Temporal trajectory and determinants of permanent gully erosion in the grassland: A long-term analysis spanning 1973–2020

Grassland ecosystems, particularly in cold and high-altitude regions, are highly vulnerable to gully erosion owing to their simple structure and environmental sensitivity, making it a severe form of grassland degradation. However, most previous studies have focused on agricultural systems, leaving limited understanding of the long-term evolution and drivers of permanent gullies in grasslands. To address this issue, we analyzed gully erosion dynamics and its determinants in a 103 km² area of the Hulunbuir grassland using remote sensing image from 1973, 1983, 2011, and 2020. Results showed that gully quantity, gully density and ground lacerative degree increased by 54.13 times, 286.66 times, and 591.01 times, respectively from 1973 to 2020, with the annual soil loss thickness of 0.023 mm. From 1973–2020, the average gully erosion rates in length, width, area, and volume were 4.64 m yr⁻¹ , 0.06 m yr⁻¹ , 17.17 m² yr⁻¹ , and 20.44 m³ yr⁻¹ , respectively. The merge of gullies (MG) showed greater linear gully erosion rate and areal gully erosion rate than newly formed gully (NFG) and continuously developing gully (CDG), while NFG showed the highest gully widening rates. Gully erosion rates in length, area and volume peaked at 4–5° slopes, with sunny and semi‑sunny aspects being more conducive to development, and linearly increased with gully drainage area. Cumulative gully growth length (ΔL), area (ΔA), and volume (ΔV) increased as a power relationship of cumulative climate indicators (Pre, R, R10, R95p, RX5day, SDII, Tem) and human activity intensity (grazing intensity, built up area, road density). The coupled effects of human activity with topography and climate exert the greatest influence on gully erosion, with the relative contribution of 37.13 % and 35.75 %, respectively. Overall, during 1973–2020, permanent gullies in the Hulunbuir grassland remained in the early lifecycle stage of development. However, intensifying anthropogenic pressures coupled with amplified climate variability progressively elevated erosion risks. This trajectory necessitates implementation of scientific gully control strategies to curb accelerated soil loss and establish sustainable human-land synergies.