Spatial heterogeneity of microtopography and its influence on the flow convergence of slopes under different rainfall patterns

This study aimed to reveal the spatial heterogeneity of the microtopography and its influence on flow convergence on sloping farmland of purple soil area in China. Methods involving artificial rainfall, pin meter and photographic measurements were adopted to generate DEM (digital elevation model). Geographic statistics and multifractal theory were used for quantitative and hydrological analyses of microtopography based on ArcGIS. Two artificial tillage practices (ridge tillage and conservation tillage) were used to simulate different types of microtopography. Ridge tillage (RT) was designed according to local agricultural customs in China, with conservation tillage (CK) used for comparison purposes. A total of 12 rainfall simulation experiments were conducted in two 1 m by 2 m boxes under increased rainfall series (1.0, 1.5, and 2.0 mm min−1) and decreased rainfall series (2.0, 1.5, and 1.0 mm min−1) on a typical slope gradient of 15°. Artificial tillage was the major contributing factor to the spatial heterogeneity of microtopography on sloping farmland of the purple soil area. Spatiotemporal variability of microtopography was expressed using semivariogram and multifractal spectrum, and spatial heterogeneity of drainage networks was expressed using general fractal dimension ΔD based on multifractal theory. In general, the drainage networks was mostly effected by microrelief. The drainage density of ridge tillage was smaller than that of the conservation tillage under different rainfall patterns, and the drainage density decreased remarkably with the increasing microrelief. Moreover, the ΔD values of ridge tillage ranged from 0.1817 to 0.5677. By contrast, the ΔD values of the conservation tillage ranged from 0.9662 to 1.3013, and thus the lower spatial heterogeneity of drainage networks in ridge tillage compared to conservation tillage. In this study, we established a novel method for analysis of the spatial heterogeneity of microtopography and demonstrated the effect of microtopography on the flow convergence of sloping farmland. These findings had important implications for clarifying the essence of microtopography of purple soil area and laying a theoretical basis and a support datum for harnessing measure of sloping farmland.