Prediction of barchan dunes migration using climatic models and speed-up effect of dune topography on air flow

This study presents and validates a workflow that quantitatively links the rate of barchan dunes migration, which can be measured from remote sensing, to the wind velocity, either measured at a meteorological station or extracted from reanalysis data. The workflow requires the selection of a sand transport law and a procedure to estimate the effect of the local topography on the near surface airflow, namely the speed-up effect, that results from the compression of streamlines as the wind climbs up the dune topography. Additionally, the estimate of sand flux under natural conditions needs to account for short duration wind gusts which are usually not fully accounted for or sampled in climatic models. Those spatial and temporal variations of wind speed have a strong influence on the local sand flux due to the non-linearity of the sand transport models. We investigate these effects by using computational fluid dynamic (CFD) modeling to estimate the speed-up effect on airflow and sand transport. We next include that effect to compare the predicted dune migration rate with remote sensing observations, at two desert barchan dune fields located along the southern rim of the Arabia Gulf. We find that, at the two sites, the speed-up effect increases the predicted sand flux by a factor of ∼3 and that the measured and predicted dune migration rates agree well if the sand transport law of Kok et al. (2012) is used, combined with the cessation threshold from Pähtz and Durán (2023) along with reanalysis data ERA5-Land with an hourly sampling. The proposed workflow is applicable to any barchan dune field on Earth or Mars.