Modis Derived Vegetation and Aridity Indices Account for Spatial Variation in Desertification Risk Index in Dry Environment

Abstract

It was estimated annually that several thousands of hectares (ha) of land has been lost to desertification and the negative impacts are manifested on the environment and general livelihood of people; reduced capacity to provide for the basic needs such as food and water. Although this is true of many countries in Sub Sahara Africa, yet the spatial pattern of the level of desertification and the areas at risk has not been sufficiently quantified and mapped. This study is aimed at determining and mapping the spatial extent of desertification risk index in the 9 frontline states of Northern Nigeria and to identify areas and population that are at risk given the current condition to enhance mitigation and adaptation strategy plan. We used both aridity and vegetation indices in combination with elevation and urban/settlement population data to determine and mapped the risk of desertification in the nine frontline states. To obtain aridity index we used De Martonne aridity index (Iar-DM) equation; this was calculated from the raster layers of mean annual temperature (MAT) and total annual precipitation (TAP) using map algebra. To monitor vegetation conditions we used eMODIS NDVI 10-day maximum-value composite MVC NDVI images at 250m spatial resolution. We created desertification risk index map from spatial overlay of NDVI/ vegetation cover, elevation, population and aridity index. The study shows that aridity in the study area increases northward in curvilinear pattern as 75 % (430,650 km2) of the region falls into three aridity categories: arid, semi-arid and dry sub humid while the remaining 25% (33,000 km2) found in southern Kebbi, Zamfara, Katsina and Bauchi falls under sub humid. Aridity index as proximate of the desertification was however found to be inadequate as the combination of vegetation index produced desertification risk index (DRI) map which has helped to identify “hot spot” these are places where risks to desertification are higher than their surrounding areas. Suggestions such as sound land management, energy substitution strategy are made to combat the menace of desertification with special attention placed on these highly vulnerable “hot spot” areas.