Landslide risk assessment is important for risk management and loss–damage reduction. Herein, we assessed landslide susceptibility, hazard, and risk in the urban area of Yan’an City, which is located on the Loess Plateau of China and affected by many loess landslides. Based on 1841 slope units mapped in the study area, a random forest machine learning classifier and eight environmental factors influencing landslides were used for a landslide susceptibility assessment. In addition, differential synthetic aperture radar interferometry (DInSAR) technology was used for a hazard assessment. The accuracy of the random forest is 0.903 and the area under the receiver operating characteristics (ROC) curve is 0.96. The results show that 16% and 22% of the slope units were classified as being at very high and high-susceptibility levels for landslides, respectively, whereas 16% and 24% of the slope units were at very high and high-hazard levels for landslides, respectively. The landslide risk was obtained based on the susceptibility map and hazard map of landslides. The results show that only 26% of the slope units were located at very high and high-risk levels for landslides and these are mainly concentrated in urban centers. Such risk zones should be taken seriously and their dynamics must be monitored. Our landslide risk map is expected to provide information for planners to help them choose appropriate locations for development schemes and improve integrated geohazard mitigation in Yan’an City.

The high sensitivity of loess slopes to water has been emphasized in many studies. However, it is still limited in terms of the understanding of slope morphological differentiation on the overall and local failure patterns in slopes, as well as on the acquisition method of hydrological dynamics. In this study, rainfall characteristics and slope surface morphological differences were introduced. Geoelectric and environmental factors were monitored. On this basis, apparent resistivity corrected by seasonal temperature and its relationship with soil water content was calibrated. The water migration characteristics and potential failure patterns of three slope morphologies were evaluated. The results are: (i) the improved resistivity method can better reflect the water flow movement within the slope, and it performs well after being corrected by temperature; (ii) the characteristics of surface runoff and water infiltration are directly affected by the cumulative rainfall value, and especially when the cumulative rainfall is >70 mm threshold, the surface runoff quickly infiltrates into the deep of the slope along the preferential paths; (iii) the interception ability of loess slope morphology to the surface runoff is concave slope > convex slope > linear slope; (iv) with the continuous rainfall, the convex surface of a slope is prone to be damaged by saturated mud flow. When the cumulative rainfall threshold is 70 mm, the preferential flow is easily excited on the concave surface of the slope, resulting in local collapse at the slope toe and mid-deep landslides.

Chinese Loess Plateau (CLP) has become one of the high‐incidence areas of landslide disasters in China, especially at the edge of the tablelands where irrigation has been practiced at a large scale since the 1960s. Heifangtai tableland, located in the CLP in Yongjing County, Gansu Province, has been selected as a case, where more than 90 slidings occurred in the past three decades. Field monitoring and laboratory tests were conducted to obtain the soil‐water characteristic curve, unsaturated soil shear strength, irrigation water infiltration, and the groundwater level change. Based on these results, a three‐dimensional numerical model of the slope was established, and the change of seepage field and slope stability before and after irrigation was investigated using simulations and compared with the observed data. The results show that flood irrigation raised the water table, and the increase of soil moisture in the flooded area was more significant than that in the nonirrigated area. The rising speed of the groundwater level was about 0.25 m/yr, with an amplitude of 0.5 m. Near the slope, the hydraulic gradient of the concave slope was steeper than the convex slope. The shear strength of the loess decreased with increasing soil moisture, and the tensile strength was about 15% of the cohesion. Numerical results showed that after three years of continuous flood irrigation at the back of the slope, the slope stability coefficient decreased by 0.12. After irrigation, the potential slip zone slightly expanded. The reason why landslides often occurred at the back of the gully or the landslide was that the water table was shallower on concave slopes and the soil moisture of the concave slopes was more susceptible to irrigation.