Evaluation of environmental degradation in northern Ethiopia using GIS to integrate vegetation, geomorphological, erosion and socio-economic factors

Abstract

The scale of human induced land degradation is very high in northern Ethiopia. However, there are only a few studies of land degradation in Ethiopia which provide an integrated assessment of the driving forces and consequences. A pilot study was made in Adwa district (Tigray) with the objective of evaluating the factors related to environmental degradation and assessing the effects of agricultural activities on the natural resources. Environmental data, a digital terrain model, vegetation, geomorphological, and erosion maps of the study area were integrated with socio-economic variables using a geographical information system (GIS). The classification of the data used in the integration, and the information extracted using the GIS gave three main groups of Tabias and four main groups of variables. The relationship among the Tabias (smallest administrative units), groups of Tabias and environmental variables were quantified using various statistical, multivariate numerical methods and fuzzy set analysis. The application of fuzzy set theory showed that each group of Tabia, recognized as a rural subsystem (RS) was associated with a group of variables. Analysis of variance showed that the three RSs were significantly different in most of the environmental variables considered. Human and livestock population densities, geomorphology, altitude and some natural and anthropogenic vegetation types were highly discriminatory. Percentage cover of evergreen scrub, bushlands and severe badlands are considered key indicators of the scale of environmental degradation. Results of the canonical correlation analysis (CCA) indicated that human pressure had more impact on the physiognomy of the vegetation than on its floristic composition. The Evergreen scrub vegetation type appeared to be expanding with increasing human influence signifying a decrease in biomass of vegetation as a result of collecting wood for fuel and other domestic uses. Bushland appeared to be expanding with the same trend. Woodland, which was abundant in one of the RSs, is considered to be the natural physiognomic vegetation type in the area and efforts to maintain it and/or recover it elsewhere in the study area are recommended. Food production in the area did not match population growth. The expected crop yield under good soil and rainfall conditions was low by any standard. The per capita energy obtained from the grain harvested in the farm plots ranged from 428 to 4347 cal per person per day (the average is far below the basic minimum required for mere subsistence) suggesting that there is a need for substantial supplementary income from off-farm activities and/or other sources. This study indicated that regional and site specific approaches and interaction with the people at all stages of the research, program development and implementation are required for sustainable rehabilitation.