Periodicities and trends in the annual rainfall series over Africa
Abstract
The object of the study is to examine the cyclical
variations and trends in the annual rainfall totals for
69 stations in Africa.
To examine the trends in the annual rainfall series,
the annual rainfall totals have been smoothed by the
Binomial Coefficient method (W.M.O. 1966). The weights
used were, 0.22 for the 1styear, 0.20 for the 1+1 years,
0.12 for the 1+2 years, 0.05 for the i+3 years, and 0.02
for the i+4 years. This 'low-pass' filter removes almost
all fluctuations shorter than ten years. The 'low-pass'
filter curves were then classified broadly into nine trend
groups ..