Recent trends in seasonal and annual precipitation indices in Tuscany (Italy)

Abstract

Global warming alters the hydrological cycle since a rise in temperature leads to an increase in the moistureholding capacity of the atmosphere at a rate of about 7 %/°C . This fact can influence the global, but also local characteristics of precipitation, such as total amount and intensity. Therefore, it is important to study changes in rainfall regime in regions with complex orography, like Tuscany, where there are strong spatial gradients in precipitation amounts. The aim of this study is to look for temporal change in precipitation from 1955 to 2007 searching for spatial differences. Daily data of 21 meteorological stations were analyzed to identify trends in seasonal and annual precipitation indices. Cluster analysis applied to principal components was applied to identify homogeneous groups of stations. A decrease in precipitation was observed at annual time scale, during winter and spring, especially in northwestern areas. Wet days highlighted a decrease in all of Tuscany, due to the same seasons. In northern Tuscany, the decrease in rainfall amount was mainly determined by a lower frequency of rainy events which in turn caused a decrease in the occurrence of extreme daily precipitation events (75th, 90th, and 95th percentile). In central-southern Tuscany, no significant changes were observed except for an increase in precipitation fraction, due to extreme events and in mean daily total amount for wet days. These results are consistent with recent findings for the Mediterranean area and confirm the usefulness of cluster analysis for the analysis of the spatial distribution of precipitation.

Changes in temporal distribution of precipitation in a Mediterranean area (Tuscany, Italy) 1955–2013

“…This pattern, with a decreasing tendency in precipitation during winter and early spring (concerning trends calculated from the middle of the 20th century), is consistent with the results of Bartolini et al . () for Tuscany, Pavan et al . () for Emilia‐Romagna, Romano and Preziosi () for central Italy, Toreti et al .…”

“…Daily rainfall data for the period 1955–2013 were collected from 35 weather stations (Table ), most of them also used in Bartolini et al . ().…”

“…Also in Italy, country characterized by an extremely complex climate and orography, recent precipitation trends were found very heterogeneous, depending on the sum of different regional climates. Some authors reported prevalence of not significant negative trends in rainfall amount and in the number of wet days (Brunetti et al, ; Diodato, ; Toreti et al, ; Bartolini et al, ) in spite of an increase in precipitation fraction due to extremes and in the hourly average intensity of rain (Pavan et al, ; Bartolini et al, ). Increased variability in precipitation and water cycle modification have been shown to be possible causes of an increase in risk of floods and droughts (Allen and Ingram, ; Mariotti et al, ; Klik and Truman, ; Huntington, ; Mauguet, ).…”

Trends of precipitation characteristics in the Czech Republic over 1961–2012, their spatial patterns and links to temperature and the North Atlantic Oscillation

“…The 90th percentiles are computed from wet days for the 1961-1990 reference period. The indices selected here have been used also in other studies for different regions around Europe (Bartholy and Pongracz, 2010;Valencia et al, 2012;Bartolini et al, 2014).…”

Linking crop yields in Tuscany, Italy, to large-scale atmospheric variability, circulation regimes and weather types

“…Bartolini et al . (2013), Vergni and Todisco (2011) and Orlandini et al . (2008) affirm that there is an increasing trend of precipitation in North Europe, while southern Europe is currently affected by a decrease in the annual precipitation and by a change in seasonal rainfall patterns.…”