Study On Cooling And Humidifying Effect Of Greenbelts Of Shijiazhuang, Hebei Province In Autumn

The environmental problems have become the hot topics among the people in recentyears. Temperature and humidity are closely related to comfort index about human life. It willbe harmful to human health when the temperature too high or humidity is too low. Greenspaces in the city have played an inestimable role in maintaining the ecological environmentand improving the benefits of ecological system. The construction of urban green spaces alsohave changed to pay more attention to its ecological function rather than artistic and itsrelated researches have more practicability. The study on ecological benefits in abroad startedearly and they have got many achievements. The trend of their study has been transformedfrom the qualitative description to quantitative research. Domestic research which still lies aqualitative description stage started late in this field and the scope of study prefers to one-side,even lack of systematic description. However, the quantitative research on benefits ofecological system has been made a lot of meaningful attempt and has obtained certainachievement. But the study on cooling and humidifying effect and comfort index ofgreenbelts in Shijiangzhuang City is relatively less than any other places, so the study aboutgreen places in Shijiazhuang is of great importance. Based on the previous study, three kindsof green spaces including the park, forestland and farmland in Shijiazhuang was seeked as theresearch object. Monitoring time was selected in month9-10,2012and month9-10,2013which were sunny days without wind（or the speed of wind less than0.2m/s）.The airhumidity below the height of1.5m above various underlying surfaces was measured atdaytime in autumn. Then analyze the basic distribute regulation of humidity from horizontaland vertical directions at different times in autumn days. What a most important thing is toanalyze the relationship between humidifying and cooling effect of vegetation and areas,shapes, environment. Finally, make an evaluation about the human comfort to various greenspaces.The results of the study mainly include the following points. First, the cooling andhumidifying effect of greenbelts with the area above0.13km2under the influence of watertends to stable. The cooling and humidifying effect will not get stronger with the bigger area. What influence the humidifying effect is water, plant density and species distributionuniformity. The cooling and humidifying effect of vegetation get stronger with the ratio ofwater area and plant area. There have significant correlation with the cooling and humidifyingeffect and plant density.Second, the cooling and humidifying effect of vegetation with the influence of water isweaker than vegetation without influence of water at7:00~9:00when there have similar areaamong greenbelts. However, the cooling and humidifying effect of greenbelts with theinfluence of water is stronger than greenbelts without the influence of water at other daytime.All above show that plant density has become the major factor to influence cooling andhumidifying effect and water is the major factor at other daytime.Third, the shape index and plant height have significant influence to cooling effect ofvegetation. The cooling effect of vegetation get stronger with the shape index bigger. Thereare significant positive correlation between cooling effect and plant height. The shape indexhas nothing relationship with humidifying effect of vegetation. Factors influence humidifyingeffect of vegetation orderd by effect extent are plant density, plant height, shape index. Thehumidifying effect of vegetation get stronger with the bigger plant density under the conditionof same environment.Fourth, the cooling and humidifying effect of the green belts in park is stronger thanother kinds of greenbelts at the high temperature but it presents an opposite regular at the lowtemperature. The temperature is low in the morning and evening in autumn and thetemperature is high at noon when the contribution of the green space is the largest, therefore,the cooling and humidifying effect of parks have an advantage over other kinds of greenspaces.Fifth, the cooling and humidifying effect of various green spaces below1.5m height atvertical direction have certain differences and it has relationship with the height of vegetation.The cooling and humidifying effect gets weakened from down to up and the effect near theground is stronger than0.2m height significantly. The vegetation with low height have largercontact area with the air, thus its cooling and humidifying effect at vertical direction changewithin a wide range compared with the plants with higher height.Sixth, the density of areas covered by grass (100%coverage) which can store large amount of water and not easy to evaporate is larger. So atmospheric humidity close to theground is higher and the humidifying effect is stronger. Forest density is small, air exchangeunder1.5m between forest and environment is good and the ability of condensed water ispoor. The humidifying effect of vegetation is weak but the cooling effect is strong due to thetall plant. The humidifying effect of farmland is strong. The cooling effect of farmland isweaker than park and is stronger than arbors.Last, the comfort index of the massive greenbelt is larger than linear green space basedon the same size area. What influence human body comfort are shape index, ratio of watererea and greenbelts area, plant density, area and so on. The human body comfort gets higherwith the shape index of greenbelts get smaller under the same condition. There havesignificant positive correlation between body comfort and shape index of greenbelts. Thebody comfort tends to high with the bigger density of greenbelts under the same condition. Onthe whole, body comfort of park is higher than greenbelts with single arbors. Comfort offarmland is the worst.