SOME ASPECTS OF THE SPATIAL AND TEMPORAL CHARACTERISTICS OF DROUGHT IN NIGERIA: A STATISTICAL APPROACH
SOME ASPECTS OF THE SPATIAL AND TEMPORAL CHARACTERISTICS OF DROUGHT IN NIGERIA: A STATISTICAL APPROACH
No Thumbnail Available
Date
1993
Authors
IWEGBU, IRINA ANDREEVNA
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Mean rainy season (April-October) precipitation series
for fourty one stations in Nigeria for a long period of
years, are used to derive a Bhalme and Mooley-type drought
index for the region. Various statistical analysis indicate
that precipitation series are more variable Over the
Sahelian, eastern Midland and western sub-sectors of the
Guinea-Savanna and Coastal zones. The rainfall series for
the Sahelian and northern Midland zones indicate a significant
trend towards increasing aridity, especially in the
last 30 years.
Map-pattern correlation method stratifies 46 per cent
of the eighty two years, and produces comparatively good
results as the more sophisticated eigenvector method, six
moisture amomaly patterns, are identified by map-pattern
correlation method indicating distinct differences between
areas north of 10°N and the rest of the country. Maps of
the mean seasonal areal coverage of drought reveal remarkable
changes in size and position from year to year.
Drought does not cover the entire country and no particular
areas were persistently affected until the 1970s and 1980s.
Since the beginning of the 1970s areas affected by drought
have increased in extent with a consequent decrease in near
normal and wet conditions particularly in the Sahelian and
the Midland zones. The 1970s and 1980s were characterized
by exceptionally high frequency of drought conditions with a
presence of consecutive years of large-scale droughts since
1982, confirming persistence of drought in Nigeria.
v
All stations are subjected to Non-Integer method of
spectral analysis and low-pass filter method in order to
identify any trends and regular periodicites in the drought
index. The low-pass filter results confirm negative trend
for the Sahelian and Midland zones (from the mid 1950s and
late 1960s respectively), indicating increasing aridity.
The drought spectrum as indicated by the Non-integer method
is dominated by peaks in the 2.1-7.9 frequency range
(Coastal and western Guinea-Savanna zones) and longer
frequencies with peaks between 11.0-11.9 and 13.0-13.9 years
in the Sahelian and the Coastal zones. Based on the number
of stations with significant quasi-11-year oscillations and
their spatial distribution a linear relationship between
drought index fluctuation and 11-year sunspot cycle may not
be realistic, as it is often portrayed in the literature.
In general, drought in Nigeria is a complex random
phenomenon, generated by non-linear atmospheric processes
sporadic in spatial occurrence, making its prediction
difficult.
Description
thesis submitted in conformity with the requirements
for the Degree of Doctor of Philosophy at
the Ahmadu Bello University
Zaria.
Keywords
ASPECTS, SPATIAL, TEMPORAL, CHARACTERISTICS, DROUGHT, NIGERIA