Geoinformation mapping of sor depression in the Northwestern Caspian

Abstract

The article discusses the results of mapping sor depressions in the Sarpinskaya lowland based on geoinformation technologies and Sentinel-2 satellite data. The research area is subject to desertification processes, which are expressed in a decrease in the productivity and density of vegetation up to its complete destruction as a result of uncontrolled pasture loads and climatic fluctuations. The consequence of these processes is an increase in the area of shifting sands, intensification of dust storms and economic losses. For these reasons, it is extremely important to timely determine the centers of desertification in order to take measures to limit pasture loads on them and carry out phytomelioration. Satellite data are widely used to monitor desertification processes. However, the presence of natural areas devoid of vegetation due to their genesis—solonchaks and sors—is practically not considered. Attributing these categories to desertification is incorrect; for this reason, they should be mapped separately and not considered in the future. Sory (sor depressions) is a closed arid drainless landform with a temporary drying up reservoir. The area of sor depressions is constant; only the ratio of areas of water, salt crust, mud, and vegetation along the periphery changes. As the water dries up and forms a white salt crust during the growing season, the albedo of the sor surface increases, due to which they can be classified as lands subject to desertification in the classification of satellite images. In total, as a result of the work, about 7 thousand objects were identified: sors, solonchaks and dry ilmens with a total area of 143 thousand hectares. More than half of the total share of all depressions has an elongated shape in the sublatitudinal direction. Sor depressions with a depth of 1–2 m predominate compared to the surrounding area. There are also salt marshes that are not expressed in relief or rise up to 1 m above the surroundings. The results obtained can be used in geomorphological and soil studies and will also allow more accurate satellite monitoring of desertification processes in the region.