The GAA is situated in a small peninsula located in the southeastern edge of the Greek
mainland. The central part of GAA is the Athens basin that covers an area of 450 km2 with

high population density, 8000 inhabitants per km2.

The climate of GAA is typical "Mediterranean”, with mild winter and dry hot summer. The monthly mean temperature varies between 9.3° in January and 27° in July and the annual precipitation is 376 mm. The prolonged sunshine duration is characteristic of the regional climate, with annual value 2884 hours.

Hourly values of ambient air temperature and humidity were measured in 23 experimental stations, being installed in the Athens urban and suburban region for a period of two years, 1997 and 1998. The sites were selected as a way to study areas with different building density and traffic load that are located along the north-south and east-west axes of the Athens basin and to get information about the boundary conditions around the basin. Seven stations were placed in the central area of Athens while fifteen stations were placed in urban areas and in a radial configuration around Athens centre. Station 2 was situated in the slope of Hymettus mountain (at an altitude of about 500 m), in an almost rural, non built-up region with moderate vegetation and no traffic. The location of the station was selected in a way that the effect of the local flows is substantially reduced. Since this station was nearly free from urban climate modifying effects, it was used as the rural station in this study, and is mentioned as "reference”.

The specific climatic conditions measured in the reference as well as in the urban stations are given in Tables 1-2. These specific years have been selected as both present extreme characteristics. In fact, 1997 is characterised by the highest heat island intensity measured in the city, while 1998 by the lowest one. Thus, use of the selected climatic data may provide the upper and lower limits of the energy cost and ecological footprint.