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transcript
1SWALIM Workshop 12-13 June, Nairobi
Monitoring Land Cover Dynamics in sub-Saharan Africa
H.D. Eva, A. Brink and D. Simonetti
2SWALIM Workshop 12-13 June, Nairobi
Outline
• Introduction
• Method
• Results
• Discussion
• The future
3SWALIM Workshop 12-13 June, Nairobi
Monitoring Natural Ressources for Development Cooperation (MONDE)
• Land– Land cover change, land availability, pressure, degradation,
phenology, fires• Forest
– Deforestation, logging, sustainable management• Biodiversity
– Protected areas, specific ecosystems• Fresh water
– Inland water quality, surface water availability in dry areas• Coastal areas and marine resources
– Fish resources, sensitive ecosystems, coastal pressure• Urban areas
– Environmental degradation around cities, urban growth
Introduction
4SWALIM Workshop 12-13 June, Nairobi
Key Questions - Thematic
• What have been the main land cover changes in sub-Saharan Africa over the last 25 years?
• What are the main drivers and pressures that have affected sub-Saharan Africa?
• What impacts do such land cover changes have?
Introduction
5SWALIM Workshop 12-13 June, Nairobi
Key Questions - Method
• Test the suitability of Remote Sensing data from different sources (i.e. MSS and TM) for detecting both spatial and thematic changes
• Test the sampling scheme
Introduction
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Methodology
• Sample of high (30-80m) resolution satellite data from the 1970’s (MSS), the 1980’s(TM) and 2000 (TM)
• Sample stratification by using the White eco-regions
• 57 samples subdivided into 511 sub-samples, resulting in 1% coverage of the area
• Land cover change assessment of 4 key classes:
– Agriculture– Forest– Natural non forest vegetation– Barren– (water)
• Extrapolation of the results by direct expansion to eco-region and full sub-Saharan level
Method
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Stratification and Sampling
Method
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Sampling and Classification
• From each sample site 9 (20 by 20 km) boxes are extracted and independently classified using unsupervised clustering
• Classes regrouped into
– Forest
– Non Forest Natural Vegetation
– Agriculture
– Barren
– (Water)
• Class identification carried out by expert knowledge with aid from existing maps,Africover (FAO), other ancillary data and Google Earth
Method
9SWALIM Workshop 12-13 June, Nairobi
Forest Cover Change in Madagascar
Method
1975 2000
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SWALIM Workshop 12-13 June, Nairobi
Agriculture expansion on Somalia
Method
1975 2000
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SWALIM Workshop 12-13 June, Nairobi
Irrigated Agriculture in Sudan
Method
20001975
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SWALIM Workshop 12-13 June, Nairobi
Land Abandonment in Angola
Method
20001975
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SWALIM Workshop 12-13 June, Nairobi
Results
• Sub-Saharan Africa’s land cover in the year 2000
• Land cover changes for Sub-Saharan Africa – 1975 to 2000
• Potential impacts
Results
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SWALIM Workshop 12-13 June, Nairobi
Sub-Saharan Africa’s land cover in the year 2000
17.3 18.8
60.8
2.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
Agriculture Forest NF vegetation Barren
land cover class
%
Results
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SWALIM Workshop 12-13 June, Nairobi
Distribution of land cover (%) by ecoregion for the year 2000
-
10.0
20.0
30.0
40.0
50.0
60.0
70.0
eco-region
%
Agriculture
Forest
NF veg.
Barren
Results
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SWALIM Workshop 12-13 June, Nairobi
Proportion of land cover (%) within each ecoregion for the year 2000
-
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
eco-region
%
Agriculture
Forest
NF veg.Barren
Results
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SWALIM Workshop 12-13 June, Nairobi
Land cover changes for Sub-Saharan Africa – 1975 to 2000
123,413
(71,325)
(58,894)
6,565
(100,000)
(50,000)
-
50,000
100,000
150,000
Agriculture Forest NF veg. Barren
land cover class
tota
l ch
an
ge (
000 h
a)
T(%)C: +57
AAC: 4,937
AA(%)C: 2.3
T(%)C: -16
AAC: -2,853
AA(%)C: -0.7
T(%)C: -5
AAC: -2,356
AA(%)C: -0.2
T(%)C: +15
AAC: 263
AA(%)C: 0.6
Results
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SWALIM Workshop 12-13 June, Nairobi
Loss of Natural Vegetation
-70.0
-60.0
-50.0
-40.0
-30.0
-20.0
-10.0
0.0
10.0
20.0
GUIN
EO-CO
NGOLI
AN
ZAMBEZIA
N
SUDANIAN
SOM
ALIA-M
ASAI
KAROO-N
AMIB
AFROM
ONTANE
GUIN
EA-CONG
OLIA/Z
AMBEZIA
GUIN
EA-CONG
OLIA/S
UDANIA
ZANZIBAR-T
ONGO-C
OAST
KALAHARI-H
IGHVELD
SAHEL
MADAGASCAR
eco-region
% o
f th
e 19
75 la
nd
co
ver
Forest
NF Veg.
Results
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SWALIM Workshop 12-13 June, Nairobi
Available Land after Agro-Ecological Zoning
0
20
40
60
80
100
120
140
160
eco-region
%
% suitable area
% suitable land used
Results
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SWALIM Workshop 12-13 June, Nairobi
Methodological Problems
• The images
– MSS – TM use different path/row system(WRS1/WRS2). This often requires mosaicing of MSS images
– Geo-referencing problems between MSS and TM
– The capacity to extract changes between MSS and TM is severely compromised by noise, spatial resolution, spectral resolution and seasonal differences
Discussion
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SWALIM Workshop 12-13 June, Nairobi
Methodological Problems
• MSS – TM - Difference in Spatial resolution
TM resolution vs. TM degraded to MSS resolution
R2 = 0.9888
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 5000 10000 15000 20000 25000 30000 35000 40000 45000
ha
ha Series1
Linear (Series1)
Discussion
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SWALIM Workshop 12-13 June, Nairobi
Methodological Problems
• The Sampling
– Stratification by eco-regions not ideal
– 1% sample is probably too low
Discussion
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SWALIM Workshop 12-13 June, Nairobi
Methodological Problems
• Classification and Visual Interpretation
– Unsupervised classification and manual class identification is time consuming and needs expert knowledge
Discussion
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SWALIM Workshop 12-13 June, Nairobi
Discussion
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SWALIM Workshop 12-13 June, Nairobi
2007 and Future
The future
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SWALIM Workshop 12-13 June, Nairobi
2007 and Future
• Senegal – Sampling• 68 Samples
The future
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SWALIM Workshop 12-13 June, Nairobi
2007 and Future
• Tanzania – Sampling• 310 Samples
The future