The impacts of watershed management on land use and land cover dynamics in Eastern Tigray (Ethiopia)

Abstract

Integrated watershed management (IWSM) was implemented to address issues of poverty and land resource degradation in the 14,500 ha upper Agula watershed, in semi-arid Eastern Tigray (Ethiopia), an area known for poverty and resource degradation caused by natural and man-made calamities. The purpose of this study was to assess the impact of IWSM and determine the land use and cover dynamics that it has induced. The change in land use and cover was assessed by integrating remote sensing and geographic information systems (GIS). Two sets of aerial photographs (taken in 1965 and 1994 at scale of 1:50,000) and Landsat ETM+ image (taken in 2000 with 30 m resolution) were used to produce the land use/land cover map and assess land use change.

The results reveal significant modification and conversion of land use and cover of the watershed over the last four decades (1965–2005). A significant portion of the watershed was continuously under intensively cultivated (rainfed) land. The area under irrigation increased from 7 ha to 222.4 ha post-intervention. The area under dense forest increased from 32.4 ha to 98 ha.

The study further shows that IWSM decreased soil erosion, increased soil moisture, reduced sedimentation and run off, set the scene for a number of positive knock-on effects such as stabilization of gullies and river banks, rehabilitation of degraded lands. IWSM also resulted in increased recharge in the subsurface water.

This study reconfirms the importance of IWSM as a key to improve the land cover of watersheds, as a contribution to poverty alleviation and sustainable livelihood.

Introduction

Land use describes the way and the purposes for which human beings employ the land and its resources. Land cover refers to physical characteristics of the land including human-made structures, which make up the earth's landscape. Historically, land use and cover changes have occurred primarily in response to population growth, technological advances, and economic opportunity (Turner et al., 1995). Human activities have directly or indirectly modified the natural environment. This is due to the fact that production demands by humans cannot be fulfilled without modification or conversion of land cover. Of the challenges facing the earth over the next century, land use and cover changes are likely to be the most significant (Mustard et al., 2005). On a global scale, forest, woodland, and grassland have been converted to other uses during the last three centuries one way or another, to support and satisfy the increasing demands of the society and economy (Agarwal et al., 2000). Human intervention caused change in land use such as land clearing, agricultural intensification, and urbanization, are currently the most consequential components of global change (Munasinghe and Shearer, 1995).

The consequence of modern society's demand for more production to meet its consumption will inevitably result in major modification and conversion of land cover. Pressures to further convert or manage natural ecosystems for human needs as well as capturing more of the global net primary productivity are also likely to increase (Mustard et al., 2005).

Understanding the implication of past, present and future patterns of human land use for biodiversity and ecosystem function is increasingly important in landscape ecology (Turner et al., 2003). Historical land use and cover patterns are a means to evaluate the complex causes and responses in order to better project future trends of human activities and land use/land cover change. If land use/land cover changes are not carried out scientifically, the negative impacts on both the environment and the socio-economic settings are not easily measurable (Gete, 2000). The study of land use/land cover aims to yield valuable information for analysis of the environmental impacts of human activities, climate change, and other forces (Belay, 2002). This has been particularly important, as changes in land use become more rapidly affecting the livelihoods of societies. Thus, understanding land use and land cover dynamics of an area plays a significant role to take corrective measures on land and its use for sustainable productivity.

This paper presents the land use and land cover dynamics observed after the implementation of integrated watershed management in Northern Ethiopia. Watershed management practices are changes in land use, and vegetation cover, with the main objective of rehabilitation of degraded lands, protection of soil and water systems. The aim of integrated watershed management is to improve the standard of living of the population living within the watersheds: decrease population pressure and increase land productivity so that sustainable livelihoods and land use practices can be secured for the population (McCormick et al., 2003). Integrated watershed management (IWSM) is a multi-objective and multi-disciplinary approach to solving natural resource management and food security problems in rural communities, particularly in dry and semi-arid areas where rainfall is scarce (Igbokwe and Adede, 2001). The overall aim of integrated watershed management is, therefore, to ensure sustainable natural resource use and equitable growth of communities.

The replicability of land resource management can be justified, if the intervention approach and the impacts are well assessed and studied. Thus, the research addresses the impacts of integrated watershed management and the changes that have followed on land use and land cover dynamics. The aims of this paper are therefore (a) to assess the land use and cover change that occurred between 1965 and 1994, and between 1994 and 2005; and (b) to assess the effects of the watershed management on curbing land degradation and improving agricultural production.