Understanding the spatiotemporal variation of urban land expansion in oasis cities by integrating remote sensing and multi-dimensional DPSIR-based indicators

Rapid urban land expansion not only stimulates socioeconomic development, but can lead to negative impacts that threaten regional food security, ecological construction, and sustainable urban development, including losses of cropland and habitats, the creation of housing bubbles, and reductions in biodiversity. Because these economic-socio-ecological problems are generally more serious in ecologically fragile areas, this study focuses on trends seen in Ganzhou District, a typical oasis city within the Heihe River Basin (HRB) in an arid-to-semi-arid area of China. We apply a remote-sensing (RS)-based method that incorporates 11 dimensional features of Thematic Mapper and Enhanced Thematic Mapper Plus (TM/ETM +) images to map changes in urban land, and also develop a series of multi-dimensional indicators within a drivers, pressures, states, impacts, and responses (DPSIR) framework to quantify urban land expansion. The results of this study show that the urban land area of Ganzhou District in 2016 had expanded by 394.43% from 1987 levels, from 1979.64 ha to 9787.86 ha. These increasing pressures, jointly driven by gross domestic product (GDP), urban population, cropland area, and the industrial structure indicator (ISI), have led to the worsening economic-socio-ecological states and impacts of urban land expansion. Specifically, between 1987 and 2016, expansion intensity (EIPI) and expansion rate pressure indicators (ERPI) increased from 60.27 ha/a to 520.88 ha/a, and from 3.04%/a to 10.21%/a, respectively. Thus, the state indicators of economic development (EDSI), population carrying capacity (FDSI), food security (FSSI), and ecological construction (ECSI) decreased by 2.21 x 10(3) USD/ha, 17.62 population/ha, 34.20, and 10.80, respectively. Moreover, the impact indicators of economic development (EDII), population carrying capacity (FDII), and food security (FSII) decreased by 150.68 x 10(3) USD/ha, 62.12 population/ha, and 27.31, respectively, while the ecological construction impact indicator (ECII) increased by 29.39 between 1997 and 2007 and decreased by 13.31 between 2007 and 2016. Data also show that the area and proportion of cropland and ecological land occupied by urban land expansion increased over time. We therefore propose a series of economic-socio-ecological responses to help limit urban sprawl and foster compact green cities. Measures include planning urban growth boundaries, revitalizing urban centers and brownfields, using and reusing urban land more efficiently, strengthening land regulations, curbing excessive cropland expansion, cultivating more urban green spaces, and optimizing the trade-offs and synergies between multiple conflicting dimensions.