| Urban green space is an important component of urban ecosystem and provides security guarantee for growing urban residents.The urban microclimate environment has directly impact on people's production and daily life,and the benefits provided by urban green space, such as humidifying,cooling,shading,regulating wind speed and easing urban heat island effect,are increasingly concerned and stressed.Exploring and studying the laws between urban green space and microclimate are very important to guide urban green system construction,improve the quality of living environment,save energy,and protect environment, etc.The maliy content of the paper was summarized as follows:Firstly,status and significance of microclimate were set forth.According to the study progress at home and abroad,the trends of microclimate were prospected.In fieldworks,based on two typical urban green plots in Xi'an,the indexes at fixed sites were observed timely and analyzed by mythology tools.The results showed:1)The diurnal fluctuation of temperature or humidity were significantly different in spring.The order of temperature is:P1＜Bare land,Under trees＜Shadow＜Lawn,P2＜Small hard square,and the order of humidity was contrary to the temperature;Intensity of illumination layered and synchronized at all levels,the shading rate of canopy was dramatic in sunny days and tended to reunification in rainy days.The diurnal changes of anion concentration varied by temperature,humidity,wind speed,human disturbance,and other factors.The range of anion concentration was 200-1600 per Cc,and showed higher levels in forest park,more than 1000 per Cc,and is up to 2800 per Cc.2)In the summer,the temperature presented a non-uniform gradient decrease in plots and changed faster near edge-side;until the distance to the edge of forest(DEF)was over 30 m that the temperature was not stable.The largest drop of daily average temperature was nearly 3.5℃,and humidity increased nearly 9 percent;It was much cooler and moister under the trees or shrubs with higher LAI.Compared with hard square,the cooling and humidification effect was significant in urban green space.3)The temperature and humidity effect of green space in the autumn was weaker than that in the summer,but the some of the difference of temperature or humidity were still significant in forest,and the trends were similar to the summer.4)The temperature and humidity effect in deciduous green space on was insignificant in winter,but evergreen vegetation can still play a role in cooling and humidifiers through the shading effect.In sum,there is certain temperature and humidity effect under the trees and shrubs in green space during the daytime and it was much more significant in morning;the maximum distinction appeared in the summer,followed by the spring and autumn,and was minor in the winter.The illumination was correlated with LAI to a certain extent,and was down exponentially.While LAI＞2.0,the rate of shading was more than 80 percent.Green space can prolong hours in outdoors and reduce the discomfort index, and that the greater scale,the better effect.By analyzing the efficiency of LVV_H,it objectively illustrated that the tree with lager crown and higher LAI was the preference for shading.At last,based on the traditional theory of ecology,ecology field theory,theory of landscape ecology,the theory of system of organic evolution and the dissipation(the law of entropy),the roles of microclimate in the construction of urban ecological environment were elaborated.According to the principles of urban planning and design,combining with ecology, forestry,landscaping,and other related knowledge and theories,the strategies to build well microclimate with the urban green space construction were summarized.In short,the urban green space is surrounded by complex and volatile energy flow, matter flow,and informational flow.The microclimate relative to the wild forestland presents an unstable performance.The state of green space to improve the microclimate is real-time, and shows regular at the macro,but complex and changeable at the micro.Increasing the amount of vegetation quantity,keeping well structure of community and maintaining a good form of the landscape,are the basis for building good microclimate,and it will play an important role to improve the quality of the environment,and conserve energy,etc. |
