| dc.description.abstract | Drought is an abnormal low rainfall condition over an extended period of time and is different from aridity, which is a condition of average low moist re availability and is a permanent feature of a region's climate. Drought is therefore a meteorological phenomenon, which represents an extended abnormal low rainfall condition in an area. This study was focused on the determination of a drought definition, persistence, frequency, and impact in terms of meteorological and hydrological conditions in the Upper Tana catchment of Kenya. Attempt was made to provide a tool for assessing the impact of drought on hydroelectric power generation in the Upper Tana catchment, and by extension, in Kenya. The objectives of the study included establishing meteoroloqical and hydrological drought indices to be used in quantitative definition of drought depending on rainfall conditions and mean daily river volume flows in relations to hydroelectric power generation systems in the Upper Tana catchment of Kenya; determination of drought frequency and persistence indices in the catchment using daily rainfall data, mean daily river flow volumes, mean monthly darn levels and mean monthly
hydroelectric power generation; establishing the role of drought in problems of hydroelectric power generation in the Catchment and; providing a tool for drought forecasting and management in relation to hydroelectric power generation from catchment. To provide solutions to the study problem and achieve the objectives of tile study, both primary and secondary data were used in an attempt to provide. Field data were on agricultural and meteorological information from the people of Upper Tana catchment; agricultural and meteorological information from the agricultural officers working in the Upper Tana Catchment sourced through field interviews using the study questionnaire administered to 480 persons determined from the population (1989 and 1999 census reports) of Upper Tana River
Catchment; hydro-meteorological information from the district hydrologists working in the Upper Tana Catchment and; power generation issues in the Upper Tana catchment from Kenya Power and Lighting (KP&L) Research and Development division and from the Tana-Athi River Development Authority (TARDA) Personnel. Secondary data on the Upper Tana Catchment collected for this study included the following rainfall data from the meteorological department, Kenya; temperature data from the Meteorological Department, Kenya; evapotranspiration rates data from the Meteorological Department, Kenya; soils data from Soils Survey department, Kenya (Kenya Agricultural Research lnstitute) hydrological data (river volume flow/discharge data), from the Surface Water Resources Department, Ministry of Water and Irrigation, Kenya); dam levels data from Kenya Power and Lighting (KP&L) Company Limited and Tana-Athi River.
Development Authority (TARDA); hydroelectric power generation data from the Kenya Power and Lighting Company Limited and; Spatial data for GIS from the Survey of Kenya department.
In data analysis, the primary data which in most cases were measured at the nominal and ordinal level, distribution tendencies were established through the use of descriptive statistical techniques of cross-tabulation and frequency analysis. The presentation of the results in the form of tables and graphs were reinforced by use of non-parametric techniques of Cramer's V and phi which are measures of association based on chi-square distribution. The spatial unit of
analysis in all cases was the administrative division, which in most cases also tended to conform to the agro-ecological zones of Upper Tana Catchment.
In the parameterization of drought, the study, aware of the deciles range techniques, weighted rainfall standardized anomalies index and the standardized rainfall anomalies techniques, opted to use the control chart technique in order to have some measure of deviation from the expected in rainfall and river discharges on a daily basis. The lower limit of the control charts at 2 sigma in this study marked the lower index for both the mean (expected in the long run and standard deviations, always normal in the long run), below which a drought condition was indicated. Time Series techniques including time sequence plot, differencing, and spectral analysis were used in this study when analyzing daily rainfall records, mean daily river flow records, mean daily dam levels, and mean daily hydro-electric power generation.
Results indicated that drought was ~a. feature of Upper Tana Catchment physiography and socio-economic set up but its definitions varied from rainfall and river discharge conditions that were considered exceptionally low as to affect various human activities to extended conditions of rainfall and river discharges that were below the lower limits of the long term daily means and/or standard deviations at various gauging stations. Frequency of drought in all cases was
found to be random or unpredictable and persistence in most cases tended to be a water year event. There was a general tendency for drought episodes to occur at the beginning and at the end of a decadal period and this in some cases tended to portray persistence beyond the calendar year but not beyond a water year. Impacts of drought were registered in crop failures, lack of pasture, migration of human and livestock, famines, drying rivers, low darn levels, and
interruption of electricity generation and supply.
In conclusions, the study noted that drought is a meteorological phenomenon in the Upper Tana Catchment climate whose definitions, frequencies, persistence and impacts vary with socio-economic activities, rainfall conditions, and hydrological characteristics. | en |
