Early Warning and Monitoring of Droughts in Africa

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Early Warning and Monitoring of Droughts in Africa

• Dr Christophe Sannier
• Lecturer in Remote Sensing GIS

United Nations International Workshop on the Use
of Space Technology for Disaster Management,
18-22 October, Munich
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Objectives

• Background to vegetation monitoring with
  satellite imagery
• Need for advanced satellite derived products for
  vegetation monitoring
• Implementation of the Vegetation Productivity
  Indicator (VPI) in Africa
• Production and interpretation of VPI products

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Existing methods used for vegetation monitoring

• Normalised difference vegetation index (NDVI)
  images are processed for every 10-day period
  (dekad) using Maximum Value Compositing (MVC) to
  minimise atmospheric effects
• Difference between current NDVI and long-term
  average or previous dekad
• Problems
• Variations in cover type are not taken account,
  therefore differences are difficult to interpret
• Severity of seasonal variations cannot be inferred

Long term Average NDVI image of Namibia for the
2nd dekad of January
NDVI image of Namibia for the 2nd dekad of
January 2000
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Monthly rainfall and vegetation response in
Namutoni, Etosha National Park, Namibia
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NDVI response of Etosha main vegetation types
Cover types exhibit a different NDVI response to
seasonal variations
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Time Series AnalysisDetermination of VPI Classes
Average
Very Low
Low
Very High
High
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NDVI image and VPI map of Etosha, 27 March 1995
VPI removes the influence of vegetation type, and
characterises departures from normal conditions
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Selected January VPI Maps for Zambia
1988 maize production 1.9 Mt
1982 maize production 0.7 Mt
2002 maize production 0.6 Mt
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Comparison of two Seasons in Zambia for Kalomo
District
152 of average
maize production
55 of average
maize production
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Proportion of country where conditions are lower
than normal
March 1999
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Time series profiles for two locations during the
1998-99 season
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Use of map products to direct field investigations
VPI for January 1998
Unclassified Pans Very Low Low Average High Very
High
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Countries where the VPI was applied successfully
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Summary

• NDVI images are difficult to interpret for
  monitoring vegetation conditions
• The VPI serves as a reliable indicator of the
  current vegetation conditions
• The method was developed in Etosha, and applied
  experimentally in Zambia to assess maize
  production.
• The method was applied successfully in Ethiopia,
  Zambia, Namibia, Jordan and Afghanistan
• In Botswana and Namibia it was used operationally
  to monitor rangeland productivity
• There needs to be sufficient institutional
  support to make the technique sustainable
• New initiatives such as AMESD (African Monitoring
  of the Environment for Sustainable Development)
  funded by the EC and presented as African
  component of GMES might provide the institutional
  support needed