Implication of Land Use Change on Flood Vulnerability in an Urban Watershed of Ibadan, Southwest, Nigeria

This study identified the relationship between land use land cover changes (LULC) and flood vulnerability (FV) in a watershed using geospatial data. Using the supervised classification method and post classification change detection technique, nature, extent and rate of land use land cover change were examined from 1972 -2013 with a view of assessing flood vulnerability on land use changes. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Digital Elevation Model (DEM) and Landsat multispectral medium resolution satellite image (Landsat) (30 m) covering Ibadan for the years 1972, 1984, 2000 and 2013 were acquired. The AsterDEM was used to delineate the urban watershed of Ibadan while the Landsat imageries were used to evaluate spectral and spatial changes in the LULC of the study area within the 41 years’ period under consideration. Analytical hierarchical process was used to standardize and integrate identified factors (slope, soil, drainage, LULC, elevation) contributing to flood which were assigned weight and overplayed in the principle of pairwise comparison. The flood vulnerability (FV) sensitivity index was developed using the multi criteria decision analysis model. The study also examined the relationship between LULC and FV. The results showed that LULC in the watershed experienced increase in built up areas by 9.4% (1972), 14.1% (1984), 15.3% (2000) and 40.2% (2013) while waterbody experienced decrease of 2.8% (1972), 0.2 (1984), 0.1% (2000) and 0.1% (2013). Highest flood vulnerability was recorded in 2013, followed by 1984; while 1972 had the least flood vulnerability. The flood vulnerability on built up, light vegetation, bare soil and water body increased by 15.66%, 12.56%, 21.24%, 34.42% for 1984 and 57.16%, 9.16%, 83.68%, 0.78% for 2013 respectively. Results revealed that rapid changes in land use play a significant role in intensifying flood risk in the urban watershed. This study concluded that change in LULC is increasing drastically in the watershed. Implication of this is that if human activities are not properly controlled and if a well-planned and effective land use policy is not put in place within the watershed, vulnerability of the area to flood disaster may assume an unprecedented dimension.