Recent trends in daily temperature extremes over the Basilicata Region, Southern Italy (1951 - 2010)

Series of annual and seasonal temperature from 18 stations, distributed all over the Basilicata region (southern Italy), were studied for the period 1951-2010. The analysis is based on high-quality and homogenous daily minimum and maximum temperature. Both minimum (Tmin) and maximum (Tmax) temperatures increased, especially after 1971. The trend is most remarkable for Tmin, with 11 stations showing a positive statistically significant trend. Seasonal results are similar except for autumn where an opposite trend has been recorded. Also Tmax show an overall positive trend, which is statistically significant only for 2 stations. Seasonal results show upward trend in spring and summer, whereas during winter and autumn, Tmax tend to decrease. Six indices were used to assess changes in both the cold and hot tails of the daily temperature distributions. The presence of trends was assessed by means of the Mann-Kendall test. Results reveal a general upward tendency for both warm days (TX90p) and warm nights (TN90p) especially due to the increase in temperature becomes since 1971. This datum is confirmed at seasonal level, with spring and summer the main seasons responsible for the trend. In general both cold days (Tx10) and cold nights (Tn10) showed negative trends. It seems that this negative trend stems from the strong decrease of Tmin during winter, spring and summer. Both annual and seasonal number of frost days (Fd) show an overall negative trend. A few positive trends can also be found in northern Basilicata. The intra-annual extreme temperature range (ETR) index shows a general positive trend. In winter, decreased ETR appears for the majority of the stations examined although the trend has been inverted in the last two normals. During spring, the trend is strongly positive, especially in the last two climate normals. Summer and autumn show a similar predominant negative trend.