Figure 2.3. Trends in mean annual rainfall
in the Sahel (1897-1990).
- UNEP (1992).
- The number of stations from
which data are taken and averaged varies for each year up to about
100. The annual rainfall series for each station is normalized by
taking away the long-term (1951-80) mean from each value and
dividing the difference by the long-term (1951-80) standard deviation.
The smooth curve is a 10-year Gaussian filter that suppresses variations
of less than 10 years, giving an indication of trends in the rainfall