Ecological effect of urban spatial expansion in river valleys: A case study in the main urban area of Lanzhou City

Abstract

[Objective] The ecological effect of urban spatial expansion is the key problem of human-environment relationship in the process of urbanization. It is of great significance to explore the complex scientific problem of ecological effect caused by urban spatial expansion from multiple angles to promote the sustainable and high-quality development of urban and ecological space. [Methods] Taking the main urban area of Lanzhou City in China as an example, this study calculated the scale, intensity, and landscape pattern indices of urban spatial expansion in 1995, 2005, 2015, and 2020 to reflect the spatiotemporal variation characteristics of urban spatial expansion in the city from 1995 to 2020, and divided the research area into 12184 grids. Using the spatial principal component analysis method, atmospheric radiation transfer equation method, and revised ecosystem service value estimation model, this study analyzed the ecological risk effect, heat island effect, and ecosystem service effect of urban spatial expansion from various angles, and discussed the impact of natural environment conditions on the ecological effect of urban spatial expansion of cities in river valleys. [Results] The results show that from 1995 to 2020, the scale and intensity of urban expansion in Lanzhou City have increased, the fragmentation of urban landscape has decreased, urban expansion has mainly occurred in the western and northern parts of the city, and the urban expansion mode has changed from group expansion to leaping expansion. The overall ecological risk effect and heat island effect in the city have shown a weakening trend, but a rising trend was observed in the river valley, and the overall pattern of effects has been characterized by high in the valley and low at the peripheries. There is a slight improvement in the ecosystem service effect, which mainly shows that the ecosystem service value in the surrounding areas of the river valley has improved significantly, and some areas in the built-up area have changed from low-value area to medium-value area. Urban expansion negatively affects the natural substrates of the region, while the natural substrates also affects the scale, direction, and mode of urban expansion. Coordinating the relationship between the two is essential for the sustainable and harmonious development of human beings and nature. [Conclusion] The research framework of ecological effects of urban spatial expansion was constructed from multiple perspectives. Urban spatial expansion has a significant impact on ecological risk, heat island, and ecosystem service effects at the grid scale, which provides a new way of quantitative visualization of the dynamic relationships between urban evolution and ecological environment.

Keywords

• |urban expansion|ecological effect|ecosystem service value estimation model|valley city|lanzhou city