Assessing the Nexus Between Landscape Degradation and Flooding in the Niger River Catchment, Southeastern Nigeria: A 40-Year Geospatial Dynamics (1992–2022)

Abstract

This paper examines the relationship between landscape degradation and flooding in the Niger River catchment of Onitsha, Nigeria, over a 40-year period (1992–2022), focusing on changes in land use and land cover characteristics. Satellite images were preprocessed and classified using Anderson's classification technique. Erdas Imagine GIS software was adopted to carry out change analysis for each of the classes generated. The Landsat images for all the years (1992, 2002, 2012, and 2022) were acquired for the months of July (wet season) and December (dry season) and analyzed. The trends in seasonal changes in land use and land cover characteristics were prominent in the wet season. This was significantly seen in changes for water body and vegetative area. Built-up areas and open spaces indicated a decrease during the wet season compared to the dry season. The notable changes occurred in water bodies and vegetation across the studied years, peaking in 1992 with 1628.82 ha for water bodies and 8993.79 ha for vegetation. In 2012, these values were 2040.93 and 8977.5 ha. The largest seasonal shifts were in vegetative areas in 2012 and built-up in 2022. After analyzing the geospatial data according to the classifications, the study uncovers a notable link between landscape degradation and increased flood susceptibility. Notably, the findings highlight that shifts in these landscape features during the wet season significantly impact flood occurrence, emphasizing the critical role of landscape degradation in exacerbating flood risks in the region.