Characteristics of thermal environment and water budget of a forest and a lawn developed

Seasonal change of heat budget was measured from June to December in 1985 at both a natural forest and a lawn in Kibougaoka Park, Shiga prefecture, in order to make clear the differences in micrometeorological and hydrological characteristics. A analyzing equipment based on the Bowen ratio method was developed originally for the present study in order to obtain each heat budget component instantaneously. Air temperature over the lawn site increased rapidly than that over the forest site on a summer midday. Humidity above and inside the forest was slightly higher than that of the lawn. On a summer clear day, about 4% of net radiation (Rn) was stored up in the space of the forest as latent heat, sensible heat, and conductive heat to vegetation. In the afternoon, a portion of sensible and vegetation heat had changed in storage state to latent heat, which shows that there was a day period circultation of moisture inside the forest space. These characteristics of heat storage and circulation of moisture is one of mechanisms which make a moderate microclimate of forest during summer. Daily evapotranspiration (ET) at the lawn site decreased with the length of clear days, and was always lower than that at the forest, while ET of the forest didn't decrease. When the accumulated solar radiation (RS) was over sbout 90MJ/m2, ET at the lawn decreased rapidly. Yearly accumulation of ET was evaluated 968mm for the forest and 605mm for the lawm, by the heat budget analysis using the measured data. Discussions of heat budget and run-off analysis showed that the soil water capacity of the lawn was about 18mm, while it was more than 83mm for the forest. The low soil water capacity of the lawn makes the surface run-off to increase during heavy rain and to decrease ET rapidly during long term clear days. The differences in micrometeorological and hydrological characteristics mentioned above seemed to appear when a forest is developed to a lawn. Therefore a careful assessment should be carried out before development of a forest.