Search Results (6)

Landslides are common natural disasters that cause serious damage to ecosystems and human societies. To effectively prevent and mitigate these disasters, an accurate assessment of landslide hazards is necessary. However, most traditional landslide hazard assessment methods rely on static assessment factors while ignoring the dynamic changes in landslides, which may lead to false-positive errors in the assessment results. This paper presents a novel landslide hazard assessment method for the Zagunao River basin, China. In this study, an updated landslide inventory was obtained for the Zagunao River basin using data from interferometric synthetic aperture radar (InSAR) and optical images. Based on this inventory, a landslide susceptibility map was developed using a random forest algorithm. Finally, an evaluation matrix was created by combining the results of deformation rates from both ascending and descending data to establish a hazard level that considers surface deformation. The method presented in this study can reflect recent landslide hazards in the region and produce dynamic assessments of regional landslide hazards. It provides a basis for the government to identify and manage high-risk areas. Full article

Multitemporal geohazard susceptibility analysis can not only provide reliable results but can also help identify the differences in the mechanisms of different elements under different temporal and spatial backgrounds, so as to better accurately prevent and control geohazards. Here, we studied the 12 counties (cities) that were severely affected by the Wenchuan earthquake of 12 May 2008. Our study was divided into four time periods: 2008, 2009–2012, 2013, and 2014–2017. Common geohazards in the study area, such as landslides, collapses and debris flows, were taken into account. We constructed a geohazard susceptibility index evaluation system that included topography, geology, land cover, meteorology, hydrology, and human activities. Then we used a random forest model to study the changes in geohazard susceptibility during the Wenchuan earthquake, the following ten years, and its driving mechanisms. We had four main findings. (1) The susceptibility of geohazards from 2008 to 2017 gradually increased and their spatial distribution was significantly correlated with the main faults and rivers. (2) The Yingxiu-Beichuan Fault, the western section of the Jiangyou-Dujiangyan Fault, and the Minjiang and Fujiang rivers were highly susceptible to geohazards, and changes in geohazard susceptibility mainly occurred along the Pingwu-Qingchuan Fault, the eastern section of the Jiangyou-Dujiangyan Fault, and the riparian areas of the Mianyuan River, Zagunao River, Tongkou River, Baicao River, and other secondary rivers. (3) The relative contribution of topographic factors to geohazards in the four different periods was stable, geological factors slowly decreased, and meteorological and hydrological factors increased. In addition, the impact of land cover in 2008 was more significant than during other periods, and the impact of human activities had an upward trend from 2008 to 2017. (4) Elevation and slope had significant topographical effects, coupled with the geological environmental effects of engineering rock groups and faults, and river-derived effects, which resulted in a spatial aggregation of geohazard susceptibility. We attributed the dynamic changes in the areas that were highly susceptible to geohazards around the faults and rivers to the changes in the intensity of earthquakes and precipitation in different periods. Full article

In forest landscape restoration, one of the key objectives is to improve the water conservation capacity of the deforested land. A rapid, accurate assessment of the effects of the restoration measures on the water conservation capacity of targeted forests can help forest managers to identify the best practices for forest restoration. However, the traditional assessment tools of forest water conservation function lack a description of forest growth, and are featured by complex computation, which fails to evaluate the effects of forest restoration on the regional forest water conservation capacity in an efficient way. To address this issue, through combining the forest restoration evaluation model (equivalent recovery area, ERA), classic forest water storage capacity estimation (total water storage capacity), this study has taken advantage of ENVI/IDL, ArcGIS Engine/C#.Net to develop the Forest and Water Assessment Tool (FWAT) for assessing the changes of the regional forest landscape and the associated forest water conservation capacity in various forest restoration scenarios. This tool has been successfully applied in the Upper Zagunao watershed, a large forested watershed in the Upper Yangtze River basin. According to the assessment, the forest water conservation capacity of the study watershed consistently increased from about 1580.76 t/hm² in 2010 to a projected 2014.34 t/hm² by natural restoration, and 2124.18 t/hm² by artificial restoration by 2030. The artificial restoration measures yield a better effect on forest water conservation function than natural restoration. By 2030, the forest water conservation capacity of artificial restoration scenario is expected to be about 7% higher than that of natural restoration scenario. The FWAT as an efficient tool to assess the effects of forest restoration measures on regional forest water conservation capacity can provide scientific support for the design of forest restoration and management strategies worldwide. Full article

Using advanced Differential Interferometric Synthetic Aperture Radar (InSAR) with small baseline subsets (SBAS) and Permanent Scatter Interferometry (PSI) techniques and C-band Sentinel-1A data, this research monitored the surface displacement of a large old landslide at Xuecheng town, Lixian County, Sichuan Province, China. Based on the MassMov2D model, the effect of the dynamic process and deposit thickness of the potentially unstable rock mass (deformation rate < −70 mm/year) on this landslide body were numerically simulated. Combined with terrain data and images generated by an Unmanned Aerial Vehicle (UAV), the driving factors of this old landslide were analyzed. The InSAR results show that the motion rate in the middle part of the landslide body is the largest, with a range of −55 to −80 mm/year on average, whereas those of the upper part and toe area were small, with a range of −5 to −20 mm/year. Our research suggests that there is a correlation between the LOS (line of sight) deformation rate and rainfall. In rainy seasons, particularly from May to July, the deformation rate is relatively high. In addition, the analysis suggests that SBAS can provide smoother displacement time series, even in areas with vegetation and the steepest sectors of the landslide. The simulation results show that the unstable rock mass may collapse and form a barrier dam with a maximum thickness of about 16 m at the Zagunao river in the future. This study demonstrates that combining temporal UAV measurements and InSAR techniques from Sentinel-1A SAR data allows early recognition and deformation monitoring of old landslide reactivation in complex mountainous areas. In addition, the information provided by InSAR can increase understanding of the deformation process of old landslides in this area, which would enhance urban safety and assist in disaster mitigation. Full article

Forest harvesting and hydropower dams can significantly affect flow regimes (magnitude, timing, duration, frequency, and variability), resulting in changes in degraded aquatic ecosystems and unstable water supply. Despite numerous studies on the effects of forest harvesting on mean flows, the impact of forest harvesting on flow regimes has been less investigated. A great difficulty lies in separating the hydrological effect of forest harvesting from that of climate variability and other watershed disturbances such hydropower dams. In this study, the Upper Zagunao River watershed (2242 km²) was selected as an example to provide a quantitative assessment of the effects of forest harvesting and hydropower dams on low flow regimes. The key findings include: (1) Forest harvesting led to a significant reduction in the magnitude and return period of low flows, and a significant increment in the variability and duration of low flows; (2) the recovery of low flow regimes occurred 40 years after forest harvesting as forest recovery processed; and (3) hydropower dams caused significant impact on all components of low flow regimes, e.g., a reduction in the magnitude, return period, and timing of low flows, and an increment in the variability and duration of low flows. Our findings highlight the negative impact of both forest harvesting and hydropower dams on low flow regimes in the Upper Zagunao River watershed. A watershed management strategy for offsetting the negative effect of hydropower dams on low flow regimes by restoring hydrological functions of subalpine forests is highly recommended in subalpine watersheds of the Upper Yangtze River. Full article

Water retention is one of the important services provided by ecosystems. Water retention is also the basis for multiple other services, such as hydropower development, river continuity, and biodiversity. However, there are clear tradeoffs among these services. Tradeoffs are already a hot topic in ecosystem services research, but the tradeoff between hydropower and river visual landscape services (RVLS) has not yet been investigated. In this study, we used the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) hydropower model for spatial mapping of watershed services. The proportion of the inflow of power stations to annual flow was proposed as the indicator for RVLS. Finally, based on an evaluation of historical hydropower development, different flow recovery scenarios were set up, and the tradeoff relationship between hydropower and landscape services was analyzed. The results showed that the tradeoff between the hydropower service and RVLS in mainstream displayed obvious spatial and temporal changes. With the development of hydropower, the increase of hydropower services caused a rapid decline in RVLS. The difference of two service scores fell from 1.0 in 1958 to 0.52 in 2015. The tradeoff intensity showed a turbulent decline downstream, which was closely related to the cascades’ development. The tradeoff was reversible. Through the flow scheduling of the reservoir group, the RVLS of each river section can be basically restored, while the hydropower service decline was only 29%. Full article