| With the reduction of green space and the degradation of ecosystem function brought by urbanization and climate change,the city is facing increased ecological risks,and the thermal environment has become one of the important ecological environment problems in the development of the city.As an important carrier of urban ecosystem,green space plays a vital role in alleviating urban thermal environmental.Taking the Hefei city center as the research object,this thesis uses remote sensing image monitoring,landscape pattern analysis,geographical statistical analysis,mathematical statistics analysis and other methods to analyze the evolution of urban green space landscape pattern and thermal environment in recent 20 years,and further discusses the thermal environment effect of urban green space landscape pattern evolution.And put forward the green space optimization strategy to alleviate the urban thermal environment,which is of great significance to optimize the urban ecological environment.The specific research results are as follows:(1)The dynamic change of green space landscape pattern in Hefei city center is remarkable.From 2002 to 2021,the total area of urban green space decreased by 65883.33ha(23.86%),and the rate of change accelerated.Among them,farmland as the main type of land use,the area and proportion decreased by 110888.1 ha and 40.16%,respectively,with the largest decrease.The area and proportion of green land increased by 37,642.23 ha and13.63 %,respectively,and the rate of increase was accelerating.Water body area increased slightly.The patches of urban green space landscape tended to be complicated and fragmented,and the patch connectivity and aggregation degree decreased,and the control degree and dominance degree of the overall landscape decreased,while the overall uniformity degree increased.(2)The change of land use structure results in the prominent effect of urban thermal environment.From 2002 to 2021,the land surface temperature in Hefei city center showed an obvious temperature difference and increased year by year.The area and proportion of high temperature area in the thermal class increased by 11047.59 ha and 4.00% respectively.The regional scope of the surface heat island is expanding continuously,showing a spatial distribution pattern spreading from the central circle,and the change trend is developing from "wind fan-shaped" to "multi-cluster",and the center of gravity of the heat island gradually migrates to the northwest direction.(3)Different green space types have different thermal environmental effects.The average land surface temperature of all landscape types showed the order of construction land > bare land > farmland > green land > water.The contribution index to thermal environment is as follows: construction land > bare land > green land > farmland > water.The land use structure of each thermal grade shows that the green space is closely related to the distribution of urban surface cold islands,mainly distributed in low temperature area,low temperature area and middle temperature area,but the proportion of green space decreases continuously,and the proportion of middle temperature area decreases the most,by 15.91%.The non-green space is mainly distributed in the sub-high temperature area and the high temperature area.The proportion of construction land in the high temperature area is more than 90%,and it is increasing year by year.(4)There is a correlation between green space landscape pattern index and land surface temperature.At landscape level,land surface temperature was negatively correlated with green space patch density,shape index,maximum patch proportion and spread index,while Shannon diversity index was positively correlated.The larger the area of green space landscape patches,the more complex the shape,combined with higher degree of connectivity and aggregation,can effectively alleviate the effect of urban thermal environment.At the type level,the larger the area of green space and water,the more complex the shape,the more continuous and concentrated the spatial distribution,the higher the proportion of farmland,the more complete and regular the patches,and the better the effect of alleviating the thermal environment.(5)Green space optimization strategy for alleviating urban thermal environment.Reasonable land use structure and effective control of green space stock will effectively deal with the effect of urban thermal environment.Hefei should strengthen the dynamic monitoring of green space and improve the utilization of space.Secondly,strictly control urban space development boundary to protect urban ecological background;At the same time,the ecological network system should be constructed to form a green space security pattern,give full play to the advantages of ecological and environmental functions,alleviate the effect of thermal environment,and create a good living environment. |
