|
Using precipitation
effectiveness variables in indexing drought in semi-arid
regions
J. A. Otun
Department
of Water Resources and Environmental Engineering, Ahmadu
Bello University, Zaria, Nigeria. E-mail:
jotun@abu.edu.ng.
Accepted 26
June, 2010 |
|
This
study proposes a new drought index based on several
precipitation-based parameters to quantify drought hazard in
semi arid region. In addition to the practice of using only
rainfall volume for indexing drought, the proposed index
verifies the potentials of nine other precipitation
effectiveness variables (PEVs) onset of rain, cessation of
rain, length of rainy and dry season, wet days and dry days
within a wet season, dry days within the year, maximum dry
spell length within a wet season and mean seasonal rainfall
depth (MAR) in quantifying the drought conditions over a
place. The conjunctive Precipitation Effectiveness Index (CPEI),
as proposed in this study, utilizes a mathematical model,
which algebraically combines “standardized seasonal PEV
difference or deficit in each prevailing PEV” and terms of
their sequent higher powers to define a single numerical
value for this “at-site” drought index approach. Some
statistical comparison tests were employed to determine the
most appropriate set of PEV that can be employed in the CPEI
model to quantify the drought conditions at each study
location. The daily rainfall data obtained from seven
synoptic stations in the semi-arid region of Nigeria were
obtained, tested and then used to verify the effectiveness
of this new method. Results obtained showed that the optimum
no of PEVs that can be effectively combined to get the
optimum CPEI values for indexing the drought in the study
area is three PEVs for Gusau and Kano, five PEVs for Sokoto
and Maiduguri and four for the rest stations under study.
The trends observed in drought values obtained using the
CPEI models employing these optimum PEVs also clearly
earmarks the 1970 -73 and 1983 -1987 historical drought
years within the study area. This approach seems to be
significant for the specific area in the Sudano-Sahelian
Region of Nigeria but would need to be verified in a wider
regional context in similar future study.
Key
words:
Drought indexing, precipitation effectiveness variables,
semi arid regions.
|
