Intersecting views of gully erosion in South Africa

Abstract

Gully erosion is an environmental problem recognized as one of the worst land degradation processes worldwide. Insight into regional gully perturbations is required to combat the serious on‐ and off‐site impacts of gullying on a catchment management scale. In response, we intersect different perspectives on gully erosion‐specific views in South Africa (SA), a country that exhibits various physiographic properties and spans 1.22 million km2. While the debate surrounding gully origin continues, there is consensus that anthropogenic activities are a major contemporary driver. The anthropogenic impact caused gullying to transcend climatic, geomorphic, and land‐use boundaries, although it becomes more prominent in central to eastern SA. Soil erodibility plays a crucial role in what extent of gully erosion severity is attained from human impact, contributing to the east–west imbalance of erosion in SA. Soil erosion rates from gullying and badlands are limited but suggest that it ranges between 30 and 123 t ha−1 yr−1 in the more prominent areas. These soil loss rates are comparable to global rates where gullying is concerned; moreover, they are up to four orders of magnitude higher than the estimated baseline erosion rate. On a national scale, the complexity of gullying is evident from the different temporal timings of (re)activation or stabilizing and different evolution rates. Continued efforts are required to understand the intricate interplay of human activities, climate, and preconditions determining soil erodibility. In SA, more medium‐ to long‐term studies are required to understand better how changing control factors affect gully evolution. More research is needed to implement and appraise mitigation measures, especially using indigenous knowledge. Establishing (semi)‐automated mapping procedures would aid in gully monitoring and assessing the effectiveness of implemented mitigation measures. More urgently, the expected changes in climate and land‐use necessitate further research on how environmental change affects short‐term gully erosion dynamics.

Predicting gully erosion susceptibility in South Africa by integrating literature directives with regional spatial data

“…A recent review by Olivier et al (2023) showed contemporary gullying to be a continued concern in SA. Gully erosion rates of up to 25.7 t ha −1 year −1 (Grellier et al, 2012) are documented, which increases to up to 123.7 t ha −1 year −1 (Favis‐Mortlock et al, 2018) when badlands are included.…”

“…Based on the database and a recent literature review of gully erosion in SA (Olivier et al, 2023), five broad categories were identified to include in the susceptibility model, namely, topography, soil, geology, climate and anthropogenic activities. Seven control factor datasets were selected to represent these five broad categories, all of which were limited to national extents (where spatial resolution is not indicated, the dataset consisted of vector data) (Table 2).…”

“…Although this impact can be considered historical, it remains an area of severe gully erosion (Olivier et al, 2023). Surprisingly, vegetable farming, a land-use not commonly associated with gully erosion in SA, had the highest correlation.…”

“…Human activities were indicated as a critical driver of gully erosion worldwide (Castillo & G omez, 2016). In SA, the political past has significantly impacted erosion distribution (Hoffman & Ashwell, 2001;Olivier et al, 2023). To spatially accommodate the historical narrative of gullying, a regional agricultural zonal map derived from 1978 data (Khuthadzo, 2019) was implemented as a factor map (Figure 4b).…”

“…[Color figure can be viewed at wileyonlinelibrary.com] therefore, regulating the volume and velocity of concentrated flow, affecting gully susceptibility (G omez-Gutiérrez et al, 2015;Parkner et al, 2006;Rossi et al, 2015). Overwhelming evidence suggests that anthropogenic activities are accelerating gully erosion (Castillo & G omez, 2016;Olivier et al, 2023). Human influences that expose gully-prone pre-conditions and/or increase concentrated include landuse change to farming (Boardman et al, 2003;Zucca et al, 2006), commercial farming intensification (cultivated and rangelands) (Shellberg & Brooks, 2012;Talbot, 1947), population pressure in communal areas resulting in deforestation and overgrazing (Grellier et al, 2012;Le Roux & Sumner, 2012) and abandonment of cultivated fields (Kakembo & Rowntree, 2003;Lesschen et al, 2008).…”