Zoning Optimization Method of a Riverfront Greenspace Service Function Oriented to the Cooling Effect: A Case Study in Shanghai

Abstract

Blue-green space commonly provides multiple ecological service functions, especially thermal environment comfort for citizens. The greenspace of the riparian buffers along 22 river channels in Shanghai was selected as the study object, and remote sensing and GIS technologies were used to obtain the quantitative composition and morphological indices of riverfront greenspace and the spatial distribution data of the land surface temperature in the study area. Through BRT modelling and statistical analyses, the interactive correlations among the three aspects, namely, the spatial patterns of riverfront greenspace, their specific functional zoning, and cooling island differentiation characteristics, were explored. The results showed that different river types served for different functional zones of the city, namely, high-density built-up zoning, new urban-growth zoning in built-up areas, suburban areas, and rural areas, and had specific regular patterns of morphosis and service function of riverfront greenspace. These also led to a significant spatial differentiation pattern of cooling intensity levels, which generally appeared in the approximate circle differentiation structure of the cooling island in the city riverfront area. The study further proposed the key factors and corresponding strategies for optimizing the greenspace pattern to strengthen the cooling intensity levels of different river types. This study summarizes the landscape composition paradigm of riverfront greenspaces at the urban mesoscale and provides adaptive planning methods for better local microclimate conditions.

Keywords: Shanghai; blue–green space; boosted regression trees (BRT); marginal effect (ME); riverfront area; spatial morphology; urban cooling effect (UCI); urban heat island (UHI).

Figure 1

Raster image of the study area and location of the backbone river corridors in Shanghai, China.

Figure 2

Framework flowchart of the study.

Figure 3

Distribution of LST values and CI intensity in the study area. (a) LST distribution; (b) CI intensity level distribution.

Figure 4

Identification of greenspace types and morphological characteristics in the riverfront area.

Figure 5

Distribution of greenspace types in the study area based on land-use classification.

Figure 6

The mean surface temperature of different greenspace types. (a) The values in the study area; (b) the values in rural areas and SUA.

Figure 7

Spatial distribution of CI at different levels. (a) Level-six and level-five CI; (b) level-four cold island; (c) level-three and level-two CI; (d) level-one CI; (e) insignificant CI.

Figure 8

Distribution pattern of three classes of greenspace in the study area based on service function. (a) Recreational greenspace system; (b) ecological conservation land system; (c) agricultural use area system.

Figure 9

ME curve of morphological factors of greenspace on LST. (a) Fv of greenspace; (b) area of greenspace; (c) LSI; (d) surface albedo.

Figure 10

ME curve of structural factors of blue-green space on LST. (a) Distance from riverbank; (b) location; (c) Wr; (d) cohesion.

Figure 11

Area percentage of each greenspace type in the CI area with six different river types. (a) Type -1 rivers; (b) Type-2 rivers; (c) Type-3 rivers; (d) Type-4 rivers; (e) Type-5 rivers; (f) Type-6 rivers. Note: j in the composition of the one cooling island level which was represented by each color column, the sum of the area proportions of all greenspace types (FL, OWL, GL, PG, AS, SRS, CL, and DL) is 100%. Observing the same color column, it can be seen which greenspace type constitutes the main body of this cooling island intensity grade; k the various color columns of each type of greenspace indicate that the greenspace type has a different proportion of cooling island area. The closer the color column is to 100%, the more it reflects that the main cooling range of this greenspace type is located at the intensity level of the cooling island represented by the corresponding color.