Multi-Indicator Assessment of Desertification Dynamics in Kebbi State, Nigeria

Abstract

This study assessed desertification in Kebbi State over a 32-year period (1991-2023) using a multi-indicator approach comprising thirteen indicators. Vegetation indicators included the Normalized Difference Vegetation Index (NDVI), Modified Soil-Adjusted Vegetation Index (MSAVI), and Normalized Difference Moisture Index (NDMI). The Modified Normalized Difference Water Index (MNDWI) was used to extract surface water. Soil indicators included the Normalized Difference Salinity Index (NDSI) and the Topsoil Grain Size Index (TGSI). Land use and land cover indicators were the Normalized Difference Built-Up Index (NDBI) and the Normalized Difference Bareness Index (NDBaI). Climate indicators included Land Surface Temperature (LST), Air Temperature (TMP), Precipitation (PRE), Aridity Index (AI), and Surface Albedo. We computed Remote sensing indices from Landsat 4 TM and Landsat 8 OLI/TIRS for 1991 and 2023, respectively, and obtained climate data from the Climate Research Unit (CRU) gridded datasets. Results revealed a decline in vegetation and moisture conditions. Maximum NDVI decreased from 0.4695 to 0.3925, and MSAVI declined from 0.5931 to 0.5637. NDMI reduced from 0.5271 to 0.2388, and MNDWI from 0.3215 to 0.1375. Soil salinity declined, with NDSI decreasing from 0.3661 to 0.1019 and TGSI from 0.6356 to 0.4399, indicating a shift to fine soil. Built-up intensity increased as NDBI rose from 0.7180 to 0.7354, while surface bareness (NDBaI) declined from 0.7411 to 0.6065. Climatic stress intensified: maximum LST decreased from 64.04°C to 56.26°C, mean temperature increased from 29.28°C to 30.34°C, annual precipitation declined from 1232.33 mm to 1004.80 mm, and AI declined from 0.96 to 0.65. Surface albedo increased from 0.2589 to 0.3020, indicating increased land exposure and degradation. This study underscores the effectiveness of employing a multi-indicator framework for desertification monitoring and understanding its dynamics in Kebbi State and other semi-arid regions.