Study On Temporal And Spatial Characteristics And Influencing Mechanism Of Thermal Environment In Central Urban Area Of Chongqing

With the acceleration of urbanization and the expansion of urban space,urban impervious surface replaces the original natural landscape,leading to more and more prominent urban thermal environment problems,among which the most obvious manifestation is the urban heat island effect.The deterioration of urban thermal environment will lead to a series of problems,such as the increase of energy consumption,the aggravation of pollution,the impact on the health of urban residents and the reduction of urban air quality,etc.,which will limit the sustainable development of the city.The construction cost of mountain cities is high,and the limited construction land leads to the characteristics of high density and high intensity of urban construction.Compared with other cities,the ecological environment of mountain cities is more fragile due to its special geographical environment,and the rapid urbanization process is easy to have a significant impact on the spatial and temporal pattern of mountain ecological environment and urban thermal environment.Therefore,the research on temporal and spatial variation of thermal environment in mountain cities and its influencing mechanism can provide scientific basis for ecological planning and construction of livable cities in mountain cities.In this paper,the temporal variation characteristics of thermal environment in the central urban area of Chongqing,a typical mountain city,are studied by using the urbanrural dichotomy method.Based on the local climate zoning(LCZ)theory,the spatiotemporal dynamic evolution process of local climate zoning in central chongqing was analyzed.Using remote sensing data and flow observation data,the spatial distribution characteristics of surface thermal environment and near-surface thermal environment in the central urban area of Chongqing are revealed.Based on the local climate zoning map,the relationship between the local climate zoning types and the surface and near-surface thermal environment in the central city of Chongqing was established.Then,the influencing factors and influencing mechanism of thermal environment in central urban area of Chongqing are analyzed from time and space scales,and the influence of heat island effect on heat wave and building energy consumption in central urban area of Chongqing is quantitatively studied.Finally,from the perspective of blue and green space,the corresponding strategies to improve the thermal environment of chongqing central urban area are put forward.The main conclusions of this paper are as follows:(1)The annual mean temperature,annual maximum temperature and annual minimum temperature in the central urban area of Chongqing showed a significant increasing trend,and the increasing rate was about 1.6 times of the global warming trend.The annual increase rate of heat island intensity increased at 0.13℃/10 a.The annual increase rate of daytime heat island intensity was more significant in spring and summer,and the annual increase rate of nighttime heat island intensity was more significant in autumn and winter.The annual growth rate of nocturnal heat island intensity was significantly higher than that of daytime heat island intensity.(2)The regional climate zoning pattern in the central urban area of Chongqing changed significantly during the study period.Dense high-rise buildings,dense middle,dense low-rise buildings and high-rise buildings,low-rise buildings,large open open lowrise buildings,low vegetation,bare rock/paving roads and bare soil/sand showed a trend of steady growth,scattered low-rise buildings falling trend,sparse trees and water body,open the middle building,the change of the dense trees and shrubs have inherent nature.(3)There were significant differences in LST among different climate subtypes.The LST of built landscape(LCZ 1-9)and bare land(LCZ E-F)were both higher,and became the most prone area of LHI,while the LST of green land(LCZ A-D)and water body were lower.It is the main source of surface cold island effect in the central urban area of Chongqing,and the surface cold island effect of water body is more significant.(4)There were also differences in air temperatures among different types of local climate subzones in the observation route,with higher air temperatures in large low-rise buildings and bare land(LCZ E-F).The near surface heat island intensity of the same local climate partition type is also related to its distribution location,building material and surrounding building type.(5)On the time scale,the influence of meteorological factors on the heat island intensity in the central urban area of Chongqing is relative humidity > rainfall > wind speed > sunshine time.Among the indicators of urbanization development,urban population and completed housing area have the greatest influence on the heat island intensity in the central urban area of Chongqing.At the spatial scale,NDVI and ISA play a leading role in the spatial distribution of land surface temperature in the central urban area of Chongqing,followed by elevation and population density,followed by topographic relief,slope and MNDVI.The impact of slope aspect decreases year by year.The explanatory power q values of different factors under the interaction are all larger than that of single factor,showing double factor enhancement and nonlinear enhancement,and there is no independent factor.The interaction of each factor with NDVI and ISA has a great influence on the spatial distribution pattern of land surface temperature in the central urban area of Chongqing.(6)When the heat island intensity increases by 1℃,the number of heat wave days in the urban area increases by 72 ℃·d,and the number of heating degree-days decreases by 86 ℃·d.(7)In the design of water landscape,the intensity of cold island can be improved by reducing impervious water surface rate in the surrounding environment.In order to increase the influence range of water cold island effect,the natural landscape types around water body should be increased as much as possible(LCZ A-C)under the condition that the size and shape of water body are constant.During the landscape design of green space in the park,the intensity of the cold island can be improved by giving priority to the increase of green space in the park.In order to increase the influence range of the cold island effect of green space in parks,it can be considered to plan the spatial location of green space in parks around the open high-rise buildings(LCZ 4 and LCZ 5).