Estimation of surface roughness (z₀) cover a stabilizing coastal dune field based on vegetation and topography

Accurate knowledge of the surface roughness and the resultant wind speed are important for many applications, such as climatic models, wind power meteorology, agriculture and erosion hazards, especially on sand dunes in and and semi-arid environments, where vegetation cover is scarce. In this study we aimed at quantifying the effects of vegetation cover and topography on surface roughness over a stabilizing dune field on the southern coast of Israel. Forty-six wind measurements were made at various distances from the coastline, ranging from 10 to 2800 m, and z_o values were calculated from the wind measurements based on the ratio between the wind gust and the average wind speed. We estimated vegetation cover using the soil adjusted vegetation index (SAVI) from Landsat satellite images for the upwind sector at various lengths, ranging from 15 to 400 m, and based on digital elevation models and differential GPS field measurements we calculated the topographic variable of the relative heights of the stations. z_o values were positively correlated with the winter SAVI values (r = 0-87 at an upwind length of 200 m) and negatively correlated with the relative height (r = -0-68 at an upwind length of 200-400 m for the inland dune stations). Using these variables we were able to create a map of estimated z_o values having an accuracy of over 64%. Such maps provide a better understanding off the spatial variability in both wind speed and sand movement over coastal dune areas.