Assessment and characterization of drought occurrence in the Lake Victoria basin of Kenya: a case study of West Kenya

Abstract

The droughts of early 1970s and early 1980s were some of the worst on record in the history of Sub-Saharan Africa.drought which in this study refers to an extended period of exceptional low rainfall, has been associated with negative effects in Africa with the drought of early 1970s and early 1980s be inc some of the worst especially in the Sahel region. The effects of these droughts of the 1970s and the 1980s led to increased attention on the climatic anomalies in Africa especially drought in the Sahel. The increased attention had hitherto largely ignored the high rainfall areas of Africa in terms of drought; occurrence and yet these areas are the granaries of the Continent,s populace. This study was aimed at finding out whether the high potential lands of Kenya are prone to drought occurrence (especially meteorological drought) . The study also was aimed at finding out, if the above was true, whether there are unique characteristics of drought occurrence in the high potential lands of Kenya that can be used as a basis for better informed resource o 1ann it)Q. Lake Victoria Basin which has the largest share of the high potential lands in Kenya was selected as the main area to be covered by the study. The Nyanza and Western Provinces (WEST KENYA) were used as representatives of the Lake Victoria Basin of Kenya and this was because nearly all the agro-climatic zones of the Basin are found there. Dai1y rainfall totals data from twelve Rainfall Recording Stations as were available at the Meteorological Headquarters. Nairobi. were used for the study. In addition. data on the daily river flows for Nzoia. Yala. Nyando. Sondu-Miriu. and Gucha-Migori were also used as supporting information as were the agricultural reports for West Kenya. The daily rainfall data used were for the period 1971-80 and were those of the months of January to July. The main statistical analysis technique used in the study was the Time-Series Analysis which allows a temporal presentation of the data. This technique therefore suited the need in the study to identify periods of abnormal low rainfall that could be described as meteorological drought conditions. Of the various Time-Series Analysis techniques. the study used the Series Plot. the Weighted (Binomial weights) Running Mean.the Auto correlation Test. and the Correlogram Test. The study first subjected the data distributions to basic statistical analysis using the Mean. Median. Mode. Kurtosis .Skewness .Frequency Tabulation. and the Analysis of Variance Test (ANOVA) so as to reveal the central or general tendencies in the data. In the study. the hypothesis investigated was that • the drought.s of the earl y 1970s and the earl 1980s never occurred in West Kenya and the food short.age experienced during the periods could not have been as a result of rainfall failure. Statistical significance tests were in all cases done at alpha 0.05 level. It was found that the droughts of early 1970s and early 1980s could be traced in the day 1v rainfall series for the months of January to Jul y between 1971 and 1985 as was characterized by depressed rainfall distributions «5rMA per day) or breaks in the rainfall series «0.25mtf' per day). The depressions «5mm per day) or breaks «0.25mm per day) were not well defined in the rainfall series distributions and this indicated more of erratic or delayed or early ending distribution of rains than well defined meteorological drought situations. The "drought conditions" traced in the rainfall distributions between 1971 and 1985 occurred in mid 1970s and in the 1970s-1980s transition period especially 1979-1981 period. Food shortage , therefore,which were experienced outside the periods above could not have been due to nature anomalies(rainfall failure) only. On the basis of the findings.it was real issued that a detailed characterization of drought occurrence in the Lake Victoria Basin of Kenya was still limited unless the daily water balance conditions in the Basin were availed. Nevertheless. it was concluded that as economic practices in West Kenya should have inbuilt "drought shock-absorbers" like food buffer stocks. of time tested drought resistant crops .and other forms of production and drought management strategies. This was because the possibility of rains not meeting the crop requirements was found to be very real in West Kenya. The study faced the problem of poor data entry and erroneous recording and it is therefore recommended that data recording. entry and Meteorological Stations or recording stations) should be managed by trained and interested personnel.