Gully erosion in India: Land degradation, geomorphology and dynamics

Gully erosion is the rapid incision of soils by concentrated overland and/or subsurface runoff. Badlands, which are barren landscapes sculpted through prolonged and intense gully erosion, occur extensively across Central and Western India. These vast and immensely degraded landscapes have had several adverse effects on the regional environment and society. Consequently, they have received considerable research attention since India’s independence, while little information exists about the characteristics of gully erosion elsewhere in India. Therefore, through a detailed pan-Indian mapping of gully erosion landforms, possibly the most extensive fieldwork ever undertaken in the domain of gully erosion research and multitemporal remote sensing, this work highlights the spatial distribution and areal extents of gully erosion, the spatial variability in gully morphological attributes and the dynamics of gully erosion and reclamation in India. Overall, the findings indicate that India not only has some of the largest gullies worldwide (widths up to 412 m and depths up to 78 m) but select locales of the country also experience some of the worst long-term rates of gully erosion (up to 800 t ha^-1 yr^-1) on our planet. Although the badlands account for a large 70% of the total gullying-affected land area in India, we have found that gully erosion in Eastern India is currently a particular cause of concern not only due to the widespread occurrence, but also because of high activity rates that seldom remain within the local permissible soil loss rates. On the contrary, the badlands are stabilised, and the gullies therein exhibit limited activity, if at all, which has prompted large-scale land reclamation activities in these regions. Gully morphological attributes such as top-to-bottom width ratio, width-depth ratio and cross-sectional area differ considerably across India, with statistically significant differences observed across climes, geomorphological settings, soil types and land cover/use classes. We have also observed that stabilised gullies are considerably (by ca. 3 times on average) larger than currently active systems. Similarly, gullies in the badlands are disproportionately larger than that of gully systems elsewhere, with bank gullies characterised by the largest dimensions among the latter. By providing critical insights into the scale, nature, and severity of gully erosion in India, this project not only addresses the glaring lack of knowledge on this subject and advances scientific understanding, but the findings also support practical strategies for sustainable land management by aiding in the identification of particularly erosion-prone regions where management efforts should be prioritised, which has relevance for the ongoing national land degradation neutrality drive.