Research On Watershed Hypsometric Integral In The Loess Plateau Based On Digital Elevation Models

Hypsometric integral is a terrain analysis factor with apparent physical and geomorphologic meanings which could reflect the landform erode stage and evolution process. As a macroscopic parameter and method in terrain analysis, the applications of hypsometric integral could reveal the quantitative characteristic of landform evolution in watershed scale. However, it still needs to be improved and enriched of the hypsometric integral analysis method, particularly in the little progress has been made of hypsometric integrals in the applications of watershed evolution and geomorphologic pattern from previous literatures. On the basis of aforementioned shortages, this paper conducts a systematic analysis on the concepts of hypsometric integral, and then, the attributes of its morphologic feature, formation factors and its classification scheme have been deeply discussed. In addition, the spectrum serial of hypsometric integrals is proposed followed with its conceptual model, geographic meaning, component features and analysis methods. Based on the methods of digital terrain analysis and geo-informatic Tupu, the spectrum serial of hypsometric integrals is applied to the loess watershed landform in the severe soil erosion area of Loess Plateau. Finally, a new understanding of loess watershed landform and its spatial differentiation characteristic has been achieved. The main research contents and conclusions are listed as following:1. Clearing the basic characteristics of hypsometric integrals. This paper puts forward the conceptual model of the spectrum serial of hypsometric integral and carries out the further derived studies on various analysis methods. The results indicate that the spectrum serial could make a good understanding for the description of the geomorphology by each integral. Well expressed hypsometric integrals of each watershed terrain features, could enrich the theory and analysis methods to some extent.2. The index groups of the hypsometric integral are selected according to the terrain features analysis of watershed landform. The experiment results show that a serial of the integral values and their corresponding curves, derived from different terrain features, could efficiently reveal the geomorphological and the evolution characteristic of watershed from the whole to the local. According to the correlation variance of the hypsometric integral of terrain features, two index groups are selected as the basic index group to analyze the morphologic characteristics and evolution process of watershed landform, i.e. boundary of watershed, watershed and main gully as a group, and watershed, stream network and main gully as the other.3. The scale effect of the hypsometric integral is analyzed with the small loess watersheds along with the time serial. The experiment of scale effect among the grading scale, data scale and region scale show that, the integral curve appears high accuracy and well calculation efficiency when the elevation grade use100; The resolution of DEM shows a weak sensitivity to the integral value, i.e. the value keeps stable with the resolution varying; When the area of the test site exceeds10km2, the integral value states a similarity to others as well as regional stability.4. A discussion on the variance characteristic of the spectrum serial of the hypsometric integral is given with two different analysis serials, i.e. the typical watersheds on the spatial serial and simulated watersheds on the time serial. The results indicate that each index of the spectrum serial has an orderly spatial distribution, and the simulated watersheds also prove that the well correspondence characteristic between the integral value and evolution stage. The multi-index maps of hypsometric integral in the severe soil erosion area reveal that, despite most of the small watersheds are in mature stage,, it still present the spatial differentiation on the evolution process from east to west and from south to north in the study area.This paper enriches the theories and methods of digital terrain analysis through the studies on the spectrum serial of the hypsometric integral of watersheds in loess plateau. The conclusions strengthen the understanding of the loess watershed landform and its spatial differentiation characteristic. This paper is an innovative and beneficial work/job for the application of the geo-informatic Tupu.