The Loess Plateau is ecologically vulnerable. Vegetation is the key factor in ecological improvement. The study of the distribution patterns of vegetation and its impact factors has important guiding meaning for ecological construction in the region. The existing single sensor cannot provide long-term and high-resolution data. We established data of NDVI with a great spatial resolution by fusing the GIMMS NDVI and the MODIS NDVI based on the ESTARFM. Furthermore, we analyzed the variation in NDVI under different topographies and its response to climatic factors and human activities in the Loess Plateau. The results manifested that: (1) The fused NDVI by the ESTARFM had a high correlation with the MODIS NDVI and can be used in subsequent studies. (2) The multi-year average NDVI of this region ranged from 0.027 to 0.973, which is specifically low in the northwest and high southeast. The NDVI manifested an upward trend in the last 31 years. Its growth rate was 0.0036/a (p < 0.01). Spatially, the area with an upward trend of NDVI accounted for 89.48% of the plateau. (3) For topography, the larger area with the extremely significant upward of NDVI was found at elevations of 500–1500 m, with slopes of 6–15°. The larger area with the extremely significant downward trend of NDVI was found at an elevation of higher than 3000 m, with a slope of greater than 35°. (4) The response of the NDVI to the climatic factors manifested a significant spatial heterogeneity. The temperature had a more significant impact on NDVI than precipitation. (5) Human activities contributed more to NDVI than climatic factors (65.22% for human activities and 34.78% for climatic factors). Among them, the area with a high contribution of human activities to NDVI increase was consistent with the area where the GGP was implemented. The distribution of areas with high contribution of human activities to NDVI decrease was in line with that of the provincial capital cities. The results served as the theoretical foundation for assessing the efficacy of environmental stewardship and for optimizing ecological restoration measures.

The flood season is the main period for runoff and sediment yield, and understanding the variations of runoff and sediment of flood events is of great significance for distinguishing the runoff-sediment processes in the Loess Plateau. In this study, we analyzed the variations of runoff and sediment at the flood event scale in the Qiaogou catchment and investigated the influencing factors. The results showed that runoff and sediment of flood events were mainly produced by rainfall with short rainfall duration and heavy rainfall intensity in the study area. Based on the 28 flood events and corresponding precipitation data from the reference period (P-I, 1986–1989) and the revegetation period (P-II, 2001–2009), we analyzed the variations of runoff-sediment processes at the flood event scale in the Qiaogou catchment, a typical catchment of the Loess Plateau. The results showed that the flood variables were lower in the revegetation period than those in the reference period, except for the flood peak discharge time and the flood duration. The sediment transport capacity per unit runoff depth in the revegetation period was weaker than that in the reference period. The hysteresis analysis indicated that the patterns of the hysteretic loop were dominated by the figure-of-eight pattern and the compound pattern, respectively, in the reference period and revegetation period. Compared to the reference period, runoff and sediment-related variables for flood events of counter-clockwise, figure-of-eight, and compound patterns were less in the revegetation period. With similar rainfall conditions, the main reason for the noticeable difference in runoff and sediment of flood events for the two periods was the variations in vegetation cover. The mentioned results indicated that revegetation performed a critical function in the variations of runoff and sediment at the flood event scale. This study revealed the variations of runoff-sediment processes of flood events and their responses to rainfall and revegetation in a typical catchment of the Loess Plateau, which can provide a basis for decision-making on soil erosion management and sustainable development of the ecological environment in the Loess Plateau.