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The impacts of watershed management on land use and land cover dynamics in Eastern Tigray (Ethiopia)
Resources, Conservation and Recycling 53 (2009) 192–198
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Resources, Conservation and Recycling journal homepage: www.elsevier.com/locate/resconrec
The impacts of watershed management on land use and land cover dynamics in Eastern Tigray (Ethiopia) Fikir Alemayehu a,b,∗ , Nurhussen Taha a , Jan Nyssen c , Atkilt Girma a , Amanuel Zenebe a , Mintesinot Behailu a , Seppe Deckers d , Jean Poesen d a
Department of Land Resource Management and Environmental Protection, Mekelle University, PO Box 231, Mekelle, Ethiopia Melca Mehaber, PO Box 110533, Addis Ababa, Ethiopia Department of Geography, Ghent University, Krijgslaan 281 S8, B-9000 Ghent, Belgium d Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven, Celestijnenlaan 200E, B-3001 Leuven, Belgium b c
a r t i c l e
i n f o
Article history: Received 19 May 2007 Received in revised form 29 August 2008 Accepted 19 November 2008 Available online 21 January 2009 Keywords: Integrated watershed management Land use and cover change Remote sensing Geographic information system (GIS) Soil and water conservation Catchment management
a b s t r a c t 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 postintervention. 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. © 2008 Elsevier B.V. All rights reserved.
1. 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,
∗ Corresponding author at: Melca Mehaber, PO Box 110533, Addis Ababa, Ethiopia. Tel.: +251 11 550 7172; fax: +251 11 663 8138. E-mail address: fi[email protected] (F. Alemayehu). 0921-3449/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.resconrec.2008.11.007
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
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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 multidisciplinary 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. 2. Materials and methods 2.1. Site description The upper Agula watershed where the study was carried out lies between 13◦ 45 to 13◦ 55 N and 39◦ 42 to39◦ 48 E in Eastern Tigray (Fig. 1). The total area of the study site is 14,500 ha. The area falls in the semi-arid agro-climatic zone having highly dissected and rugged terrain. The altitude of the study area ranges from 2040 to 2840 m a.s.l. Agro-ecologically it is classified as highland and midland areas with mean annual air temperature of 22.8 ◦ C and maximum 27.2 ◦ C and an annual precipitation ranging from 515 mm to 872 mm (Gebremedhin, 2004). The area has a bimodal rainfall pattern. The small rains occur between November and March and the major rainy season from June to September. The small rains are not reliable and insufficient for crop production. Soils are predominantly light coloured, sandy mainly of metamorphic origin (Gebremedhin, 2004). Subsistence agriculture is the major stay of livelihood of the people. The major crops of the study area are barley (Hordeum vulgare), wheat (Triticum sativum), teff (Eragrostis teff) and millet (Eleusine coracana). The erratic rainfall coupled with poor soils and a low ground cover and a high human and livestock population pressure on land resources have contributed to a multitude of serious problems, such as degradation of vegetation cover, accelerated soil erosion, crop yield decline and human suffering. To address these serious and urgent problems Integrated Watershed Management measures are underway in Upper Agula watershed since 1998. The project has been implemented by Eastern Tigray Develop-
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Fig. 1. Location map of the study area.
ment Programme with the support of Irish Aid. It was a 3 years resource management and development project. The purpose of this intervention was to adopt integrated watershed management as a technological intervention averting the land degradation and restoring a farming system with a scope for modern agriculture (Fig. 2). The components of the intervention include: physical and biological soil and water conservation (including gully stabilization, hill side terracing, exclosures and planting on hill slopes (forage grass and (multi-use) trees), irrigation, horticulture, beekeeping, and improved crop technology. The budget for the implemen-
Fig. 2. Physical soil and water conservation structures such as stone bunds, soil bunds and runoff collection ponds are also part of the improved land management in the watershed.
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tation of various activities was 166,666 D (Igbokwe and Adede, 2001).
Table 1 Description of land use and cover classes used for analysis of change between 1965, 1994 and 2005.
2.2. Data source and analysis of time series images
Land cover type
Description
Intensively cultivated land
Annual and perennial crops (>70% of the land), frequently observed on level lands (plains, plateaus, foot slopes and valley floors). Annual and perennial crops, covering 40–70% of the land; includes large patches of woods, shrubs, and grasses. 20–40% of the mapping unit is under cultivation; the rest is constituted of shrubs, grassland, degraded land, exposed rocks and sands. Remnant of high natural forest, found in small patches around churches, steep slopes and less populated areas. Canopy cover of 50–80%. Total canopy cover around 90%, typically a mix of trees (60%), shrubs (20%), grasses (10%) and unproductive or unutilizable land (10%). Canopy cover of 65%, with 30–40% trees, 15–25% bushes, 20% herbs and grasses and 15% unproductive bare land. Composed of trees, high shrubs, and low herbs. Consists of trees and herbs; an intermediate between grassland and woodland. Composed of trees, bushes and grasses Constituted by strata of very few trees, bushes, shrubs and scattered herbs or grasses. The canopy cover of bush/shrubs is 40–60% and that of herbs or grasses is 15–20% Consists of a stratum of bushes, shrubs and herbs/grasses. Consists of shrubs, usually not exceeding 3 m in height, with a canopy cover >30%. Ground cover often poor and composed of patches of dense and open shrublands, grasslands and some scattered trees. Consists of grassland with scattered or grouped shrubs. Consists of open grassland, shrubs and very few trees; found scattered all over the region in flat water logged areas and on steeper slopes. Characterized by strata of shrubs and grasses or herbs. Land devoid of vascular plants; composed of exposed rock, sand and soil surfaces. Residences, administrative buildings, small industrial and trade enterprises. Water table at or near the surface, grasses and widely scattered or grouped trees around the riverbanks.
The research focuses mainly on detecting changes, delineating, and mapping areas that have experienced land use/land cover change over a 40-year time period (1965–2005) using aerial photographs and Landsat imagery. The data for land use/cover were obtained from aerial photographs of 1965 and 1994, with an approximate scale of 1:50,000. In order to detect the change after intervention, a satellite image (Landsat with 30 m resolution taken on February 2000) was analysed. Contour lines were digitized from 1:50,000 topographic maps with 20 m contour interval. The digitized contours were interpolated to produce a Digital Elevation Model (DEM) in ILWIS GIS software. DEM was used to transform the aerial photos to orthophoto for the delineated area. Aerial photographs, satellite images, and topographic maps were geo-referenced using 50 ground control points collected from GPS readings. From the geo-referenced aerial photographs an orthophoto mosaic was created. Processing of images was carried out using ILWIS GIS software and Arc view (version 3.2) software. Preliminary aerial photo interpretation and classification of each land use/land cover type was delineated from aerial photos (1965 and 1994) using mirror stereoscope. Normalized Difference Vegetation Index NDVI was produced from TM band 4 and TM band 3 that is (TMB4 − TMB3)/(TMB4 + TMB3) to enhance the land cover of the study area. The land use/land cover classes from the Landsat image were produced from visual interpretation and digitized on screen using ILWIS GIS software. The description given for land use land cover classification was adapted from the Land use and land cover of Tigray region prepared by BoANRD (2001) (Table 1). However intensive field survey was carried out to check the preliminary interpretation and necessary corrections were taken. The field assessments were conducted with help of mobile pocket computer (IPAQ GPS mounted) which holds the geometrically corrected aerial photographs and satellite image interpretation maps. The field survey helped to update the (2000) Landsat image in order to generate the current land use and cover map for 2005. In addition to data collected from image processing, focused group discussions were organised to obtain information around specific topics allowing different groups of people to express their opinion and views and reflect on key issues such as natural resources management, land use and land cover dynamics and environmental change. Moreover a total number of 90 households were selected for this study. After acquiring the list of households, a systematic random sampling procedure used to select a total of 90 sample households. For the purpose of this study both structured and semi-structured (with open and close end questions) questionnaires were prepared to conduct the research. The survey had a set of questions related to demographic characteristics, crop and livestock proportion, household assets on (land holding, livestock, beehives, etc.), land use and management, were the main issues included (both before and after intervention with a marked year). 3. Results 3.1. Land use and land cover change detection over the period 1965–2005 Eighteen major land use and cover types were identified (Table 2 and Fig. 3). During the period 1965–2005 intensively cultivated land
Moderately cultivated land
Sparsely cultivated
Dense forest
Dense woodland
Open/bushed woodland
Wooded shrub grassland Wooded grass land
Wooded bush grassland Bush shrubland
Bush shrub grassland Shrubland
Shrub grassland Open grassland or shrub grassland
Degraded shrub grassland Bare land Built-up area Wetland
constituted more than 50% of the catchment (Table 2 and Fig. 4). Detection of land use and cover for a period of four decades showed a change on dense forest, bush shrub land, shrub land, built up area and wetland (Fig. 4). The area under assured well irrigation increased from 7.1 ha to 222.4 ha after the intervention. Correspondingly, the area under dense forest increased from 32.5 ha to 98 ha (Fig. 5). In 1994 important changes in land use and cover were observed: wooded shrub grassland, shrub grassland, bare land and wetland ceased to exist. On the other hand new land cover types emerged in 1994. These include dense woodland (5.6 ha), open/bushed woodland (10.9 ha) and wooded grassland (192.4 ha) (Table 2). However, in 2005 the land cover types wetland and bare land re-emerged (Table 2 and Figs. 3 and 4).
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Table 2 Land use and cover changes for the period 1965–2005 in upper Agula watershed. Cover type
1965 Area (ha)
Intensively cultivated land (rainfed) Intensively cultivated (irrigation) Moderately cultivated land Sparsely cultivated land Dense forest Dense woodland Open/Bushed woodland Wooded shrub grassland Wooded grassland Bush shrub-land Bush shrub grassland Shrub-land Shrub grassland Open grassland/shrub grassland Degraded shrub grassland Bare land Built up area Wetland Total
7405.1 7.1 525.7 1889.6 37.5 – – 113.6 – 1475.3 325.7 415.9 1268.0 293.4 251.8 235.9 35.0 198.4 14,477.9
1994 %
Area (ha) 51.1 0.1 3.7 13.3 0.3 – – 0.8 – 10.4 2.3 2.9 8.9 2.1 1.8 1.7 0.3 1.4
100
7980.2 55.2 68.2 – 32.5 5.6 10.9 – 192.4 177.0 1392.6 114.7 – 80.0 4295.2 – 73.1 – 14,477.9
2005 % 55.1 0.4 0.5 – 0.2 0.1 0.1 – 1.4 1.2 9.7 0.8 – 0.7 30.0 – 0.5 – 100
Area (ha) 7483.5 222.6 330.1 557.7 98.0 – 352.6 47.8 538.0 358.8 1241.7 1248.7 179.8 25.7 1224.9 331.0 244.1 215.7 14,477.9
% 51.7 1.5 2.3 3.9 0.7 – 2.4 0.3 3.7 2.4 8.6 8.6 1.2 0.2 8.5 2.3 1.7 1.5 100
Fig. 3. Land use and cover changes in the upper Agula watershed 1965–2005. The archipelago-like land units that appear at the south-west of the catchment, correspond to irrigated land, located downstream of the catchment and which is gradually expanding.
3.2. Observed changes on vegetation, soil, groundwater and farm produce following the watershed management The conservation efforts implemented in 1998 were to reduce soil erosion and to maintain or improve the productive capacity of soil resources. Thus, following the IWSM interventions, obser-
Fig. 4. Major land use and cover changes from 1965 to 2005 (IC = intensively cultivated; SL = shrub-land).
vations focussed on reduction of soil loss, vegetation cover, soil moisture increase and land productivity. The combination of different soil and water conservation measures had the potential to reduce surface run-off and erosion, this in turn increased infiltration. Before the intervention, most of the study area used to be
Fig. 5. Olive (Olea europaea ssp. africana) forest in the upper part of the catchment.
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affected by recurrent flooding hazard coming from the upper slopes and sediment deposition took place; 50% of the respondents living in the middle of the catchment were affected. After the implementation the problem of flood hazard and sedimentation in the middle watershed was completely solved. Since 2003, 115 wells have been developed in the study area. Most of the wells are found on the middle catchment, where the ground water gives a good response to increased infiltration on the upper slopes. Here, water is available within 1–2 m, while in the lower catchment water depth is between 8 and 10 m. The availability of wells has opened up an opportunity for 97 households to grow crop and vegetables twice a year. On the eastern slopes of the catchment, honey production is important. This is related to the increased availability of water (development of new water resources), and improvements in the ecology of the adjacent area through exclosure measures. Before intervention traditional hives were used by respondents, and the honey obtained was in the range 4–5 kg/harvest. After the intervention, respondents indicated that honey obtained from modern beehives has increased tremendously and has now reached 20–25 kg/harvest and farmers are able to harvest twice a year. Before the intervention very few households had knowledge on how to make different kinds of physical structures of SWC to prevent soil erosion. After the intervention, most households in the survey (89%) have adopted and practice stone-faced trench bunds and hillside terracing. These conservation measures are easily replicable and cheap and the practice is spreading to other areas at a fast rate. 50% of farmers are preparing compost in the house or on their plots so as to keep the fertility of the soil. 75% of households are planting trees on their own plots or around the homestead with the purpose of protecting farm fertility and supplementing incomes. 45.6% of households now have access to irrigable land, 60% of them have improved their houses into tin-roofed structures and 60% of respondents now have food available from 5 to 8 months. Adoption of conservation agronomic practices in the watershed resulted in better productive performance of crops over time due to decrease in soil erosion and enrichment of the soil. The three most important crops (teff wheat and barley) have all shown marked yield increases between 1997 and 2004. Specifically, average teff yields have increased from 0.3 t/ha to 0.6 t/ha, wheat has increased from 0.5 t/ha to 0.8 t/ha and barley has increased from 0.45 t/ha to 0.75 t/ha. Combined with increased fertilizer use, the adoption of conservation agronomic practices in the watershed resulted in better productive performance of crops due to decreases in soil erosion, in flooding and to enrichment of the soil. 4. Discussion and conclusions 4.1. Causes of land use and land cover changes between 1965 and 1994 Remote sensing and GIS-based change detection studies have predominantly focused on providing the knowledge of how much, where, what type of land use and land cover change has occurred (Weng, 2001). The aerial photo interpretation reveals that there was an expansion of cropland between 1965 and 1994. During this period sparsely cultivated land, wooded shrub grass land and shrub grass land have vanished. This is due to population pressure which results in the expansion of agricultural land and settlement. The predominant motive for land use change is production of food and fibre (Mustard et al., 2005). As stated by the farmers, the catchment was covered mainly by natural vegetation until the 1960s, with dominance of Juniperus and Acacia. Still the remnants of these trees are found around churches and communal areas in small patches. Furthermore, growing pressure from human and livestock population and the repeated drought conditions caused forest devastation
Fig. 6. Expansion of wetlands in the valley bottoms.
for fuel wood trade as a means of income to overcome the drought period. The 1965 aerial photographs show the presence of wetland in plain areas following valley bottoms and along rivers in the catchment. Farmers confirmed that they used the wetland for grazing purposes. However, this land cover feature had disappeared in 1994 due to mainly removal of vegetation cover. Change in vegetation cover can alter surface fluxes of energy and water and modify surface climate (Mustard et al., 2005). Consequently, human induced soil degradation was exacerbated. 4.2. Causes of land use and land cover change between 1994 and 2005 The rehabilitation of vegetation in many places of the catchment has improved the forest cover. Farmers also confirmed during focus group discussions, that the vegetation cover has increased and the change that has been observed at present was the result of the intervention, i.e. the establishment of exclosures. Riparian trees along the valley bottoms following the rivers which had not been observed in 1994 have developed in 2005. This was well observed during the field surveys. The trees were planted during the forestation activities to stabilize gullies. Though their numbers are small, remnants of natural forests are found around churches and on steep slopes. The degraded shrub grassland which covered a large portion of the watershed in 1994 was generally converted into other cover types such as shrubgrassland. This was observed during field surveys in which the vegetation cover that was very small and scattered in 1994 has at present grown up and changed into shrub-land, bush shrub grassland and bush-grassland. In some areas trees 3 m tall and above were observed. Hence the improvement of the vegetation cover has certainly been the result of the extensive soil and water conservation work that had been implemented in the study area. The 1994 aerial photograph analysis results show that intensively cultivated land constituted a larger portion of the catchment (55.11%), when compared with 1965 (51.1%) and 2005 (51.7%). The above changes explain the reduced bush and shrub cover in 1994. On the other hand, a remarkable increment was observed in built up areas compared with 1994. This change was the result of the expansion of the two towns Atsbi and Haike Meshal. The two towns were still small on 1994 and recently both towns are expanding at the expense of cultivable and grazing land. The wetland that had disappeared in 1994 re-emerged in 2005 (Fig. 6). The wetland has indeed developed as a consequence of extensive gully treatment to prevent flooding and erosion. A review by Nyssen et al. (2004) indicates the benefits of soil and water con-
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servation (SWC) measures in controlling runoff and soil erosion. Wetland development of the flat plain area in the lower and middle catchment is attributed to SWC structures such as check dams in gullies and trenches dug to intercept and store runoff. Farmers stated this cover type is a recent phenomenon following the stabilization of gullies. The emergence of wetland is attributed to the improvement of vegetation cover and the intensive soil conservation measures undertaken in the upper watershed. This change is taken as an indicator of the success of the SWC measures, because following the emergence of wetland there has been an increase of the groundwater table which is tapped through shallow wells.
ing problems in the lower parts of the watershed, stabilized gullies and river banks, rehabilitation of degraded lands and improved ecological balance in general. Similar studies elsewhere in northern Ethiopia (Woldeamlak, 2003; Liu et al., 2008; Munro et al., 2008; Nyssen et al., 2009) reported the effectiveness of sustained conservation efforts at catchment level in controlling soil erosion and in improving hydrology and land productivity. The improvement of vegetation cover in the watershed decreased the depth to the groundwater which could be managed and used for irrigation.
4.3. The impacts of IWSM on land use and cover change
The studied watershed underwent remarkable changes in land use and covers during four decades and the changes exhibit a dynamic nature. Throughout the period 1965–2005 more than half of the watershed was occupied by intensively cultivated land. Over the 40 years observation period, the area under assured well irrigation increased from 7.1 ha to 222.4 ha (see also Fig. 7). The area under dense forest increased from 32.5 ha to 98 ha. Major observed changes after the implementation of integrated watershed management are: reduced soil erosion, and increased soil moisture availability which could be explained by the increase in crop production, increased ground water recharge (as observed in the abundance of shallow wells), reduced sedimentation and run off problems in the lower parts of the watershed, stabilized gullies and river banks, rehabilitation of degraded lands and improved ecological balance, introduction of modern beehives and increase in honey production. To conclude, ecological changes caused by the destruction of natural vegetation, removal of soil by erosion and drying out of rivers as the result of mismanagement of land have been reversed as a result of the integrated watershed management intervention. While the IWSM intervention researched shows encouraging results for both vegetation cover and farmer livelihoods, in order to be sustainable, it is essential to maintain a high level of farmers participation. The
The erratic rainfall coupled with poor soil and ground cover and high human and livestock population pressure on land resources have contributed to a number of serious problems, such as degradation of vegetation cover, accelerated soil erosion, crop yield decline and human suffering. The major observed changes during the last four decades were the conversion of forest land, bush, shrub, and woodland to cropland, grazing land, and built-up areas. A similar land use and cover study made by Solomon (1994) in southern Ethiopia indicated that the influence of land use and cover depends very much on the nature of the land and the level of management techniques used. The rapid changes in land use and cover of the study area have been driven by factors such as population pressure, expansion of rural towns, large-scale overgrazing, and recurrent drought and poor land management. Marked land use/land cover dynamics are also observed in dense forest, wetland, shrub-land, and intensively cultivated (irrigation) land. The positive impact of the watershed management in the study area could be explained in terms of reduced soil erosion rates, increased soil moisture availability which could be deduced from the increased in crop production, reduced sedimentation and flood-
4.4. Conclusion
Fig. 7. Ground-based photo-monitoring of the area downstream of the watershed. The upper photograph was taken in 1975 (©Neil Munro), the lower in 2006 (©Jan Nyssen). An irrigation scheme was developed in this valley floor, some 10 km downstream from the watershed (extreme SW of the 2005 map – see Fig. 3). Despite the fact that the area is located outside of the formal Watershed Management Project area, stone bunds and improved vegetation cover on the slopes can be observed. The fig tree is a permanent element, a control, in this landscape.
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study highly recommends the up-scaling of such intervention in similar agro-ecologies. Acknowledgements The authors wish to thank Habtamu Mulatu, Fekadu Getnet, Ermiyas Ayenekulu and Steven Fisher for their useful comments and suggestions that helped to improve this paper. Funding for this study was provided by the VLIR – Mekelle University IUC Programme. Farmers and authorities from Hayke Meshal and surrounding villages are greatly acknowledged for their hospitality. References Agarwal C, Green MG, Grove JM, Evans TP, Schweik CM. A Review and assessment of land use change models. Dynamics of space, time, and human choice. Center for the Study of Institutions, Population, and Environmental Change, Indiana University, and USDA Forest Service, Northeastern Research Station, South Burlington, VT, USA; 2000. p. 90. Belay T. Land use/land cover changes in the Derekolli catchment of the South Welo zone of Amhara region, Ethiopia, vol. XVII, no. 1. EASSRR; 2002. p. 20. Bureau of Agriculture, Natural Resources. Land use land cover of Tigray. Mekelle, Tigray, Ethiopia: Land Use Planning and Regulatory Division; 2001. p. 213. Gebremedhin T. Assessing and mapping areas susceptible to water erosion using integrated remote sensing GIS tools and minimal ground survey in the Atsibi subWatershed. A case study in Tigray region, Ethiopia. Enschede, The Netherlands: International Institute for Geo-information Science and Earth Observation; 2004. Gete Z. Landscape dynamics and soil erosion process modeling in the North-Western Ethiopian highlands. PhD thesis. Institute of Geography, University of Berne, Switzerland; 2000. Igbokwe KN, Adede J. Integrated watershed management in Eastern Tigray, Ethiopia. Mid term impact evaluation report, Nairobi, Kenya, 2001. p. 72. Liu BM, Collick AS, Gete Z, Enyew A, Easton ZM, Steenhuis TS. Rainfall-discharge relationships for a monsoonal climate in the Ethiopian highlands. Hydrological Processes 2008;22(7):1059–67.
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Resources, Conservation and Recycling journal homepage: www.elsevier.com/locate/resconrec
The impacts of watershed management on land use and land cover dynamics in Eastern Tigray (Ethiopia) Fikir Alemayehu a,b,∗ , Nurhussen Taha a , Jan Nyssen c , Atkilt Girma a , Amanuel Zenebe a , Mintesinot Behailu a , Seppe Deckers d , Jean Poesen d a
Department of Land Resource Management and Environmental Protection, Mekelle University, PO Box 231, Mekelle, Ethiopia Melca Mehaber, PO Box 110533, Addis Ababa, Ethiopia Department of Geography, Ghent University, Krijgslaan 281 S8, B-9000 Ghent, Belgium d Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven, Celestijnenlaan 200E, B-3001 Leuven, Belgium b c
a r t i c l e
i n f o
Article history: Received 19 May 2007 Received in revised form 29 August 2008 Accepted 19 November 2008 Available online 21 January 2009 Keywords: Integrated watershed management Land use and cover change Remote sensing Geographic information system (GIS) Soil and water conservation Catchment management
a b s t r a c t 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 postintervention. 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. © 2008 Elsevier B.V. All rights reserved.
1. 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,
∗ Corresponding author at: Melca Mehaber, PO Box 110533, Addis Ababa, Ethiopia. Tel.: +251 11 550 7172; fax: +251 11 663 8138. E-mail address: fi[email protected] (F. Alemayehu). 0921-3449/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.resconrec.2008.11.007
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
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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 multidisciplinary 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. 2. Materials and methods 2.1. Site description The upper Agula watershed where the study was carried out lies between 13◦ 45 to 13◦ 55 N and 39◦ 42 to39◦ 48 E in Eastern Tigray (Fig. 1). The total area of the study site is 14,500 ha. The area falls in the semi-arid agro-climatic zone having highly dissected and rugged terrain. The altitude of the study area ranges from 2040 to 2840 m a.s.l. Agro-ecologically it is classified as highland and midland areas with mean annual air temperature of 22.8 ◦ C and maximum 27.2 ◦ C and an annual precipitation ranging from 515 mm to 872 mm (Gebremedhin, 2004). The area has a bimodal rainfall pattern. The small rains occur between November and March and the major rainy season from June to September. The small rains are not reliable and insufficient for crop production. Soils are predominantly light coloured, sandy mainly of metamorphic origin (Gebremedhin, 2004). Subsistence agriculture is the major stay of livelihood of the people. The major crops of the study area are barley (Hordeum vulgare), wheat (Triticum sativum), teff (Eragrostis teff) and millet (Eleusine coracana). The erratic rainfall coupled with poor soils and a low ground cover and a high human and livestock population pressure on land resources have contributed to a multitude of serious problems, such as degradation of vegetation cover, accelerated soil erosion, crop yield decline and human suffering. To address these serious and urgent problems Integrated Watershed Management measures are underway in Upper Agula watershed since 1998. The project has been implemented by Eastern Tigray Develop-
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Fig. 1. Location map of the study area.
ment Programme with the support of Irish Aid. It was a 3 years resource management and development project. The purpose of this intervention was to adopt integrated watershed management as a technological intervention averting the land degradation and restoring a farming system with a scope for modern agriculture (Fig. 2). The components of the intervention include: physical and biological soil and water conservation (including gully stabilization, hill side terracing, exclosures and planting on hill slopes (forage grass and (multi-use) trees), irrigation, horticulture, beekeeping, and improved crop technology. The budget for the implemen-
Fig. 2. Physical soil and water conservation structures such as stone bunds, soil bunds and runoff collection ponds are also part of the improved land management in the watershed.
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tation of various activities was 166,666 D (Igbokwe and Adede, 2001).
Table 1 Description of land use and cover classes used for analysis of change between 1965, 1994 and 2005.
2.2. Data source and analysis of time series images
Land cover type
Description
Intensively cultivated land
Annual and perennial crops (>70% of the land), frequently observed on level lands (plains, plateaus, foot slopes and valley floors). Annual and perennial crops, covering 40–70% of the land; includes large patches of woods, shrubs, and grasses. 20–40% of the mapping unit is under cultivation; the rest is constituted of shrubs, grassland, degraded land, exposed rocks and sands. Remnant of high natural forest, found in small patches around churches, steep slopes and less populated areas. Canopy cover of 50–80%. Total canopy cover around 90%, typically a mix of trees (60%), shrubs (20%), grasses (10%) and unproductive or unutilizable land (10%). Canopy cover of 65%, with 30–40% trees, 15–25% bushes, 20% herbs and grasses and 15% unproductive bare land. Composed of trees, high shrubs, and low herbs. Consists of trees and herbs; an intermediate between grassland and woodland. Composed of trees, bushes and grasses Constituted by strata of very few trees, bushes, shrubs and scattered herbs or grasses. The canopy cover of bush/shrubs is 40–60% and that of herbs or grasses is 15–20% Consists of a stratum of bushes, shrubs and herbs/grasses. Consists of shrubs, usually not exceeding 3 m in height, with a canopy cover >30%. Ground cover often poor and composed of patches of dense and open shrublands, grasslands and some scattered trees. Consists of grassland with scattered or grouped shrubs. Consists of open grassland, shrubs and very few trees; found scattered all over the region in flat water logged areas and on steeper slopes. Characterized by strata of shrubs and grasses or herbs. Land devoid of vascular plants; composed of exposed rock, sand and soil surfaces. Residences, administrative buildings, small industrial and trade enterprises. Water table at or near the surface, grasses and widely scattered or grouped trees around the riverbanks.
The research focuses mainly on detecting changes, delineating, and mapping areas that have experienced land use/land cover change over a 40-year time period (1965–2005) using aerial photographs and Landsat imagery. The data for land use/cover were obtained from aerial photographs of 1965 and 1994, with an approximate scale of 1:50,000. In order to detect the change after intervention, a satellite image (Landsat with 30 m resolution taken on February 2000) was analysed. Contour lines were digitized from 1:50,000 topographic maps with 20 m contour interval. The digitized contours were interpolated to produce a Digital Elevation Model (DEM) in ILWIS GIS software. DEM was used to transform the aerial photos to orthophoto for the delineated area. Aerial photographs, satellite images, and topographic maps were geo-referenced using 50 ground control points collected from GPS readings. From the geo-referenced aerial photographs an orthophoto mosaic was created. Processing of images was carried out using ILWIS GIS software and Arc view (version 3.2) software. Preliminary aerial photo interpretation and classification of each land use/land cover type was delineated from aerial photos (1965 and 1994) using mirror stereoscope. Normalized Difference Vegetation Index NDVI was produced from TM band 4 and TM band 3 that is (TMB4 − TMB3)/(TMB4 + TMB3) to enhance the land cover of the study area. The land use/land cover classes from the Landsat image were produced from visual interpretation and digitized on screen using ILWIS GIS software. The description given for land use land cover classification was adapted from the Land use and land cover of Tigray region prepared by BoANRD (2001) (Table 1). However intensive field survey was carried out to check the preliminary interpretation and necessary corrections were taken. The field assessments were conducted with help of mobile pocket computer (IPAQ GPS mounted) which holds the geometrically corrected aerial photographs and satellite image interpretation maps. The field survey helped to update the (2000) Landsat image in order to generate the current land use and cover map for 2005. In addition to data collected from image processing, focused group discussions were organised to obtain information around specific topics allowing different groups of people to express their opinion and views and reflect on key issues such as natural resources management, land use and land cover dynamics and environmental change. Moreover a total number of 90 households were selected for this study. After acquiring the list of households, a systematic random sampling procedure used to select a total of 90 sample households. For the purpose of this study both structured and semi-structured (with open and close end questions) questionnaires were prepared to conduct the research. The survey had a set of questions related to demographic characteristics, crop and livestock proportion, household assets on (land holding, livestock, beehives, etc.), land use and management, were the main issues included (both before and after intervention with a marked year). 3. Results 3.1. Land use and land cover change detection over the period 1965–2005 Eighteen major land use and cover types were identified (Table 2 and Fig. 3). During the period 1965–2005 intensively cultivated land
Moderately cultivated land
Sparsely cultivated
Dense forest
Dense woodland
Open/bushed woodland
Wooded shrub grassland Wooded grass land
Wooded bush grassland Bush shrubland
Bush shrub grassland Shrubland
Shrub grassland Open grassland or shrub grassland
Degraded shrub grassland Bare land Built-up area Wetland
constituted more than 50% of the catchment (Table 2 and Fig. 4). Detection of land use and cover for a period of four decades showed a change on dense forest, bush shrub land, shrub land, built up area and wetland (Fig. 4). The area under assured well irrigation increased from 7.1 ha to 222.4 ha after the intervention. Correspondingly, the area under dense forest increased from 32.5 ha to 98 ha (Fig. 5). In 1994 important changes in land use and cover were observed: wooded shrub grassland, shrub grassland, bare land and wetland ceased to exist. On the other hand new land cover types emerged in 1994. These include dense woodland (5.6 ha), open/bushed woodland (10.9 ha) and wooded grassland (192.4 ha) (Table 2). However, in 2005 the land cover types wetland and bare land re-emerged (Table 2 and Figs. 3 and 4).
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Table 2 Land use and cover changes for the period 1965–2005 in upper Agula watershed. Cover type
1965 Area (ha)
Intensively cultivated land (rainfed) Intensively cultivated (irrigation) Moderately cultivated land Sparsely cultivated land Dense forest Dense woodland Open/Bushed woodland Wooded shrub grassland Wooded grassland Bush shrub-land Bush shrub grassland Shrub-land Shrub grassland Open grassland/shrub grassland Degraded shrub grassland Bare land Built up area Wetland Total
7405.1 7.1 525.7 1889.6 37.5 – – 113.6 – 1475.3 325.7 415.9 1268.0 293.4 251.8 235.9 35.0 198.4 14,477.9
1994 %
Area (ha) 51.1 0.1 3.7 13.3 0.3 – – 0.8 – 10.4 2.3 2.9 8.9 2.1 1.8 1.7 0.3 1.4
100
7980.2 55.2 68.2 – 32.5 5.6 10.9 – 192.4 177.0 1392.6 114.7 – 80.0 4295.2 – 73.1 – 14,477.9
2005 % 55.1 0.4 0.5 – 0.2 0.1 0.1 – 1.4 1.2 9.7 0.8 – 0.7 30.0 – 0.5 – 100
Area (ha) 7483.5 222.6 330.1 557.7 98.0 – 352.6 47.8 538.0 358.8 1241.7 1248.7 179.8 25.7 1224.9 331.0 244.1 215.7 14,477.9
% 51.7 1.5 2.3 3.9 0.7 – 2.4 0.3 3.7 2.4 8.6 8.6 1.2 0.2 8.5 2.3 1.7 1.5 100
Fig. 3. Land use and cover changes in the upper Agula watershed 1965–2005. The archipelago-like land units that appear at the south-west of the catchment, correspond to irrigated land, located downstream of the catchment and which is gradually expanding.
3.2. Observed changes on vegetation, soil, groundwater and farm produce following the watershed management The conservation efforts implemented in 1998 were to reduce soil erosion and to maintain or improve the productive capacity of soil resources. Thus, following the IWSM interventions, obser-
Fig. 4. Major land use and cover changes from 1965 to 2005 (IC = intensively cultivated; SL = shrub-land).
vations focussed on reduction of soil loss, vegetation cover, soil moisture increase and land productivity. The combination of different soil and water conservation measures had the potential to reduce surface run-off and erosion, this in turn increased infiltration. Before the intervention, most of the study area used to be
Fig. 5. Olive (Olea europaea ssp. africana) forest in the upper part of the catchment.
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affected by recurrent flooding hazard coming from the upper slopes and sediment deposition took place; 50% of the respondents living in the middle of the catchment were affected. After the implementation the problem of flood hazard and sedimentation in the middle watershed was completely solved. Since 2003, 115 wells have been developed in the study area. Most of the wells are found on the middle catchment, where the ground water gives a good response to increased infiltration on the upper slopes. Here, water is available within 1–2 m, while in the lower catchment water depth is between 8 and 10 m. The availability of wells has opened up an opportunity for 97 households to grow crop and vegetables twice a year. On the eastern slopes of the catchment, honey production is important. This is related to the increased availability of water (development of new water resources), and improvements in the ecology of the adjacent area through exclosure measures. Before intervention traditional hives were used by respondents, and the honey obtained was in the range 4–5 kg/harvest. After the intervention, respondents indicated that honey obtained from modern beehives has increased tremendously and has now reached 20–25 kg/harvest and farmers are able to harvest twice a year. Before the intervention very few households had knowledge on how to make different kinds of physical structures of SWC to prevent soil erosion. After the intervention, most households in the survey (89%) have adopted and practice stone-faced trench bunds and hillside terracing. These conservation measures are easily replicable and cheap and the practice is spreading to other areas at a fast rate. 50% of farmers are preparing compost in the house or on their plots so as to keep the fertility of the soil. 75% of households are planting trees on their own plots or around the homestead with the purpose of protecting farm fertility and supplementing incomes. 45.6% of households now have access to irrigable land, 60% of them have improved their houses into tin-roofed structures and 60% of respondents now have food available from 5 to 8 months. Adoption of conservation agronomic practices in the watershed resulted in better productive performance of crops over time due to decrease in soil erosion and enrichment of the soil. The three most important crops (teff wheat and barley) have all shown marked yield increases between 1997 and 2004. Specifically, average teff yields have increased from 0.3 t/ha to 0.6 t/ha, wheat has increased from 0.5 t/ha to 0.8 t/ha and barley has increased from 0.45 t/ha to 0.75 t/ha. Combined with increased fertilizer use, the adoption of conservation agronomic practices in the watershed resulted in better productive performance of crops due to decreases in soil erosion, in flooding and to enrichment of the soil. 4. Discussion and conclusions 4.1. Causes of land use and land cover changes between 1965 and 1994 Remote sensing and GIS-based change detection studies have predominantly focused on providing the knowledge of how much, where, what type of land use and land cover change has occurred (Weng, 2001). The aerial photo interpretation reveals that there was an expansion of cropland between 1965 and 1994. During this period sparsely cultivated land, wooded shrub grass land and shrub grass land have vanished. This is due to population pressure which results in the expansion of agricultural land and settlement. The predominant motive for land use change is production of food and fibre (Mustard et al., 2005). As stated by the farmers, the catchment was covered mainly by natural vegetation until the 1960s, with dominance of Juniperus and Acacia. Still the remnants of these trees are found around churches and communal areas in small patches. Furthermore, growing pressure from human and livestock population and the repeated drought conditions caused forest devastation
Fig. 6. Expansion of wetlands in the valley bottoms.
for fuel wood trade as a means of income to overcome the drought period. The 1965 aerial photographs show the presence of wetland in plain areas following valley bottoms and along rivers in the catchment. Farmers confirmed that they used the wetland for grazing purposes. However, this land cover feature had disappeared in 1994 due to mainly removal of vegetation cover. Change in vegetation cover can alter surface fluxes of energy and water and modify surface climate (Mustard et al., 2005). Consequently, human induced soil degradation was exacerbated. 4.2. Causes of land use and land cover change between 1994 and 2005 The rehabilitation of vegetation in many places of the catchment has improved the forest cover. Farmers also confirmed during focus group discussions, that the vegetation cover has increased and the change that has been observed at present was the result of the intervention, i.e. the establishment of exclosures. Riparian trees along the valley bottoms following the rivers which had not been observed in 1994 have developed in 2005. This was well observed during the field surveys. The trees were planted during the forestation activities to stabilize gullies. Though their numbers are small, remnants of natural forests are found around churches and on steep slopes. The degraded shrub grassland which covered a large portion of the watershed in 1994 was generally converted into other cover types such as shrubgrassland. This was observed during field surveys in which the vegetation cover that was very small and scattered in 1994 has at present grown up and changed into shrub-land, bush shrub grassland and bush-grassland. In some areas trees 3 m tall and above were observed. Hence the improvement of the vegetation cover has certainly been the result of the extensive soil and water conservation work that had been implemented in the study area. The 1994 aerial photograph analysis results show that intensively cultivated land constituted a larger portion of the catchment (55.11%), when compared with 1965 (51.1%) and 2005 (51.7%). The above changes explain the reduced bush and shrub cover in 1994. On the other hand, a remarkable increment was observed in built up areas compared with 1994. This change was the result of the expansion of the two towns Atsbi and Haike Meshal. The two towns were still small on 1994 and recently both towns are expanding at the expense of cultivable and grazing land. The wetland that had disappeared in 1994 re-emerged in 2005 (Fig. 6). The wetland has indeed developed as a consequence of extensive gully treatment to prevent flooding and erosion. A review by Nyssen et al. (2004) indicates the benefits of soil and water con-
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servation (SWC) measures in controlling runoff and soil erosion. Wetland development of the flat plain area in the lower and middle catchment is attributed to SWC structures such as check dams in gullies and trenches dug to intercept and store runoff. Farmers stated this cover type is a recent phenomenon following the stabilization of gullies. The emergence of wetland is attributed to the improvement of vegetation cover and the intensive soil conservation measures undertaken in the upper watershed. This change is taken as an indicator of the success of the SWC measures, because following the emergence of wetland there has been an increase of the groundwater table which is tapped through shallow wells.
ing problems in the lower parts of the watershed, stabilized gullies and river banks, rehabilitation of degraded lands and improved ecological balance in general. Similar studies elsewhere in northern Ethiopia (Woldeamlak, 2003; Liu et al., 2008; Munro et al., 2008; Nyssen et al., 2009) reported the effectiveness of sustained conservation efforts at catchment level in controlling soil erosion and in improving hydrology and land productivity. The improvement of vegetation cover in the watershed decreased the depth to the groundwater which could be managed and used for irrigation.
4.3. The impacts of IWSM on land use and cover change
The studied watershed underwent remarkable changes in land use and covers during four decades and the changes exhibit a dynamic nature. Throughout the period 1965–2005 more than half of the watershed was occupied by intensively cultivated land. Over the 40 years observation period, the area under assured well irrigation increased from 7.1 ha to 222.4 ha (see also Fig. 7). The area under dense forest increased from 32.5 ha to 98 ha. Major observed changes after the implementation of integrated watershed management are: reduced soil erosion, and increased soil moisture availability which could be explained by the increase in crop production, increased ground water recharge (as observed in the abundance of shallow wells), reduced sedimentation and run off problems in the lower parts of the watershed, stabilized gullies and river banks, rehabilitation of degraded lands and improved ecological balance, introduction of modern beehives and increase in honey production. To conclude, ecological changes caused by the destruction of natural vegetation, removal of soil by erosion and drying out of rivers as the result of mismanagement of land have been reversed as a result of the integrated watershed management intervention. While the IWSM intervention researched shows encouraging results for both vegetation cover and farmer livelihoods, in order to be sustainable, it is essential to maintain a high level of farmers participation. The
The erratic rainfall coupled with poor soil and ground cover and high human and livestock population pressure on land resources have contributed to a number of serious problems, such as degradation of vegetation cover, accelerated soil erosion, crop yield decline and human suffering. The major observed changes during the last four decades were the conversion of forest land, bush, shrub, and woodland to cropland, grazing land, and built-up areas. A similar land use and cover study made by Solomon (1994) in southern Ethiopia indicated that the influence of land use and cover depends very much on the nature of the land and the level of management techniques used. The rapid changes in land use and cover of the study area have been driven by factors such as population pressure, expansion of rural towns, large-scale overgrazing, and recurrent drought and poor land management. Marked land use/land cover dynamics are also observed in dense forest, wetland, shrub-land, and intensively cultivated (irrigation) land. The positive impact of the watershed management in the study area could be explained in terms of reduced soil erosion rates, increased soil moisture availability which could be deduced from the increased in crop production, reduced sedimentation and flood-
4.4. Conclusion
Fig. 7. Ground-based photo-monitoring of the area downstream of the watershed. The upper photograph was taken in 1975 (©Neil Munro), the lower in 2006 (©Jan Nyssen). An irrigation scheme was developed in this valley floor, some 10 km downstream from the watershed (extreme SW of the 2005 map – see Fig. 3). Despite the fact that the area is located outside of the formal Watershed Management Project area, stone bunds and improved vegetation cover on the slopes can be observed. The fig tree is a permanent element, a control, in this landscape.
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study highly recommends the up-scaling of such intervention in similar agro-ecologies. Acknowledgements The authors wish to thank Habtamu Mulatu, Fekadu Getnet, Ermiyas Ayenekulu and Steven Fisher for their useful comments and suggestions that helped to improve this paper. Funding for this study was provided by the VLIR – Mekelle University IUC Programme. Farmers and authorities from Hayke Meshal and surrounding villages are greatly acknowledged for their hospitality. References Agarwal C, Green MG, Grove JM, Evans TP, Schweik CM. A Review and assessment of land use change models. Dynamics of space, time, and human choice. Center for the Study of Institutions, Population, and Environmental Change, Indiana University, and USDA Forest Service, Northeastern Research Station, South Burlington, VT, USA; 2000. p. 90. Belay T. Land use/land cover changes in the Derekolli catchment of the South Welo zone of Amhara region, Ethiopia, vol. XVII, no. 1. EASSRR; 2002. p. 20. Bureau of Agriculture, Natural Resources. Land use land cover of Tigray. Mekelle, Tigray, Ethiopia: Land Use Planning and Regulatory Division; 2001. p. 213. Gebremedhin T. Assessing and mapping areas susceptible to water erosion using integrated remote sensing GIS tools and minimal ground survey in the Atsibi subWatershed. A case study in Tigray region, Ethiopia. Enschede, The Netherlands: International Institute for Geo-information Science and Earth Observation; 2004. Gete Z. Landscape dynamics and soil erosion process modeling in the North-Western Ethiopian highlands. PhD thesis. Institute of Geography, University of Berne, Switzerland; 2000. Igbokwe KN, Adede J. Integrated watershed management in Eastern Tigray, Ethiopia. Mid term impact evaluation report, Nairobi, Kenya, 2001. p. 72. Liu BM, Collick AS, Gete Z, Enyew A, Easton ZM, Steenhuis TS. Rainfall-discharge relationships for a monsoonal climate in the Ethiopian highlands. Hydrological Processes 2008;22(7):1059–67.
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