Investigation of urban heat island in Greek cities

In recent years, research on climate change has increased, due to the increase in average global temperature observed mainly in the '80s and '90s. However, one of the main factors that may affect its measurement is to measure the urban heat island effect. In this graduate thesis, the possible existence of the urban heat island in Greek cities is investigated. Urban areas account for only 1% of the Earth's surface, but at the same time, most of the best preserved stations with many years of record data are placed in the center or on the edge of urban centers. Thus, it is difficult to measure the temperature, without taking the contribution of urbanization into account (Connolly and Connolly, 2014). In this thesis, we investigated whether urbanization factors (such as the growth of population, construction activity and vehicles) lead to changes in the microclimate in urban centers and the emergence of increased temperatures. For this purpose, data on different scales (10 min-1 per month) were used by different agencies. The comparison took place in different regions: (a) In different suburbs of the Attica region. For this purpose, we used stations in the center of Athens, in suburbs with high population and building density, in suburbs with low population and building density and more greenery and suburbs outside the congested area of the basin. For greater safety, at least two stations were selected from each category (chapter 5). (b) In the same way, in other cities the analysis was carried out with stations located both in the center and outside (chapter 6). (c) In different cities all over Greece for a duration of the last 65 years (chapter 7). We confirmed the existence of the urban heat island effect in all Greek cities investigated, with an intensity ranging from 0.3 to 1.5°C. The more densely populated a city is, the higher temperatures it presents, with smaller standard deviation. The phenomenon is most noticeable in winter months and during the evening hours. In the study of monthly temperatures over the last 65 years throughout Greece, it was found that only stations located in city centers and airports recorded an increase in slopes. Altogether, for the above mentioned period, there has been an increase in the mean temperatures of 0.018 °C per decade. More specifically, the slope of the temperature changes per decade is constantly growing, starting from negative values in the period 1950-1980, continuing with positive ones until 2000 and then decreasing until 2013 (remaining in positive values though). So, it follows the increase in population and construction activity. Finally, it was estimated that the urban heat island causes a reduction in the annual energy consumption and a negligible increase in evapotranspiration during the summer months.