Areal Extent of Dust Emission Events and Source Geomorphology in Northern Africa from MSG-SEVIRI Data

Ofer Lavi Bekin,Onn Crouvi,Dan G Blumberg

doi:10.3390/rs12172775

Ofer Lavi Bekin, Onn Crouvi + Show 1 more

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https://doi.org/10.3390/rs12172775

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Abstract

In this study we (1) mapped the areal extent of current dust sources over Northern Africa between 8°W–31°E and 22°N - Mediterranean coast; and (2) identified and characterized the geomorphic units and soil types that emit dust from these areas. We used the full resolution (3 km) data from the MSG-SEVIRI to map dust sources over a 2-year period between 2005–2006, and examined these regions with remotely sensed images and geomorphic and soil maps. A total of >2600 individual dust emission events were mapped; with frequency up to 34 events in the 2-year study period. The areal extent of dust emission sources exhibited a lognormal distribution with most sources ranging from 20 to 130 km2. Most dust events were singular and related to a variety of specific geomorphic units. Dust events that created hotspots were mostly located over playas and fluvial landforms, and to a lesser extent over sand dunes and anthropogenic affected regions. About 20% of dust hotspots were offset a few kilometers from clear geomorphic units. Quantitative analysis of emissions revealed that dust sourced from various geomorphic units, among them playas (12%) and fluvial systems (10%). The importance of sand dunes as dust-emission sources greatly differs between examined datasets (7% vs. 30%). Our study emphasizes the importance of scattered dust emission events that are not considered as hotspots, as these sources are usually neglected in dust emission modeling.

Highlights

Mineral dust is a key element in controlling physical and biogeochemical exchanges among the atmosphere, land and ocean [1,2,3,4]
Emissions were detected originating from multiple geomorphic units: Playas, sand dunes edges, and agricultures fields; and (3) northeastern Libya adjacent to the Mediterranean coast (F in Figure 1); most emissions originate from the foothills of Al-Akhdar Mountains (400–700 m asl), characterized by playas, alluvial fans, wadis and agricultural fields
While part of the difference between these two studies can be explained by the improved assignment of dust source geomorphology due to the high spatial resolution used in the current study, another part is probably related to the spatial coverage of the studied areas: Whereas the study of Crouvi et al, [5] covered all of northern Africa, the Sahara and the Sahel, the current study focused on smaller portion of this area, and did not include the Sahel and NW Africa (Mauritania), which are known for their abundant and vast active and stabilized sand dunes, comprising some of the most active dust sources in the world

Summary

Introduction

Mineral dust is a key element in controlling physical and biogeochemical exchanges among the atmosphere, land and ocean [1,2,3,4]. Crouvi et al [5] spatially correlated the latter results with a global soil map and showed that dust is being emitted mostly from sand dunes, leptosols, calcisols, arenosols and rock debris Despite these recent advances, our understanding of dust-source geomorphology and the accurate identification of dust sources over North Africa remains loosely constrained. Identification of dust sources using higher spatial resolution is required in order to accurately identify the landforms that emit dust, as was previously done in Australia [19] and South Africa [20] In these studies the geomorphic units that emit dust were determined by overlying a RS-based identification of point-source dust emission on a geomorphological map; the areal dimension of the dust emission events was mostly neglected in previous studies

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