| With the accelerated process of urbanization and industrialization, urban heat island effect has become one of the serious environmental problems in the society. The urban green patches both can produce oasis effect on all scales, which play an effect role of alleviating urban heat island effect. The shape feature of green patches is an important factor to affect the efficiency of cooling and humidifying. The small green patches as important parts of urban green space system in cities, carrying out on the correlation studies between the shape feature of small and medium sized green patches and cooling and humidifying efficiencies, is of great practical significance. It provides a scientific guidance for the future urban green space system planning. Thus it fully enhances the cooling and humidifying efficiencies of the small green patches, and save the land for urban construction and practice intensive society the advanced concept. This study aims at carrying out the correlation between the shape features and the cooling and humidifying efficiencies of totally 79 small and medium sized green patches in Beijing Olympic Forest Park, Chaoyang Park, Dongshengbajia country park, Haidian Park and Heqing Road a side, acquiring the correlation between the shape feature of small green patches in different time periods and the effects of cooling and humidifying, and exploring the optimal interval of the cooling and humidifying efficiency of shape feature variable of small and medium sized green patches in different periods; According to the area demand of different green patches in urban green space construction, cope an mathematical model and strategies for the construction of the corresponding shape feature variables and the effects of cooling and humidifying, which providing scientific guidance and theoretical basis to improve the ecological benefits for a limited green patches area. The experimental work and research results are as follows:(1) 79 small and medium green patches of canopy density, green area, green space shape in Beijing (perimeter and perimeter to area ratio, rectangular perimeter ratio, shape index and shape index, reciprocal) as the research object. According to the experiment of the temperature and humidity difference between the green patches measured, study the correlation between the characteristics of the green space and the effect of cooling and humidification at different periods of time. The results showed that the efficiency of cooling and humidifying in the medium and small green patches was varied in different time periods. There are also varieties in different area classification standards. The correlation between the characteristics of green space resulting in such phenomenon and the cooling and humidification was also varied in different time and area.(2) Medium and small sized green patches have the city cold island effect and the wet island effect, can effectively alleviate the urban heat island effect in a certain extent. In the morning (10:00-12:00), the average temperature of the small green patches in the city is lower 6.1℃ than that of the surrounding environment, and the average relative humidity is higher 17.64%than that of the surrounding environment. In high temperature period (12:00-14:00), the average temperature of the small green patches in the city is lower 6.82℃ than that of the surrounding environment, and the average relative humidity is higher 16.79% than that of the surrounding environment. In the afternoon (14:00-18:00), the average temperature of the small green patches in the city is lower 7.01℃ than that of the surrounding environment, and the average relative humidity is higher 18.80% than that of the surrounding environment. In all day (10:00-18:00), the average temperature of the small green patches in the city is lower 6.64℃ than that of the surrounding environment, and the average relative humidity is higher 17.74% than that of the surrounding environment.(3) The canopy density and shape characteristics of related variables of green patches in most of the time in the measured had a significant or extremely significant negative correlation with the effect of cooling and humidifying. The three variables, perimeter area ratio, rectangular perimeter ratio and shape index of green patches, impact more on the temperature and humidity benefit of small and medium sized green patches, but impact less on canopy density and perimeter, and last on area.(4) The linear and logarithmic relationship between the characteristic variables of small and medium sized green patches and the efficiency of cooling and humidifying was studied quantitatively. The linear function relationship between the characteristic variables of green patches and the efficiency of cooling and humidifying in high temperature and all day periods was studied quantitatively, and the mathematical model and coping strategies are given.(5) At different time periods, the effect of shape characteristic parameter in cooling and increasing humidity is not consistent. In high temperature period (12:00-14:00), when the shape index is located in the 1.08-1.63 region, the green patches can play the best role of cooling and humidification, which the average temperature and humidity were 7.51℃ and 18.40% respectively. In the afternoon (14:00-18:00), when the perimeter area ratio is located in the 0.0201-0.0436 region, the green patches can play the best role of cooling and humidification, which the average temperature and humidity were 7.64℃ and 21.46% respectively. In all day(10:00-18:00), when the shape index is located in the 1.08-1.63 region, the green patches can play the best role of cooling and humidification, which the average temperature and humidity were 7.20℃ and 19.59% respectively. When the value of shape characteristic parameter is in the optimal range, the green patch can play a significant role in cooling and humidifying.(6) Study on the green patches of different area, and study the correlation between the high temperature period (12:00-14:00) and all day (10:00-18:00) correlation variables and the benefit of cooling and humidifying, giving a result that:shape characteristic variables have different effects on the benefits of cooling and humidifying of green patches in different area. Compared with medium green patches (3-5ha area), because of the instability of the internal environment, the shape feature of the small green patches (1-2ha area) has a greater impact on the efficiency of cooling and humidifying. In the planning of small green patches (about 1-2ha), we should pay more attention to the reasonable design and grasp of the shape, and make it better to play the role of cooling and humidification.(7) In high temperature period (12:00-14:00) and all day (10:00-18:00), green patches of different area can both play a good role in reducing the temperature and increasing humidity, so as to achieve the purpose of effective mitigation of urban heat island effect. So in the city planning of green space system, in an effort to improve the vegetation canopy density and green patches, should follow the design standards of the green shape with nearly circular and numerable. On the urban scale, improve the uniformity of the distribution of green space patches as far as possible. In the area that its urban greening land is highly scarce or does not have the conditions to build large green space like Beijing city, the construction of evenly distributed small and medium sized green patches should be advocated, because their role is very significant and can be achieved. The effect of cooling and humidification of evenly distributed medium and small green patches is better than that of large green patches. |
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