International Journal of Geosciences, 2013, 4, 1003-1008
http://dx.doi.org/10.4236/ijg.2013.47093 Published Online September 2013 (http://www.scirp.org/journal/ijg)
Retrospective Analysis of Land Cover and Use Dynamics in
Gilgel Abbay Watershed by Using GIS and Remote Sensing
Techniques, Northwestern Ethiopia
Amare Sewnet Minale
Department of Geography and Environmental Studies, Bahir Dar University, Bahir Dar, Ethiopia
Received June 1, 2013; revised July 5, 2013; accepted August 2, 2013
Copyright © 2013 Amare Sewnet Minale. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
This study was aimed at examining land cover changes for the last 35 years and its causative factors in Gilgel Abbay
watershed by using GIS and remote sensing, survey and population data. The land use and cover changes study will
help to apply the appropriate land use. The land cover/use status for the years 1973, 1986, 1995 and 2008 were exam-
ined using land sat images. The changes in different land cover units such as forest, wood and bush lands, grass, wet-
lands and water bod ies, and farm and settlements were analyzed. Population change, tenure, poverty and lack of market
and credit facilities in the watershed area were analyzed as causes of land cover changes. The results of the study have
shown that during the last 35 years forest, grass lands, wetlands and lake areas were converted to farm and settlement
areas. There was rapid increase of population with growth rates of 4.9% and 3.5% (1984-1994 and 1994-2007), respec-
tively per annum which caused more land cover changes.
Keywords: Gilgel Abbay Catchment; Land Conversion; Causes of Land Cover Change; Population Increase;
Socio-Economic Factors
1. Introduction
Interpreting and conceptualizing the land cover/use
changes contribute to complex dynamics of land cover
and is important for policy and planning actions [1,2].
Land use changes are caused by both natural and socio-
economic factors [3]. Land use land/cover (LULC) is
perhaps the most prominent form of global environ-
mental change phenomenon occurring at spatial and
temporal scales. Land cover is the physical and biologi-
cal cover of the surface of land, whereas land use is the
syndromes of human activities such as agriculture,
forestry and building construction that alter land surface
processes [4]. The conversion of natural land to cropland,
pasture, urban area, reservoirs, and other anthropogenic
landscapes represents the form of human impact on the
environment [5]. Roughly 40% of earth’s land surface is
under agriculture, and 85% has some level of anthro-
pogenic influence [6]. Therefore, large-scale land cover
change is largely a rural phenomenon, but many of its
drivers can be traced to the consumption demands of the
swelling urban population [7]. Deforestation, wetland
drainage, and grassland degradation have all amounted to
a globally significant alteration of the land co ver changes.
Large scale environmental phenomena like land degra-
dation and desertificatio n, biodiversity loss, habitat des-
truction and species transfer are consequences of land
use by converting natural land covers [8].
The relationship between land cover and use change
and its causative factors is complex and dynamic. The
land cover and use change is mainly manipulated by both
natural and socio-economic factors. Some studies sug-
gested that demographic dynamics contribute more than
any other process to land cover changes [9] while others
suggested the superiority of economic factors [10]. Other
socio-economic factors of land cover change include
poverty, tenure security, and availability of market and
credit facilities. Each of th e above causes was associated
with one or more ultimate causes for land cover change,
if remedied would solve the problem. These factors have
become apparent between, as well as within, individual
regions and countries. Thus, the diversity of causative
factors of land cover change must be considered within
the regional variati o ns [11].
In Ethiopia, different micro studies from aerial photo
and satellite images have revealed that agricultural land
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1004
has been expanded extensively at the expense of other
land uses. Population pressure with other institutional
and socio-economic factors was often cited as a primary
reason for conversion to crop lands in Ethiopia [12-14].
This in turn has an implication to dependency of the poor
people on the environmental resource in the coun try. The
land tenure system in the place so far in the country has
not been secured and the land has been privatized. In
highlands of Ethiopia, land is seriously degraded owing
to problems related to land tenure security and other fac-
tors of degradation. Gilgel Abbay watershed (GAW), sub
area of Lake Tana Basin, is one of such areas, where the
above problems could be manifested.
Accurate information on land-cover changes and the
forces and processes behind is essential for designing a
sound environmental policies and management. The
land-cover analysis provides the baseline data required
for proper understanding of how land was used in the
past and the types of changes to be expected in the future.
This research was therefore, aimed at analyzing the link
between land cover changes and its causative factors in
GAW. Identifying the driving forces behind land use
changes, and developing appropriate measures to mini-
mize their ecological effec ts have great deal of importance
for land use planning. Specifically, this study determines
land cover and use status with special reference to its
causes and evaluation of their consequences through time
in GAW. Accordingly, one of the most densely popu-
lated areas of Ethiopia, the GAW, area of Lake Tana,
was proposed for the study.
2. Study Area and Methodology
2.1. Study Area
Gilgel Abbay Watershed comprises Gilgel Abbay River
and its tributaries. Gilgel Abbay Watershed is located
northwestern Ethiopia and stretches between latitudes
10˚57'N - 11˚54'N and longitudes 36˚38'E - 37˚23'E (Fig-
ure 1). The elevation ranges from 1780 m to 3400 m.
The slope is steeper at the southern part of the watershed
and declines to north wards. Gilgel Abbay River contrib-
utes more than 40% of the volume of Lake Tana’s water
and covers abou t 32% of the Lake’s total catchment with
total area of about 4865 km2. Gilgel Abbay Watershed
falls into two traditional climate zones: “Woina Dega”
(warm) and “Dega” (temperate like highland). The mean
annual rainfall and temperature for the whole watershed
was 1553 mm and 18˚C, respectively. According to [15]
there are about 1.5 million people in Watershed and
about 90% of the population live in rural areas and pri-
marily depend on agriculture.
2.2. Data Sources and Methods of Analysis
The present study used satellite images, socio-economic
Figure 1. Map of the study area.
surveys and population censuses to understand land
cover and use dynamics and factors that bring changes.
Land sat MSS (Multi-spectral Scanner) acquired on
01-02-1973 with path and row of (182p52r) with 4 bands
and, Land sat TM, 1986, 1995 and 2008 (Thematic
Mapper) acquired on 08-03-1 98 6, 1 7- 03 - 19 95 a n d 08- 0 3-
2008 with path and row of 170p52r and 169p52r,
170p52r and 170p52r respectively were used for land
cover and use analysis. These MSS and TM images wer e
geo-referenced, enhanced and transformed before actual
cover change detection. Since MSS and TM images have
different resolutions, they were re-sampled to the same
size using the nearest neighbor re-sampling technique.
Radiometric correction including correcting the images
for sensor irregularities and minimizing unwanted at-
mospheric noise and terrain effects was done by ERDAS.
The sub-setting and mos a i c k i n g to cover the study wa-
tershed was made for some images.
First unsupervised classification was conducted to get
the major land parcels in the watershed. Based on this
information, supervised classification by the help of GPS
points was used to produce thematic land cover maps.
The GPS points were collected from the study area by
frequent visit of sampled parts of the watershed. The
high resolution spot image of 2006 was also used to de-
tect the present land covers. More than 300 signatures
were used for each land unit to convert the images into
thematic land covers. However, because of low resolu-
tion of images, only major land cover types were consid-
ered. The farm and settlement areas were included in the
same land cover, because settlements in the rural areas
are near their farmlands and the swamps, ponds, riparian

A. S. MINALE
1005
vegetation and marsh areas were also categorized under
wetlands. The major land cover classes were: forest; ag-
riculture and settlement; wood and bush lands; grass
lands; water bodies and wetlands (Table 1).
After classification, calculation of the area in hectare,
comparison of the land use land cover statistics within
and between land class units and years was made and the
trend was determined. Percentage change to determine
the trend of change then is calculated by
211
100
ttt
CA AA , where At1 is the area of one type
of land use in t1 ti me; At2 is the area of the same type in
t2 time. C is a simple and effective method of weighing
relative change of area of one type of land use.
Survey data using structured questions, interview and
focus group techniques were included to substantiate the
image analysis. Population data about districts which
covers about 75% of total watershed from three censuses
were obtained from central statistics office and were used
for change detection in catchment’s population size,
growth and spatial variation.
3. Results and Discussion
3.1. Land Cover and Use Dynamics in GAW
The forest cover includes natural densely grown trees
found in some pocket areas of the watershed. It was con-
stituted only 1.2% of the total watershed in 1973, and
had shown rapid declining during the study time. Its per-
centage share was 0.6%, 0.4% and 0.3% respectively
over the specified years (Table 2 and Figure 2). There
was 73.3% forest cover loss from 1973-2008 from wa-
tershed. The trend was mainly related to rapid population
growth and demand for farming land and construction as
well as fuel wood. Wood and bush land covers have
shown increment from 3.1% in 1973 to 5.1%, 7.6% and
7.7% respectively during the last 35 years (Table 2 and
Figure 2). This shows that, although the proportion was
small, wood and bush land covers have shown continu-
ous increment. Within the specified years grass land has
shown continuous declining change from 20.6% in 1973
to 13.9%, 11.6% and 9.3 % respectively, with very fast
and rapid conversion rate (Table 2 and Figure 2). This
was related to easy accessibility of farming activities and
redistribution of grass lands to landless farmers.
This land cover has shown increasing change during
the specified years. The percentage change was 26.1% in
1973 and 34 .9%, 36.3% and 41.2% r espectively on tho se
years (Table 2 and Figure 2). This was the larger expan-
sion and share than other land use types. This implies
that agriculture and settlement areas have been exten-
Table 1. Land classification and their descriptions.
No. Land class Description
1 Forest Tree-covered land where the trees cover density is greater than 10%.
2 Wood and bush lands Areas with sparse trees mixed with short bushes, grasses and open areas; less dense than the forest with
little useful wood, mixed with some grasses
3 Grass lands Land predominately covered with gra sses, forbs, grassy areas used for communal grazing.
4 Agriculture and
settlement Areas used for crop cultivation, both annuals and perennials, and the scattered rural settlements that are closely associated with the cultiv a ted fields.
5 Water b o dies Areas covered by La k e , Rivers and stream s in the catchment permanently
6 Wet lands Wetlands include areas that waterlogged and swampy in the wet season, and dry in the dry season, perennial
marshy areas and riparian vegetations.
Source: Amare and Kameswara, 2011.
Table 2. Land cover and use changes in GAW from 1973 to 2008.
Land cover classes Year 1973 Year 1986 Year 1995 Year 2008 1973-2008
Area in ha*. % Area in ha. % Area in
ha. % Area in ha. % Total loss or gain
Forest 9328 1.2 4527 0.6 3298 0.4 2581 0.3 −6747
Wood and bush lands 24,645 3.1 39,980 5.1 60,148 7.6 60,863 7.7 36,218
Grass land 162,481 20.6 109,550 13.9 91,748 11.6 73,026 9.3 −89,455
Farm and settlement
land 205,993 26.1 274,947 34.9 286,261 36.3 324,536 41.2 118543
Lake Tana 301,899 38.3 302,946 38.4 301,082 38.1 282,990 35.9 −18,909
Wet lands 84,069 10.7 56,465 7.2 45,878 5.8 44,419 5.6 −39,650
Total 788,415 100 788,415 100 788,415 100 788,415 100

A. S. MINALE
1006
Figure 2. Land cover and use maps of GAW in 1973, 1986, 1995 and 2008. Source: Amare and Kameswara, 2011.
sively expanded from the conversion of grass, forest and
wetlands. Because, each member of the family added has
to get land for farming and settlement from other land
cover units. The share of Lake Tana in 1973 was about
38.3% and on next period it showed slight increase to
38.4%. But after 1986, the Lake Tana area had shown
declining trend from 38.1% in 1995 to 35.9% in 2008
(Table 2 and Figure 2). There was 6.26% loss of Lake
Tana area for the last 35 years to other land covers. The
rate of conversion of Lake Tana to other land cover is
recent event. From the watershed wetlands have declined
from 10.7% in 1973 to 7.2%, 5.8% and 5.6% over the
specified years respectively (Table 2 and Figure 2).
From 1973-2008 about 47.16% of wetlands were con-
verted to other land units. This implies that wetlands
degradation and their ecological and economical impor-
tance was lost.
The land cover changes that have been recognized in
GAW had shown continuous expansion of arable land in
order to meet the increasing food demands of the grow-
ing population. Arable land expands at the expense of
forest, grass and wetlands. In the watershed, there was
declinging of grass, wetlands and forest land covers from
1973-2008. But the Lake Tana area change was increas-
ing on the first period but decreased for the last two pe-
riods. The land covers of wood and bush lands and farm
and settlement areas have been increasing for the whole
periods.
3.2. Causes of Land Cover and Land Use Change
in GAW
The most cited causes of land cover change in many lit-
eratures are population increase. However, the relation-
ship between population and land cover change is debat-
able issue. Some such as [16] argues that increase in
population has positive effect on resource available.
However, [17] on the other hand finds in Ethiopian high-
lands that population pressure lead to land degradation.
Similarly, studies in different parts of Ethiopia have
shown that population pressure has been found to have
negative effect on scrublands, riparian vegetation and
forests [12,18]. In Gilgel Abbay watershed districts
population for the last 25 years has been growing very
rapidly. It has doubled itself in less than 20 years. Age
proportion of young population under 15 was 48.3%.
The total population of water shed districts in 1984 was
580,258 and in 1994 popu lation of the same districts was
863,432 and in 2007 population of districts became
1,162,956 [15,19,20]. The growth of population per year
from 1984 to 1994 was 4.9% and from 1994-2007 it was
3.5 % (Table 3). Although its growth is declining, it is
still increasing rapidly and brought the scarcity of land,
deforestation and soil erosion in the watershed. This im-
plies that the land cover and use change that is obtained
from image analysis was because of population increase
in the Gilgel Abbay watershed. Furthermore, shortage of

A. S. MINALE 1007
Table 3. Population of districts in GAW from 1984-2007.
Census years Growth rate
Districts 1984 1994 2007 1984-1994 1994-2007
Sekela 65,699 85,950 138,652 3.1 6.1
Achefer 160,274 238,255 329,074 4.9 3.8
Mecha 156,904 244,801 292,210 5.6 2.0
Bahir
Dar
Zuria 197,581 294,424 403,020 4.9 3.7
Total 580,258 863,432 1,162,956 4.9 3.5
Source: (CSA, 1984; 1994; 2008).
land has forced farmers to cultivate steep slopes and
shallow soils that are vuln erable to degrad ation and leads
to cover change to any one form.
Intensive interview and focus group discussion was
held with community in the stu dy watershed to find other
causes of land cover change other than population in-
crease. It was believed that land is not individually
owned and has affected investment and managed on this
resource. Prior to 1975 in Ethiopia land was in hands of
lords but after 1976 the land became the prime property
of the government [21]. As the result of this, there was
mismanagement of land, including overgrazing and
clearing of forests for different purposes. Poverty is also
linked to land cov er changes in that the poor over use the
natural resources to escape from poverty. [22] has shown
that in Ethiopian highlands, rural poor households have
caused land degradation.
The empirical evidence is obtained by comparing the
food produced and required especially, at the upper part
of the catchment because of degraded land the gap is
very wide. In most cases actual production of variety of
crops per household per year was less than the amount of
food crops needed to feed their family per year. In most
cases, the actual production was lower than the required
food crops by 16.6%, 4.1%, 4.2% and 5.0% per year,
respectively (Table 4). By monetizing the agriculture
output, the income generated from the land by individual
household had a range from US $97 to US $1090/annum,
with a mean income of US $630. As the result of this,
many people in the watershed have to get income for
living from other sources such as selling fire wood, cow
dung and others that are obtained from exploitation of
environmental resources. From the interview held be-
cause of uneven distribution of income and lack of good
management practices over the natural resources, poverty
was prevalent, especially at the upper part of the catch-
ment. Most respondents expressed insecurity of the ten-
ure and rights over the land and better productivity can
be achieved thr ough secured ownership rights to the land
holders.
Table 4. Average required and actually produced crops by
sample households.
Sample kebeleRequired average crops per quintals
1 - 5 6 - 10 11 - 15 16 - 20 21 - 25Total
Abbay sengab 12 9 13 4 38
Lijome 11 20 11 42
Ambo mesk 6 17 14 3 40
Total 6 40 43 27 4 120
Sample kebeleActual average crops
produced per ye ar per quintals
1 - 5 6 - 10 11 - 15 16 - 20 21 - 25
Abbay sengab13 14 8 1 2 38
Ambo mesk2 8 6 19 7 42
Lijome 5 13 9 7 6 40
Total 20 35 23 27 15 120
Because of small land holding size and shortage of
land in highlands of Ethiopia, plowing steep slopes is
contributing to land degradation [17]. In Gilgel Abbay
watershed the average land size of farmers is 0.89 ha.
Farmers didn’t have enough land to plough and tried to
expand their plot by clearing forests and communal
grazing near their plot of farm lands. Farmers are poor to
buy agricultural input and there are no roads which pene-
trate to rural villages and farmers’ knowledge about the
market was very limited. Thus, land tenure insecurity,
poverty, lack of land and inaccessibility to market and
road facilities were the causes of land cover changes in
the watershed.
4. Conclusion
There was land cover change in the watershed because of
demand for agriculture and settlement land for increasing
population, problems related to land policy and lack of
infrastructures. The conversion was very rapid on forest;
wetlands and grass because of lack of strategies to con-
trol and manage these resources. Hence, there should be
strategies of managing open access resources through
participation of local people in the management. There
should be also land use planning by identifying the
proper land for specific purpose so that the marginal
lands will not be put into use. Population increase has
played a major role on land cover changes and there
should be strategies that are proposed to strengthen fam-
ily planning programs. Catchment management should
involve the well-judged use of natural resource with ac-
tive participation of institutions, individuals, organiza-
tions, in harmony with the ecosystem components.

A. S. MINALE
1008
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