The cooling effect of plant (forest) and water surface (lake) on the thermal environment in urban area was studied by the field observations and numerical experiments. At first, field observations were carried out at the three sites, that is, around a single tree, the Senzokuike Pond and the Meiji shrine. In all the cases, the cooling effect of forest or pond was shown remarkable, and the cooling ratio per the unit area decreased in proportion to their scales Secondly, 3D numerical experiments were performed to investigate the heat and momentum transfer from the water surface. The results show that the differences of roughness height between water surface and surrounding area have much effect on the mechanism of heat and momentum transfer.