Abstract:[Objective] The spatial distribution characteristics and laws of geological disasters were determined at the Huangshui River basin in Qinghai Province, in order to provide data support and a scientific basis for disaster prevention and reduction. [Methods] Geological hazard sites were identified by small baseline subset interferometric synthetic aperture radar (SBAS-InSAR). By combining topographic factors, geological factors, environmental factors, meteorological factors, and human activities, the spatial distribution law of disasters was analyzed, and a logistic regression (LR)-frequency response (FR) model was established and tested. The return probability value was used to evaluate susceptibility. [Results] ① The potential geological disasters distributed in the Huangshui River basin were mainly landslide and collapse, and many kinds of potential geological disasters occurred simultaneously. Landslides and unstable slopes usually developed on slopes with low slope and were accompanied by a large number of tension and shear cracks that were especially obvious in the rainy season, posing a threat to the safety of traffic and residents below the mountain. Landslides and unstable slopes on both sides of river valleys may also block rivers and form barrier lakes, further aggravating disaster risks. Slope collapses mostly developed in the steep mountain walls with relatively loose rock structure or severe weathering. Due to geological fragility coupled with stimulation by natural factors such as rainfall, situations easily develop and result in falling mountain soil and rocks that pose a threat to residential areas and traffic lines below. ② Geological disasters were primarily located in the 2 425—3 650 m elevation area of the study area, and the northeast direction was the slope direction of geological disasters. Normalized difference vegetation index (NDVI) decreased with the increase in geological hazards, increased with the increase of slope, relief, and daily precipitation, and decreased with the increase of distance from the fault. ③ The high-risk and relatively high-risk areas in the Huangshui River basin, covering an area of about 5 937.60 km2, accounting for about 38.78% of the total area of the study area, and were mainly concentrated in the south and north border areas of Huangshui River basin, Huangzhong-Datong-Haiyan Junction, and the surrounding slopes of the construction area. ④ The evaluation results were tested. The area under curve (AUC) of the receiver operating characteristic curve (ROC curve) of model prediction performance was 0.787. The FR in the prone area decreased step by step from high to low, and this result was in good agreement with the distribution of actual disaster points. ⑤ Fault core density was the main control factor of geological hazard development in the Huangshui River basin, followed by slope direction, relief degree, and road core density. Section curvature had the least influence on geological hazard development. [Conclusion] ① SBAS-InSAR technology effectively identified potential geological hazards in the Huangshui River basin, and the susceptibility evaluation results obtained by the LR-FR model were reliable. ② The distribution of geological disaster prone areas in the Huangshui Basin had obvious spatial differences, mainly located in the areas with higher elevation, lower vegetation coverage rate, greater rainfall, and close to the fault. Fault core density was the main control factor of geological disaster susceptibility. ③ The geological disasters in the Huangshui Basin were characterized by frequent, sudden, and high risk occurrences that seriously impacted local people’s lives, regional economic development, and the ecological environment. Therefore, the monitoring, early warning, and prevention of these disasters are particularly important.

Abstract:[Objective] The characteristics and driving factors of landscape pattern changes and the spatiotemporal evolution of landscape ecological risk was analyzed in order to provide a theoretical basis for integrated watershed management, watershed ecosystem management, and sustainable development.[Methods] A landscape ecological risk assessment model was proposed using the landscape index method based on land use data in 2000, 2010, and 2020 from the Huangshui River basin. Spatiotemporal dynamic characteristics of landscape patterns and ecological risk were examined by coupling ArcGIS 10.6, Fragstats 4.2, and GeoDa 1.20. Factors driving spatially stratified heterogeneity of landscape ecological risk were identified using geographic detectors.[Results] ① Grassland and cropland were the dominant land use types in the Huangshui River basin. Land transfer mainly occurred between cropland, grassland, and construction land. Urban expansion was the main feature of land use/land cover changes over the past 20 years. ② From 2000 to 2020, landscape ecological risk in the Huangshui River basin initially increased and then decreased, and there was a negative correlation between ecological service value and landscape ecological risk. ③ Spatial distributions of landscape ecological risk in the Huangshui River basin mainly presented high-high and low-low agglomerations. Elevation was the main factor driving the spatially stratified heterogeneity of ecological risk. The interaction between driving factors had an enhancing effect on spatially stratified heterogeneity of landscape ecological risk. ④ Spatial distribution of landscape ecological risks had an obvious altitude gradient effect. According to the altitude gradient, the Huangshui River basin was divided into three ecological risk control zones:key control area, strict control area, and general control area.[Conclusion] Ecological governance and ecological restoration were the main reasons for the decline of the landscape ecological risk index in the Huangshui River basin. Different management and control strategies should be implemented for different ecological risk control zones. Land use optimization management and land use control should be primary concerns with respect to ecological risk control.

Abstract:[Objective] The spatio-temporal distribution and variation characteristics of soil erosion in the Huangshui River basin in the upstream region of the Yellow River were analyzed in order to provide basic data and a basis for decision-making in relation to soil and water conservation and erosion prevention.[Methods] Based on MODIS and Landsat images, precipitation, population density, and the economy in 2000 and 2018, we used low altitude UAV remote sensing, the RUSLE model, and geostatistics to calculate, validate, and analyze the spatio-temporal variability of a soil erosion model in the Huangshui River basin.[Results] ① The average soil erosion modulus of Huangshui River basin in 2000 was 477.81 t/(km2·yr), and the percentage of the area with slight erosion was 72.06%. The percentage of area with moderate, strong, and severe erosion was 3.46%. Mild and moderate erosion areas were mainly located in the mountains and wastelands in the Northern Qilian Mountains, the Central Daban Mountains, and the Southern Laji Mountains, with high altitude and low vegetation coverage. ② In 2018, the average soil erosion modulus of the Huangshui River basin was 1 625.30 t/(km2·yr). The percentage of area with mild erosion was 55.38%, and the percentage of area with moderate, strong, and severe erosion was 21.26%. The area of moderate erosion was mainly located in the urban agglomeration area and where river beaches were located in the southeast part of the study area. The strong erosion and extra-strong erosion areas were sporadically distributed in bare areas in the Qilian Mountains and the Daban Mountains. ③ From 2000 to 2018, the area of slight erosion decreased by 16.68%, the area of moderate erosion increased by 8.15%, the area of strong erosion increased by 5.60%, and the area of severe erosion increased by 4.05%. The region with increasing erosion was mainly located in the bare mountains and urban areas.[Conclusion] Low-altitude UAV remote sensing technology can effectively validate the calculation results of the regional soil erosion model. Soil erosion in the Huangshui River basin has be accelerated over time, and showed great spatial differences. The spatial pattern of soil erosion intensity has evolved from mild, slight to moderate in the Qilian Mountains and the Daban Mountains. This evolution tendency is related to the warmer-wetter climate and intensified human activity.

Abstract:Effects of eco-environmental construction projects on soil and water loss from 2000to 2009were studied by taking the Huangshui River basin as the study area.Landsat TM/ETM data of 2000and 2009 were used to derive the data of land cover and vegetation in combination with the Aster DEM.The study was conducted by the“Standards for Classification and Gradation of Soil Erosion” (SL190-2007)and with the support of GIS techniques.Results showed that soil erosion on slope in the Huangshui River basin was reduced somewhat in the last ten years.The intermediate and above soil erosion in 2009was reduced by 309.11km2 as compared with that in 2000,but gully erosion tended to increase,with a net increase of 706.87km2.This illustrates that the engineering measures are effective to soil erosion on slope,but insignificant to gully erosion.