Teresa Nanni

Temperature, precipitation and extreme events during the last century in Italy

Abstract The paper summarises activities within a broad-based research program for the reconstruction of the evolution of Italian climate in the twentieth century. The main result of the program is that Italian climate is becoming warmer and drier. The decrease of precipitation depends on the reduction in the number of wet days, as precipitation intensity displays a positive trend. Moreover, there is a tendency both toward an increase of heavy precipitation events and long dry spells. Most of the observed signals appear to be due to changes in atmospheric circulation causing an increase in the frequency of subtropical anticyclones over the western Mediterranean basin. This hypothesis is also supported by the evolution of Italian total cloud amount in the 1951–1996 period.

Precipitation intensity trends in northern Italy

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

Chapter 1 Mediterranean climate variability over the last centuries: A review

Publisher Summary This chapter discusses a necessary task for assessing to which degree the industrial period is unusual against the background of pre-industrial climate variability. It is the reconstruction and interpretation of temporal and spatial patterns of climate in earlier centuries. There are distinct differences in the temporal resolution among the various proxies. Some of the proxy records are annually or even higher resolved and hence record year-by-year patterns of climate in past centuries. Several of the temperature reconstructions reveal that the late twentieth century warmth is unprecedented at hemispheric scales and is explained by anthropogenic, greenhouse gas (GHG) forcing. The chapter discusses the availability and potential of long, homogenized instrumental data, documentary, and natural proxies to reconstruct aspects of past climate at local- to regional-scales within the larger Mediterranean area, which includes climate extremes and the incidence of natural disasters. The chapter describes the role of external forcing, including natural and anthropogenic influences, and natural, internal variability in the coupled ocean–atmosphere system at subcontinental scale.

Chapter 3 Relations between variability in the Mediterranean region and mid-latitude variability

Publisher Summary The Mediterranean climate is under the influence of both tropical and mid-latitude climate dynamics, being directly affected by continental and maritime air masses with significant origin differences. The peak of the winter season occurs between December and February, when the mid-latitude cyclone belt has usually reached its southernmost position. However, spring and autumn also contribute to a significant amount of precipitation. Being located at the southern limit of the North Atlantic storm tracks; the Mediterranean region is particularly sensitive to interannual shifts in the trajectories of mid-latitude cyclones that can lead to the remarkable anomalies of precipitation and, to a lesser extent, of temperature. Storm-track variability impacts primarily the western Mediterranean, but it hasa signature clearly detected in the eastern Mediterranean as well. The complex orography that characterizes most regions surrounding the Mediterranean basin can modulate and even distort climate anomaly patterns that otherwise would be geographically much more homogenous. Lack of water in winter and spring reflects in the crop yield. However, too much water in winter is harmful by drowning the seeds and retarding root development. The variability of precipitation plays a crucial role in the management of regional agriculture, in environment, in water resources and ecosystems, as well as social development and behavior.

A high-resolution 19611990 monthly temperature climatology for the greater Alpine region

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 1x1 km grids allowing temperature description of the orographically complex Alpine terrain with an accuracy of 1 °C have been made available for further applications at the web pages of the Central Institute for Meteorology and Geodynamics.

Trends in Italian total cloud amount, 1951-1996

Trends in Italian total cloud amount are analysed for the period 1951-1996. The data are a set of 35 station records that were extracted from the 3-hourly Italian Air Force dataset. A method is discussed to obtain daily mean cloud amounts avoiding biases due to missing observations: less than 2 % of the days have no observations, but more than 20 % of them have at least one missing value. Trend analysis is applied to regional Northern and Southern Italy average series. Seasonal and annual trends were estimated by means of least squares linear fitting. Significance was tested using the non parametric Mann-Kendall test. The results show that there is a highly significant negative trend in total cloud amount all over Italy. It is evident in all seasons and is particularly steep in winter where both in Northern and Southern Italy the decrease exceeds 1 okta in 50 years.

The atmospheric temperature in Italy during the last one hundred years and its relationships with solar output

SummaryWe 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.

Dendroclimatic Information on Silver Fir (Abies Alba Mill.) in the Northern Apennines

The main studies on silver fir were aimed at investigating the relationship between annual ring growth rhythms and climate factors. The aim of the present work is to know how the silver fir responds to both the environmental factors and meteorological parameters as a function of altitude and soil characteristics. The results are that the ring growth depends mainly on winter mean temperature of the same year considered in the chronologies, from summer precipitation and from mean summer temperature of the preceding year. The influence of winter mean temperature appears more pronounced in shallow soil at high altitude. The effect of mean summer temperature and of summer precipitation is greater at low altitude, and at high altitude only in shallow soil.

Climate Variations in Italy in the Last 130 Years

Series of annual and seasonal temperature and precipitation representing, respectively, northern and southern Italy are compared for trend in the period 1865–1996. Temperature and precipitation trends are almost always apposite except for the northern winter where they have a correlated behaviour till about 1980. The result is that the Italian climate is becoming warmer and drier. Monthly mean values of daily minimum and maximum temperature and of daily temperature range (DTR) have a positive trend. In particular the DTR reaches its maximum values in about 1945 then it decreases increasing suddenly in the last ten years.

Trends in High Frequency Precipitation Variability in Some Northern Italy Secular Stations

Recent studies on changes in precipitation intensity have found for some areas evidence of an increase in the proportion of total precipitation contributed by heavy and extreme rainfall events in the last 80 years. The purpose of the paper is to verify whether such a signal can also be detected in Northern Italy where daily precipitation (DP) is available starting from the beginning of the 19’ century. The analysis is performed on 5 stations: Genoa (1833–1998), Milan (1858–1998), Mantova (1868–1997), Bologna (1879–1998) and Ferrara (1879–1996). It gives evidence that in Northern Italy there is a positive trend in the proportion of total precipitation contributed by heavy precipitation events (i.e. DP > 25 mm and DP > 50 mm). The trend is mainly caused by the last 60–80 years and is particularly evident in the periods 1930–1960 and 1975–1995. It is more evident in the western than in the eastern area.