Seasonal distribution of mono-modal, monsoonal rainfall
across the semi-arid ecotone of sub-Saharan of West Africa is highly variable
and unpredictable. The ever-present risk of drought and crop failure in this
environment often results in food shortages that are met by emergency food aid.
Humanitarian assistance planners would be better prepared for such
interventions in a timely manner if they have reliable indicators that forewarn
the impending failure of the rains. A good indicator would be a characteristic
of the seasonal rainfall distribution that can be shown to be reasonably invariant
over time and space. The objective of this study is to investigate whether such
invariance existed for the seasonal median date (meaning the date when 50% of
the seasonal total occurs). Such invariance is expected since the sun’s cyclic
declination forces the advance and retreat of the Inter-tropical Front over
West Africa. We examined the statistical properties of the seasonal median date
for 1349 station-years of rainfall records for 30 rainfall stations in Burkina
Faso and Niger with coordinates ranging from 9.88° to 18.5° north latitude and -4.77° to 13.2° longitude. The results showedthat the median date was quite narrowly
distributed over years with rather weak dependence on geographical coordinates.
It can therefore be used as a reasonable ex-ante indicator of the success or
failure of the rains as the rainy season progress.
Cite this paper
N. Persaud, M. Elrashidi, X. Zhou, X. Zhao and X. Chen, "Invariance in the Seasonal Median Dates for Mono-Modal Monsoonal Rainfall Distribution over the Semi-Arid Ecotone of Sub-Saharan West Africa," International Journal of Geosciences, Vol. 4 No. 6, 2013, pp. 1-7. doi: 10.4236/ijg.2013.46A2001.
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