城市公园景观秋冬季动态热效应

Diurnal variations of landscape thermal effect in city parks from the later autumn to early winter

在北京市3个公园中选择裸地、道路、林地、草地4种主要景观类型,通过2013年10月、11月、12月的实地监测数据,定量揭示不同景观类型地表温度、近地表空气温度和湿度的日间变化特征,并分析日间温湿度的均值、幅度大小、空气温湿度的匹配程度。4种景观类型日间地表和空气温度均呈单峰变化趋势,裸地、道路、林地、草地的地表温度最高值分别出现在14:00、12:00、14:00、12:00,空气温度最高值则都在14:00,相对湿度最大值出现在8:00,最小值在14:00。从日间均值来看,地表温度为裸地>道路>草地、林地,裸地的日均空气温度最高,4种景观的相对湿度差异不显著。从日间变化幅度来看,所有景观类型的地表温度均明显大于空气温度,尤其是裸地和道路的日间变化比林地和草地更加明显。通过定量分析4种景观类型的日间热环境动态变化,可以为城市热环境改善、景观设计和生态规划提供科学依据。

The urban landscape pattern is increasing changed as cities replace their natural land cover with impervious surfaces, buildings, and other infrastructure. The impacts of landscape changes have become a growing concern particularly for the ecosystem service in recent decades. It is well-known that city parks could provide multiple ecosystem services including temperature regulation services in different seasons. Some thermal characteristics of city parks may directly contribute to the degree of comforts for the mankind, such as the land surface temperature （LST）, near-surface air temperature （NAT）, and relative humidity （RH）. Generally, landscape types and pattern in parks are responsible for the extent and degree of local thermal effects. In this study, three city parks were selected to analysis the diurnal variations of thermal effects in Beijing. We measured LST, NAT, and RH in the grassland, forest, road, and bare land for three months from the later autumn to early winter. The study aims to assess the variations of LST, NAT, and RH as well as their relationships among different landscape types. The results showed that： （1） the lowest LST and NAT are at 8：00 whereas the highest values are different according to the types of landscape. The highest values of LST and NAT are at 14：00,12：00,14：00,12：00, respectively. The relative humidity reaches its lowest value at 14：00 （2） In the daytime, the decreasing orders of mean LST, NAT, and RH are bare land 〉 road 〉 grassland≈forest, bare land 〉 forest≈grassland=road, grassland≈road≈forest≈bare land, respectively. The LST and NAT are increasing with the decreasing RH for all landscape types. （3） The maximum difference in LST, NAT, and RH decrease as： bare land （13.5℃） 〉 road （10.0℃） 〉 grassland （7.5℃） 〉 forest （5.9℃）, bare land （7.4℃） ≈ road （7.3℃） 〉 forest （6.3℃） 〉 grassland （5.7℃）, bare land （20.8%） = road （20.8%） ≈grassland （19.5%）≈forest （18.8%）, respectively. （4） The relationship between LST and NAT are complex due to the various solar radiations in a day. Specifically, the daily variation of LST is greater than that of NAT for all the landscapes. The daily variation of LST and NAT is low in forest compared with the high variations in temperature of the grassland, bare land, and road. （5） The combination of temperature and humidity is represented by the difference between NAT and dew-point temperature. The hydrothermal environment reaches the driest and hottest conditions at 14：00. By quantifying thermal effects of different landscape types in city parks, this study can provide useful implication on the urban management to improve the thermal environment and related ecosystem services.