Abstract
A hypsometric integral (HI) is a topographical index with important geomorphological meaning. It can both describe the development state of the watershed and reflect the strength of activity in the geological structure. Based on this index, the integral curve method was used to analyze the HI characteristics of watersheds in the region west of the Lvliang Mountains on the Loess Plateau of Shanxi Province, China, in combination with 30-m resolution Shuttle Radar Topography Mission data. In order to accurately characterize erosion development within the watershed, the HI characteristics of each topographic feature object in the watershed were comprehensively analyzed. The results of HI scale effects show that HI was not strongly dependent on the spatial resolution of Digital Elevation Model (DEM) data, but had some scale dependence on the stable area of the watershed. The spatial distribution of the HI shows that the HI values of the watersheds in the southern loess residual tableland were the largest, and the degree of erosion was the weakest; the HI values of the watersheds in the north-central part of the loess hilly-gully region were relatively small, and the degree of erosion was stronger. This result is consistent with the results of the spatial distribution of sediment yield in literatures. The reasons for the spatial distribution of the HI were analyzed in terms of geological formations and climatic environments. The results show that for the study area, tectonic activity, formation lithology, rainfall, and agrotype were not the main factors affecting the HI values. The structure of the paleotopography and erosion cutting due to the uplift of the Lvliang Mountains and later water erosion controlled the spatial distribution state of HI. Thus, for the study area, the HI value cannot reflect the strength of tectonic activity. The combination of topographic feature object method and the HI index further quantified the erosion development state of the watershed.
Highlights
A hypsometric integral (HI) is a macroscopic indicator that can be used to study the quantitative relationship between the area of a regional horizontal section of an area and its elevation, which can reflect the state of watershed development (Chen et al, 2003; Hamdouni et al, 2008; Andreani et al, 2014; Qing et al, 2020; Gharehchahi et al, 2021)
In order to deeply characterize the developmental features within the watershed, the study synthesized the area elevation integration characteristics of each topographic feature object within the watershed
The area elevation integral features of the topographic feature objects and the watershed showed that the HI value was the largest in the southern loess residual loess area, which had the weakest erosion of the watershed
Summary
A hypsometric integral (HI) is a macroscopic indicator that can be used to study the quantitative relationship between the area of a regional horizontal section of an area and its elevation, which can reflect the state of watershed development (Chen et al, 2003; Hamdouni et al, 2008; Andreani et al, 2014; Qing et al, 2020; Gharehchahi et al, 2021). The method was an important geographic concept extension for the study of area elevation integrals on the Loess Plateau watershed. Duan et al (2020) did a study on the spatial distribution characteristics of elevation integrals of watershed areas on the Loess Plateau in western Shanxi, and analyzed the correlation of integrals of individual geomorphic objects. The study started by calculating the HI values of the watershed in the eight sample areas and analyzing the status of their development including the integral value and curve of each sub-basin (Figure 5). The HI difference between the watershed and the main gully was not very regular on the loess hilly-gully area (Figure 10), with some sub-watersheds in Linxian showing anomalously high values. These results indicated that the amount of eroded material varies over time between by approximately 10–20%
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