Accuracy assessment for image classification
Accuracy assessment is a vital validation technique and a requirement in remote sensing (Okeke & Karnieli, 2007) because it tells us how well-generated classifications perform. One of the most popular techniques for displaying accuracy rating data is in the form of a confusion or error matrix (Congalton, 1991). Based on the findings of the post-classification accuracy assessment, it was determined that in 2022, wetland had the highest overall user accuracy evaluation (100%) and settlement had the lowest (75.3%) in the Legabora watershed, whereas in Satame, bare land had the highest overall user accuracy evaluation (100%) and forest had the lowest (81.7%). As shown in Table 4, the producer accuracy for the same study periods in Legabora was (85.7%) for bare land, (92.5%) for forest, (91.8%) for settlement, (89.8%) for cropland, and (83.6%) for water bodies, respectively.
Table 4
Accuracy assessment table for eight LULC classes in Satame and Legabora (2022)
Year
|
LULC
|
WSD
|
ST
|
WB
|
BL
|
SL
|
WL
|
CL
|
GL
|
FL
|
UA%
|
K
|
2022
|
ST
|
Legabora watershed
|
45
|
3
|
5
|
1
|
0
|
5
|
1
|
0
|
75.3
|
0.83
|
WB
|
0
|
51
|
1
|
7
|
0
|
3
|
0
|
1
|
78.5
|
BL
|
0
|
4
|
60
|
3
|
1
|
1
|
4
|
0
|
82.2
|
SL
|
4
|
0
|
1
|
65
|
0
|
0
|
4
|
0
|
87.8
|
WL
|
0
|
0
|
0
|
0
|
6
|
0
|
0
|
0
|
100
|
CL
|
0
|
0
|
0
|
0
|
1
|
114
|
0
|
1
|
98.3
|
GL
|
0
|
3
|
3
|
0
|
0
|
4
|
60
|
2
|
83.3
|
FL
|
0
|
0
|
0
|
6
|
0
|
0
|
5
|
49
|
81.7
|
PA%
|
91.8
|
83.6
|
85.7
|
79.3
|
75
|
89.8
|
81.1
|
92.5
|
|
OAA
|
89.8
|
2022
|
ST
|
Satame watershed
|
56
|
2
|
0
|
0
|
0
|
3
|
0
|
3
|
87.5
|
0.85
|
WB
|
0
|
77
|
0
|
5
|
0
|
5
|
1
|
0
|
87.5
|
BL
|
0
|
0
|
1
|
0
|
0
|
0
|
0
|
0
|
100
|
SL
|
2
|
3
|
0
|
89
|
0
|
2
|
0
|
6
|
87.3
|
WL
|
0
|
0
|
0
|
0
|
9
|
2
|
0
|
0
|
81.8
|
CL
|
0
|
2
|
0
|
2
|
0
|
82
|
0
|
2
|
91.1
|
GL
|
2
|
2
|
0
|
0
|
0
|
2
|
80
|
0
|
93
|
FL
|
1
|
4
|
0
|
0
|
0
|
5
|
0
|
49
|
81.7
|
PA%
|
91.8
|
85.6
|
100
|
92.7
|
100
|
81.2
|
98.8
|
81.7
|
|
OAA
|
84.2
|
The user accuracy was highest for bare land (100%) and lowest for forest (81.8%), while producer accuracy was highest for wetland and bare land (both at 100%) and lowest for cropland (81.2%) in the Satame watershed, respectively. Throughout our field observation and transaction walk with the help of Google Earth Engine, we gathered a total of 893 Ground Control Points (GCPs) from a GPS. Of these, 493 points were used for supervised classification, with the remaining 400 GCPs being used to calculate the accuracy of satellite images. We followed the approaches proposed by Lillesand et al. (2008): a minimum of 50 points for each LULC type with less than 4000km2 of area and lower than 12 categories. Based on the confusion matrix, which includes both the producer's and user's accuracy, the accuracy metric was developed (Asokan & Anitha, 2019; Thakkar et al., 2017). In order to compute the user accuracy, we divided the number of correctly classified pixels in each class by the number of training set pixels per classified class, which indicates the percentage of correctly classified pixels per LULC class (Othow et al., 2017). A research study conducted by Belete et al. (2021), reported that producers' and users' low accuracy records may have been caused by the homogeneity of land cover classes at the spectral level.
The number of samples in each class was weighted to determine the overall classification accuracy for both watersheds, i.e., the sum of all samples on the diagonal divided by the total number of cells (45 + 51 + 60 + 65 + 6 + 114 + 60 + 49)/501, which is 89.8%. This result showed that in Legabora, 89.8% of LULC categories have been correctly classified, compared to Satame, where the percentage was (56 + 77 + 1 + 89 + 9 + 82 + 80 + 49)/526, or 84.2%. In total, kappa statistics of 0.83 were obtained for the classification period of 2022 images, indicating that there is 83% and 85% better agreement than would be predicted by chance alone for the Legabora and Satame watersheds, respectively, as shown in Table 4. The columns contain reference data, while the rows offer classifications produced from remotely sensed data. Bolded diagonal numbers demonstrate properly categorized sites based on reference data, whereas off-diagonals represent incorrectly classified data.
Table 4 (Inserting near here)
Note
CL; Crop land, GL = Grass land; FL = Forest land; SL = Shrub land; BL = Bare land; WL = Wetland; ST = Settlement land; WB = Water body; UA = User accuracy; PA = Producer accuracy; OAA = Overall accuracy; K = Kappa statistics; WSD = Watershed
In a study by Hassan et al. (2016), the kappa coefficient is associated with three possible groups of the covenant: the value over 0.80 shows strong agreement, the value between 0.40 and 0.80 denotes moderate covenant, and the value below 0.40 indicates poor covenant (Belete et al., 2021). Therefore, this kappa accuracy was generally regarded as reasonable for the subsequent analysis and change detection. For all LULC, as shown in Table 4, kappa statistics showed a strong correlation between the classification map and ground reference data. Finally, it was calculated following the previous study approach proposed by Tilahun (2015).
$$\text{K}= \frac{\text{N}{\sum }_{\text{i}=1}^{\text{n}}{\text{m}}_{\text{i}\text{i}}{-{\sum }_{\text{i}=1 }^{\text{n}}\left({\text{G}}_{\text{i}}{\text{C}}_{\text{i}}\right)}^{}}{{\text{N}}^{2}-{\sum }_{\text{i}=1}^{\text{n}}\left({\text{G}}_{\text{i}}{\text{C}}_{\text{i}}\right)}$$
5
…………………………………………………………………………….
Where: i denotes the class number, (N) represents the total number of classified values in comparison to truth values, (mii) is the number of values that fall into the truth class i and are also classified as values found along the diagonal of the confusion matrix, (Kløve et al.) is the sum of all predicted values belonging to class i, and (Gi ) indicates the total number of truth values in class
Spatio-temporal distributions of LULC change within the Satame and Legabora watersheds
During the 1976 study period, shrublands and grasslands were the most common land cover types, covering 32.9% and 32.4% of the Satame watershed, followed by croplands at 24.8%, the forest at 5.5%, and bare lands at the lowest percentage, respectively. Notably, settlement lands were entirely lost during this period, as per the data presented in Fig. 3. However, a shift in land cover was observed in the second study period conducted in 1991, with croplands being the dominant land use type at 37.7%, followed by grasslands at 26.7%, shrublands at 25.1%, forest lands at 3.9%, and wetlands at 3% (Fig. 3). Settlements constituted the smallest percentage of land usage on the study site during this period (Table 5).
Table 5
Spatial coverage and eight LULC classes distribution for each time phase
WSD
|
LULC
|
1976
|
1991
|
2001
|
2011
|
2022
|
(ha)
|
%
|
(ha)
|
%
|
(ha)
|
%
|
(ha)
|
%
|
(ha)
|
%
|
Satame watershed
|
ST
|
0
|
0
|
8.73
|
0.04
|
7.11
|
0.03
|
17.28
|
0.08
|
255.33
|
1.12
|
WB
|
657.08
|
2.88
|
657.54
|
2.88
|
663.03
|
2.91
|
657.54
|
2.88
|
657.54
|
2.88
|
BL
|
52.2
|
0.23
|
170.91
|
0.75
|
2.43
|
0.01
|
25.11
|
0.11
|
14.85
|
0.07
|
SL
|
7498.11
|
32.89
|
5710.14
|
25.05
|
3855.24
|
16.91
|
3034.08
|
13.31
|
1707.66
|
7.49
|
WL
|
292.6
|
1.28
|
686.7
|
3.01
|
605.43
|
2.66
|
196.2
|
0.86
|
71.1
|
0.31
|
CL
|
5656.32
|
24.81
|
8591.67
|
37.69
|
13733.19
|
60.24
|
13659.66
|
59.92
|
16904.97
|
74.15
|
GL
|
7379.12
|
32.37
|
6080.67
|
26.67
|
993.96
|
4.36
|
693.72
|
3.05
|
1080.27
|
4.74
|
FL
|
1262.02
|
5.54
|
891.09
|
3.91
|
2937.06
|
12.88
|
4513.86
|
19.79
|
2105.73
|
9.24
|
Total
|
22797.45
|
100
|
22797.45
|
100
|
22797.45
|
100
|
22797.45
|
100
|
22797.45
|
100
|
Legabora watershed
|
ST
|
0
|
0
|
0
|
0
|
0.99
|
0
|
62.84
|
0.2
|
263.79
|
0.85
|
WB
|
376.02
|
1.2
|
376.02
|
1.2
|
376.02
|
1.2
|
376.02
|
1.2
|
376.04
|
1.2
|
BL
|
274.76
|
0.88
|
1177.38
|
3.79
|
33.93
|
0.11
|
78.77
|
0.25
|
389.97
|
1.25
|
SL
|
7990.92
|
25.71
|
5549.04
|
17.9
|
3052.53
|
9.8
|
3638.36
|
11.73
|
1489.77
|
4.79
|
WL
|
0
|
0
|
0
|
0
|
230.76
|
0.74
|
62.01
|
0.19
|
43.47
|
0.15
|
CL
|
7440.92
|
23.91
|
10125.27
|
32.5
|
17424.03
|
56.1
|
17970.29
|
57.83
|
22969.25
|
73.9
|
GL
|
14266.68
|
45.9
|
12491.13
|
40.2
|
7261.81
|
23.4
|
4897.15
|
15.75
|
3097.19
|
9.97
|
FL
|
730.88
|
2.4
|
1361.34
|
4.4
|
2700.11
|
8.65
|
3994.74
|
12.85
|
2450.7
|
7.89
|
Total
|
31080.18
|
100
|
31080.18
|
100
|
31080.18
|
100
|
31080.18
|
100
|
31080.18
|
100
|
Croplands made up about 59.9% (13659.7 ha) of the stud area in 2011, followed by forests (19.8%) and shrubs (13.3%), or 3034.1 ha Fig. 4. Settlements cover the lowest amount of land area. Although wetlands and bare land accounted for the lowest proportion of the Satame watershed in the final study period (2022), approximately 74.2% of the watershed was covered by croplands, followed by forest at 9.2% and 7.5% of shrublands. In 1976, wetland and settlement lands were completely lost, and grassland made up 45.9% of the Legabora watershed, followed by shrublands (25.7%). About 73.9% of the total land area was covered by cropland during the last study period (2022) in Legabora, and the remaining share was covered by other LULC classes. (Table 5) provides an illustration of the spatial extent of LULC changes and their distribution for each time phase.
Table 5 (Inserting near here)
Figure 3 (Inserting near here)
Figure 4 (Inserting near here)
Trends and dynamics of LULC change in Satame and Legabora from 1976 to 2022
State of cropland LULC from 1976 to 2022
As elsewhere in Ethiopia, the majority of the rural populations in the Legabora and Satame watersheds depend heavily on agriculture, particularly crop cultivation. The study area underwent significant LULC changes, according to an analysis of LULC trends over the past five consecutive study periods (Table 6). The LULC trend analysis from 1991 to 2001 showed that in Satame (midland) and Legabora (highland), respectively, cropland increased at annual increasing rates of 514.2 and 729.9 ha/year at the expense of other land cover classes (Table 6). Between 2001 and 2011, the Satame LULC class also experienced a − 7.4 ha/year annual decline, but it steadily increased in Legabora (Fig. 5). Growing demand for more land for eucalyptus plantations and open-up settlements may be the cause of the decline in cropland. In the Legabora watershed, cropland has been the most prevalent LULC type over the course of the study, accounting for 23.9% in 1976 and 57.8% in 2011. Similar to this, the area covered by cropland in the Satame has steadily increased, rising from 24.8% in 1976 to 60.0% in 2011. In the final period (2022), the situation had changed, and it occupied 74.2% of the Satame and 73.9% of the Legabora watersheds, respectively, while other LULC types accounted for the remaining shares.
Table 6
Rate of LULC dynamics from 1976 to 2022 in Satame and Legabora
WSD
|
LULC
|
1976–1991
|
1991–2001
|
2001–2011
|
2011–2022
|
1976–2022
|
AC (ha)
|
RC (ha/year)
|
AC (ha)
|
RC (ha/year)
|
AC (ha)
|
RC (ha/year)
|
AC (ha)
|
RC (ha/year)
|
AC (ha)
|
RC (ha/year)
|
Satame watershed
|
ST
|
8.73
|
0.58
|
–1.62
|
–0.16
|
10.2
|
1.02
|
238.1
|
23.8
|
255.3
|
5.67
|
WB
|
0
|
0.46
|
5.5
|
0.55
|
–5.5
|
–0.55
|
0
|
0
|
0
|
0.46
|
BL
|
118.7
|
7.91
|
–168.5
|
–16.9
|
22.7
|
2.27
|
–10.3
|
–1.03
|
–37.4
|
–0.83
|
SL
|
–1788
|
–119.2
|
–1854.9
|
–185.5
|
–821.16
|
–82.1
|
–1326.4
|
–132.6
|
–5790.5
|
–128.7
|
WL
|
394.0
|
26.3
|
–81.27
|
–8.13
|
–409.23
|
–40.9
|
–125.1
|
–12.51
|
–221.6
|
–4.9
|
CL
|
2935.4
|
195.7
|
5141.5
|
514.2
|
–73.5
|
–7.4
|
3245.3
|
324.53
|
11248.7
|
249.97
|
GL
|
–1298.5
|
–86.6
|
–5086.7
|
–508.7
|
–300.2
|
–30.02
|
386.6
|
38.66
|
–6298.9
|
–139.9
|
FL
|
–370.95
|
–24.73
|
2045.97
|
204.6
|
1576.8
|
157.7
|
–2408.1
|
–240.81
|
843.7
|
18.8
|
Legabora watershed
|
ST
|
0
|
0
|
0.99
|
0.10
|
61.9
|
6.2
|
200.95
|
20.10
|
263.8
|
5.86
|
WB
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
BL
|
902.6
|
60.17
|
–1143.45
|
–114.4
|
44.8
|
4.48
|
311.2
|
31.12
|
115.2
|
2.56
|
SL
|
–2441.9
|
–162.8
|
–2496.5
|
–249.7
|
585.8
|
58.6
|
–2148.6
|
–214.7
|
–6501.2
|
–144.5
|
WL
|
0
|
0
|
230.76
|
23.08
|
–168.8
|
–16.9
|
–18.54
|
–1.85
|
43.47
|
0.97
|
CL
|
2684.4
|
178.96
|
7298.8
|
729.9
|
546.3
|
54.6
|
4998.96
|
499.90
|
15528.3
|
345.1
|
GL
|
–1775.6
|
–118.4
|
–5229.3
|
–522.9
|
–2364.7
|
–236.5
|
–1799.9
|
–179.9
|
–11169
|
–248.2
|
FL
|
630.5
|
42.03
|
1338.8
|
133.9
|
1338.8
|
133.9
|
–1544.1
|
–154.4
|
1719.8
|
38.2
|
According to the LULC classification, cropland was determined to be the most common land cover type across all evaluation periods in the Satame and Legabora watersheds. This demonstrated that in order to increase crop production, croplands were expanded and shrubs and grassland were planted instead. The need for food crops and more accessible land for settlements may also be contributing factors to this growth. According to data gathered through key informant interviews and discussions with FGDs, population pressure was what caused the expansion of croplands as well as the decrease in the amount of grassland and forestland cover. These results support earlier research by Shiferaw and Singh (2011), Siraj et al. (2018), and Hailu et al. (2020), who, respectively, reported a 65% augmentation in cropland.
Table 6 (Inserting near here)
Figure 5 (Inserting near here)
State of wetland LULC between 1976 and 2022
(Table 5) demonstrated that certain LULC classes in the Satame and Legabora watersheds experienced spatiotemporal changes. In the Satame watershed, wetland accounted for total land areas of 3%, 2.7%, 0.9%, and 0.3% in 1991, 2001, 2011, and 2022. Wetlands covered a total land area of 686.7 ha in 1991, 605.4 ha in 2001, and 192.2 ha in 2011 (Fig. 4). However, this coverage declined to 71.1 ha (0.31%) in 2022. This demonstrated that the wetland area maintained declining trends over the spatiotemporal study periods. In summary, the LULC trend analysis revealed that wetlands diminished by (–221.6 ha) between 1976 and 2022, with a percentage change of − 75.7 and an annual decreasing rate of (–4.9 ha/year) in Satame, whereas in the similar study period, wetland area demonstrated increasing trends by 43.5 ha with a percentage change of 100 and an annual increasing rate of (0.97 ha/year) in Legabora watershed, respectively (Table 6). The outcomes of Belayneh et al. (2018), who found a significant decline and complete drying up of wetlands in Ethiopia, are in direct opposition to the study results in the Legabora watershed. Likewise, Hailu et al. (2020) discovered that the area of the wetland decreased steadily from 1973 to 2019, with an average shrinking rate of 172.6 ha/year.
State of bare land LULC from 1976 to 2022
For the two study watersheds of Legabora and Satame, we created classified LULC maps as depicted in Figs. 6 and 7. However, the LULC analysis showed that the area covered by bare land in the Satame (midland) watershed steadily decreased between 1976 (52.2 ha) and 2022 (14.9 ha) over the course of the study span. But in general, the LULC findings showed that bare land decreased by − 37.4 ha in the final comparison period of the Satame watershed (1976–2022), with a percentage change of − 71.6%, and an annual decreasing rate of − 0.83 ha/year has been observed over the last 45 years. This may have been linked to the use of appropriate land management techniques and practicing water and soil conservation activities across sloppy areas, which in turn reduced soil erosion (e.g., wind and water). However, the results of the current study are consistent with a study done in the Wallecha watershed from 1984 to 2000, which showed a trend of consecutively decreasing bare land from 4.8 to 3.2% Barana et al. (2016) and Hailu et al. (2020) also reported that the area of bare land decreased from 7% in 1973 to 1.3% in 2019.
Figure 6 (Inserting near here)
Figure 7 (Inserting near here)
Status of forestland LULC from 1976 to 2022
Forest land covered 2.4%, 8.7%, and 12.9% of the Legabora watershed in 1976, 2001, and 2011, respectively. During the fourth and fifth study periods, the forest cover in this watershed showed an increasing and decreasing trend. In addition, there was also an increase in the forest cover class of the Satame from its level of 3.9% in 1991 to 12.9% in 2001 and 19.8% in 2011 (Table 5). This increase may be related to activities like soil and water conservation carried out as part of a sustainable natural resource management programme, as stated by Barana et al. (2016). When compared to its first period (1976), it also displayed declining trends during the second study period, with a net increase in forestland cover. However, in general, the LULC findings confirmed that forest land was reduced by − 370.9 ha (Fig. 8) in the initial comparison period (1976–1991) of the Satame watershed, with a percentage change of − 29.4% and an annual decreasing rate of − 24.7 ha/year. In the Legabora watershed, it also decreased between 2011 and 2022 by − 1544.1 ha, with a percentage loss of − 38.7% (Table 7) and − 154.4 ha/year annual decreasing rate. The following factors contributed to the loss of the forest and were mentioned by informants for the current study: The expansion of cropland in 1991 is related to the decline in the trend of forest cover. In addition, KIIs and FGDs explained that the military government was replaced in 1991/92, creating an open access situation that left forestlands unenforced and illegally converted to other uses (Demissie et al., 2017). Young people without farms and farmers with little farmland cut down trees for firewood and charcoal, which negatively affects the existing changes to forestland.
Table 7
LULC change in (ha) and percent for five investigation periods in Satame and Legabora
WSD
|
LULC
|
1976–1991
|
1991–2001
|
2001–2011
|
2011–2022
|
1976–2022
|
(ha)
|
(%)
|
(ha)
|
(%)
|
(ha)
|
(%)
|
(ha)
|
(%)
|
(ha)
|
(%)
|
Satame watershed
|
ST
|
+ 8.73
|
+ 873
|
–1.6
|
–18.6
|
+ 10.2
|
+ 143.04
|
+ 238.1
|
+ 1377.6
|
+ 255.3
|
+ 0
|
WB
|
+ 0
|
+ 0
|
+ 5.5
|
+ 0.8
|
–5.5
|
–0.83
|
+ 0
|
+ 0
|
+ 0
|
+ 0
|
BL
|
+ 118.71
|
+ 227.4
|
–168.5
|
–98.6
|
+ 22.7
|
+ 933.3
|
–10.26
|
–40.86
|
–37.4
|
–71.6
|
SL
|
–1788
|
–23.9
|
–1854.9
|
–32.5
|
–821.2
|
–21.29
|
–1326.4
|
–43.72
|
–5790.5
|
–77.2
|
WL
|
+ 394.02
|
+ 134.6
|
–81.3
|
–11.8
|
–409.2
|
–67.59
|
–125.1
|
–63.8
|
–221.6
|
–75.7
|
CL
|
+ 2935.4
|
+ 51.9
|
+ 5141.5
|
+ 59.8
|
–73.5
|
–0.54
|
+ 3245.3
|
+ 23.8
|
+ 11248.7
|
+ 198.9
|
GL
|
–1298.5
|
–17.6
|
–5086.7
|
–83.7
|
–300.2
|
–30.21
|
+ 386.6
|
+ 55.7
|
–6298.9
|
–85.4
|
FL
|
–370.9
|
–29.4
|
+ 2045.97
|
+ 229.6
|
+ 1576.8
|
+ 53.69
|
–2408.1
|
–53.4
|
+ 843.7
|
+ 66.9
|
Legabora watershed
|
ST
|
+ 0
|
+ 0
|
+ 0.99
|
+ 0
|
+ 61.85
|
+ 6247.5
|
+ 200.95
|
+ 319.8
|
+ 263.8
|
+ 100
|
WB
|
+ 0
|
0
|
+ 0
|
+ 0
|
+ 0
|
+ 0
|
+ 0
|
+ 0
|
+ 0
|
+ 0
|
BL
|
+ 902.62
|
+ 328.51
|
–1143.45
|
–97.1
|
+ 44.8
|
+ 132.2
|
+ 311.2
|
+ 395.1
|
+ 115.2
|
+ 29.54
|
SL
|
–2441.88
|
–30.56
|
–2496.51
|
–44.9
|
+ 585.8
|
+ 19.2
|
–2148.6
|
–59.1
|
–6501.2
|
-436.37
|
WL
|
+ 0
|
+ 0
|
+ 230.8
|
+ 0
|
–168.8
|
–73.1
|
–18.5
|
–29.9
|
+ 43.5
|
+ 100
|
CL
|
+ 2684.4
|
+ 30.02
|
+ 7298.8
|
+ 72.1
|
+ 546.3
|
+ 3.14
|
+ 4998.9
|
+ 27.8
|
+ 15528.3
|
+ 67.6
|
GL
|
–1775.6
|
–12.45
|
–5229.3
|
–41.8
|
–2364.7
|
–32.6
|
–1799.9
|
–36.8
|
–11169.5
|
–360.63
|
FL
|
+ 630.5
|
+ 86.3
|
+ 1338.8
|
+ 98.3
|
+ 1338.8
|
+ 49.6
|
–1544
|
–38.7
|
+ 1719.8
|
+ 70.18
|
Additionally, the 1990s civil war and the extraction of local building materials and fuel wood contributed to the degradation of forestland. Moreover, the expansion of cropland and the 1985–1986 famine caused a decline in forest cover, leading to families extracting resources from their surroundings. Furthermore, the LULC analysis showed that between 1976 and 2022, in the Satame and Legabora watersheds, respectively, the forest cover of the study landscape increased at an annual rate of 18.8 and 38.2 ha/year (Fig. 5). Similar to the current study, Andualem et al. (2018) reported that the forest LULC increased by 1.46% between 2007 and 2018. In a similar vein, Gebrelibanos and Assen (2013), verified that the amount of forest cover increased steadily between 1964 and 2006. Unlike the current study, WoldeYohannes et al. (2018) found that between 1985 and 2010, the amount of forest land decreased by 1.71 ha/year. Likewise, Hassen and Assen (2017), reported that the area covered by forests decreased by 23.1% between 2004 and 2014. According to Agidew and Singh (2017), the amount of forest land in northeastern Ethiopia has decreased. As a result, the findings showed that between 1976 and 2022, the forest land in both study watersheds increased at rates of 18.8 and 32.2 ha/year, respectively. FGDs discussants noted that the eucalyptus tree plantation has contributed to the increase in forestland cover due to its importance for building materials and fuel wood, as well as the income generation of local communities.
State of Grassland LULC between 1976 and 2022
In Satame, grassland covered a total area of 7379.1 ha (32.4%) in 1976, 6080.7 ha (26.7%) in 1991, 993.9 ha (4.4%) in 2001, and 693.7 ha (3.1%) in 2011, respectively (Figs. 3 and 4), while between 1976 and 1991, grassland was the dominant LULC, making up 45.9% and 40.2% of the total land area in the Legabora watershed, respectively. According to the current LULC change analysis, grasslands in Satame showed a significant decline by (–1298.5 ha) with a percentage change of − 17.6% (Table 7; Fig. 8), and an annual decreasing rate of − 86.6 ha/year between 1976 and 1991, and by (–6298.9 ha) with an annual shrinking rate of − 139.9 ha/year in the final comparison period, respectively. This LULC class showed a shrinking trend of (–1775.6 ha) with a percentage loss of (–12.5%) and an annual decreasing rate of − 118.4 ha/year in Lagabora’s first comparison period, whereas in the second and third comparison periods, it displayed a similar trend of − 5229.3 and − 2364.7 ha with an annual decreasing rate of − 552.9 and − 236.5 ha/year, respectively (Table 6). Satellite data, which shows a continuous decrease over the study period and is linked to recurrent fires that happen during the dry season and the expansion of farming activities, is supported by FGDs and key informant interviews.
Furthermore, according to responses from the local community gathered through interviews and focus groups, a rise in the demand for agricultural production on already-existing land and the construction of new homes in the study landscape may have contributed to the loss of grassland. The FGDs discussants in the interview session agreed that growing populations have increased demand for food, building materials, and timber, which has caused agricultural land to spread into mountainous and hilly areas, which in turn has resulted in the obliteration of shrub and bush land ecosystems. As a result, the current study revealed that settlement and the conversion of grassland to croplands are frequent occurrences in the study landscape. Abate (2011), reported that grasslands declined by 73 ha/year between 1972 and 1985. Agidew and Singh (2017), stated that in northeastern Ethiopia, between 1973 and 2015, there was a decline in grassland. Bekele et al. (2018), reported that the amount of grassland in the Awash River Basin progressively decreased from 1985 to 2011.
Figure 8 (Inserting near here)
State of shrub LULC from 1976 to 2022
When compared to the other LULC classes in the Satame watershed, which made up 3855.2 ha (16.9%) and 3034.1 ha (13.3%) between the third and fourth periods, shrub land had the second and third highest percentage cover, respectively, as depicted in Figs. 6 and 7. On the other hand, shrublands steadily decreased in the third comparison period, with a percentage change of − 21.3% and an annual shrinking rate of − 82.1 ha/year. According to the current LULC change investigation, shrublands in the Legabora watershed significantly decreased by − 2441.9 ha with a percentage change of − 30.6% (Fig. 9) and an annual decreasing rate of − 162.8 ha/year between 1976 and 1991; however, it increased by 585.8 ha with a percentage change of 19.2% and an annual increasing rate of 58.6 ha/year, respectively, in the third comparison period (2001–2011). Hence, the results indicated that over the past 45 years, the shrublands in the Satame and Legabora watersheds declined at rates of − 128.7 and − 144.5 ha/year, respectively. This may be caused by the fact that they serve as the local communities' primary sources of building materials and firewood, as well as by the expansion of cropland and settlement areas at the expense of shrublands. In the discussion session, FGDs discussants confirmed that charcoal sales contribute to the destruction of shrublands, bushlands, and forests in rural poor communities as a means of generating additional revenue. This result is consistent with a number of earlier studies conducted in different areas of the country. For example, according to Angessa et al. (2019), the Lake Wanchi watershed's shrub land has vanished at a rate of 1.3% per year. According to Agidew and Singh (2017), between 1973 and 2015, the percentage of shrublands decreased from 28.4–24.6%. Amare (2015), came up with comparable results that described the decline of bush land cover. Mikias (2015), claimed that between 1973 and 2010, shrub land increased at a rate of 22.08 ha/year, which is in contrast to the findings of the present study.
State of settlement LULC from 1976 to 2022
In the initial comparison period for Satame as well as for Legabora between 1976 and 1991, there was almost no settlement cover. In the Satame watershed, the percentage of land that falls under this class over the course of the various study periods was 8.7 ha (0.04%) in 1991, 17.3 ha (0.08%) in 2011, and quickly increased to 255.3 ha (1.1%) of the total land area in 2022. In the Legabora watershed, the settlement's size increased from 0% in 1976 and 1991 to 0.2% in 2011 and then augmented to 0.9% in 2022 (Table 5). Based on the current investigation of the LULC change, settlement land indicated a slight increase of 8.7 ha with a percentage change of (873%) and an annual increasing rate of 0.58 ha/year in the initial comparison period, while in the third period (2001–2011), it was augmented by 10.2 ha with a percentage of 143% (Fig. 9) and an annual increasing rate of 1.02 ha/year, respectively, in the Satame watershed, similarly, between 2001 and 2011, Legabora showed an increasing trend of 61.9 ha with a percentage change of 6247.5% and an annual increasing rate of 6.2 ha/year. However, in the fourth and fifth comparison periods, the trend intensified by 200.9 and 263.8 ha with percentage changes of 319.8% (Fig. 9) and 100% and annual increasing rates of 20.1 and 5.9 ha/year, respectively. In this study, we found that between 1976 and 2022, settlement land in the Satame and Legabora watersheds steadily increased at rates of 5.7 and 5.9 ha/year, respectively. The increase in settlement might be attributed to residential growth and the occupancy of public lands by settlers. Additionally, the expansion of settlements onto other lands may have been influenced by population growth. According to Miheretu and Yimer (2017), in the Gelana sub-watershed, settlement areas grew between 1964 and 2014.
Table 7 (Inserting near here)
Figure 9 (Inserting near here)
LULC change matrix in the Satame and Legabora watersheds for five investigation periods
To ascertain a loss and gain in the land size of the main LULC classes, the LULC conversion matrices were examined. Table 8 provides a summary of the findings from the analysis between 1976 and 2022. All of the land areas in the study watersheds have experienced significant changes (both gains and losses), though the magnitude of each LULC class change has varied. The results showed that between 1976 and 2022 there were significant LULC dynamics in which (52 ha) of bare cover, (1094) of forestland, (5656) of cropland, (7498) of shrub lands, (7179) of grasslands, water bodies (1099), and (293 ha) of wetlands were transformed one to another in Satame, respectively, whereas (262) of bare cover, (630) water bodies, (14220) grassland, and (7946) of shrublands were transformed one to another in Legabora, respectively. In Satame, the shrublands, which covered 6693 ha in 1976, decreased to 1698 ha in 2022, whereas Legabora, which covered 7263 ha in 1976, decreased to 1463 ha in 2022. It was taken from one land use category and given to another, then lost to another land use type. As a result, Satame and Legabora had unchanged coverage of 805 and 683 ha, respectively. It gained 321, 399, 98, and 31 ha from cropland, grassland, forestland, and wetland in Satame, respectively. Similar to this, its original coverage was changed to cropland, grassland, forestland, and settlement with an area of 5386, 172, 903, and 71 ha, respectively (Table 8). The majority of the 89.3% altered shrub cover (71.8%) was transformed into cropland, followed by the conversion of forestland and grassland, each at 12% and 2.3%, respectively. In the Satame watershed, the forest cover has been replaced by cropland (634 ha), shrublands (98 ha), and grassland (31ha) over the past 45 years. In Satame, grasslands of 351, shrublands of 321, and forestlands of 170 ha were transformed into cropland, whereas in Legabora watersheds, grassland, bare land, shrublands, and forestlands were transformed into cropland by 379, 238, 67, and 49 ha, respectively.
Table 8
illustrates the overall gain and losses in LULC classes in between 1976 and 2022
|
LULC
|
WSD
|
LULC change from the initial year 1976 (ha)
|
ST
|
BL
|
WB
|
CL
|
WL
|
GL
|
SL
|
FL
|
Row
|
Loss
|
LULC to final yr. 2022 (ha) LULC to final yr. 2022 (ha)
|
ST
|
Satame Watershed
|
0
|
0
|
0
|
111
|
0
|
63
|
71
|
14
|
260
|
260
|
BL
|
0
|
0
|
1
|
8
|
0
|
4
|
1
|
0
|
14
|
14
|
WB
|
0
|
0
|
542
|
18
|
3
|
64
|
47
|
14
|
688
|
146
|
CL
|
0
|
44
|
40
|
4627
|
160
|
5491
|
5386
|
634
|
16742
|
12115
|
WL
|
0
|
1
|
1
|
14
|
4
|
25
|
20
|
3
|
67
|
63
|
GL
|
0
|
5
|
36
|
351
|
69
|
40
|
172
|
31
|
1063
|
1023
|
SL
|
0
|
1
|
43
|
321
|
31
|
399
|
805
|
98
|
1698
|
893
|
FL
|
0
|
1
|
76
|
170
|
22
|
619
|
903
|
288
|
2079
|
1791
|
Column T
|
0
|
52
|
1099
|
5656
|
293
|
7179
|
7498
|
1094
|
0
|
|
Gain
|
0
|
52
|
557
|
1029
|
289
|
7139
|
6693
|
806
|
–
|
–
|
NC
|
–260
|
38
|
411
|
–11086
|
226
|
6116
|
5800
|
–985
|
–
|
–
|
NP
|
0
|
0
|
1
|
–2.39
|
56.50
|
152.90
|
7.2
|
–3.42
|
–
|
–
|
ST
|
Legabora watershed
|
0
|
4
|
0
|
4
|
0
|
103
|
137
|
8
|
256
|
256
|
BL
|
0
|
1
|
9
|
238
|
0
|
131
|
6
|
0
|
385
|
384
|
WB
|
0
|
0
|
300
|
0
|
0
|
0
|
0
|
0
|
300
|
0
|
CL
|
0
|
195
|
216
|
6555
|
0
|
10436
|
5296
|
327
|
23025
|
16470
|
WL
|
0
|
0
|
2
|
12
|
0
|
23
|
10
|
0
|
47
|
47
|
GL
|
0
|
42
|
69
|
379
|
0
|
1993
|
628
|
9
|
3119
|
1126
|
SL
|
0
|
6
|
17
|
67
|
0
|
652
|
683
|
37
|
1463
|
780
|
FL
|
0
|
14
|
17
|
49
|
0
|
882
|
1186
|
311
|
2460
|
2149
|
Column T
|
0
|
262
|
630
|
7304
|
0
|
14220
|
7946
|
692
|
0
|
|
Gain
|
0
|
261
|
330
|
749
|
0
|
12227
|
7263
|
381
|
–
|
–
|
NC
|
–256
|
–123
|
330
|
–15721
|
–47
|
11101
|
6483
|
–1768
|
–
|
–
|
NP
|
–256
|
–124
|
1.1
|
–2.39
|
0
|
5.57
|
5800
|
–5.68
|
–
|
–
|
The conversion matrix analysis showed that there were also significant gains to the forest (806 and 382) from other LULC classes, but the gains from crop cover (634 and 327 ha) and shrublands (98 and 37 ha), respectively, were highest in Satame and Legabora. Table 8 shows the total increase and decrease in LULC classes between 1976 and 2022. In Satame, the analysis of LULC change over the final comparison period (1976–2022) revealed a rise in the area covered by the settlement, cropland, and forest cover, while it revealed a decline in the area covered by bare land, shrub cover, wetland, and grass cover (Table 6). For settlement, cropland, and forest cover during the same time period, the annual rate change (increment) was 5.7, 249.9, and 18.8 ha/year, respectively. The Legabora watershed showed a trend towards an increasing tendency for settlement, bare land, wetland, cropland, and forest cover between 1976 and 2022, but a trend towards a decreasing tendency for shrublands and grassland cover. In Satame, cropland had been gained from other LULC categories; the largest gain came from grassland, followed by shrub, forest, and wetland, with extents of 5491, 5386, 634, and 160 ha, respectively (Table 8). Between 1976 and 2022, crop cover in the Legabora watershed expanded by 10436, 5296, 327, 216, and 195 ha, respectively, from other LULC classes, which include grassland, shrublands, forestland, wetland, and bare cover.
Table 8 (Inserting near here)
Note
Those figures in bold are the sum of diagonals and represent overall persistence (i.e., the landscape that did not change). The NP symbolizes the net change to persistence ratio (i.e., the net change versus the diagonals for each class). Where net change, loss, gain, and Net persistence is calculated using the equations given below.
$$\text{N}\text{e}\text{t} \text{P}\text{e}\text{r}\text{s}\text{i}\text{s}\text{t}\text{e}\text{n}\text{c}\text{e}= \frac{\text{N}\text{e}\text{t} \text{c}\text{h}\text{a}\text{n}\text{g}\text{e} }{\text{D}\text{i}\text{a}\text{g}\text{o}\text{n}\text{a}\text{l}\text{s} \text{o}\text{f} \text{e}\text{a}\text{c}\text{h} \text{c}\text{l}\text{a}\text{s}\text{s}}$$
6
…………………………………...………………………….
$$Net change=Gain-Loss$$
7
…………………………………………………………………………….
$$Loss=Row total-Diagonals of each class \left(unchanged\right)$$
8
………………………………………
$$Gain=Column total-Diagonals of each class\left(unchanged\right)$$
9
……………………………………
Between 1976 and 2022, in the Legabora watershed, settlement experienced a larger negative net change to persistence ratio, while shrublands, grassland, and wetland showed positive ratios; moreover, forestland, bare land, and cropland had negative ratios as well, representing the dominant trends in the study area. The net change-to persistence ratio was closer to zero for the other land use and land cover types, indicating that they were more likely to persist rather than decrease or increase. These findings are summarized in Table 8. Across the entire landscape, a total of 6,306 ha (i.e., the sum of diagonal elements) did not change during the period covered by the study. The largest net increase in the Satame watershed occurred in the grassland cover class, which was mainly converted from cropland and forestland. Similarly, in Legabora, grassland saw the highest net increase, primarily from cropland and forestland. According to the results, between 1976 and 2022, the net change to persistence ratio was greater for forest (negative), grasslands (positive), cropland (negative), wetland (positive), and shrub land (positive) in the Satame watershed, respectively. The study also found that a total of 9843 ha of land remained unchanged throughout the entire Legabora watershed during the same period, as shown in Table 8.
LULC change and their drivers in Satame and Legabora watershed
We gathered data from KIIs and focus groups about the various factors that influence LULC changes as well as local residents' opinions of the LULC changes adopted by references (Mariye et al., 2022b). According to the summary results of the KIIs, field observations, preference ratings, and FGDs, LULC changes in the Satame and Legabora watersheds were found to be primarily caused by proximate and underlying drivers (Munthali et al., 2019). The informants identified a total of nine factors as the primary influences of LULC changes in the Satame and Legabora watersheds of south-central Ethiopia (Fig. 10). On the other hand, there were variations in each of the elements that the local community saw as being responsible for LULC changes (Angessa et al., 2019). Here, the primary proximate (direct) drivers of LULC change in the study site were identified as infrastructure development, settlement expansion, charcoal production, and agricultural expansions. However, the underlying (indirect) drivers for the observed LULC change in the study landscape were viewed as poverty, land-related policy, population growth, and community conflicts (Fig. 10). The majority of FGD participants identified population growth, agricultural expansion, settlement, charcoal production, and forest fire as the main proximate (direct) drivers of deforestation in the Satame and Legabora watersheds (Angessa et al., 2019). In order to expand cropland, the discussants and KIIs also identified fire as a crucial primary tool for cleaning forests (Betru et al., 2019). According to the LULC change analysis, crop land has grown significantly in the study area over the past 45 years (1976–2022). The major ranking order of the observed LULC change drivers are summarized in Fig. 10. The top five drivers of LULC changes in the Legabora watershed were perceived to be poverty, infrastructure development, agricultural expansion, and settlement expansion, with population growth coming in first and agricultural expansions second, respectively (Munthali et al., 2019). However, in the Satame watershed, agricultural expansion and population growth were ranked first and second, respectively, in terms of the main LULC drivers, followed by settlement expansion, wood extraction, and poverty (Fig. 10). Similar findings came up in KIIs and FGDs, where it was determined that population growth, settlement, and agricultural expansion were the main factors contributing to the LULC change in the study site. Key informants and FGDs agreed that early marriage, high birth rates, and low mortality were the main causes of the Satame and Legabora watersheds' rapid population growth.
Figure 10 (Inserting near hear)
Most local communities overwhelmingly believed that population growth accelerated during the study span. To corroborate local community population growth observations, the population data between 1981 and 2022 was estimated (Munthali et al., 2019). The populations of the Satame and Legabora watersheds were increased from 96,348 to 265,643 and from 82,143 to 295,643 (Fig. 11), respectively (CSA, 2007; KTARDO, 2019). Indeed, the population growth of the Satame and Legabora watersheds has been augmented by 275.7% and 359.8% between 1981 and 2022 (Munthali et al., 2019). The population disclosed an escalating tendency and became more uniform at the Legabora watershed during the entire study span (1981–2022). The growth was trustworthy and positively linked with cropland expansion between similar study spans (Fig. 11). Compared to the previous watershed, the population growth rate at the Satame watershed was more or less uneven between the similar study times. The population growth rate exhibited declining trends from 2001 to 2007, but after 2010, when cropland did not significantly change, the growth trend changed and revealed increasing trends (Fig. 11). Prior research also identified population growth as one of the main forces behind LULC changes (Bewket, 2002). Some research studies conducted in Ethiopia found population growth as major driver of LULC changes adopted by references Poverty is one of the significant observed factors that is causing LULC changes in the Satame and Legabora watersheds. Many watershed societies are unable to purchase agricultural inputs due to their extreme poverty and lack of financial resources. Because of their extreme poverty, watershed communities in south-central Ethiopia are also forced to clear forest land for additional farmland or to sustain their lives, as adopted by references (Munthali et al., 2019).
In the absence of well-organized economic policies, unsustainable use of natural resources such as land, water, and forests leads to severe environmental difficulties, including biodiversity loss, soil wearing away, deforestation, and forest cover degradation (Munthali et al., 2019). The findings of this study are consistent with other studies conducted in Africa that report high poverty as an underlying factor for LULC alterations (Haller et al., 2008; Kindu et al., 2015). Regarding land tenure policy, the military government of Ethiopia announced the nationalization of all rural land, abolishing private and public property rights, and granting all land use rights (Meshesha et al., 2014). During the FGDs, the elders explained that the land reform of 1975 changed the land system by nationalizing all rural land, turning "cultivators into landlords". This situation provides fertile ground for the expansion of cropland to other LULC types in the watershed (Angessa et al., 2019). This policy makes the state the sole owner of property and land-related resources, making it impossible for the state to monitor and enforce regulations. Key informants and FGDs discussants provided information that most land policies and strategies failed because they were not properly implemented and integrated (Fig. 10). Due to poor land management, forested areas have been converted to settlements and agricultural land and are severely degraded (Meshesha et al., 2014). Studies conducted by Bewket and Abebe (2013), Degife et al. (2018), documented the issue of land tenure as an important indirect driver of LULC changes in diverse highland watersheds in Ethiopia.
The focus group discussants and key informants remarked that conversion of various land use categories to cropland is a relatively easy process. For instance, in Ethiopia, farmers can enjoy more legal rights to land by converting forests to arable land since the law states that forests are state-owned. Discussions with local elders and natural resource management professionals revealed that several impoverished households in the study watershed rely heavily on the sale of firewood and charcoal for their survival tactics (Degife et al., 2018; Kindu et al., 2015). This dependence on woody plants is also seen in other rural areas of Ethiopia, where certain plants are cultivated for both domestic use and income generation. Similar observations have been made in other regions of the country, as documented in several studies (Degife et al., 2018; Kindu et al., 2015; Mezgebu & Workineh, 2017).
Figure 11 (Inserting near hear)
Consequences of LULC change perceived by local community
According to the discussants in the FGDs, the changes in land use and land cover (LULC) had various consequences, such as deforestation (94%, 82%), soil erosion and land degradation (92%, 76%), shortage of livestock fodder (90%, 90%), loss of biodiversity (84%, 96%), the decline in production (76%, 80%), decline in water resources (72%, 94%), and local climate change (58%, 62%) in the Legabora and Satame watersheds, respectively (Fig. 12). The current demographic changes and the continued variation in LULC, coupled with uncertain climate conditions, significantly affect livelihoods and put the farmer’s production system under pressure. Our filed observations, FGDs, and KIIs also marked that some native trees, which were used for house construction and are highly valuable medicinal plants, are in danger, like Prunes Africana, Podocarpus falcatus, and Cordia Africana. The study demonstrates that bushlands and shrublands have been extensively degraded and replaced by settlements and croplands over the past four and a half decades. This implies that there is a possibility that both flora and fauna may be at risk, but we were unable to estimate their extent. A decrease in plant biodiversity contributes to deterioration in the sustainability of the environment and the loss of the genetic resources of plants. As a result, economic and medicinal values will be lost (Bewket, 2002). A significant majority of survey respondents in Legabora and Satame, specifically (84%, 96%), reported a decline in plant biodiversity, which included the loss of valuable woody species and medicinal plants, which was consistent with a study done by Belete et al. (2021).
Furthermore, 94% of FGDs discussants indicated that the study area experienced a shift in household energy use from fuel wood to crop residue, cow dung, and eucalyptus plantations due to deforestation (Fig. 12). Prior to 25 years ago, 94 percent of households used natural forests and shrublands as a source of energy, but today only a small number of them have access to these areas to gather wood for cooking and heating. Female participants in the focus group discussions explained that in the past, when the women collected fuel wood from the natural forest, they had opportunities for social interaction, informal communication with their friends, and discussion of social issues. Since they no longer have this means of communication, 94% of respondents now rate deforestation as a disadvantage (Fig. 12). In the interview sessions, 72% of survey respondents indicated that the nearby water sources have dried up, and climate change is blamed for the drying of small brooks and springs. Women are forced to travel long distances to fetch water for household consumption (Fig. 12). To get to water sources for drinking, male farmers in the present day must transport their livestock over long distances. The major LULC changes observed at the Satame and Legabora watersheds were the remarkable expansion of cropland at the expense of existing natural resources, such as grassland and shrubs (Table 8). In the Satame and Legabora watersheds, a significant amount of grassland and shrublands has been converted to cropland (5491, 538 ha of grassland and 10436, 5296 ha of shrublands converted to cropland between 1976 and 2022) (Table 8). This will have a negative impact on the current free grazing system, and, ultimately, the community will have to reduce its livestock population, which will have a detrimental effect on household income and the consumption of livestock products.
Figure 12 (Inserting near here)
According to data from field research and KIIs, the public grassland decreased as agriculture was expanded on communal grazing lands. As a result, a small plot of land is frequently used to graze an excessive number of livestock, which may contribute to environmental degradation. A similar effect was reported by Desalegn et al. (2014), in the highlands of Ethiopia, where they noted that the lack of livestock fodder posed a significant problem. In the study area, 92% of the survey respondents stated that the local area was exposed to high soil erosion and degradation (Fig. 12). On damaged soils, plant growth is poor, which intensifies the issue of eroding soil. The naturally occurring vegetation that covered the study watershed has been severely reduced, and it has been replaced by settlements and farmland. Consequently, the area of land that is more susceptible to soil erosion has grown over time, but this study was unable to quantify it. FGDs and key informants stated that soil wearing away and the associated soil fertility problem were significant consequences for the decline of agricultural production, mainly in the upper part of the Satame and Legabora watersheds respectively (Mariye et al., 2022a). FGDs and KIIs also marked that the area was primarily comprised of forest, grasslands, and that many different wild animals, such as tigers, elephants, warthogs, and buffalo. However, it is now difficult to find animals like buffalo because the forests have been cleared and the rate of deforestation has increased. During the FGDs, 76% of respondents explained that in the past, farmers had produced adequate yields. However, they are currently losing some of their farms as the land becomes less fertile and they do not get enough yields. Moreover, 76% of survey respondents said that the agricultural sector is less profitable because of the area's high exposure to soil erosion and land degradation (Fig. 12).