Indicator-based vulnerability assessment of riparian zones in Nigeria's Ibadan region due to urban settlement pressure

Abstract

Riparian zones are important natural resources that provide a variety of functions and ecosystem services. The vegetation within the riparian zones is gradually being replaced by built-up land with little or no indication of a distinct riparian buffer, affecting its functionality. In this study, we used indicators derived from the remote sensing images supplemented with field-based observations to analyse the vulnerability of riparian zones in the Ibadan region, Nigeria. The changes in the landscape pattern of the riparian zones were studied over 20 years (2000-2019) by analysing and manipulating Landsat (7 & 8) and Sentinel-2 datasets using ERDAS IMAGINE 2015, ArcGIS 10.4 and Google Earth Engine. Existing base maps and field surveys were used to identify factors influencing modifications in riparian zones. Using selected indicators, the vulnerability of Ibadan's riparian zones was assessed and mapped. The vulnerability and settlements within the riparian zone were classified into four levels of vulnerability (low, medium, high, and very high) and three levels of urbanisation (low, medium, and high settlement density). The findings show significant changes in land cover within riparian zones. The changes were caused by human activities such as farming activities, construction of buildings, infrastructure development (e.g. construction of roads), and other human interferences (movements of humans, cattle grazing, etc.). It was discovered that 23.16 percent of the riparian zone is classified as low vulnerable, 75.93 percent as medium vulnerable, 1.05 percent as high vulnerable, and 0.03 percent as very high vulnerable. Furthermore, most of the areas with low, medium and high settlement density indicate medium vulnerability. Vulnerability assessment and its magnitude are context-specific where for various ecosystems such as riparian zones even a medium vulnerability could have a significant impact. The present study must only be considered as the preliminary observation to delineate zones that are immediately suffering urbanisation pressure. Any further critical evaluation would require evaluation of interlinked processes such as the ecological processes, impact on individual species, water and nutrient availability, etc. Nevertheless, the present study demonstrates the application of remote sensing archived temporal data to have first-hand information on the vulnerability of riparian zones with prominent indicators that could be retrieved from the remotely sensed images.