QUANTIFYING VEGITATIVE COVER CHANGES IN HAMESA-ABAYA RIVER BASIN BY USING REMOTE SENSING DATA, SOUTHWEST ETHIOPIA

Abstract

Vegetation cover is one of the most beneficial resources on earth hosting great diversity of living things that deliver essential ecosystem services. However, the forest cover of Lake Abaya basin is recognized as among the most fragile, as they are under constant threat from anthropogenic human impacts. The present study undertakes assessment on the status of vegetation cover change and long term rainfall pattern in Hamesa-Abaya basin. Vegetation cover change between 2005 and 2010 was calculated using Normalized Difference Vegetation Index (NDVI) using open source ILWIS 3.3 Academic. The long term annual rainfall was analyzed using XLSTAT and the statically analysis to test for significant trends in annual rainfall through time was tested using a “parametric Buishand Homogeneity test”. Total Suspended Solid was determined following the standard gravimetrical method. There is decrease in vegetation cover in Hamasa watershed during the five years. The results of NDVI for the year 2005 and 2010 identified Sparse Vegetation is the major land cover throughout Hamesa watershed. In 2005, bare land covers 24 % of the total area and shows an intense increase to 46 % in 2010, whereas all vegetation categories (Spares Vegetation, Moderate vegetation and Forest) between 2005 and 2010 showed a rapid decrease. Forest cover in Hamasa watershed was already low 0.7% in 2005 and further reduced to 0.3 % during 2010. The annual rainfall in Hamesa watershed did not show a change during the period 1988-2015. The most dominant vegetation cover (Sparse Vegetation) has the lowest tree cover density and has limited controlling effect on soil erosion. This result is in line with the high amounts of suspended solids, largely consisting of Total Inorganic Suspended Solids (TISS), in Hamesa River and one of the major causes of turbidity in Lake Abaya. This increased Total Inorganic Suspended Solids (TISS) is not linked to the long term rainfall pattern since there is no significant change in rainfall, thus the very high Total Inorganic Suspended Solids (TISS) probably linked with the very low vegetation cover in Hamesa-Abaya basin. The impact of suspended solids raises concerns on the biological diversity of the River and has significant effect on turbidity of Lake Abaya. To overcome the problem and to support the continual provision of ecosystem services, restoration of degraded vegetation is crucial. The results of this study stress the urgent need for measures that prevent further vegetation loss in Hamesa-Abaya basin.