Analysis of temporal and spatial distribution characteristics and influencing factors of alluvial fan geomorphology in the middle of the northern foothills of Qilian Mountains, northwest China

Abstract

Geomorphological analysis is central to alluvial fan studies, but research on the long-term evolution trends of alluvial fans and the interaction of spatial and temporal factors remains limited. This study aims to fill this gap by exploring the long-term evolution of alluvial fan morphology and the long-term impact of climatic factors on morphological changes. The research uses satellite images from 1983 to 2023, GDEMV3 30-metre resolution digital elevation model, and regional annual precipitation data, combined with Geographic Information Systems (GIS), remote sensing technology, and statistical methods (such as Sen's Trend Test and Mann-Kendall Test), focusing on three regions in the middle section of the northern Qilian Mountains foothills. The results show: (1) Spatially, there is a significant inverse relationship between the number and average area of alluvial fans. The northwest region has the most alluvial fans but the smallest average area, while the southwest has the fewest but the largest. As the rank of alluvial fans increases, their area grows, but their number decreases. The area and slope of alluvial fans follow a power function relationship with watershed area—larger watersheds tend to have larger and gentler alluvial fans. (2) Temporally, from 1983 to 2023, the overall area of alluvial fans has significantly decreased, especially in the northwest, while the overall slope has slightly increased. Both the area and slope of alluvial fans are strongly correlated with annual precipitation; increased precipitation promotes area expansion and reduces slope. This study enriches geomorphological literature and provides new perspectives for related research.