Mapping the dynamics of urban land creation from hilltop removing and gulley filling projects in the river-valley city of Lanzhou, China

To expand urban area and protect farmland effectively, Hilltop Removing and Gulley Filling Projects (HRGFP) in the river-valley city of Lanzhou, China have been carried out over the last decades. However, monitoring the dynamic characteristic and scale of the projects and the impact on the local eco-environment caused by HRGFP is necessary. Here, we conducted field investigations and used aerial remote sensing images and the Spatial Expansion Intensity Index (SEII), Terrain Niche Index (TNI), Biophysical Composition Index (BCI), and Remote Sensing Environment Index (RSEI) to monitor the dynamic characteristics of new plots and changes in the local environment. The total area of the new plots from HRGFP around Lanzhou was about 203.18km2 in 1989–2016 with a continuous shift away from the urban area to the low hills, gentle slopes, and gullies in the north, which has greatly enlarged the urban area and increased economic development. We found that the new plots were converted to new forest and grassland in addition to buildings. RSEI indicated that the environment quality improved in 3984 km2 of the study area, or 55.73% of the total area, after a short period of degradation. Our results indicated that HRGFP in Lanzhou have enlarged the urban area and increased economic development, and improved environment under the guidance of the local government.

Road Landscape Morphology of Valley City Blocks under the Concept of “Open Block”—Taking Lanzhou City as an Example

The unique valley geographical environment and the congestion-prone road landscape make valley city traffic jammed easily. In this paper, under the background of “open blocks”, two open patterns, which correspond to two different road landscapes ("ideal grid opening" and "open under realistic conditions"), are proposed. Taking Lanzhou city as an example, six basic statistical characteristics are used to compare and analyze the changes of road network topology in blocks to find out which open pattern is more suitable for valley cities. The results show that the pattern "open under realistic conditions" has a significant effect on the improvement of network performance and capacity. Specifically, breaking the "large blocks" and developing the small-scale blocks help to alleviate the traffic pressure. Besides, the opening of blocks located along river valley has a more positive effect on improving road network performance than the blocks sited in the inner area of cities.