Study on the Evolution Law of Surface Landscape Pattern in Earthquake-Stricken Areas by Remote Sensing: A Case Study of Jiuzhaigou County, Sichuan Province

Abstract

Earthquakes not only cause the destruction of surface buildings and a large number of casualties, but also have an important impact on regional land-use change. Timely understanding of land cover and its changes before and after earthquakes is of great scientific significance for studying the restoration and reconstruction of the natural ecosystem and the sustainable development of the social economy in disaster areas. At present, there are few studies on land cover changes before and after earthquakes in the earthquake-stricken areas, especially the quantitative assessment of land cover changes before and after earthquakes at the micro scale of landscape spatial distribution. Therefore, this article is based on remote sensing data and uses an earthquake in Jiuzhaigou, Sichuan, as an example. By calculating the land-use degree comprehensive index and its rate of change, the transfer matrix of land-use, quantitative expression methods of the landscape via the landscape pattern index are analyzed from the points of view of the spatial–temporal evolution law of the landscape pattern of land cover before and after the earthquake. The experimental results showed that the area of forest, cropland, shrub. and grassland types in the study area changed greatly, and the area of grassland types in Shuanghe Township changed most obviously, as they increased from 6.57 km2 in 2015 to 7.43 km2, and then decreased to 6.21 km2 in 2020. During the earthquake recovery period, the comprehensive index of land-use degree for most towns in the study area showed an upward trend, and the land cover types were improved. After 2017, the PD and LSI of the study area showed a downward trend, among which the bare land type changed greatly, with the PD value decreasing from 0.38 in 2017 to 0.21 in 2020, and the LSI value decreasing from 58.29 in 2017 to 40.69 in 2020. This indicates that the degree of landscape fragmentation and the spatial heterogeneity of the land surface in the study area are reduced in the later stage of earthquake recovery. After 2017, the AI value of the study area showed an upward trend, and the AI value of the bare land type increased from 63.97 in 2017 to 78.25 in 2020, indicating that the connectivity between landscape patches in the study area was enhanced in the later stage of the earthquake. This also reflects that the ecological environment of the study area gradually showed a good trend in the later stage of the earthquake. The results of this paper not only reveal the spatial–temporal evolution of land cover in Jiuzhaigou County before and after the earthquake, but also help the relevant national decision-making departments to formulate corresponding policies and measures.