**4.5 The effect of vegetation cover and water surfaces**

Vegetation significantly affects the overall environmental conditions that prevail in the city centres (Givoni, 1998) in two distinct, and equally important ways. Firstly, by shading the various materials (see 4.4) and secondly, by maintaining low surface temperatures through the process of transpiration. However, it should be noted that the surface temperatures of vegetative cover depend on the characteristics of the species, and mainly their ability to withstand drought. In this study, the grass surfaces measured temperatures according to their thickness and irrigation patterns. The temperature of surfaces of thick and regularly irrigated grass was lower than the environmental temperatures throughout the day. This was also the case for various surfaces of evergreen shrubs. On the contrary, a grass surface, which was fairly worn and dry, developed a maximum surface temperature of 45 oC, which was approximately 10 oC higher than the air temperature.

Water has a very positive contribution to the microclimate, because of its high heat capacity (1160 Wh/m3K (Oke, 1995)), and its ability to evaporate, which causes considerable air and surface temperature reduction with a simultaneous increase of relative humidity levels (Oikonomou, 2004). In this study, the temperatures of water surfaces (mainly fountains in two squares in Athens) measured were very low (mean maximum T=25,5 oC) compared to the corresponding air temperatures.
