Land Cover Dynamics (from 1986 to 2015) and its Relation with Area Closure and Slope in Hita-Borkena Watershed, Northeastern Ethiopia

Background: Land cover dynamics take place as a result of the integration of both physical and man-made factors. This situation is common in Ethiopia and in the study watershed as well. The study was intended to assess the land cover dynamics through 1986 – 2015 and to identify its relation with slope and landscape restoration that incorporates area closure. The analysis was made based on the interpretation of satellite images. Methods: Both ERDAS IMAGINE 9.1 and ARC GIS 10.3 software were employed in order to generate land cover maps of the study area from satellite images. Also, slope map of the study area was processed from DEM of Ethiopia. Results: The study found out that forestlands and shrublands shrunk through 1986 – 2015, grasslands expanded mainly due to the implementation of landscape restoration including area closure since 2001. Cropland expanded remarkably. Similarly, the coverage of bareland and settlement also increased. Conclusions: Based on the results of the study, it is concluded that similar restoration activities shall be implemented in similar environments in Ethiopia to keep the natural resources, and the vegetation cover of Hita-Borkena watershed shall be improved. grassland on both mid (12–36%) and steep (> 36%) slopes between 2001 and 2015. F-G-S was found to be higher in coverage compared to cropland on steep slope through 1986–2015. The overall coverage of F-G-S is, however, decreasing. This calls for the coordinated efforts of local people, local, zonal, regional and federal concerned oces, and NGOs (Non-Governmental Organizations) improve the vegetation coverage of the study watershed.

. Hence, this study is executed with the notion that the above-mentioned essences of assessing land cover changes will be achieved.
The study area, Hita-Borkena watershed, is found in Kalu district, South Wollo Zone, Amhara region, northeastern Ethiopia. It is one of the areas in the district which doesn't receive su cient amount of rainfall and is among the severely degraded parts of Ethiopia. Several efforts have been made by district's o ce of agriculture being in combination with WFP's (World Food Program's) MERET (Managing Environmental Resources to Enable Transitions to More Sustainable Livelihoods) project to restore the area and thereby bene t the residents (Kalu District Agriculture O ce 2013).
Thus, the objectives of this study were to analyze land cover dynamics in 1986, 2001, and 2015; to compare the land cover conditions in the three periods; to evaluate how much the landscape restoration affected the land cover conditions of the study area; to examine the relations among land cover dynamics, slope and area closure. A combination of GIS and remote sensing technologies were used for achieving these objectives.

Materials And Methods
The Study Area Hita-Borkena watershed is found in the southern part of Kalu district, South Wollo Zone of Amhara National Regional State of Ethiopia. It is located between 10 0 55 10 -10 0 59 4 N and between 39 0 44 53 -39 0 47 30 E (Fig. 1). Its total area is 20.94 square km. Its elevation ranges from 1471-2096 meter above sea level (m asl).
The mean annual temperature for the years 2000-2011 was 21.6 0 C (Kombolcha Meteorology Station 2013). The study area enjoys two rainy seasons: Kiremt (main rainy season usually exist between July and September) and Belg (small rainfall occurs mainly in March and April). The mean annual rainfall for the years 2000-2011 was 1069.47 mm (Fig. 2).
The study watershed is mainly covered by volcanic rocks formed during Tertiary period of Cenozoic era. The rocks are composed of Oligo-Miocene Trap basalts and are with faults and fractures (Abbate et al. 2014;Mengesha et al. 1996).
The study area consists of three main soil types: Cambisols, Regosols and Vertisols. Cambisols are the most dominant soil types covering 87.3% of the area of the watershed. The study watershed is part of the Awash River basin. It is mainly drained by Borkena River and also by a smaller stream called Hita.
The dominant vegetation types include different acacia species and Euclea racemoca (locally called "Dedeho"). Agriculture is the main economic base of the residents of the study watershed. People in the watershed practice a

Analysis Of Land Cover Dynamics
In order to analyze the land cover dynamics of the study watershed, cloud-free three satellite images was The three years are selected on the basis of the period of implementation of MERET project in the study area. The year 1986 is selected because it is 15 years before the implementation of the project in the study watershed. The year 2001 is selected because it is the time when the project had begun. The year 2015 is selected because it is 14 years after the implementation of the project. Hence, using these reference years, it is possible to see the impact of the project on the land cover conditions of the study watershed.
The satellite images were clipped to t the size of the study area. The images were radiometrically and geometrically corrected, and were georeferenced to Transverse Mercator geographic projection using WGS84 as a datum (Belay 2002: Messay 2011. Then, unsupervised classi cation was done to identify major land cover classes depending on their re ectance properties. Field visits and observations were made so as to collect ground truths, i.e. to identify the major land cover classes. Incorporating data obtained from eld visits and observations, supervised classi cation was made to produce three separate land cover maps for the three reference years. Such process led to the identi cation of six major land cover classes: forestland, shrubland, grassland, cropland, settlement and bareland. Accuracy assessment (Messay 2011) was calculated for the 2015 land cover map. The overall accuracy was 86.57% with a Kappa coe cient of 0.84. Furthermore, the producer's and user's accuracies were also calculated. The calculations were made using the following formulas taken from Congalton and Green (2009): Where n = total number of points (sample) k = number of categories (1, 2, 3, …, k) n ii = correctly mapped point for each land cover type (diagonal values usually bold type) n i+ = number of map data points for each land cover type (row total) n + i = number of ground data points for each land cover type (column total) The area covered by each land cover class in each year was determined. The change of each land cover class in the two time intervals: 1986-2001 and 2001-2015 was computed. In doing such analysis, graph and tables were used. These all processes were conducted by integrating ERDAS IMAGINE 9.1 and ArcGIS 10.3 software.
In order to analyze the link between land cover dynamics and slope, rst a slope map was produced from the DEM (Digital Elevation Model) of Ethiopia by surface analysis using spatial analyst tool of ArcGIS and then the slope map was classi ed into three classes based on Aklilu (2006): gentle slope (0-12%), mid slope (12-36%) and steep slope (> 36%). The area of each land cover type on each slope class for the three land cover maps was calculated using overlay analysis. To assess the relation between slope and area closure, the area of Forestland, Grassland and Shrubland (F-G-S) was aggregated for each slope class in the reference years. Also, emphasis was made on the improvement of vegetation on mid and steep slopes since area closures are located on such slopes.

Accuracy of the Land Cover Classi cation
The error matrix for the land cover map of 2015 revealed that the overall accuracy is 86.57% with a kappa coe cient of 0.84 (Table 1). These accuracy values indicate that it is possible to undergo analysis since they ful ll the accuracy level demanded from land cover maps, which are derived from satellite imageries (  their spatial coverage is insigni cant compared to the major ones. The description of the major land cover types is given in Table 2.

Shrublands
Areas that contain shrubs and thorny bushes and are less in density than forestlands. They include a bush canopy (> 50%) which is mixed with some trees and that of grass cover (< 50%).
They are non-herbaceous species whose branches begin from the base of their stem and are usually

Croplands
Land used for the growth of seasonal and perennial crops, which are mostly grown by rainfall and sometimes by traditional irrigation means. The source of irrigation water is mostly Borkena river.
Settlements These are referring to both rural and urban settlements. Those located in rural areas can be of clustered or scattered dwelling units. Urban settlements are those with better road and social service facilities than the rural counterparts.

Barelands
Parcels of land mostly covered with no or little plant cover and contain exposed rocks. They are indicators of high rate of degradation in the given area.

Trends Of Land Cover Dynamics
The study found that forestland and shrubland diminished during the analysis period. The available forest was mainly deforested between 2001 and 2015 that give rise to the clearing of forest that covers 110.3 ha, i.e. 50% of the forest cover in 1986. The decreasing trends of forestland and shrubland, and increasing trends of cropland, bareland and settlement in the study watershed happened due to population pressure. Grassland exhibited a unique trend over the 29-analysis period (    As can be seen in Fig. 6a, cropland was the major land cover type on the gentle slopes in the watershed. On the other hand, forestland, grassland and shrubland shrank down on the same slopes through 1986-2015. Though the mid slopes in the watershed were dominated by cropland, grassland showed an increasing trend in the analysis period (Fig. 6b) mainly due to area closure. However, due emphasis should also have been given to forestland and shrub-land. This is because the watershed could be protected not only by grassland but also by forestland, shrubland and different SWC measures. In relation to grazing land, Aklilu (2006) identi ed that it is mostly located on gentle and mid slopes of Beressa watershed, Ethiopia.
In 1986 and 2001, unlike gentle and mid slopes, steep slopes in the watershed predominantly contained shrubland. In 2015, three land cover types: cropland, grassland and shrubland, were dominating the watershed (Fig. 6c) Comparisons were made in order to show how the amount of vegetation including forests, grasses and shrubs in combination and cropland on gentle, mid and steep slopes changed in the watershed between 1986 and 2015.
As revealed in Fig. 7a, cropland showed a considerable increase in the gentle slope throughout the analysis period for the reason that such slope is favorable for crop production. On the other hand, forestland, grassland and shrubland (F-G-S) in combination exhibited opposite trend.
In 1986, F-G-S on mid slopes covered almost 30% of the area of the watershed while cropland constituted only 11%. F-G-S on the same slopes declined to 18 and 14% in 2001 and 2015, respectively, whereas there was the corresponding rise in the size of cropland in the indicated years (Fig. 7b). Though not possible to resume the vegetation cover in 1986, the present F-G-S has been conserved as a result of the restoration project that incorporates area closure in the study watershed.

Conclusions
This study using GIS and remote sensing technologies con rmed that the major land cover types of the study watershed have undergone changes through 1986-2015. Forestland received a signi cant shrinkage throughout the analysis period, which implies that serious deforestation took place in the indicated years. The same trend, though the rate is relatively minimal, is followed by shrubland that could happen because of the fact that the shrinking of forest leave pressure on shrubs. Unlike the earlier land cover types, grassland decreased trend between 1986 and 2001, but it enjoyed an increasing trend through 2001-2015 due to MERET project that incorporates area closure. The project was introduced in the watershed in 2001.
Cropland expanded at the expense of mainly shrubland and grassland. Bareland and settlement have also expanded throughout the analysis period, though the rate is different from cropland. The area coverage of bareland was being tackled by MERET project especially after 2001. However, low participation of local people after MERET project, i.e. 2012, and recent railway construction are now mainly contributing to the expansion of bareland. As it is also true in other areas of the world, settlement has got an increasing trend in the study watershed through 1986-2015 because of population pressure.
In this study, it is witnessed that cropland was the main land cover type on gentle slope (0-12%) throughout the analysis period. Here, it is mandatory to acknowledge the contribution of area closure for the increasing trend of Link between land cover dynamics and slope in Hita-Borkena watershed, northeastern Ethiopia