Search

We discuss the evolution of summer temperature extremes over Western Europe during 1961–2004 in the context of current climate warming. Using a parametric approach, we investigate the role of properties and changes in probability density functions of daily temperatures in modifying the frequency of severe, isolated events. In this perspective, the recent intensification of extremely warm events over Europe turns out to be well consistent with a pure, nonuniform shift of mean values, with no room for conjectures about increasing temperature variability.

An extensive analysis of the HISTALP database is presented with the aim of giving a comprehensive picture of secular climate variability and change in the Greater Alpine Region (GAR, 4–19 E, 43–49 N). The HISTALP database encompasses 242 sites and concerns temperature, pressure, precipitation, cloudiness, sunshine duration, vapour pressure and relative humidity. The analyses are based on four regional mean records representing different GAR low-level areas and on an additional mean record representing high-level locations. The first goal of the paper is to give an overview of the seasonal and annual records for the different variables, aiming to highlight both variability on decadal time scale and long-term evolution. Then it focuses on trend and correlation analysis. Trends are presented both for the period of common data availability for all regional average series and for moving windows that permit studying the trends over a wide range of timescales. Correlations among the different variables are presented both for the regional average series and for their high-pass-filtered versions. The analyses, beside highlighting a warming that is about twice as large as the global trend, also show that the different variables have responded in different ways to this warming and that the mutual interactions linking the different variables are often present only at specific temporal scales and only in parts of the GAR and in defined seasons. In spite of this complex behaviour, which may also be due to some residual inhomogeneities still affecting the data, the analyses give evidence that the HISTALP database has an excellent internal consistency and show that the availability of a multi-variable database turns out to be very useful in order to evaluate the reliability of the reconstruction of each variable and to better understand the behaviour and the mutual interactions of the different variables. Copyright © 2009 Royal Meteorological Society

The main object of the presented study was the creation of a high-resolution monthly temperature climatology for the greater Alpine region (GAR). This climatology, which is determined from observational averages for the period 1961-1990, necessitated a multinational, high-quality temperature dataset, in which especially inhomogeneities due to different methods of means estimation had to be regarded. Based on multilinear regression techniques and regionalisation, significant model improvements could be reached by adjusting for mesoscale effects in cold air pools, coastal and lakeshore belts, urban areas and slopes. The final 1 x 1 km grids allowing temperature description of the orographically complex Alpine terrain with an accuracy of I degrees C have been made available for further applications at the web pages of the Central Institute for Meteorology and Geodynamics.

This work presents a novel method for estimating missing values in daily precipitation series. It is aimed at identifying the event time location with good accuracy and reconstructing the correct amount of daily rainfall. In addition, the statistical properties of the time series, i.e. both probability distribution and long-term statistics, are preserved. The completion method is based on a two-step algorithm that uses information from a cluster of neighboring stations. First, wet and dry days are tagged, and subsequently, the full precipitation amount for wet-classified days is estimated by a modified multi-linear regression approach. This method avoids overestimation of the number of wet days and underestimation of intense precipitation events, which are typical side effects of common regression-based approaches. Copyright © 2009 Royal Meteorological Society

Monthly Northern and Central Italy precipitation climatologies, obtained by means of a procedure aiming at capturing the local dependence of precipitation on elevation, are presented. The procedure consists in considering each cell of a high-resolution grid and in making use of the closest 15 stations in order to perform a weighted linear regression of precipitation versus elevation: the weights are determined by the distances of the stations from the grid point and by the level of similarity between the stations' cells and the considered grid cell in terms of elevation, slope steepness, slope orientation and distance from the sea. The study is based on a dataset of about 3200 1961–1990 monthly precipitation normals. The performance of the procedure is evaluated by reconstructing the monthly precipitation normals of each station and by comparing them with the corresponding observed values. Such comparisons are performed by means of five error estimators: the mean absolute error and the mean error, both evaluated in absolute and relative form, and the root mean squared error. The mean absolute error is slightly more than 10 mm for the monthly precipitation, which turns out to be between 10% and 14% of the monthly precipitation.

The paper presents monthly 30-arc-second-resolution Northern and Central Italy temperature climatologies and discusses the procedure we adopt to superimpose the information of temperature secular records onto these climatologies. The climatologies are obtained by means of a step-wise linear regression method which aims at determining the temperature dependence on geographical and morphological variables. Such a method is applied to a database of about 800 monthly 1961–1990 temperature normals. In the first regression (temperature vs. elevation) the recorded data are considered; the further regressions concern the residuals obtained after taking into account the effect of each variable, in order of importance. An estimated secular anomaly record can be obtained for each point of the climatology grid by means of a distance-weighted average of the temperature anomaly records of the stations surrounding the grid point.

This paper describes the HISTALP database, consisting of monthly homogenised records of temperature, pressure, precipitation, sunshine and cloudiness for the ‘Greater Alpine Region’ (GAR, 4–19°E, 43–49°N, 0–3500m asl). The longest temperature and air pressure series extend back to 1760, precipitation to 1800, cloudiness to the 1840s and sunshine to the 1880s. A systematic QC procedure has been applied to the series and a high number of inhomogeneities (more than 2500) and outliers (more than 5000) have been detected and removed. The 557 HISTALP series are kept in different data modes: original and homogenised, gap-filled and outlier corrected station mode series, grid-1 series (anomaly fields at 1° × 1°, lat × long) and Coarse Resolution Subregional (CRS) mean series according to an EOF-based regionalisation. The leading climate variability features within the GAR are discussed through selected examples and a concluding linear trend analysis for 100, 50 and 25-year subperiods for the four horizontal and two altitudinal CRSs. Among the key findings of the trend analysis is the parallel centennial decrease/increase of both temperature and air pressure in the 19th/20th century. The 20th century increase (+1.2 °C/+ 1.1 hPa for annual GAR-means) evolved stepwise with a first peak near 1950 and the second increase (1.3 °C/0.6hPa per 25 years) starting in the 1970s. Centennial and decadal scale temperature trends were identical for all subregions. Air pressure, sunshine and cloudiness show significant differences between low versus high elevations. A long-term increase of the high-elevation series relative to the low-elevation series is given for sunshine and air pressure. Of special interest is the exceptional high correlation near 0.9 between the series on mean temperature and air pressure difference (high-minus low-elevation). This, further developed via some atmospheric statics and thermodynamics, allows the creation of ‘barometric temperature series’ without use of the measures of temperature. They support the measured temperature trends in the region. Precipitation shows the most significant regional and seasonal differences with, e.g., remarkable opposite 20th century evolution for NW (9% increase) versus SE (9% decrease). Other long- and short-term features are discussed and indicate the promising potential of the new database for further analyses and applications. Copyright © 2006 Royal Meteorological Society.

The paper describes the development of a dataset of 192 monthly precipitation series covering the greater alpine region (GAR, 4–18 ° Eb y 43–49°N). A few of the time series extend back to 1800. A description is provided of the sometimes laborious processes that were involved in this work: from locating the original sources of the data to homogenizing the records and eliminating as many of the outliers as possible. Locating the records required exhaustive searches of archives currently held in yearbooks and other sources of the states, countries and smaller regional authorities that existed at various times during the last 200 years. Homogeneity of each record was assessed by comparison with neighbouring series, although this becomes difficult when the density of stations reduces in the earliest years. An additional 47 series were used, but the density of the sites in Austria and Switzerland was reduced to maintain an even coverage in space across the whole of the GAR. We are confident of the series back to 1840, but the quality of data before this date must be considered poorer. Of all of the issues involved in homogenizing these data, perhaps the most serious problem is associated with the differences in the height above ground of the precipitation gauges, in particular the general lowering of gauge heights in the late 19th century for all countries, with the exception of Italy. The standard gauge height in the early-to-mid 19th century was 15–30 m above the ground, with gauges being generally sited on rooftops. Adjustments to some series of the order of 30–50% are necessary for compatibility with the near-ground location of gauges during much of the 20th century. Adjustments are sometimes larger in the winter, when catching snowfall presents serious problems. Data from mountain-top observatories have not been included in this compilation (because of the problem of measuring snowfall), so the highest gauge sites are at elevations of 1600–1900 m in high alpine valley locations. Two subsequent papers will analyse the dataset. The first will compare the series with other large-scale precipitation datasets for this region, and the second will describe the major modes of temporal variability of precipitation totals in different seasons and determine coherent regions of spatial variability. Copyright  2005 Royal Meteorological Society.

In this study, we set out to investigate the linkage of frost frequency to monthly mean temperature and its sensitivity to temperature changes. According to other related studies, the linkage between frost frequency and monthly mean temperature is approximated month per month via hyperbolic tangent functions. These models are validated using three validation experiments including split sample tests and temporal cross-validation. As there are quality-checked station data in Austria, whose temporal resolution and length allow for such a validation procedure, the validation experiments are conducted there. After the performance of the empirical models is evaluated and found adequate, the hyperbolic tangent approach is applied to about 500 stations within the so called Greater Alpine region (GAR), which extends from about 4 °E to 18 °E and from 44 °N to 49 °N. Using these models, it is possible to derive the sensitivity of frost frequency for any location for which the annual temperature cycle is known. This strategy is explicitly demonstrated for the Po Plain, where vertical temperature profiles on a monthly base are on hand as well as in Austria, where spatially high resolved maps of monthly mean temperature are available. Moreover, at stations for which long-term homogenised series of monthly mean temperature are available, reconstructions of frost frequency via the empirical models are done, returning to historical periods where no measurements of minimum temperature exist. On the basis of these findings, the impact of a possible future warming can be assessed, which is essential with regard to glaciers, permafrost and avalanches. Reduction in frost might bring positive economic aspects for agriculture, but negative consequences for low level skiing areas. Copyright © 2005 Royal Meteorological Society.

A homogenized 236 year daily regional sea-level pressure (SLP) record is constructed for the Po Plain (north Italy) by means of six station records: Bologna, Genoa, Lugano, Milan, Padua and Turin. Station records are subjected to a first homogenization in order to reduce all observations to sea level and to 0°C and to correct the bias introduced by calculating daily means using different sets of observation hours. A second homogenization is performed by means of comparison with other Italian and European series. After homogenization, the root-mean square error of the yearly station records is evaluated within 0.2 hPa after 1880, whereas for the periods 1834–1880 and 1765–1833 it is estimated as between 0.2 and 0.3 hPa and as around 0.4 hPa respectively. Trend analysis is applied to the annual and seasonal regional records and concerns both SLP and its day-to-day variability. The results show that neither the SLP nor its day-to-day variability have an evident trend when considering the entire 1765–2000 period. However, if the series is divided roughly in two parts, then significant trends can be highlighted. The annual and seasonal regional SLP records are also compared with corresponding regional temperature series. The results show that, especially in spring and in summer, temperature and SLP are in good agreement. Copyright © 2004 Royal Meteorological Society

Daily precipitation series from 75 Italian stations, for the period 1951–95, are clustered into six regions and the average is calculated for each area. For each average series, the seasonal and annual total precipitation and the number of wet days are calculated. The relationship between precipitation and atmospheric circulation is examined using correlation analysis. Atmospheric circulation is represented by five indexes: the well known North Atlantic oscillation index, a blocking frequency index, a Mediterranean oscillation index based on the 500 hPa geopotential record for Algiers, a Western European zonal circulation index (WEZCI) constructed from Madrid + Barcelona and Trondheim + Lund surface pressure records, and a new Mediterranean circulation index (MCI) constructed from Marseille and Jerusalem surface pressure records. All the indexes are calculated using monthly series; then seasonal and yearly averages are obtained. The indexes that show the most interesting correlation with total precipitation and number of wet days are WEZCI and MCI. Trend analysis of the index series gives evidence of a signal connected to a strong increase in winter air pressure in the Mediterranean area starting around 1980. Copyright © 2002 Royal Meteorological Society.

This paper proposes a methodology to study daily precipitation series that include a significant proportion of missing data, without resorting to completion methods based on randomly generated numbers. It is applied to a data set consisting of 75 station records (1951–2000) covering the Italian territory. They are clustered by principal component analysis into six regions: the north-west, the northern part of the north-east, the southern part of the north-east, the centre, the south and the islands (i.e. Sicily and Sardinia). Complete annual and seasonal regional average series are obtained from the incomplete station records, and analysed for droughts and extreme precipitation events. Droughts are identified by means of two indicators: the longest dry period and the proportion of dry days. The most remarkable result is a systematic increase in winter droughts over all of Italy, especially in the north, due mainly to the very dry 1987–93 period. Extreme events are analysed considering 5 day regional totals. In this case, however, an attempt to search for a statistically significant trend is not successful because of the scarcity of events in such a short period. The reliability of the regional series is checked by computing some basic statistics concerning total precipitation, rainy days and precipitation intensity and comparing them with the same statistics computed for regional series obtained by station records completed with methods based on random number generators. Copyright © 2002 Royal Meteorological Society.

High-resolution monthly temperature climatologies for Italy are presented. They are based on a dense and quality-controlled observational dataset which includes 1484 stations and on three distinct approaches: multi-linear regression with local improvements (MLRLI), an enhanced version of the model recently used for the Greater Alpine Region, regression kriging (RK), widely used in literature and, lastly, local weighted linear regression (LWLR) of temperature versus elevation, which may be considered more suitable for the complex orography characterizing the Italian territory. Dataset and methods used both to check the station records and to get the 1961–1990 normals used for the climatologies are discussed. Advantages and shortcomings of the three approaches are investigated and the results are compared. All three approaches lead to quite reasonable models of station temperature normals, with lowest errors in spring and autumn and highest errors in winter. The LWLR approach shows slightly better performances than the other two, with monthly leave-one-out estimated root mean square errors ranging from 0.74 °C (April and May) to 1.03 °C (December). Further evidence in its favour is the greater reliability of local approach in modelling the behaviour of the temperature-elevation relationship in Italy's complex territory. The comparison of the different climatologies is a very effective tool to understand the robustness of each approach. Moreover, the first two methods (MLRLI and RK) turn out to be important to tune the third one (LWLR), as they help not only to understand the relationship between temperature normals and some important physiographical variables (MLRLI) but also to study the decrease of station normals covariance with distance (RK).

An analysis of 67 sites of daily precipitation records over the 1951–1996 period for Italy is presented. Seasonal and yearly total precipitation (TP), number of wet days (WDs) and precipitation intensity (PI) are investigated, and the trends both for the single station records, and for some different area average series are studied. PI is analysed by attributing precipitation to ten class-intervals, removing the influence of variations in the number of WDs to yield changes in the underlying shape of the WD amount distribution. The results show that the trend for the number of WDs in the year is significantly negative throughout Italy, stronger in the north than in the south: this trend is mainly a result of the winter. Moreover, they show that there is a tendency toward an increase in PI. This increase is globally less strong and significant than the decrease in the number of WDs. It is not concentrated in one specific season, but changes from area to area, and is generally weak in winter, due to a significant decrease of winter TP. In northern Italy, the increase in PI is mainly owing to a strong increase in the heaviest events, while in central–southern Italy, it depends on a larger part of the distribution of WD amounts. The analysis of the evolution of the class-interval contributions shows that the positive trend of the heaviest events starts in the 1970s, as does the negative trend of lightest events. Copyright © 2001 Royal Meteorological Society.

A new daily precipitation dataset, for the period 1920–1998, comprising seven stations located in the northeastern Italy is presented. Seasonal and annual precipitation and number of rainy days have been analysed and a study aimed at investigating precipitation intensity and extreme events has been performed. Precipitation intensity has been analysed through studying both the mean precipitation amount per wet day and dividing precipitation into heavy and non-heavy classes. In addition, the return period of the extreme events has been calculated for 30-year running windows and its variations have been examined. The results show a negative trend in the number of wet days associated with an increase in the contribution of heavy rainfall events to total precipitation. This is in agreement with a reduction in return period for extreme events since 1920. Copyright © 2001 Royal Meteorological Society

Series of annual and seasonal temperature and precipitation representing respectively northern and southern Italy are compared for trend, interannual variability and periodicity in the period 1866–1995. Temperature and precipitation trends are almost always anticorrelated except in winter in the North where an anomalous behavior is evident till about 1980. The result is that the Italian climate has become warmer and drier especially in the South since about 1930.The interannual variability does not present significant maxima, but only minima that cannot be related tothe start of a trend either for temperature or for precipitation. The power spectra of the series show broad significant peaks containing the quasi-biennial oscillation and other well known periodicities probably due to solar cycles or to the North Atlantic ocean-atmosphere oscillation (NAO).

Recent studies on changes in precipitation intensity encompassing North America have found evidence for an increase in the relative amount of precipitation contributed by heavy and extreme rainfall events in the last 80 years. Within this context, the purpose of this paper is to verify whether such a signal can also be detected in northern Italy, where daily precipitation data are available from the beginning of the 19th century. The analysis is performed by applying the non-parametric Mann–Kendall test to mean anomaly series obtained through averaging the anomalies of some precipitation intensity statistics over five stations: Genoa (1833–1998), Milan (1858–1998), Mantova (1868–1997), Bologna (1879–1998) and Ferrara (1879–1996). It provides evidence that in northern Italy, the number of rainy days has a stronger and more significant negative trend than the corresponding precipitation amount, both on a yearly basis and in all of the seasons. As a consequence, precipitation intensity has a positive trend. The increase in precipitation intensity causes a significant positive trend in the proportion of total precipitation contributed by heavy precipitation events (i.e. daily precipitation >25 mm and daily precipitation >50 mm). The trend is mainly caused by the last 60–80 years, and is particularly evident in the periods of 1930–1945 and 1975–1995. The increase in precipitation intensity is connected to a modification of the distribution of daily precipitation values in a year, with trends that grow from the lower to the upper percentiles, and up to 4 mm/100 years for the 95th percentile. Copyright © 2000 Royal Meteorological Society

Series of annual and seasonal precipitation from 32 stations, distributed over all Italian territory and divided in two groups climatically homogeneous, were studied for the period 1833–1996. The series were checked for homogeneity and the time series analysis was performed with the Mann Kendall test and its progressive application according to Sneyers (1990). The results show considerably different trends for different seasons and zones. On a yearly basis a decreasing trend is present over all Italy, but it is statistically significant only in the Central-South. On a seasonal basis a decreasing trend is significant only for spring in Central-South, and for autumn in the North.

Historical series of monthly mean temperatures from 27 Italian stations, updated to 1993, are analysed. Building on previous analysis the following new results were obtained: there is an upward trend in seasonal and annual temperatures during the last 20 years; a positive trend, stronger at southern stations compared to northern stations, is apparent from 1920 to 1950, after when temperature shows no significant trend until 1985 when it starts to increase again. Data from Northern Italy show similar characteristics to a subset of data from a global climatic database, for the period 1881–1988. This comparison, however, suggests that good station coverage is important for the construction of a more detailed picture of seasonal climate variability.

The trends and the fluctuations in variability of surface air temperature in Italy has been investigated by statistical analysis of historical data covering the recent 100 years. 27 stations were used for the analysis and these were distributed all over the Italian territory divided into two climatically homogeneous zones. The temperature trends are different in each climatic zone and season, while the interannual variability shows a similar seasonal dependence for the North and South of Italy. In particular, summer temperature shows a characteristic pattern with alternating minima and maxima reaching significant values in the period 1940–1970: a maximum for the North between 1940–1960 and a minimum for the South between 1960–1970.

We analyze surface air temperature historical data with a principal focus on the last one hundred years and on the Italian territory. We find, using only statistical methods that this area can be divided in two climatically homogeneous zones: in both of these zones we find a positive temperature trend for the last one hundred years. This trend is always steeper for the winter temperatures and more pronounced for northern than for southern stations. In the historical temperature series power spectrum we identify two broad significant peaks, one containing the well known quasi-biennial oscillation and the other either solar periodicity related to the inversion of the sun magnetic polarity (Hale cycle) or the North Atlantic ocean-atmosphere oscillation.

The present study aims at improving data availability and quality for the last 80–90 years for daily precipitation in the Calabria region (southern Italy). First, the original database was homogenised and the gaps filled in for 129 daily rain gauges for the 1916–2006 period. Then, precipitation variability and change were evaluated at an adequate spatial resolution. Monthly and annual total precipitation (P), number of wet days (WDs), and precipitation intensity (PI) were calculated for each series. With regard to the monthly total precipitation a general negative trend, albeit not everywhere significant, was detected, in particular for the autumn–winter period, while in summer the tendency was toward an increase in total precipitation. The monthly behaviour of WDs was not very different from that observed for P: a diffuse negative trend was detected in most months, particularly evident and significant in January, with the exception of April and the summer months, for which the tendency was toward an increase. Regarding the PI, a general negative and often significant trend was found for the entire region and for almost all the months, except summer. Attention was also focused on tendencies in the different PI categories, revealing negative trends in high-intensity categories, especially coming from the winter season. Finally, running trend analysis revealed that the previously discussed tendencies were not persistent throughout the series length, but depended on the period examined. This important aspect should be taken into account when different results based on different time windows are compared. Copyright © 2010 Royal Meteorological Society

[1] We investigate changes in the probability density functions and the probability of moderate extremes for maximum and minimum daily temperature anomalies in Italy from 1951 up to 2008. Evaluation of trends in time-varying percentiles and higher-moment analysis of empirical density functions give no evidence of long-term changes in scale or shape of daily anomaly distributions, their temporal evolution being essentially driven by a forward, nonuniform shift in the mean. In this context, on the basis of an appropriate theoretical model for daily anomalies, we provide a realistic representation of the temporal evolution of moderate warm and cold extremes by explicitly considering the inherent nonlinearity between changes in the mean and those in exceedance probabilities. Consistency between expected and observed exceedance probabilities suggests that changes in moderate extremes can be well understood with a simple, rigid shift of the density functions alone, without invoking any change in shape.

How strong is the resemblance between two states of the atmosphere leading to the same outcome? In the following pages this question was addressed by studying the resemblance of the surface pressure fields, obtained by NCEP reanalyses, corresponding to “intense” precipitation events over 5 Italian climatic areas. Such “intense” precipitation events were selected by means of 45 daily precipitation records covering the period from 1951 to 2000.

Land-ocean coupling was investigated for the Adige River-Adriatic Shelf system by analyzing precipitation, water discharge and suspended load records over the period 1922-2000 and by comparing them with the Pb and porosity depth profiles of 4 marine cores taken along the riverborne sediment transport pathway on the shelf. The results show that precipitation was affected only by minor variations in yearly and seasonal amounts but was accompanied by a significant decrease (increase) in the number of wet days (precipitation intensity). River discharge - which is strongly influenced by total precipitation as well as by the number of wet days (in contrast to the quantitatively less important precipitation intensity) - shows a continuous decrease throughout the whole period. A significant decrease in suspended load is recorded after the 1940s, and meteorological and hydrological data suggest a major discontinuity over the same period, which was also recorded by marine sediments as a significant decrease in accumulation rates of fine materials. After the 1970s a further change in water discharge is observed in the river-system lowlands, recorded on the Adriatic shelf as intermittent sediment accumulation, and probably related to major floods. Changes seem to be mostly anthropogenic, such as progressive withdrawal of water and sediment for agricultural and civil uses, as well as damming for irrigation purposes and for generation of electricity. © Inter-Research 2006.

The Italian monthly temperature (mean, maximum and minimum) and precipitation secular data set was updated and completely revised. Station density and metadata availability were greatly improved and the series were subjected to a detailed quality control and homogenisation procedure. The data homogenisation is described in detail. The bias affecting original data is quantified by studying the temporal evolution of the mean adjustments applied to the series and examined in the light of the stations history. The results stress the importance of homogenisation in climate change studies. The final data set was clustered into climatically homogeneous regions by means of a Principal Component Analysis. Yearly and seasonal trend analyses were performed both on regional average series and on the mean Italian series. The results highlight a positive trend for mean temperature of about 1 K per century all over Italy; it is generally higher for minimum temperature than for the maximum temperature. The progressive application of trend analysis shows that, in the last 50 years, behaviour is the opposite; the maximum temperature trend being stronger than that of the minimum temperature. This has led to a negative trend in the daily temperature range that for the last 50 years has become positive. Precipitation shows a decreasing tendency, even if low and rarely significant, the negative trend being only 5% per century on a yearly basis. Copyright  2006 Royal Meteorological Society.

[1] The paper investigates precipitation variability in the greater Alpine region (GAR) (4–19°E, 43–49°N) based on 192 instrumental series of homogenized and outlier checked monthly precipitation and on the 1° gridded version of the same data set. Compared to the previous data sets, the one used in this paper adds a full century of data (earliest series starting in 1800) by exploiting the early instrumental period as much as possible in terms of series length and spatial density. The records were clustered into climatically homogeneous subregions, by means of a principal component analysis, and average subregional series were calculated. The principal component analysis was applied also in T-mode to investigate the most recursive precipitation patterns that characterize the examined area. Yearly and seasonal trend analysis was performed both on subregional average series and on the mean GAR series. It was also applied to moving windows, of variable width ranging from 2 decades to 2 centuries, in order to investigate any trends over decadal to secular timescales. Beside trends in total precipitation, precipitation seasonality was also analyzed as an important indicator of climate changes. Links between precipitation variability in the Alpine region and atmospheric circulation, and the North Atlantic Oscillation in particular, were also studied.

[1] A new data set of 45 daily precipitation series, covering quite uniformly Italian territory for the period 1880–2002, was recovered. The series have been homogenized on daily basis, completed by means of statistical methods and grouped into five regions by a Principal Component Analysis. Seasonal and yearly total precipitation, number of wet days, and precipitation intensity were analyzed for each station record and averaged into five regional series for a synthetic description of the results. Proportion and frequency of daily rainfall amounts, belonging to six precipitation class-intervals, defined on the basis of some percentiles of the precipitation distribution, were also analyzed. The results show a negative significant trend in the number of wet days all over Italy, and a positive trend in precipitation intensity, which is significant only in the northern regions. The negative trend in wet days has persisted since the end of 19th century and is due to the marked decrease in the number of low intensity precipitation events. An increase in the number of events belonging to the highest intensity class interval was observed too, but only in northern regions.

It has been suggested and experimentally verified by us in the laboratory that secondary particles are produced in the atmosphere by large micrometeorites. Gas bubbles, detected inside some black magnetic spherules (b.m.s.), can be displaced, or can escape, due to inertial force induced by decelartion in the cooling phase. The splash of the molten magnetite sheet upon the bursting of the gas bubble can produce numerous drops which solidify as secondary b.m.s. less than 8 μm in size. This mechanism provides an explanation for the existence of extraterrestrial b.m.s. within the 1–8 μm range.