Abstract
The study area has three sand accumulations: Two in Wadi Fatmah and one in Wadi Ash Shumaysi, midwest of Saudi Arabia. The spatial extents of these sand accumulations have significantly increased over the last few decades. Multi-source satellite imagery, such as CORONA (1967, 1972), SPOT 5 (2013), LandSat TM (1986), and LandSat 8 OLI (2013), enabled monitoring and analysis of the interplay between the changes in the anthropogenic activities and spatial expansion of the areas of sand accumulation. The main driving force of the spatial expansion could be strongly linked to extensive changes in the anthropogenic regimes in the middle zone of Wadi Fatmah and its surrounding landforms and mountain masses. In this context, the once dominant agricultural lands of the middle zone of Wadi Fatmah have been transformed into abandoned agricultural areas. Extensive off-road driving has resulted in soil degradation. Excavation and mining activities for urban spatial expansion are widespread over the valley floor, the adjacent bajada, and the mountain blocks. These anthropogenic activities have remarkably induced strong wind erosion of the soil in severe arid conditions in the middle zone of Wadi Fatmah and Wadi Ash Shumaysi. Wind erosion has eventually produced a sufficient sand budget to be transported into the areas of sand accumulation. The primary consequence of the excess sand budget has been an increase in the spatial extents and dune migration rates of sand accumulations in the study area. However, this increase varies from one sand accumulation to another. In this study, we used multi-source remote sensing imagery and the state-of-the-art COSI-Corr technology to characterize sand accumulations in the study area and to determine the spatio-temporal changes in both the spatial extents and the dune migration rates. The mean annual migration rates of sand dunes in the three sand accumulations ranged from 5.5 and 7.2 to 8.6 m/yr. Analysis of the spatial extent and migration rates of sand accumulations indicates that the study area may have experienced desertification in response to changes in the anthropogenic regimes through the last few decades.
Highlights
In response to sparse vegetation cover and the availability of sand supply, wind acts in arid regions to form sand accumulations [1]
Until 40 years ago, Wadi Fatmah valley was the main source of various agricultural crops for the major surrounding big cities, such as Makkah, Taif, and Jeddah [72]
The primary source of water for the agricultural and other domestic activities in the middle zone of Wadi Fatmah was the underground water discharged from shallow alluvial aquifers [67,73]
Summary
In response to sparse vegetation cover and the availability of sand supply, wind acts in arid regions to form sand accumulations [1]. Earth observation satellites have served the community by providing a systematic and long archive of remote sensing images over the last 50 years They have enabled scientists to carry out many dune-related studies, such as dune mapping and taxonomy [30,31], pattern analysis of dune fields [32,33,34], spatial analysis of dune fields [35,36], topographic and morphologic variations of dune fields [37,38,39], mineralogic and sedimentologic characteristics [40], and climatic changes [41]. The results of this study will provide an outline of the temporal and spatial characteristics of the aeolian activity in the study area, which can help local authorities and environmental planners avoid its consequences in the future
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