Recent changes of temperature extremes over Italy: an index-based analysis

Abstract

The assessment of climate change impacts requires updated estimates of the tendencies in temperature extremes. With the objective of studying recent variations in frequency and intensity of temperature extremes over Italy, a collection of daily minimum and maximum temperature time series was selected for the calculation of a set of indices recommended by the Expert Team on Climate Change Detection and Indices (ETCCDI). The trend of each index was investigated through a non-parametric statistical analysis over the last half-century (1961–2011), and its spatial variability was illustrated through trend maps. Mean national-scale trends were also assessed at annual and seasonal level. The results show that mean annual series exhibit a general warming tendency from 1961 to 2011, with significant trends for summer days, tropical nights, heat waves, and percentile-based indices at most stations, with warming trends more pronounced in summer and spring and weaker in winter and autumn. As a changepoint was identified in 1977 for the minimum (Tmin) and maximum temperature (Tmax) Italian annual series, the trend analysis was also performed for the two sub-periods 1961–1977 and 1978–2011. Non-significant “cooling” trends characterize the sub-period 1961–1977, while significant “warming” trends were identified over the period 1978–2011. This study updates previous research in the extent of time series, in the number of indices and in the approach followed for their analysis, providing useful information for evaluating the impacts of temperature extremes in the context of a changing climate in Italy.