Trends in daily temperature extremes over the Basilicata region (southern Italy) from 1951 to 2010 in a Mediterranean climatic context

Changes in annual and seasonal temperatures were studied from 18 stations, distributed all over the Basilicata region (southern Italy), for the 1951-2010 period. The analysis is based on high-quality and homogenous daily minimum and maximum temperatures. Both minimum (Tmin) and maximum (Tmax) temperatures increase, especially after 1971. Seasonal results show upward trends in Tmin in winter, spring and summer, whereas they show downward trends in Tmin in autumn, especially in the last normal 1981-2010. Tmax also shows upward trends in spring and summer, whereas it tends to decrease during winter and autumn. The intra-annual extreme temperature range (ETR) index also shows a general positive trend, especially during spring. Eleven indices were used to assess the changes in both the cold andwarm tails of the daily temperature distribution. The presence of trends was assessed by means of the Mann-Kendall test. The results reveal a general upward tendency onwarm days (TX90),warm nights (TN90) and tropical nights (T20) especially because of an increase in temperature after 1971. This datum is fully confirmed in summer which is the season mainly responsible for this trend. The annual occurrence of summer days (SU) and very warm days (TX99) is weakly increasing. The majority of cold extremes, i.e. very cold nights (TN1), cold days (TX10), cold nights (TN10), frost days (FD) and ice days (ID) showed negative trends, thus confirming the overall warming trend in the Basilicata region. This negative trend could stem from the strong increase of Tmin during winter, spring and summer.