Assessment of the impact of arificial reservoirs to the microclimate

The subject of this postgraduate thesis is the study of the impact of a reservoir to the climate of the surrounding area (microclimate). Two of the most significant reservoirs of Greece were studied, the dam of Pournari and the dam of Mornos. Changes to the microclimate are the result of the changes to the energy balance due to the presence of the water body, which has greater heat capacity than the ground and absorbs greater latent heat because of the increase of evaporation. The theoretical approach using the energy balance is difficult to give quantitative results because of the existence of several unknown variables. At the main body of the research, statistical analyses on meteorological measurements like temperature, humidity, precipitation, etc around the dam area are done. Two groups of meteorological data, those referring to the climate before the dam construction and those after are compared. Statistical methods (Kruskal-Wallis test, graphical double mass curve, rank sum test, two sample t test, difference of proportions test) tested whether these two groups come from the same population or not. In every case, the data included measurements both near and away from the dam. Possible climate change at a distance from the reservoir may have been caused by general climate changes irrelative to the reservoir fill. Thus, it is avoided to attribute this climate difference to the presence of the dam. According to the statistical analysis of the meteorological data, the only climate change that is objectively verified is a small increase at the value of the minimum temperature at the station near the dam in comparison to the station located away from the dam. Because the change is observed only to one of the meteorological parameters, it can not be stated that the construction of a reservoir causes significant changes in the microclimate. In addition, the inhabitants' opinion about the dam influence on the climate was studied. Questionnaires were distributed to the urban population of Arta and Lidoriki, which are the settlements closest to the dams. The answers were analyzed using the Statgraphics statistical software. According to the answers of questionnaires, it seems that most of the climatic conditions changed after the reservoir construction. It has to be pointed out that the questionnaires offer a subjective opinion, while the actual climate conditions are obtained by the meteorological measurements.