The document provides a flow diagram exercise that asks students to identify two trigger mechanisms that can lead to desertification based on columns listing processes. Students are asked to create flow diagrams for each trigger mechanism showing how the processes eventually result in desertification, referring to an example diagram in their textbook. The document also provides a hint about the nature of the diagrams and an extension question about rainfall patterns in the Sahel region based on a figure from the textbook.

1. Desertification Flow Diagram Exercise
The following table contains two columns of processes that combine
and eventually lead to desertification.
Each column has a different trigger mechanism.
Task – Using the flow diagram (fig C, p199 WW) as a guideline,
identify each of the trigger mechanisms and create a flow diagram
for each showing the processes that eventually lead to
desertification.
Hint – The flow diagram will not be a simple flow of boxes but will
have processes that are beyond human control – see example in text
book.
Roots no longer hold soil together, leaves Desertification
no longer protect soil from wind and rain
Less vegetation means less protection
Increase in population from winds and rainfall
Trees cut down Climatic Change – Less Rain
Desertification Increase in cattle
Loose top soil blown away by wind or Loose top soil blown away by wind or
eroded by rainfall eroded by rainfall
Deforestation for fire wood Grassland grazed more intensively,
roots may be eaten as well as grass
Climatic Change – Less Rain
Extension – Using figure B, p198 WW, describe the pattern of
rainfall in the Sahel between 1940-2000. Use actual figures and
dates quoted from the graph to aid your answer.