Comparisons suggest more efforts are required to parameterize wind flow around shrub vegetation elements for predicting aeolian flux

Effects of stone-made wind shelter structures over an arid nebkha foredune

Beach users often use a range of strategies to shelter from the wind and blown sand. This involves building structures made of stacking stones. Different from other portable wind blockers, stone-made wind shelters can remain in the landscape for a long time. The process of stone removal from their original place and stone-stacking at another location has well-known effects on rock-dwelling wildlife. Less known are the impacts of stone wind shelters on biogeomorphological processes of beach-dune systems, especially those in arid coastlines, where foredunes formed by nebkhas are naturally discontinuous. This is the case of Playa del Inglés beach (Gran Canaria, Spain), the main sediment input to the Maspalomas dunefield, where the presence of stone wind shelters (goros) made by users has increased in recent decades following an increase of visitors. This research aims to investigate the effects of stone wind shelters on the dynamics of an arid beach-dune system at various spatiotemporal scales. The methodology includes the use of aerial photography to study the appearance and evolution of stone shelters in Playa del Inglés and some of their long-term effects on the foredune. Field data was also collected to investigate the effects that stone shelters have over a representative foredune nebkha in detail, by monitoring the changes (topography, airflow, and vegetation) of an individual landform as we progressively remove pebbles from a previously built stone shelter. Results show that stone stacking has an impact on airflow and sediment transport dynamics around landforms, limiting sediment accumulation inside nebkhas and therefore arid foredune growth. Stone stacking also constrict vegetation growth and its ability to retain sediment. The impacts of these artificial structures can be reverted following their removal but that the process of dismantling stones must be carefully planned. We elaborate some recommendations here to do it avoid damaging foredune vegetation.

Wind speed acceleration around a single low solid roughness in atmospheric boundary layer

Air flow around vegetation is crucial for particle transport (e.g., dust grains, seeds and pollens) in atmospheric boundary layer. However, wind acceleration around vegetation is still not well understood. In this work, air flow around a single low solid roughness element (representing a dense shrub patch or clump) in atmospheric boundary layer was numerically investigated, with emphasizing wind acceleration zone located at the two lateral sides. The maximum value of dimensionless horizontal wind speed as well as its location of occurrence and the geometrical morphology and area of wind acceleration zone were systematically studied. It reveals that they could alter significantly with the change of roughness basal shape. The maximum value of dimensionless resultant horizontal speed decreases monotonously with observation height, while the area of wind acceleration zone shows a non-linear response to observation height. The dependence of the maximum speed location on observation height is generally weak, but may vary with roughness basal shape. These findings could well explain the disagreement among previous field observations. We hope that these findings could be helpful to improve our understanding of aeolian transport in sparsely vegetated land in arid and semi-arid region, and wind dispersals of seeds and pollens from shrub vegetation.