| With the accelerated development of global industrialization and modernization,cities have become the fastest-growing socio-economic places in various countries.The increase in the population of the city has promoted the development of construction projects and has also met the needs of human use.However,the construction of buildings,business centers,industrial parks,and transportation facilities in the city has reduced natural land cover,increased the area of impervious surfaces,and the continuous deterioration of the air environment.Most cities around the world also have an urban heat island effect.There are many related studies on urban heat island effect,but the main focus is on the contribution of vegetation to heat island effect.However,compared with vegetation,the water body is not affected by the seasons and is a more stable type of coverage,but the water body has a greater impact There are few studies on the regulation mechanism,so it is of great significance to study the influence of water on the heat island effect.This study takes Hanoi City,Vietnam as a research area,classifies land use based on Landsat remote sensing images from 1996 to 2019,and analyzes the temporal and spatial distribution and change characteristics of the city's heat island;at the same time,combining spatial analysis techniques The characteristics of the thermal environment of the water body and its impact on the surrounding thermal environment.The main findings are as follows:(1)From 1996 to 2019,in only 23 years,the plant area of Hanoi City in Vietnam disappeared 1950 km2,and the total area covered by vegetation reduced from 69.2%(1996)to11.3%of the total surface area(2019).In contrast,the total construction area of Hanoi City increased by 1625 km2,and the construction land area increased by 84.3%from the original area;the proportion of bare land area in the total land surface area increased from 13.9%(1996)to25.5%(2019).Since 1996,the surface area of the water body landscape has also decreased,and the total surface area of the water body has decreased from 7.8%(1996)to 6%(2019).Among them,the total area of water increased by 2.91km~2,but the area of rivers and ponds was decreasing.The area of rivers decreased by about 13.55km~2,and the area of ponds decreased by about 4.73km~2.(2)From 1996 to 2019,the area of heat island effect in Hanoi increased from 61.99 km2 to2132.83 km~2,an increase of nearly 34 times,and the proportion of heat island effect area in the total surface area also increased from 1.8%in 1996 to 8.3%in 2007 and 63.66%in 2019,the heat island effect in Hanoi has been significant year by year.The area of the built heat island accounted for 76%of the total heat island effect area.The heat island intensity distribution areas of Hanoi City are concentrated in the basin of the Red River Delta,which is also the main development center area in the east of Hanoi City.Qingnian County and Bazhan County.The closer to the bustling development center,the higher the intensity and concentration of the heat island reversal.In addition,the intensity of the heat island also spread to the northeast and southeast of the city.(3)This study extracts relevant data of Hanoi,Vietnam in 2019 for analysis.In the heat island area distribution,the water body heat island area is the smallest(3.09 km~2),followed by the vegetation heat island area(226.99 km~2)and bare geothermal island area(272.38 km~2),and the construction geothermal island area(1630.35 km~2)is the largest.According to the type of surface cover,84.63%of the construction land area,73.59%of the bare land area,26.54%of the vegetation area and 1.56%of the water body area belong to the heat island distribution area.In addition,the vegetation area and water body area belonging to the heat island distribution area are mostly distributed in the center of the urban area,and the surrounding architectural areas are densely distributed.(4)When the proportion of vegetation increases,the R~2 and regression coefficient of the water body decreases,and the cooling effect of the water body also decreases,and when the value of the cumulative proportion of vegetation increases in the range of 900m×900m,it will also affect the cooling function of the water body area.,This is due to the concentration effect of the vegetation area on the heat island effect cooling efficiency.Therefore,when the cooling effect on the heat island effect in the study area is increased,the increase in the proportion of vegetation will mask the cooling effect of the water body on the heat island effect.(5)The shape of the water body will affect the cooling effect of the water body.The cooling effect of surface water is stronger than that of linear water.The cooling effect of rivers is stronger than that of lakes.For example,the cooling distance of rivers can reach 250m,but the lake can only reach 200m.(6)The thermal environment characteristics of different types of water bodies have different influencing factors.The temperature of the water body is mainly related to the shape and area,and the type of surface coverage around it.Among them,the area,width and area of the water body are the main factors affecting the temperature of the water body.The surface temperature of the river is significantly negatively correlated with the width,while the surface temperature of the river is significantly positively correlated with the area ratio of surrounding construction land.The type of coverage around the river also has a greater effect on the cooling effect of the river.The temperature of the lake is significantly negatively correlated with the shape index and area of the lake,and the temperature of the lake is significantly positively correlated with the proportion of the construction land area around the lake.The lower the temperature of the lake.For surface water bodies,their own properties are also important factors affecting the temperature of the water body,but for linear water bodies,the surrounding environment is an important factor affecting the temperature of the water body.In addition,when the water surface area reaches 0.45km~2 or the width reaches 130m,the temperature change of the water body tends to be stable. |
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