Spatial variation and threshold analysis of the urban wetland cooling effect-a case study of Changchun city

Abstract

Due to the complexity of the surrounding environment, the cold and wet effects of urban wetlands and the quantitative descriptions of the cold and wet effects of the wetlands are not clear. Therefore, the focus of current research is gradually shifting towards the impact of the microspatial morphology and quantity differentiation of urban wetlands. This paper adopts the July 4, 2016 Landsat 8 data of cloud cover that is less than 0.2, the 10th band as the data source using single window algorithm surface temperature inversion, and further analysis of urban spatial distribution characteristics of land surface temperature. Secondly, based on the numerical analysis of the difference in surface temperature between urban wetland types, shapes, and independent wetland space sizes, the cold temperature effect and spatial distribution of urban wetlands were discussed. Temperature inversion results show that the lowest temperature is 17.94°C, which appears in the Songhuajiang wetland, and the highest temperature is 32.52°C, which appears in the FAW Industrial Concentration Zone in the main urban area of Changchun City. From the perspective of the spatial difference of the temperature distribution, the areas with high temperatures are generally distributed in the industrial concentration area in the southwest of Changchun, followed by other areas with high temperatures in the western part of Changchun. Low-temperature areas are mainly distributed in areas with relatively high distribution densities of rivers and lakes in the northeast and central parts of Changchun. This shows that the temperature is directly related to the urban building density. The temperature is higher in places with high building density. Wetland water bodies generally belong to low temperature areas and are generally 1-2°C lower than the surrounding environment. For the main urban area, the wetland water body is, on average, 2-4°C lower than the surrounding environment, while in areas with high building density, the wetland water temperature is 6-8°C lower than the surrounding area. And further urban wetlands with micro difference threshold temperature distribution characteristics are as follows: (1) The cold and wet effects of the wetland are related to its shape; and, the cooling and influence range of circular wetlands are larger than that of striped wetlands. (2) The cooling effect of a wetland in a circular wetland typified by a lake wetland is not related to the size of the water area when the area exceeds 92 hm2; and, the cooling range of a strip-shaped wetland has nothing to do with the width of the water surface. However, impact range is related to the width of the water surface, the larger the width of the river surface, the larger the range of influence. (3) The cooling effect of wetlands are related to the surrounding environment. When the surrounding area is hard ground, the cooling rate is large, and when the surrounding area is green land, the cooling rate is small.