Abstract
The drainage density (Dd) is an important index to show fluvial geomorphology. The study onDdis helpful to understand the evolution of the whole hydrological and geomorphic process. Based on the Shuttle Radar Topography Mission 90-m digital elevation model, the drainage network of basins along the eastern margin of the Qinghai–Tibet Plateau is extracted using a terrain morphology-based method in ArcGIS 10.3, andDdis calculated. The spatial characteristics ofDdare analyzed, and the relationship betweenDdand its influencing factors, e.g., the topography, precipitation, and vegetation coverage, is explored. Our results show that terrains with a plan curvature ≥3 can represent the channels in the study area.Ddranges from 2.5 to 0.1 km/km2, increases first, and then decreases from north to south on the eastern margin of the Qinghai–Tibet Plateau.Dddecreases with increasing average slope and average local relief. On the low-relief planation surfaces,Ddincreases with increasing altitude, while on the rugged mountainous above planation surfaces,Dddecreases rapidly with increasing altitude.Ddfirst increased and then decreased with increasing mean annual precipitation (MAP) and normalized difference vegetation index (NDVI), andDdreaches a maximum in the West Qinling Mountains with a semi-arid environment, indicating thatDdin different climatic regions of the eastern margin of the Qinghai–Tibet Plateau was mainly controlled by precipitation and vegetation.
Highlights
The Qinghai–Tibet Plateau is the largest and highest plateau with strong tectonic activity and fast geomorphological evolution on Earth (Pan et al, 1995; Pan and Li, 1996; Li and Fang, 1999)
The results show that in the areas where Mean annual precipitation (MAP) is less than 600 mm, drainage density (Dd) increases with the increase of MAP, showing a strong positive correlation, and passing the significance test at 0.01, while in the areas where MAP exceeds 600 mm, Dd slightly decreases with the increase of MAP, showing a strong negative correlation with a significance level of 0.01
Dd is the largest in the West Qinling Mountains (Figure 8B). It indicates that the combination of precipitation and vegetation in different climatic regions controls the intensity of surface runoff erosion, affecting Dd
Summary
The Qinghai–Tibet Plateau is the largest and highest plateau with strong tectonic activity and fast geomorphological evolution on Earth (Pan et al, 1995; Pan and Li, 1996; Li and Fang, 1999). In addition to a huge terrain steep change zone between the Qinghai–Tibet Plateau at an altitude of 4,000 m and the Sichuan Basin at an altitude of 500 m, the eastern boundary of the plateau in other sections is not clearly defined The mountains in this area are large, the canyons are deep, and only on the watershed divides where headward erosion of modern rivers has not yet reached are planation surfaces preserved (Liu et al, 2019). In order to set a suitable Cp threshold to obtain a more precise valley network, first, four small basins were selected as the experimental area, they are the Shagou River, Liulingou River, Zhongdashigou River, and Daqinggou River from the Qilian Mountains, West Qinling Mountains, Western Sichuan Plateau, and Yunnan Plateau, respectively. A grid with a cell size of 5,000 × 5,000 m was chosen to segment the study area and obtain Dd of each cell (Figure 4B)
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