SPATIO-TEMPORALASSESSMENT OF RIPARIAN VEGETATION DEGRADATION AND ITS ENVIRONMENTALCONSEQUENCIES IN OSOGBO CITY, NIGERIA

Abstract

The environment has been engendered by the continuous removal of riparian vegetation in the urban centres of Osogbo that desires proactive measure to prevent the occurrence of devastating urban flooding. The rapid urban growth of Osogbo has necessitated the need for this study. This study therefore attempts to make use of multi-temporal images and GIS techniques to assess spatio-temporal changes of riparian vegetation and environmental consequences in the city. Landsat TM 1986, Landsat ETM+ 2000 and Landsat OLI TIRS 2015 are utilized by the study. In addition, a topographic map, 1:50,000 of 1962 is used as a base map. Land use information are extracted for spatio-temporal and NDVI is carried out on the images to detect temporal vegetation degradation analysis. 100m Buffers are created around river Osun within the urban section to detect the magnitude of urban encroachment. Stochastic Markov model and cellular automata model are used to predict the extent of land use/cover change in 2050. A change of 49.04km2 in riparian vegetation, 37.06km2 decrease in water bodies and a decrease of 0.54km2 in sparse vegetation. Built-up, forest and bare ground increased by 29.72km2, 1.34km2 and 5.49km2 respectively between 1986 and 2000. Between year 2000 and 2015, a change of 37.36km2 in riparian vegetation. 26,56km2 decrease in the water bodies and a decrease of 7.55km2 occurred in sparse vegetation. Built-up, forest and bare ground increased by 26.06km2, 28.67km2 and 4.07km2.The mean NDVI value of the riparian vegetation was 0.20 in 1986 and 0.17 in 2015. With the increased rate of 34.42%, 20.91% and 21.5% in waterbody, built-up and bareground respectively and a reduced rate of -9.47%, -27.5% and -29.98% in forest, riparian vegetation and sparse vegetation respectively as projected for 2050, there is bound to be more environmental consequences. The prediction was validated using confusion matrix, allocation disagreement and quantity disagreement.