The analyses of temperature extremes can be very useful because they are highly representative of the climatic tendency of an area. In this study, 19 temperature series registered in southern Italy have been analysed for detecting trends through the Mann–Kendall non‐parametric test. The tendencies have been detected since 1951 for the maximum and minimum monthly temperatures and for several indices of daily extremes. As a result, the minimum and maximum monthly temperatures mainly denote a positive trend for spring and summer months and a marked negative one in September. Moreover, the trend analysis on the extreme temperature indices shows opposite behaviours: a clear positive tendency in the frequency and intensity of the highest values and some negative trends for the lowest ones.

A deficit in precipitation may impact greatly on soil moisture, snowpack, stream flow, groundwater, and reservoir storage. Among the several approaches available to analyze this phenomenon, one of the most applied is the analysis of dry spells. In this paper, an investigation of the spatial and temporal patterns of dry spells, in a region of southern Italy, has been carried out on a daily precipitation dataset. First, the frequency distributions of the sequences of dry days have been analyzed. Then, the regional areas most affected by dry events have been evaluated at annual and seasonal scale. Finally, the long-term trend of the dry spells has been estimated at annual and seasonal scale. Results show that the lower probabilities of long dry spells occur in the main reliefs of the region, while the highest values have been detected in the Ionian side. The spatial distribution of the mean and maximum length values of the dry spells evidenced a west-east gradient. The trend analysis mainly revealed a negative behavior in the duration of the dry spells at annual scale and a positive trend in the winter period.

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ABSTRACT:Changes in the statistical distribution of rainfall amounts have been studied in four Mediterranean regions: the French and Spanish Mediterranean coasts, Sardinia Island, and the Calabrian region, in Italy. The largest precipitation series (from 70 to 150 years) in these zones have been collected and studied at yearly and monthly time scales by means of different parametric and nonparametric techniques. Nonparametric procedures have focussed on continuous time series changes, while possible changes at the end of the 20th century have been studied developing a parametric method. Among the results obtained, the 1984/1985 to 1994/1995 and 1994/1995 to 2004/2005 decades have been revealed as some of the driest ones since data are available in central and western Mediterranean. Despite that, such a finding is not always accompanied with a trend in the entire rainfall series. On the one hand, the low precipitation amounts detected in Central Mediterranean are caused in its major contribution by a diminution of the winter rainfall. On the other hand, a diminution of the spring and winter rainfall is the cause of the driest records since data are available in Western Mediterranean. Possible relations between the dry records and seasonal SLP-based indexes have been studied. The seasonal configurations of the North Atlantic Oscillation (NAO) have been calculated and their time series have provided a good perspective on the evolution of the most contributive synoptic patterns to climate variability at the region. The high frequency of positive seasonal phases of winter, spring and autumn NAO at the end of the 20th century and beginning of the 21st have been found as possible dynamic mechanism causing the last decades dryness. Moreover, moving correlations suggest a strengthening in the correlation between those seasonal NAOs and precipitation anomalies in Central and Western Mediterranean.