| Urban blue-green space is the common name for urban water bodies and green spaces,which are an important part of the ecosystem and play an important role in regulating outdoor microclimate and mitigate the urban heat island effect.With the rapid development of cities,natural features such as vegetation and water bodies are being replaced by hard paved surfaces,and the area of blue-green space has been drastically reduced,further aggravating the urban heat island effect and seriously affecting outdoor thermal comfort.It is urgent to optimize the landscape indicators of blue-green space(lakeshore distance,walkway height to width ratio,plant layout and tree canopy size)and to improve the ability of blue-green space to regulate outdoor microclimate.This study takes Guilin city as an example and selects two lakeshore walkways and their attached blue-green spaces as research objects.By monitoring different weather environment parameters in winter and summer,the microclimate characteristics of the lakeshore walkways are analyzed and grasped;based on the orthogonal design test method,a simulation scheme is designed and various working conditions are simulated using ENVI-met software to propose a mathematical model and an optimal design scheme for the thermal comfort evaluation of the lakeshore walkways.The results of the study showed that solar radiation was the main factor affecting surface temperature,with a 13% cooling rate for natural features and 9.5% for artificial hard-paved surfaces under the same working conditions.The southern shore of the lake had a higher ability to regulate the environmental microclimate than the northern shore.The distance between the walkway and the lakeshore and the air temperature significance level of the walkway in winter and on cloudy days in summer were 0.021 and 0.037 respectively.The warming effect of the blue-green space gradually converted to a cooling effect when the distance between the walkway and the lakeshore exceeded 140 m in winter.The Universal Thermal Climate Index(UTCI)thermal stress levels was medium(26～32°C)and strong thermal stress level(32～38°C)when the walkway was 4 m from the lakeshore in summer,with a good thermal environment.The average air temperature of the walkway with the tworow open green walks was the highest,18.04°C in winter and 33.36°C in summer,and the warming effect was weaker at night than during the day in winter;the warming and humidity reduction effect of the one-sided composite green walks was the best in winter,0.141°C and0.40% respectively,and it was conducive to increasing the air flow rate,and the cooling effect of the two-sided composite green walks was the best in summer,0.093°C.In hot and sunny weather in summer,the percentage of very strong thermal stress level(38～46°C)was54.55% for the two-row open green walks,72.73% for the two-sided composite green walks and 63.64% for the one-sided composite green walks.In cloudy weather,the percentage of moderate and above thermal stress levels was 46.15% for the two-row open green walks,medium thermal stress levels for two-sided composite green walks and 76.92% for the onesided composite green walks.The smaller the height to width ratio of the walkway,the better the moisture reduction and warming effect,and the smaller the size of the tree canopy,the better its ability to regulate the surrounding environment.Air temperature and mean radiation temperature are significantly and positively correlated to the UTCI and Physiological Equivalent Temperature(PET).The combination of walkway height to width ratio of 1.0,two-sided composite green walks and tree canopy size of 9 m reduces air temperature by 0.131°C and mean radiation temperature by 2.717°C compared to the measured results.The relationship between landscape indicators of bluegreen spaces and the microclimate of the surrounding environment is established,and an outdoor thermal comfort evaluation model of urban blue-green spaces in northern Guangxi is proposed to provide reference for outdoor microclimate regulation and optimal design of blue-green spaces in the region. |
