Abstract
In this paper, we used Landsat thematic mapper (TM) and enhanced thematic mapper (ETM) data from 1990, 2002, and 2011 to analyze the spatial and temporal patterns of desertification using seven factors; the normalized difference vegetation index (NDVI), the topsoil grain size index (TGSI), land surface albedo, the topographic wetness index (TWI), land surface temperature (LST), the perpendicular drought index (PDI), and the elevation of Hogno Khaan, which lies in a semiarid region of central Mongolia. We normalized the indicators, determined their weights, and defined five levels of desertification; none, low, medium, high, and severe. Sets of rules were constructed, and a multi-criteria evaluation (MCE) approach was used to assess desertification and test the correlations between the seven variables in comparison to the different levels of desertification, with field and reference data used for accuracy. We provide a review of the literature on MCE applied to desertification assessment issues based on satellite data. At the first step, major desertification factors were computed for satellite data. The next step was the construction of pairwise comparison matrix. Then, the weight of each factor was determined by the contribution of an analytical hierarchy process. Finally, the susceptible areas to desertification in the study area were identified using a multi-criteria evaluation method. We found that more than 15% of the total land area in Hogno Khaan suffered from severe desertification in 2011, increasing from 7% in 1990. Our analysis showed that the highest correlations were between TGSI and albedo, PDI and TGSI, and PDI and albedo at all levels of desertification. LST was less strongly correlated with TGSI, albedo, and PDI. The correlation of TWI with PDI and NDVI in the non- and low desertification areas produced R values of 0.15 and 0.58, respectively. The correlation analysis indicated a significant positive correlation between TWI and both NDVI and PDI for all years in non- and low desertification areas. Comparing elevation and NDVI, the highest correlation was found for severe desertification in 2002, although correlations for severe desertification were lower in 1990 and 2011.
Highlights
The United Nations Convention to Combat Desertification (UNCCD), which has been ratified by 195 countries, identifies land degradation and desertification as two of the most pressing current environmental concerns [1,2]
Enhanced Thematic Mapper Plus (ETM+) images from Landsat 7 were recorded on August 2002 and Thematic Mapper (TM) images from Landsat 4–5 were recorded on 8 September 1990 and August 2011, http://landsat.usgs.gov
The southern and northwestern parts of Hogno Khaan have seen an expansion of desertification, with a gradual intensification in the last twenty years
Summary
The United Nations Convention to Combat Desertification (UNCCD), which has been ratified by 195 countries, identifies land degradation and desertification as two of the most pressing current environmental concerns [1,2]. The breadth, complexity, and dynamism of the desertification process have so far precluded the development of a comprehensive desertification model, and assessment and monitoring techniques have relied on the use of indicators [3,4]. Various methods have been used to analyse desertification, including empirical approaches [12,13], remote sensing applications [14,15,16,17,18,19], and modelling [20,21]. With the development of remote sensing technology, especially when combined with geographic information system (GIS) technology, researchers have an effective method for conducting desertification research over large areas [17,22]. By analysing remote sensing imagery over a long period of time, it has become possible to quickly and accurately assess desertification trends, thereby aiding in the prediction and management of this problem
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