Dune transformations driven by vegetation change arising from environmental and anthropogenic impacts

Parabolic dunes are one of a few common aeolian landforms that are highly controlled by eco-geomorphic interactions. Parabolic dunes, on the one hand, can be developed from highly mobile dune landforms, barchans for instance, in an ameliorated vegetation condition; or on the other hand, they can be reactivated and transformed back into mobile dunes due to vegetation deterioration. The development and transformations of parabolic dunes are also highly sensitive to changes in many environmental factors such as precipitation, temperature, wind regime, as well as changes in land management and other anthropogenic factors. The eco-geomorphic interrelationships and fundamental mechanisms controlling the dune transformations, however, are incompletely understood. This study combines fieldwork investigation, remote sensing, and Cellular Automaton modelling, to explore both: 1) the dune stabilisation and barchan-to-parabolic dune transformation, as well as 2) the dune reactivation and parabolic-to-barchan dune transformation, under the influence of climatic changes (e.g., drought stress and wind energy), and human disturbance (e.g., grazing activity). Extensive suites of simulations are used to explore boundary conditions, parameter controls, and external forces on both dune transformations. The results show that the characteristics of vegetation play an essential role in the processes of dune transformations, in particular, the species (annual grasses vs. perennial shrubs) and their capabilities of withstanding wind erosion and sand burial. This study has introduced a dune stabilising index (S*) that captures the interactions between key parameters and establishes the linkage between the system controls and the geometry of a stabilising dune. The dune surface erodibility significantly influences the threshold of climatic forces that reactivates an initial vegetated parabolic dune and transforms its lobe into a mobile barchan dune with arm remnants left behind. The Extended-DECAL can be easily adapted to a different dune system to explore various scenarios under the changes in both natural and anthropogenic controls and to assist in planning judicious land-management practices.