Evaluation of Green Space in Terms of Its Effect in Reducing Temperature

To derive the relative contribution of woodland area and amount of anthropogenic heat emissions to temperature formation from Eq. (2.1), we obtained Eq. (2.2), which applies when the Y-value is identical to the intercept. Here X1 is the woodland area (m2) and X2 is the amount of anthropogenic heat emission (GJ/day):

0.0001 (Xi) = 0.0033 (X2) (2.2)

From Eq. (2.2), the cooling effect of trees per grid cell (150 x 150 m = 22,500 m2) would be equivalent to offsetting 681.8 GJ of anthropogenic heat emissions per day. To explore the implications, let us convert this 681.8 GJ/day into the anthropogenic heat emissions from commercial buildings, which are typical of the type and size of buildings in Minato-ku, and consider how many square meters of floor area this emission intensity would equate to. Referring to the heat emission intensities of commercial buildings (August estimates) given in the Ministry of Land, Infrastruc­ture, Transport and Tourism and Ministry of the Environment (2004), the intensity of anthropogenic heat released per day from a commercial building ranked as having from 2,000 m2 to less than 5,000 m2 of floor area is stated as being 3,220.29 kJ/m2/day in total (sensible heat, 2,925.66 kJ/m2/day; latent heat, 270.87 kJ/m2/day; sewage heat, 23.76 kJ/m2/day). Using these emission intensities, and calculating back from the calculated cooling effect (681.8 GJ/day), we derive a figure of 211,726 m2 as the total floor area of multiple commercial buildings of the type typical in Minato-ku. That is, 681.8 GJ/day of heat would be equivalent to the anthropogenic heat emissions per day from approximately 70 commercial buildings each with a floor area of about 3,000 m2. Note that this figure of 681.8 GJ anthropogenic heat released per day, as described in detail in the 2003 Investigative Report, is the total amount of heat released to the atmosphere, primarily from external air conditioning units and ventilation systems in an office environment that has heat sources such as lights, computers, air conditioners, ventilation systems, kitchen equipment, water heaters, and various other equipment in operation, together with the waste heat released through sewage systems.

Therefore, from Eq. (2.2), the presence of trees covering an area of 22,500 m2 would have the effect of moderating or offsetting a temperature rise of 2.25 °C caused by 681.8 GJ of heat released per day from all the various systems and equipment installed in approximately 70 office buildings each having a floor area of approximately 3,000 m2.