A new method of tree structure for analysing nested watershed shape

A new method based on tree structure is proposed to study the relationship of multi-scale watershed shapes. Considering the nested relationship of watershed characteristics, the method uses a tree structure to reflect different watershed scales. We investigated the Loess Plateau of Shanxi Province, China, using 30-m resolution Digital Elevation Models (DEMs). The study consists of three stages: (1) by using Geographic Information System (GIS) tools, different scale watersheds were extracted from the DEMs and used to build a tree structure model based on spatial inclusion relationships; (2) the tree structure was transformed into a table based on the size of watershed area; and (3) the shape was quantified by roundness and tightness coefficients to analyse shape relationships among different scales of watersheds. The application of the method to 15 types of geomorphological features suggests that the smaller the watersheds are, the rounder they tend to be. The new tree structure method introduced here provides a good understanding of nested relationships between watershed characteristics. •Watershed characteristic of nested relationships among different scales described well by tree structure model.•Serialization based on area weight is used to traverse tree structure nodes into semi-table structure.•Jonckheere-Terpstra test is used to compare coefficients of roundness and tightness among different geomorphological types.•The result revealed that the smaller watersheds are, the rounder they are.•The serialization based on tree structure and its nodes is useful to analyse watershed in different scales.