Journal of Kenya Meteorological Society
Intraseasonal characteristics of the wet and dry spells over Kenya
Wilson Gitau*, Laban A. Ogallo* and Joseph N. Mutemi**
*IGAD Climate Prediction and Applications Centre, **Department of Meteorology, University of Nairobi
(Manuscript received 3 September 2007, in final form 18 January 2008)
The aim of the study was to investigate the spatial-temporal characteristics of the wet and dry spells during the wet seasons over Kenya in order to develop predicting tools that can be used to reduce vulnerability of the agricultural and other rain-dependent sectors to the negative impacts of extreme rainfall events within the season. Daily rainfall observations from 12 stations distributed over the study region and extending from 1971 to 2000 was used. The methods used were frequency distribution, fitting of a Markov chain model and gamma distribution function.
Results from the frequency distribution indicated that the 1-day wet and dry spells were the most dominant, with the frequency decreasing as the lenght of the spell was increased. Longer wet/dry spells were dominant in the wet/dry parts of the country. Results from Markov chain models showed that the first-order Markov chain model described the occurrence of wet/dry spells well. Simulated patterns of the wet/dry spells from the developed model compared well with the observations especially over the highlands and close to large water bodies. An exponential distribution was found to be quite adequate in describing daily rainfall amounts for 1.0mm threshold. The gamma distribution with a shape parameter close to 0.6 was most appropriate with thresholds of 3.0 and 5.0mm.