Green infrastructure as a strategy for building resilience against stormwater in Ibadan

Abstract

Insufficiency and near absence of green infrastructure (GI) which have been shown to offer cost-effective nature-based solutions in mitigating urban flood and managing stormwater in major cities in Nigeria have increased their vulnerability to destructive floods in recent years. This study conducted a spatial assessment of GI and its potential effectiveness on stormwater management in Ibadan, Nigeria, with the use of remotely sensed data. Change detection between 2000 and 2020 was conducted based on four land use categories (built-up, green area, bare surface, and water bodies) because it coincided the period of rapid land use changes and occurrence of devastating flooding in the city and environs. Normalized Difference Vegetative Index (NDVI) calculated from Landsat image data and Digital Elevation Model (DEM) data to determine areas liable to flooding were also assessed using geospatial analysis. The results showed that the infill development of Ibadan has drastically reduced the available GI from 37.64% in the year 2000 to 22.84% in the year 2020 while built-up areas increased from 51.97% in the year 2000 to 69.04% in the year 2020. In 2000, NDVI ranged from -0.37 to 0.02 in the inner city showing poor vegetation. By 2020 the elements of GI are mostly fragmented with small coverage and more than 70% of the area occupied by built-up areas without vegetation cover. Vegetal cover decreased with time due to increasing impervious surfaces, creating many high flood zones and stormwater. It is concluded that provision and effective management of GI in the city can serve as a valuable tool to mitigate the problems of excessive stormwater.