The effects of urbanization on the Athens National Observatory (NOA) long records are investigated, in the present study, examining the mean monthly maximum and minimum air temperature for the period 1925-1996, for NOA and the corresponding time series for Aliartos (ALI), a rural station located 70 km NW of Athens. The existing small urbanization effect in NOA before the second world war period increased after the war and up to about 1990, when the effect became stationary. The urbanization effect in NOA referred mainly to maximum temperature and to the warmer seasons of the year. It is attributed to the extensive building of Athens after the war around NOA site and up to the sea which increases the temperature of the sea breeze. The effect is also attributed to the rapid increase of the population and the number of motor vehicles mainly after 1970. Moreover the decreasing trend of precipitation during the period 1970-1990 may have contributed to the increase of maximum air temperature. The urbanization effect on maximum temperatures of NOA amounts about 2 Β°C in spring, summer and less in fall, while no urbanization effect is clear in winter.

The patterns of monthly precipitation distributions in Greece, during the months of the year, are studied. Using factor analysis T-mode on mean monthly precipitation for a long period, we try to establish characteristic patterns of precipitation distribution. Only two of the eigenvectors (factors) were found statistically significant, namely factor I, explaining 67% of total variance and referring to the months of the period from October to March (cold period) and factor II, explaining 23% of total variance and referring to the months from April to September (warm period). During the cold period precipitation is maximum on Western Greek mainland and along the Western Asia Minor coast and islands while minima are shown in Cyclades islands, Attika, Thessaly, Macedonia and Thrace. On the other hand, during the warm period precipitation shows maxima in Central and North continental areas and the interior of Peloponese while minima appeared again in Cyclades, Dodecanese and Crete. Finally, the various areas of the country are distributed in 4 categories, depending on the combination of plus or minus of the normalized factor scores, for each period.