Efficiency Of Temperature And Humidity In Changsha Urban Forests

In order to objectively reflect the effect of the temperature and humidity of the urban forest, play the environmental effects of the Urban Forest, this article observe and analysis the temperature and humidity of Changsha Urban forest and Changsha weather station from2005to2011, the main results are as follows;(1) Temperature. Experimental results show that urban forest can reduce the maximum temperature in the summer and also raise the minimum temperature in the winter, urban forest have obvious characteristics of warm in winter and cool in summer. By comparison the monthly mean maximum temperature in urban forest and Changsha weather station, the temperature of inner forest is lower uo to7.8℃.The Urban forest makes different effects on the average temperature, the average maximum and minimum temperature of inner forest in five different weather types, especially strongest in sunny. The cooling effect on the temperature is strongest in June and July.(2) Soil temperature.The changes of soil average temperature inner and outside of forest are basically the same every month. The temperature of soil which depth from5to15cm was reducing gradually as the depth of the soil in spring and summer, and increasing in autumn and winter, the temperature of inner forest is always lower than outside the forest.The soil temperature at Oto20cm deep in and outside the forest changes are consistent under different weather conditions such as in fair weather, less cloudy, cloudy weather conditions. At0-15cm depth, the soil temperature is lower than outside the forest; at0-20cm depth, the change is the same in the cloudy and rainy days. By the influence of solar radiation and the canopy shielding effect, the soil temperature of inner forest is lower than outside the forest, and especially in sunny, it can be reduced by5.6℃, the difference of the soil temperature is a little, no more than2℃in winter. With the weather conditions followed by sunny, few clouds, more cloudy, cloudy, rainy, the solar radiation decreases, the difference of soil temperature is gradually decreasing, as demonstrated by sunny5.6℃, less cloudy5.1℃, more cloudy4.7℃, cloudy3.6℃, rainy3.2℃, which indicate the significantly effect of Urban forest in reducing the maximum temperature and enhancing the minimum temperature especially in sunny days.(3) Relative Humidity.The results show that:the average relative humidity changes of urban forest are basically the same. Due to the urban forest regulating, the relative humidity of inner forest is significantly higher than outside, and it is contrary in winter. The maximum of relative humidity is about85%in February, the minimum is76%in July.We can see from the average annual change in the relative humidity, in the sunny and cloudy days, the forest annual average relative humidity is less than Changsha weather station, the relative humidity is greater than the other weather inside the forest, the relative humidity value is close (less than1%).The relative humidity in and outside Forest is significantly different in different weather conditions, are expressed in rainy day>heavy day> more cloudy>less cloudy>sunny day. By comparison the urban forest and Changsha weather station, we can see that the maximum difference is14%in the sunny days of July, and the minimum difference is2.2%in March, By comparison the gap and Changsha weather station, the maximum difference is14.2%in the cloudy days of January, the minimum difference is3.6%in the less cloudy day in March.(4) Vapor pressure. In five different weather conditions, the vapor pressure within the forest were lower than outside the forest, the highest value of vapor pressure is in high temperature, high evaporation July, August, the lowest value is in the low temperature, low evaporation January, February. The vapor pressure difference is not obvious; the biggest difference is in August, about1.5hpa. By comparison the inner forest and Changsha weather station, the maximum difference is14.2hpa in the sunny days of July; the minimum difference is0.3hpa in the rainy day in December. By comparison the Gap and Changsha weather station, the maximum difference is4.7hpa in the sunny days of July; the minimum difference is0.3hpa in the rainy day in January.(5) Saturation deficit.The saturation deficit trends between inner and outside the forest are basically consistent. The difference is relatively small in spring and winter, but large in summer and autumn. The outside saturation deficit is higher than inner forest, but lower in autumn and winter. The maximum difference is2.9hpa in the sunny days of July, and the minimum difference is0.1hpa in the cloudy days of February.