Geographic Variation in Growing Season Rainfall during three Decades in Nigeria Using Principal Component and Cluster Analyses |
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| Authors: | A Amissah-Arthur S S Jagtap |
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| Institution: | (1) International Institute of Tropical Agriculture, Crop Ecology and Modelling Unit, Ibadan, Nigeria, NG |
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| Abstract: | Summary Reports of changes in the seasonal and annual rainfall in Nigeria suggests that a more detailed analyses of the geographic
extent of these changes and of their impact on agriculture could be of value. Variation in the growing season (April to September)
rainfall from stations across Nigeria was analysed over the 30-yr period, 1960–90. Regression analyses were used to examine
long-term trends. Principal component and cluster analyses were used to group stations with similar trends in standardised
seasonal rainfall. Mean accumulated standardised seasonal rainfall were used to examine short- and medium-term trends for
each of the groups identified. Significant (P ≤ 0.05) decreases in rainy season rainfall were found at 8 stations mostly in the Guinea and arid/semi-arid savannas of northern
Nigeria, whereas no station showed significant increases. Examination of the monthly (April through September) rainfall showed
that only three – Kano, Sokoto and Potiskum in the arid/semi-arid savanna – of the twenty-three stations used in the analysis
had declining rainfall trends for each of the months April to September and subsequently declining seasonal rainfall trends.
However, 12 to 15 stations had consistently declining rainfall trends in atleast some but not all the growing season months.
However, a similar pattern was not the case in terms of increasing rainfall trends, where only one to three stations had consistently
increasing rainfall trends in some but not all of the months from April to September. Stations that showed increasing rainfall
trends were in the southern parts of Nigeria.
Six groups with similar patterns in standardised seasonal rainfall were identified by Principal Component and Cluster analyses.
For most of the groups, the period from 1967 to 1973 was that of consistently below average seasonal rainfall. However, the
timing and extent of the decline varied with location. Common to stations in four of the six groups was a negative trend in
seasonal rainfall for the period considered. The geographic variation in seasonal rainfall trends has tremendous agricultural
significance since there are indications that the reliability of the season is decreasing from the humid forest zone with
positive seasonal trends to the arid/semi-arid savanna with significant negative seasonal trends.
Received June 24, 1998 Revised December 18, 1998 |
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