Measuring temperature trends in the Mediterranean basin

Climate change has been the subject of intensive research in recent decades, with temperature being one of the key variables that helps to characterise the Earth's climate. This study analyses the main features and temperature trend recorded on the Mediterranean coast. Daily maximum and minimum temperatures recorded over 40 years (1965–2004) at 52 stations spanning the coast of the Mediterranean Sea were examined for long-term trends. Four statistical indicators, namely, the median, the interquartile range, the Yule-Kendall index, and the robust kurtosis were calculated in order to group measuring stations that displayed similar features. The lowest recorded temperatures, around 15.8 and 7.5 °C for the maximum and minimum, respectively, were reached on the Black Sea, whereas the highest recorded temperatures, 21.1 and 13.0 °C, were obtained at low latitudes. Skewness was slightly positive at most stations. Moreover, temperature distributions were flatter than the Gaussian distribution. The final part of this study considers temperature trends using a harmonic model that yielded an increase of around 0.004, 0.023, and 0.039 °C year−1 for the first, second, and third terciles, respectively, when considering maximum temperature, and slightly higher for the minimum temperature, 0.010, 0.025, and 0.044 °C year−1, respectively. The amplitude of the maximum and minimum temperature yearly cycle presented the highest value on the Black Sea, whereas the lowest was found at low latitude stations. Finally, annual amplitude trends ranged from 0.006 to 0.027 °C year−1 for maximum temperature and were slightly higher for minimum temperature, between 0.011 and 0.029 °C year−1.