Drainage Density and Its Controlling Factors on the Eastern Margin of the Qinghai-Tibet Plateau

The drainage density (D-d) is an important index to show fluvial geomorphology. The study on D-d is 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, and D-d is calculated. The spatial characteristics of D-d are analyzed, and the relationship between D-d and 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. D-d ranges from 2.5 to 0.1 km/km(2), increases first, and then decreases from north to south on the eastern margin of the Qinghai-Tibet Plateau. D-d decreases with increasing average slope and average local relief. On the low-relief planation surfaces, D-d increases with increasing altitude, while on the rugged mountainous above planation surfaces, D-d decreases rapidly with increasing altitude. D-d first increased and then decreased with increasing mean annual precipitation (MAP) and normalized difference vegetation index (NDVI), and D-d reaches a maximum in the West Qinling Mountains with a semi-arid environment, indicating that D-d in different climatic regions of the eastern margin of the Qinghai-Tibet Plateau was mainly controlled by precipitation and vegetation.