Drought Frequency and Persistence in the Upper River Tana Basin in Kenya

Abstract

Drought is an abnormal low rainfall condition over an extended period of time in the Upper River Tana basin in Kenya as distinct from aridity, which is a condition of spatial low average moisture availability, is the focal area of study. This study evaluated drought frequency and its persistence using local farmer's information, daily rainfall data and mean river discharges. The drought was analyzed using data on agricultural activities, daily rainfall and mean daily discharges. The data analysed using a number of tools and these were cross-tabulation, frequency analysis, Cramer’s V and Phi statistics, Control chart, and Time Series techniques in order to determine drought periods, frequency and persistence. The results indicate that drought is a meteorological phenomenon of Upper River Tana basin hydro-climate conditions as well as its socio-economic set up. The definition of drought and therefore meanings of drought, however, vary by agro-climatic zones, socio-economic activities, rainfall conditions, and hydrological characteristics. The frequency of drought in all cases tends not to have a definite pattern and therefore less predictable while persistence tends to be restricted to a water year. Most drought episodes identified are widespread and thus confirming the fact that drought is an issue in the study area. Drought episodes tend to occur at the beginning and at the end of a decadal period and in some cases tend to portray persistence beyond the calendar year but not beyond a water year. These results have implications for planning farming activities.