From the graph above, we can understand that the Tokyo’s humidity is decrease begin from Nov till Feb, and increase in March until August, and then begin to decrease from September. The high humidity is recorded in period of July-August, when the precipitation level is low. However, humidity is influenced not only from temperature but also the local and regional air pressure characteristics. In local level, such as Tokyo, humidity also could be influenced by high sky building, traffics, every impervious surface, etc which is influence land surface temperature. From the graph is seen that humidity has linear and positive correlation with temperature, but negative correlation with precipitation in July-August
The termonology of relative humidity (the ratio of the partial pressure of water vapor in the air-water mixture to the saturated vapor pressure of water at “some day” conditions) is generally used in daily weather forecast. Generally in high altitude and natural tropical forest in equator have high humidity level. High humidity will reduce the effectiveness of sweating to cool the body due to the reduced rate of water evaporation from the skin. This phenomenon could be measured using a heat index table, which is usually used during the monsoonal dry season in equator and summer season in high altitude.
In Japan, especially in city with much impervious surfaces and low precipitation, summer seasons is the time when peoples need to be carefully from heatstroke due to heatwave. in year 2011 at least 26 people died. And Hita City, in Oita Prefecture recorded had the highest temperature level (35.4 degree Celsius)