E. Ferrari

Influence of the North Atlantic Oscillation on winter rainfall in Calabria (southern Italy)

Seasonal rainfall amounts, directly responsible for availability of water resources on a specified area, are strongly dependent on the climate system. In order to highlight some features of such dependence, generally circulation indexes based on the difference in the sea level pressure between two geographic areas are taken into account. In the present study, the relationships between winter rainfall series observed in the Calabria region (southern Italy) and the North Atlantic Oscillation Index (NAOI) have been analysed. Firstly, a correlation analysis between precipitation and the NAOI was performed. Subsequently, the influence of the different phases of the NAO on the winter precipitation has been detected by a composite analysis, and by identifying changes in the behaviour of the probability density functions (gamma distribution) fitted on monthly rainfall. The results evidence a clear link existing between the phases of the climatic index and the amount of winter rainfall.

A stochastic model for the analysis of the temporal change of dry spells

In the present paper a stochastic approach which considers the arrival of rainfall events as a Poisson process is proposed to analyse the sequences of no rainy days. Particularly, among the different Poisson models, a non-homogeneous Poisson model was selected and then applied to the daily rainfall series registered at the Cosenza rain gauge (Calabria, southern Italy), as test series. The aim was to evaluate the different behaviour of the dry spells observed in two different 30-year periods, i.e. 1951–1980 and 1981–2010. The analyses performed through Monte Carlo simulations assessed the statistical significance of the variation of the mean expected values of dry spells observed at annual scale in the second period with respect to those observed in the first. The model has then been verified by comparing the results of the test series with the ones obtained from other three rain gauges of the same region. Moreover, greater occurrence probabilities for long dry spells in 1981–2010 than in 1951–1980 were detected for the test series. Analogously, the return periods evaluated for fixed long dry spells through the synthetic data of the period 1981–2010 resulted less than half of the corresponding ones evaluated with the data generated for the previous 30-year period.

Stochastic analysis of long dry spells in Calabria (Southern Italy)

A deficit in precipitation may impact greatly on soil moisture, snowpack, streamflow, groundwater and reservoir storage. Among the several approaches available to investigate this phenomenon, one of the most applied is the analysis of dry spells. In this study, a non-homogeneous Poisson model has been applied to a set of high-quality daily rainfall series, recorded in southern Italy (Calabria region) during the period 1981–2010, for the stochastic analysis of dry spells. Firstly, some statistical details of the Poisson models were presented. Then, the proposed model has been applied to the analysis of long dry spells. In particular, a Monte Carlo technique was performed to reproduce the characteristics of the process. As a result, the main characteristics of the long dry spells have shown patterns clearly related to some geographical features of the study area, such as elevation and latitude. The results obtained from the stochastic modelling of the long dry spells proved that the proposed model is useful for the probability evaluation of drought, thus improving environmental planning and management.

A combined stochastic analysis of mean daily temperature and diurnal temperature range

In this paper, a stochastic model, previously proposed for the maximum daily temperature, has been improved for the combined analysis of mean daily temperature and diurnal temperature range. In particular, the procedure applied to each variable sequentially performs the deseasonalization, by means of truncated Fourier series expansions, and the normalization of the temperature data, with the use of proper transformation functions. Then, a joint stochastic analysis of both the climatic variables has been performed by means of a FARIMA model, taking into account the stochastic dependency between the variables, namely introducing a cross-correlation between the standardized noises. The model has been applied to five daily temperature series of southern Italy. After the application of a Monte Carlo simulation procedure, the return periods of the joint behavior of the mean daily temperature and the diurnal temperature range have been evaluated. Moreover, the annual maxima of the temperature excursions in consecutive days have been analyzed for the synthetic series. The results obtained showed different behaviors probably linked to the distance from the sea and to the latitude of the station.

Analysis of the spatial correlation structure exhibited by daily rainfall in Southern Italy

The investigation of the spatial correlation structure exhibited by ground-based rainfall measurements can provide useful results for understanding, from a climatic point of view, the effects produced by the interaction between meteorological patterns and morphological features of a given territory. The central aspect of this study is the description of the spatial inhomogeneity and anisotropy that characterizes the correlation structure of daily rainfall. In the proposed approach, the analysis is developed by assuming that the correlation structure exhibited by the rainfall heights can be interpreted through a suitable deformation of the spatial coordinates providing a homogeneous and isotropic field. The technique has been applied to the daily rainfall recorded at the rain gauges network of the Crati River basin (Southern Italy). The results show that the elliptic deformations of the spatial structure exhibited by the correlation structure of the rain gauges are closely related to the physiographic features of the territory.

A Methodology for Evaluation and Mapping of Flood Risk. Case Study of Oued Mekerra in the West of Algeria

Mapping of flood risk is a necessary phase for the establishment of prevention plans from flood risk, and is absolutely mandatory for defining the constructability rules in areas subject to flooding. The mapping of risk is based on the flood evaluation with specified return period. The proposed methodological approach is structured in three steps, characterized by the adoption of hydrological, hydraulic and mapping techniques, respectively. In the hydrological step, the input conditions are defined by the flow-duration-frequency modelling, the synthetic hydrographs and the objective of safety to attribute to an area through variables related to the vulnerability factor. The hydraulic calculation provides information on the hazard factor and allows the evaluation of the local rating curve. The mapping technique allows the translation of the results obtained following the two previous steps in the form of geographic maps, which respond to the hydrological model and operate as both pre- and post-processors of the hydraulic model. An application of the methodology proposed for the flood risk mapping is shown with reference to the Mekerra watershed in Western Algeria, aiming at an implementation of a prevention plan against the risk associated with