Remote sensing monitoring shows that the vegetation in the whole area of Jiuzhaigou Valley Scenic and Historic Interest Area has gradually recovered after the earthquake

Tech 2023-06-10 08:25:54 Source: Network

People's Daily Online, Beijing, June 9 (Reporter Zhao Zhuqing) On June 9, the Institute of Space and Space Information Innovation of the Chinese Academy of Sciences (hereinafter referred to as the "Institute") and the UNESCO International Space Technology Center for Natural and Cultural Heritage (HIST) released the results of remote sensing monitoring of dynamic changes in the Jiuzhaigou Valley Scenic and Historic Interest Area World Heritage Site (hereinafter referred to as "Jiuzhaigou Valley Scenic and Historic Interest Area") after the earthquake. The analysis of the results shows that the vegetation in Jiuzhaigou Valley Scenic and Historic Interest Area has been gradually restored, and the Spark Sea, which has attracted much attention, has returned to its former beauty

People's Daily Online, Beijing, June 9 (Reporter Zhao Zhuqing) On June 9, the Institute of Space and Space Information Innovation of the Chinese Academy of Sciences (hereinafter referred to as the "Institute") and the UNESCO International Space Technology Center for Natural and Cultural Heritage (HIST) released the results of remote sensing monitoring of dynamic changes in the Jiuzhaigou Valley Scenic and Historic Interest Area World Heritage Site (hereinafter referred to as "Jiuzhaigou Valley Scenic and Historic Interest Area") after the earthquake. The analysis of the results shows that the vegetation in Jiuzhaigou Valley Scenic and Historic Interest Area has been gradually restored, and the Spark Sea, which has attracted much attention, has returned to its former beauty.

On August 8, 2017, an earthquake of magnitude 7.0 occurred in Jiuzhaigou Valley Scenic and Historic Interest Area, severely damaging the ecological environment quality in the heritage site, and changing the visual landscape aesthetics of 5 heritage sites out of 27 heritage sites. In order to promote the recovery and development of Jiuzhaigou Valley Scenic and Historic Interest Area, in accordance with the requirements of the Convention on the Protection of the World Cultural and Natural Heritage and its operating guidelines, the research team of researchers from Kongtianyuan and HIST Fu Bihong continued to carry out research on Jiuzhaigou Valley Scenic and Historic Interest Area's Natural landscape, water environment, vegetation coverage, secondary geological disasters and their temporal and spatial changes, and released relevant monitoring and assessment results.

Ecological environment: The vegetation in the entire area is gradually recovering, and the vegetation coverage is close to the level before the earthquake

Remote sensing image analysis shows that the vegetation coverage area of Jiuzhaigou Valley Scenic and Historic Interest Area in 2017 (before the earthquake) accounted for 82.11% of the total area of the region. After the earthquake on August 8, 2017, the proportion of vegetation coverage decreased to 79.91%. With the development of post earthquake recovery and reconstruction, the proportion of vegetation coverage areas increased to 81.07% and 80.91% in 2020 and 2022, respectively, reflecting the gradual restoration of vegetation and an overall upward trend, with vegetation coverage approaching the pre earthquake level.

The research team divided the vegetation coverage of Jiuzhaigou Valley Scenic and Historic Interest Area into five grades: high, high, medium, low and low. Among them, the area of low and low vegetation coverage areas is significantly reduced, and transformed into medium and high vegetation coverage. The overall coverage structure is improved, and the stability of vegetation coverage tends to increase, indicating that the ecological restoration and management after the Jiuzhaigou Valley Scenic and Historic Interest Area earthquake has played a positive role in recent years. Among them, the vegetation restoration is concentrated in Rize Valley and Zechawa Valley of Jiuzhaigou Valley Scenic and Historic Interest Area Natural Heritage Site, and the vegetation restoration situation in the southwest edge of the Panda Sea Wuhua Sea line is the best.

Further in-depth research has shown that low vegetation coverage areas are mainly distributed in patches in high-altitude mountainous areas and valley areas with larger slopes. Low and medium vegetation coverage areas are mainly surrounded by low vegetation coverage areas in strips. The areas with low and low vegetation coverage transformed into medium and high vegetation coverage are spatially distributed in blocks, strips, and scattered stars, reflecting that the entire region has gradually entered the vegetation restoration period.

Water environment: Spark Sea has undergone post disaster recovery and reconstruction, and the water body and surrounding ecological environment have gradually recovered

The Jiuzhaigou Valley Scenic and Historic Interest Area earthquake caused serious damage to the Spark Sea Dike Dam, which is about 30-35 meters long. On the one hand, a large-scale collapse occurred on the north side of the Spark Sea Embankment, causing a decrease in the level of the Spark Sea water, and almost all of the calcareous mounds were exposed to the water. The degradation of the calcareous mounds due to water loss caused a significant change in the visual landscape, greatly affecting the aesthetic and ornamental value; On the other hand, the collapse of the calcified embankment also deprives the Spark Sea of its original water storage and regulation functions. As the level of the Spark Sea decreases, a huge head difference is formed between the upstream and downstream. The impact of the upstream water flow may cause the continuous collapse of the Spark Sea dam, leading to a series of secondary geological disasters, including the collapse of the travertine dam and travertine mound.

As an important heritage site of Jiuzhaigou Valley Scenic and Historic Interest Area Heritage Site, Spark Sea is the monitoring focus of the research team. Based on remote sensing images, after post disaster recovery and reconstruction, the calcified dam in the Spark Sea breach area has been repaired, and its water body has also been basically restored. It was reopened to the public in October 2020. From the images obtained by drones in July 2022, it can be seen that the restored Spark Sea Dam is stable, with sufficient upstream water and clear water. The surrounding vegetation has been basically restored, and Spark Sea has gradually returned to its former beauty.

Remote sensing monitoring shows that after the earthquake in August 2017, the dam broke, and the length of the dam breach was about 30-35 meters. The white calcification was prominent, the water area was about 0.0532 Square kilometre, and the downstream lake water was turbid. In June 2020, the calcified embankment is being repaired, and the water body begins to accumulate, with an area of about 0.0648 Square kilometre. In July 2022, the storage area of water body is about 0.111 Square kilometre, the water body is clear, and the landscape before the earthquake will be restored.

Spatial distribution and changes of landslides: After the earthquake, the area of landslide prone areas gradually decreases, and the area of areas with high and extremely high geological hazards greatly decreases

Overall, the susceptibility of landslides after earthquakes has decreased year by year, entering a transition period of long-term and steady recovery after earthquakes. The susceptibility of landslides in the early post earthquake period is mainly controlled by factors such as seismic faults and seismic intensity, and the overall shape is elliptical in a northwest direction with a large area. As time goes by, the controlling factors for the susceptibility of landslides after earthquakes have shifted to slope deposits, rainfall, and terrain. The high susceptibility areas are generally distributed in a narrow strip in a northwest direction, with a significant reduction in area.

In order to quantitatively study the spatial distribution and changes of landslide susceptibility after earthquakes, the research team calculated the proportion of landslide susceptibility levels in 2017, 2017-2019, and 2019-2020. The results show that in 2017, the proportion of medium and high level prone areas was the highest, with 31.18% and 13.56% respectively. The proportion of extremely low landslide prone areas was 10.88%, indicating that earthquake disturbance caused a high susceptibility to landslides in the core area of the heritage site, which is generally in a relatively prone state. The post earthquake landslide susceptibility results from 2017 to 2019 show that compared to 2017, the high and extremely high susceptibility areas rapidly decreased to 11.00%, while the proportion of extremely low susceptibility areas rapidly increased from 13.56% to 51.87%. The post earthquake landslide susceptibility results from 2019 to 2020 show that compared to 2017 to 2019, the high and extremely high susceptibility areas continue to decrease, with the total proportion decreasing from 11.00% to 8.71%. The extremely low susceptibility areas continue to expand, with the proportion increasing from 51.87% to 55.57%. The above research shows that the risk of geological disasters in the Jiuzhaigou Valley Scenic and Historic Interest Area heritage site has been greatly reduced after natural recovery and artificial treatment and restoration.

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