30 years air temperature data analysis in Athens and Thessaloniki, Greece

Climate change has a major influence on urban environment, and it will continue to pose challenges in the future. The recorded observations on climate change is in line with the projected increase of the average annual temperature in Europe between 2 and 4 °C until the end of the century, as well as with the change of rainfall patterns and the prevalence of drier conditions in the summer months in the Mediterranean area and wetter winters in the Nordic countries. The frequency and intensity of extreme weather events such as heat waves and floods are expected to increase in the coming years. The socioeconomic impacts of climate change in urban areas are also very important. Demographic changes, such as the increase of the average life expectancy and the intense urbanization will increase the percentage of people who are vulnerable to conditions of high temperature and heat waves, with negative effects on health, productivity, social life and use of open public spaces. Furthermore, high temperatures can cause problems in fields such as transport, energy and water supply, along with an indirect effect on agriculture, tourism, urban microclimate and air quality. The current paper attempts to analyze the ambient air temperature in Athens and Thessaloniki for 30 years, namely the period 1983–2012, in order to explore trends in the two largest Greek cities. Descriptive statistics such as average minimum, average maximum and average monthly values of dry-bulb temperature, minimum, average and maximum daily temperature values of the three decades (80s, 90s and 00s) and the cumulative frequency of hourly temperatures per decade, were calculated, analyzed and presented. The number of days with maximum temperature above 25 °C (summer day) and equal or greater than 35 °C, in accordance with internationally agreed criteria and indicators, were also calculated. Likewise, long periods with daily maximum temperature above 35 °C were recorded and presented. The analysis was based on hourly measurements of two meteorological stations, of the National Observatory of Athens and the Aristotle University of Thessaloniki, for the relevant period. The results prove a statistically significant raising trend in temperature values in the studied areas from decade to decade, in addition to the statistically significant increase in the number of days with average above 25 °C and with a maximum equal or greater than 35 °C. The conclusions drawn are particularly useful for planning and implementing policies of adaptation to climate change in different sectors in favour of environment protection and human well-being. © 2016, Springer International Publishing Switzerland.