Seven "green and blue" areas of different kinds are selected in Paris in order to measure their "cooling effect" during summer heat-waves. Air temperature is measured at two meters height in three different locations of each site : one sensor is located in the middle of the green or blue area, one is located from 5 to 50 m away and the last one is located from 50 to 150 m away from the green or blue area. The intra and intersites temperature differences are qualitatively analysed all along the day regarding to the morphology and the land-use of the sensor environment. Results show that the smaller is the park, the lower will be its cooling effect. The canal does not refresh well the air during night-time whereas its does refresh during day-time. Large areas mainly composed of low vegetation and a judicious distribution of trees seem to have the best potential to decrease the air temperature inside and outside the green area during day-time as well as during night-time. Quantitative analysis as well as denser measurement network should be implemented in order to confirm those preliminary conclusions.