Homogenization of instrumental time series of air temperature in Central Italy (1930−2015)

ong-term and high quality instrumental air temperature data are important for reducing the uncertainty of past temperature trends at local and global scales, and for the projection of future expected changes. Currently this type of data is limited in the Mediterranean, which is particularly important since this region is considered a hot spot for climate change. To cover the data gap for Central Italy, a set of territorially dense long-term time series of temperature data covering different climate areas in the Abruzzo region is presented in this work. Due to the possible presence of inhomogeneities (non-climatology irregularities in the data set), a homogenization process was applied to the data. Monthly maximum and minimum temperatures measured at 22 stations were homogenized for the period 1930-2015 using the software HOMER v.2.6. All stations had at least 1 break in the time series, for a total of 89 and 80 inhomogeneities identified in the maximum and minimum temperature series, respectively. The annual amplitude of breaks in the annual series ranged between 0-4.44 degrees C for the maximum temperatures and 0.01-3.75 degrees C for the minimum temperatures. The trend of annual mean temperatures showed increasing temperatures at a regional level starting in the early 20th century, with a greater rate especially after 1980 (0.060 degrees C yr(-1)). The temperature trends, analysed in 3 different intervals (1930-1979, 1950-2015 and 1980-2015) for the 22 time series, demonstrate a slight increase in the rate of warming in the coastal and hilly area during the period 1930-1979 and highlight the importance of local measurements.