centre for geospatial science dr didier leibovici 1 extracting dynamics of multiple indicators for...
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Dr Didier Leibovici
1
CENTRE FORGEOSPATIALSCIENCE
Extracting Dynamics of Multiple Indicators for Spatial recognition of Ecoclimatic zones in Circum-
Saharan Africa
Didier Leibovici and Gilbert Quillevere
Centre for Geospatial Sciences, University of Nottingham, Nottingham UKIRD-US166 Désertification, Maison de la Télédétection, Montpellier France
Dr Didier Leibovici
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CENTRE FORGEOSPATIALSCIENCE
ROSELT network www.roselt-oss.orglong term monitoring of desertification
representativeness of 30 observatories arid, semi-arid, dry sub-humid
circum-Saharan region
Biophysical Ecological Socio-economical
Spatio-temporal variations
Ecoregion delineation homogeneous zones
Dr Didier Leibovici
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CENTRE FORGEOSPATIALSCIENCE
focusing on ecoclimatic variations (physical climatic aspects) arid semi-arid dry sub-humid
indicators
aridity index P/ETo ~0.10 ~0.35 ~0.50 (annual)
mensual variations !? (see ombrothermal diagrams Le Houérou)
e.g.
WORLDCLIM 1950-2000 www.worldclim.org/current.htmFAO www.fao.org
averages over 50 years
Dr Didier Leibovici
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CENTRE FORGEOSPATIALSCIENCE
clustering the dynamics
capturing spatio-temporal variations
12 x 10 values at 298249 pixels (grid 5’’)
meaningful correlations among 120 variables ?!120 indicators
2982
49 lo
catio
ns kmeansor
PCA + kmeans
?
12 months
2982
49 lo
catio
ns
10 indicators
tensorial structure
analysing interactions
space x time x indicators
PTAk+
kmeans
Principal Tensor Analysis on k-modes (k=3)offers a generalisation of PCA
Dr Didier Leibovici
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CENTRE FORGEOSPATIALSCIENCE
Principal Tensor Analysis on k-modes (k=3) R add-on package www.r-project.org
PCA PTAk
1st principal tensor of a
2-way table, of 3-way table
matrix calculus to tensor algebra
Dr Didier Leibovici
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CENTRE FORGEOSPATIALSCIENCE
{{
{
298249 x 10 x 12
decomposition of Sum of Squares
like PCA but a multi-level hierarchy
PCA of 298249 x 10 (63.66%)23.15% 6.95% 3.31% …
recursive algorithm
Dr Didier Leibovici
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CENTRE FORGEOSPATIALSCIENCE
s latitude gradients from Sahara (<>)i drought/extreme conditions ETo, dM, Tmax<> rain related indicators Q3, P, PETom all year more during months 5 to 10
s sea shore and low relief<>high reliefi temperature Tmin, Tave but also Q3<> altitude Alt m all year more during months 5 to 10
vs111 39.15%
12vs111 298249 10 14.24%
Dr Didier Leibovici
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CENTRE FORGEOSPATIALSCIENCE
s Maghreb and equatorial <> Sudan-Sahel zonei temperature Tmin, Tave, Tmax, and altitude Alt<> rain and aridity indicators Q3, P, PETo, dMm wet hot months 7, 8, 9 and dry months 12, 1, 2 <> mid seasons months 4, 5, 10
s oceanic equatorial <> gradient North-South in Maghreb i (<>) temperature Tmin, Tave, Tmax, and evapotranspiration ETom 6, 7, 8, 9<> dry months 11, 12, 1, 2
vs333 1.64%
Vs222 16.33%
Dr Didier Leibovici
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CENTRE FORGEOSPATIALSCIENCE
s gradiant N&S Sudan-Sahel zone<> north Maghreb and equatorial i rain related indicators Q3, P, PETo, dM (<>)m 6, 7, 8, 9 <> dry months 11, 12, 1, 2
12vs222 298249 10 3.53%
10 vs222 298249 12 0.84%
s north Maghreb and Guinea area(<>)i (<>) temperature Tmin, Tave, Tmax, evapotranspiration ETo m end of dry months 3, 4, 5 <> 7, 8
Dr Didier Leibovici
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CENTRE FORGEOSPATIALSCIENCE
kmeans clustering of selected (s) in 15 classesshapefile on Catalogue Service Web mdweb.roselt-oss.org
classes proximity from hierarchical clustering
• ecoclimatic pattern• ROSELT covers all the classes in arid, semi arid, sub humid zones• observatories mainly of one class (but 1/3 of 2 calsses: 80% area in 1 class)•0.08dd is between 9km and 7.5km
Dr Didier Leibovici
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CENTRE FORGEOSPATIALSCIENCE
Some drawbacks
• resolution (1’) relatively to observatory size (~20 pixels … ) • 50 years average (WORLDCLIM) … periods • number of classes• only ecoclimatic delineation
Some solutions• better resolutions available • introducing periods (within the 50 years) and performing a PTA4
space x months x period x indicators• multilevel classification (cutting the tree) : e.g. kmeans with 40 +hierachical tree of them• intercepting classes from same methodology on different domains
ecolimatic soil-vegetation socio-economic or using all indicators together (allowing correlation between domains)
months
loca
tions
indicators
months
loca
tions
indicators
period
Dr Didier Leibovici
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CENTRE FORGEOSPATIALSCIENCE
Extracting Dynamics of Multiple Indicators for Spatial recognition of Ecoclimatic zones in Circum-Saharan Africa
Didier Leibovici and Gilbert Quillevere
Centre for Geospatial Sciences, University of Nottingham, Nottingham UKIRD-US166 Désertification, Maison de la Télédétection, Montpellier France
[email protected] – Questions?
months
loca
tions
indicators