From badland to bushland? : Analysis of geomorphic process dynamics and vegetation development in a sub-humid calanchi area based on high-resolution UAS data (2014–2024)

Kurzfassung/Abstract

Badlands are among the most rapidly developing landscapes whose evolution is often controlled by threshold-driven geomorphic processes. This study employs quantitative, multi-temporal analysis to examine the spatio-temporal evolution (2014–2024) of a sub-humid calanchi badland in the upper Val d'Orcia (Italy). We investigate geomorphic dynamics over five consecutive two-year periods, focusing on the interplay between surface processes, vegetation development, and precipitation. Vegetation patterns were mapped semi-automatically from high-resolution orthomosaics (0.05 m), while geomorphic change detection analysis was carried out on DSMs of 0.25 m resolution. Despite stable mean slope gradients, specific sectors exhibited intensified geomorphic activity, designated ‘geomorphic hotspots’. Annual erosion rates vary between −0.4 cm and − 4 cm. The topographic evolution is primarily driven by irregular high-magnitude events. Water erosion showed a significant spatial reduction of 50% from 2014 to 2024. Furthermore, we document a geomorphic process not previously described in badlands: gravitational bulging, a subsurface sediment deformation induced by water infiltration, swelling of clays and overburden pressure. Vegetation establishes particularly in moist, low gradient depositional areas and evolves fragmented to a continuous structure. Although the erosional area decreased over the monitoring period, erosion rates remained relatively constant, suggesting a transition from high-frequency to high-magnitude, event-driven processes during the observation period. This behaviour suggests that the system operates close to a geomorphic threshold, where intrinsic dynamics, rather than changes in mean climatic conditions, control landscape evolution. Overall, the period 2014 to 2024 represents a phase of progressive badland stabilisation controlled by intrinsic geomorphic dynamics under a normal precipitation regime.