Vegetation Change in North Africa through the analysis of satellite data, 1982 - 2006
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Transcript of Vegetation Change in North Africa through the analysis of satellite data, 1982 - 2006
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Vegetation Change in North Africa through the analysis of satellite data,
1982 - 2006
Professor Stephen Young
Department of Geography, Salem State College
IGC - 2008, Tunis, Tunisia – August 13, 2008
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Vegetation Change in North Africa
OUTLINE
Why this research?
Overview of Data Set & Methodology used.
Overview of where land cover change is occurring.
Overview of persistent vegetation change.
Overview of the Driving Forces behind the changes.
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Vegetation Change in North Africa
Why this research?
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Global Vegetation Change From 1982/83 to 1998/99
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Why this research?
Have already mapped vegetation change at the global scale and now focusing on the regional scale.
Have researched Australia, East Asia, South Asia, and Southwest Asia – now looking at North Africa.
Looking for strong temporal signals of PERSISTENT vegetation change.
Trying to understand those signals in context with global environmental change.
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Why this research?
In particular
Colleagues at this conference may be able to help me understand the vegetation changes which are occurring in North Africa.
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Data Used
GIMMS AVHRR land cover data NOAA / NASA AVHRR data – 8 km resolution
Coarse resolution picks up broad change
Normalized Difference Vegetation Index (NDVI)
(NIR - red) / (NIR + red) High correlation with photosynthesis
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Data Pre-Processing
GIMMS AVHRR data Base data: NDVI 15-day MVC
Re-composited: Monthly Max Composites, January 1982 – December 2003
Re-composited: Annual Average Composites
Re-composited endpoints (1982 + 1983) ÷ 2 = 1982/83 (2002 + 2003) ÷ 2 = 2002/03
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Global Scale NDVI GIMMS dataAnnual Average 1987
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Desert Pixels & All Global Land Pixels
-2
-1
0
1
2
3
4
5
6
82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 0 1 2 3
Years
Perc
ent
Global Land Cover Sahara 2Linear (Global Land Cover) Linear (Sahara 2)
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Data Used
SPOT VEGETATION data (1km) SPOT IMAGE – 1 km resolution
Finer resolution than GIMMS
Normalized Difference Vegetation Index (NDVI) (NIR - red) / (NIR + red) High correlation with photosynthesis
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Data Pre-Processing
SPOT VEGETATION data Base data: NDVI 10-day MVC
Re-composited: Monthly Max Composites, April 1998 – Dec 2006
Re-composited: Annual Average Composites 1998 used Jan, Feb, March of 1999
Re-composited endpoints (1998 + 1999) ÷ 2 = 1998/99 (2005 + 2006) ÷ 2 = 2005/06
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SPOT VEGETATION NDVI Annual Average 2001
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SPOT VEGETATION
0
20
40
60
80
100
120
140
160
180
200
1998 1999 2000 2001 2002 2003 2004 2005 2006
Years
Sca
led
ND
VI
All Africa Sahara Vegetation
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Methodology
Pairwise Comparison (Univariate Differencing) GIMMS: 2002/03 minus 1982/83 = change SPOT: 2005/06 minus 1998/99 = change
Percent Change (2002/03 minus 1982/83) / 1982/83 = Percent Change (2005/06 minus 1998/99) / 1998/99 = Percent Change
Profiling Graphing change through the period
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Results
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All Africa ChangeGIMMS: 1982 to 2003
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Table – All Africa Change
Classification (% Change) # of Pixels % of Land PixelsMajor Decrease (decrease > 20%) 3895 0.1%Decrease (decrease 10 to 20%) 22426 3.8%Minor Decrease (decrease 5 to 10%) 60269 9.9%Little Change (between -5 and +5%) 343420 56.9%Minor Increase (increase 5 to 10%) 72695 12.1%Increase (increase 10 to 20%) 70061 11.6%Major Increase (increase > 15%) 33456 5.6%All Land Pixels 606222 100%
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North Africa ChangeGIMMS, 1982 to 2003
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Table – North Africa Change
Classification (% Change) # of Pixel % of Land PixelsMajor Decrease (decrease > 20%) 502 0.1%Decrease (decrease 10 to 20%) 2081 1.4%Minor Decrease (decrease 5 to 10%) 9173 6.2%Little Change (between -5 and +5%) 125815 85.6%Minor Increase (increase 5 to 15%) 4645 3.2%Increase (increase 10 to 20%) 3067 2.1%Major Increase (increase > 15%) 1710 1.2%All Land Pixels 146993 100%
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Profiles of Change from 1982 to 2003
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Profiles of Change from 1982 to 2003
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Vegetation Change in North AfricaGIMMS Data - 1982 - 2003
Change is highly variable year to year
Few Persistent Changes
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All Africa ChangeSPOT: 1998/99 to 2005/06
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All Africa ChangeSPOT: 1998/99 to 2005/06
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North Africa – Areas of Decline
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North Africa – Areas of Decline
60
70
80
90
100
110
120
130
140
150
160
1998 1999 2000 2001 2002 2003 2004 2005 2006
Years
Sca
led
ND
VI
Series1 Series2 Series3
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North Africa – Areas of Decline
60
70
80
90
100
110
120
130
140
150
160
1998 1999 2000 2001 2002 2003 2004 2005 2006
Years
Sca
led
ND
VI
Series4 Series5
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North Africa – Areas of Decline
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North Africa – Areas of Decline
60
70
80
90
100
110
120
130
140
150
160
1998 1999 2000 2001 2002 2003 2004 2005 2006
Years
Sca
led
ND
VI
Series1 Series2 Series3 Series4 Series5
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North Africa – Same Areas of DeclineGIMMS Data, 1982/3 – 2002/3
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Mesopotamian Wetlands, Iraq Areas of Decline
GIMMS DataWetlands
0.1
0.12
0.14
0.16
0.18
0.2
0.22
0.24
0.26
0.28
0.3
82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 0 1 2 3
Years
ND
VI
Wetlands
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India South Interior Karnataka
Annual Integrated NDVI
y = 0.0222x - 39.313
4.5
5
5.5
1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002
YEARS
Trend line:
NDVI
5 yr moving average
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India South Interior Karnataka
Annual Integrated NDVI Annual Rainfall
y = 0.0222x - 39.313
4.5
5
5.5
1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002
YEARS
Trend line:
NDVI
5 yr moving average
y = -33.752x + 8499.8
4000
5000
6000
7000
8000
9000
10000
11000
12000
Years
Rainfall in mm
Trend line :
5 yr moving average
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North Africa – Areas of Increase1 – West Nile Delta, 2 – North Central Algeria, 3 – Atlas Mountains, 4 – South Morocco
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North Africa – Areas of Increase1 – West Nile Delta, 2 – North Central Algeria, 3 – Atlas Mountains, 4 – South Morocco
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GIMMS Data – Western Nile Delta
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Arc of Irrigation Temporal Profiles
50
70
90
110
130
150
170
190
210
82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 0 1 2 3
Years
Scal
ed N
DVI
Region - 1 Region - 2 Region - 3 Region - 4 Region - 5
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3-year Running Average
50
70
90
110
130
150
170
190
82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 0 1 2 3
Years
Scal
ed N
DVI
Region - 1 Region - 2 Region - 3 Region - 4 Region -5
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Conclusions
Unlike other parts of the world, patterns of declining photosynthesis (NDVI) in North Africa are highly variable – with few areas of persistent change.
Climate must be the major driver of change for most of the region.
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Conclusions
Areas in Morocco indicated in the literature as suffering from desertification – also have patterns of great variability.
The influence of human activity is hidden by strong climate variability.
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Conclusions
There are some regions in North Africa which do show signs of persistent increase.
Like other regions of the world, the main driver of persistent increases in photosynthesis (NDVI) is agriculture and in particular related water resources.
Future research will focus on analysing precipitation data for North Africa with NDVI data.
.
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Thank You