Trends in the daily intensity of precipitation in Italy from 1951 to 1996

Abstract

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.KEY WORDS: daily precipitation; heavy precipitation events; Italy; trend analysis; precipitation intensity INTRODUCTIONEver increasing attention is devoted by climatologists to the study of precipitation trends, because, owing to possible variations or changes in the climate, the geographic distribution of rainfall frequency and intensity could be subjected to substantial modifications (IPCC, 1996). This could determine, in some areas, prolonged periods of unusually dry conditions, reducing the availability of water resources, while other areas could be affected by wetter than normal conditions, with an increase in the flood risk. In this respect, we can remember the last two decades, during which, in the winter season, rain scarcity was experienced in many areas of the Mediterranean Basin (Schö nwiese and Rapp, 1997;Piervitali et al., 1998;Buffoni et al., 1999), whereas in central and northern Europe, a tendency towards an increase in precipitation was generally observed (Alexandersson, 1996;Hurrell and Van Loon, 1997;Wibig, 1999).The topic is very complex, and model simulations sometimes give disagreeing forecasts for the future (Henderson-Sellers and Hansen, 1995;IPCC, 1996). On a global scale, an increase in the rainfall should occur at middle and high latitudes, and a reduction at lower ones (Hulme et al., 1998;Trenberth, 1998;Doherty et al., 1999). Moreover, there are some indications of a possible rise in precipitation intensity (PI), pointing to an increase in the number of heavy precipitation events (Fowler and Hennessy, 1995;Gregory and Mitchell,...

Detection of a possible change point in atmospheric variability in the North Atlantic and its effect on Scandinavian glacier mass balance

“…A change point in 1931 marks a shift in the NAO from being predominantly positive up to this point to increasingly negative until the 1960s (Figure 3). A change point in the 1970s is associated with a trend towards more positive NAO values and has been the subject of much previous research (Bardossy and Caspary, 1990;Smith, 1995;Vincent and Vallon, 1997;Weber, 1997;Hoppe and Kiely, 1999;Kiely, 1999;Werner et al 2000;Brunetti et al, 2001). The change point in 1980 is identified as having the highest probability (0.87) of the four change points identified, the timing of which is consistent with the findings of Hurrell (1995).…”

“…A number of studies have identified a change point in climate as having occurred during the early 1970s (Hoppe and Kiely, 1999;Kiely, 1999) resulting in increases in precipitation in Ireland (Kiely, 1999) and Scotland (Smith, 1995), a change in the meteorological controls of Glacier de Sarennes during the ablation season (Vincent and Vallon, 1997), increasing precipitation intensity in Italy (Brunetti et al, 2001), increasing temperature at 300 hPa in the lower and middle latitudes (Weber, 1997) and increasing 700 mb heights over western Canada (McCabe and Fountain, 1995). This period also corresponds with a shift in the seasonal zonal frequency over Europe as outlined by Bardossy and Caspary (1990).…”

Changes in the probability of extreme daily precipitation observed from 1951 to 2002 in the Iberian Peninsula

“…A suitable approximation for daily precipitation data is given by the gamma distribution, which allows a compact description of the entire distribution by two parameters (Groisman et al, 1999(Groisman et al, , 2005Brunetti et al, 2001;Voss et al, 2002). We have chosen to base our analysis on the gamma distribution to give a uniformly rigorous and systematic approach.…”

“…In order to understand changes in the observed precipitation as an indicator of climate changes, daily precipitation series must be analysed (Jones et al, 1999;Karl et al, 1999;Brunetti et al, 2001). The analysis of daily precipitation in the Iberian Peninsula has received scarce attention, probably because of the lack of highquality daily data.…”

Spatial and temporal variability of the daily rainfall regime in Catalonia (northeastern Spain), 1950–2000

“…The results of Goodess and Jones (2002) for the Iberian Peninsula show a tendency towards more, less-intensive rain across much of Iberia, with a tendency towards days of increasingly intensive rain along the southeastern Mediterranean coast. Brunetti et al (2000Brunetti et al ( , 2001 detected positive trends for rainfall intensity for several gauges in northeastern Italy. These positive trends are due to an increase in extreme precipitation.…”