The Slope Association Type as a Comparative Index for the Evaluation of Environmental Risks

Abstract

The topography is one of the determining site characteristics, of which the slope inclination is significant for natural science aspects, including the estimation of water erosion risk and as a criterion for agricultural subsidies. The slopes within an area vary greatly and occupy very different proportions of the area. Algorithms that take this heterogeneity into account were developed in the 1970s with the medium-scale agricultural site mapping (MMK). It also contains the slope association types (SAT, in German: “Hangneigungsflächentyp”), which classifies different slopes and summarizes them as one value per reference area. The SAT can be used across various scales and different targets. Applicability is given to soil and water conservation tasks, administrative tasks as field selection or agricultural subsidies, and over a wide range of scales from small catchments areas to whole landscape analyses. Thus, one value on an area basis characterizes an important topographic factor.

Using model simulation to evaluate soil loss potential in diversified agricultural landscapes

“…These flow accumulation zones and branched networks are mainly formed in Erosion 3D due to the Horton overland flow (Horton, 1945) and encourage higher erosion rates when the combined momentum flux of surface runoff and droplet impact exceeds soil specific resistance to erosion (Equation 2). However, these effects confirmed that common slope evaluation schemes as described by Deumlich et al (2021) can only be used as indicators but were not able to assess small-scale soil erosion in the field. Introducing the patchy field structure resulted in both reduction and promotion of erosion effects.…”

“…These were primarily related to the convex and concave relief shapes. As shown in Figure 4, patches with the same crop rotation and the same slope classification according to Deumlich et al (2021), resulted in rather different sediment discharge, which can only be caused by different topography conditions. In summary, the slope is a significant factor of soil erosion by water as described in numerous studies (de Roo, 1993).…”

“…Effect of topography on sediment discharge. Exemplarily shown for patch 60 and 68 both in the low yielding part of the experiment, subject to the same crop rotation, and classified as flat with moderate inclined portions according to Deumlich et al (2021). Mean of sediment discharge [kg m 2 ] of one crop rotation (5 years) for simulated precipitation (50 year event) in May (S2) and August (S3).…”

“…In Figure 4, the influence of the spatial heterogeneity is exemplarily shown for patches 60 and 68, both in the low yielding part of the experiment, subject to the same crop rotation, and classified as flat with moderate inclined portions according to Deumlich et al (2021). During the S2 scenario, the average soil loss for a 50 year event varies substantially with 1.9 kg m 2 (patch 60) and 0.5 kg m 2 (patch 68).…”

“…Study area: (a) slope characteristics according to Deumlich et al (2021), numbers refer to patch‐ID (b) patchCROP field (c) overview map…”