Land Cover Changes Between 1958 and 1986 in Kalu
District, Southern Wello, Ethiopia
Authors: Tekle, Kebrom, and Hedlund, Lars
Source: Mountain Research and Development, 20(1) : 42-51
Published By: International Mountain Society
URL: https://doi.org/10.1659/0276-
4741(2000)020[0042:LCCBAI]2.0.CO;2
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Introduction
Repeated aerial photographs and/or satellite images
play a major role in setting up inventories of natural
resources because they give a visual assessment of land
cover changes over a period of time and provide quanti-
tative information on the trade-offs between different
land cover categories. Historical investigations of land
cover changes have helped to acquire information on
salt marsh vegetation and wetlands (Larson et al 1980;
Civco et al 1986; Jean and Bouchard 1991), mountain-
ous regions (Schreier et al 1994; Schweik et al 1997),
dry lands in the tropics (Mwalyosi 1992), coastal sage
scrub (Davis et al 1994), and vegetation succession on
dunes (van Dorp et al 1985). In these and other studies,
most results are in line with general assumptions about
land cover changes. Some, however (eg, Pandee and
Chapman 1983), have shown that land cover changes
based on estimates, interpolations, etc., and those
based on historical data sets such as aerial photographs
do not concur.
In many developing countries, agricultural produc-
tion has not kept pace with population increase due to
such factors as land tenure systems, political insecurity,
and wars. Empirical evidence of land cover changes
delivered by repeated aerial photographs and/or satel-
lite images can greatly contribute to planning more
appropriate management of available resources, espe-
cially in developing countries, where other kinds of
background data are often lacking. However, to come
up with fruitful recommendations, studies on land cov-
er changes have to be supplemented by investigations
of their causes and effects.
This study is part of a project on “Natural regenera-
tion of degraded hillslopes in Wello, Ethiopia.” An ini-
tial reconnaissance survey was conducted before the
study area was selected. The study area was chosen main-
ly because (1) it had undergone substantial land cover
changes, especially since the early part of the century,
(2) it included a variety of physiographic features (high-
lands, plains, steep and gentle slopes, river valleys, etc.),
each of which influences land cover categories in a dif-
ferent way, and (3) it was subjected to high population
pressure. Within the broader context of understanding
and describing landscape dynamics, the specific objec-
tives of the present paper are (1) to identify and deter-
mine overall trends of major land cover changes over a
period of 28 years (1958–1986) and (2) to relate these
changes to physiographic and socioeconomic processes.
Description of the study area
The study area covers about 110 km
2
and features alti-
tudes between 1705 and 3000 m. Geologically, the
region belongs to the Trap Series of Tertiary volcanics
and is part of Ethiopia’s central lava highlands and mas-
sifs. The major soil classifications are Cambisols,
Phaeozems, and Lithosols (Anonymous 1988). Mean
annual temperatures range between 15 and 20°C.
Annual rainfall, which is heavy during the summer
months (June–August), ranges between 800 and 1200
mm (Anonymous 1988).
The study area (Figure 1A,B) is located in Kalu,
one of the most densely populated districts in
Ethiopia, with no less than 250 persons/km
2
(Anony-
mous 1988). The population in Kalu increased by
42
Land Cover Changes Between 1958 and 1986
in Kalu District, Southern Wello, Ethiopia
Kebrom Tekle and Lars Hedlund
This paper evaluates
changes in land
use/land cover (here-
after land cover) in a
specific area in Kalu
District, Southern
Wello, Ethiopia, by
comparing two aerial
photographs from
1958 and 1986. An
attempt is also made
to discuss possible implications of these land cover
changes for land degradation. By applying Geographic
Information Systems (GIS), two maps of the study area
(for the years 1958 and 1986) were produced. The
maps show a decrease in coverage by shrublands, river-
ine vegetation and forests, and an increase in remain-
ing open areas, settlements, floodplains, and a water
body. The areal extension of nine categories of land
cover was calculated and, by overlaying the two maps,
the percentage of each type of land cover that was con-
verted into other categories was computed. Land cover
changes were most noticeable for shrublands, with a
decrease of 15.5 km
2
(–51%), and for remaining open
areas (ie, excluding cultivated areas and settlements),
with an increase of 14.3 km
2
(+333%). Areas under cul-
tivation remained more or less unchanged. By and
large, land cover changes observed in this study were
the result of clearing of vegetation for fuelwood, grazing
lands, new cultivation areas, etc., thus contributing to
the current problem of land degradation in the country.
If coordinated efforts are not made to rehabilitate
degraded hillslopes, further deterioration of shrublands,
forests, and riverine vegetation into areas with little or
no plant cover will adversely affect the hillslopes and
eventually those areas that are currently used for crop
production.
Keywords: land degradation; land use changes; GIS;
remote sensing; Ethiopia.
Peer reviewed: January 1999. Accepted: August 1999.
Mountain Research and Development Vol 20 No 1 Feb 2000: 42–51
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212% from 1970 to 1984 compared with 57% for the
whole Wello region (CSO 1974; CSA 1991). The popu-
lation of Kombolcia, the district’s capital town, more
than doubled between 1984 (18,583) and 1994
(39,466) (CSA 1991; CSA 1995b).
Except for a small percentage of the population
living in the urban area, the inhabitants are farmers
engaged in crop production and livestock rearing. The
region (including the study area) is generally classi-
fied as intensively cultivated. According to data com-
piled by FAO, UNEP, and UNESCO, the study area is
in a high soil degradation risk zone, where runoff is
estimated to cause soil loss of 50–100 tons/ha/y
(Anonymous 1988). Over 65% of people in the study
area are said to have suffered from the 1984 food
shortage (Anonymous 1988).
Sources of information
In conducting this study, our main sources of informa-
tion were two black and white aerial photographs (scale
1:50,000) taken in 1958 and 1986. Land cover data for
43
Research
FIGURE 1A Map of Ethiopia
showing the approximate
location of the study area in
Kalu District.
FIGURE 1B Hillslope cultivation leading to land degradation in the study
area. (Photo by M. Coendet, 1982)
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Mountain Research and Development Vol 20 No 1 Feb 2000
44
Kebrom Tekle and Lars Hedlund
FIGURE 2 Land use cover in
the study area in 1958.
FIGURE 3 Land use cover in
the study area in 1986.
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1958 is based on aerial photo M BNRB M73 no. 10840
and data for 1986 on aerial photo S 13 03 no. 0111. Both
photos were acquired from the Ethiopian Mapping
Authority (EMA). Ground checking was done to com-
pare information (on categories such as remaining open
areas, shrublands, etc.) on the aerial photos with existing
features of land cover on the ground. The topographical
map (EMA 1993) provided sound information on eleva-
tion, settlements, and drainage in the study area. Various
atlases, statistical reports, and other relevant documents
on the study area and the district were of great help. Pri-
or knowledge of the region and discussions with the local
population also contributed to the study.
Methodology
The study depended on the use of computer-assisted
interpretation of digitized aerial photos. The two aeri-
al photographs used for this study were scanned at
the Swedish Land Survey office with a resolution of
1100 and 1200 dots per inch and were saved in TIFF
format. Before interpretation, the original image files
were enhanced through sharpening with Adobe Pho-
toshop 1996 software, saved in TIFF format and
imported into Thinkspace’s Map•Factory. It was also
possible to enlarge the original scale of the scanned
aerial photos from 1:50,000 to about 1:3000. This
facilitated the interpretation of specific features in
the aerial photographs.
To investigate the changes that occurred between
1958 and 1986, nine land cover categories (hereafter
categories) were distinguished: cultivated areas, shrub-
lands, forests, rural settlements, riverine vegetation,
remaining open areas, floodplain, urban settlements,
and a water body (Table 1). These nine categories,
identified from the scanned aerial photos, were screen
digitized manually as polygon coverage in raster for-
mat. A color was selected for each of the nine cate-
gories (Figures 2 and 3). Each image was georefer-
enced according to the Universal Transverse Mercator
(UTM) system by selecting five reference points with
known coordinates that were later digitized from a
1:50,000 topographic map. To successfully transform
coordinates, four control points had to be selected
somewhere near the corners and one near the center
of each image.
The control points were marked on the digitized
aerial photos and registered in UTM coordinates using
the ESRI Grid Module of the ArcInfo GIS program. The
images were then rubber-sheeted in ArcInfo using the
Grid Warp function to transform the coordinates into
UTM. The overlapping areas from the two images (1958
and 1986) were clipped from the georeferenced images.
Computation of area in the nine categories was
made by exporting the two images from ArcInfo to
Map•Factory. By overlaying the two images, the area
(%) converted from each of the categories to any of the
other categories was calculated.
45
Research
TABLE 1 The nine land cover
categories for which changes
were detected for the period
between 1958 and 1986 (listed
in the order of magnitude of
coverage in 1958).
Land cover General description
Cultivated areas
Areas allotted to rainfed crop production, mostly of cereals in subsistence
farming
Shrublands Land covered by small trees, bushes, and shrubs, in some cases mixed with
grasses; less dense than forests
Forests Areas covered by trees forming closed or nearly closed canopies; predominant
species are Juniperus procera and Olea europaea ssp cuspidata
Rural settlements Areas composed of small villages and/or scattered hamlets; mostly located on
the slopes or at the foot of the highlands
Riverine vegetation Vegetation along the main river valleys draining to the floodplain of River
Borkenna; the middle part of the river valleys is generally covered by dense
shrub vegetation
Remaining open areas Areas that include a group of features (such as barren eroded lands mostly on
top of mountains, open areas near homesteads, grazing areas) that are difficult
to distinguish on the aerial photos because of their similar tones
Floodplain Area covered by the lower course of River Borkenna, carrying a large volume of
water during the rainy season but covered most of the year by sand and
different sizes of gravel and stones
Urban settlements Land occupied by small and large buildings, roads, factories, and an air strip
Water body Area covered by a small dammed lake fed by rainfall and small streams
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