Effects of rainfall variability on sugarcane production in Mumias sub county, Kakamega county, Kenya

Temporal rainfall variability phenomenon is the degree to which rainfall amounts change at a given area through time either from month to month, season to season or year to year in relation to long-term average. The associated extreme events such as increase in rainfall amounts or drought adversely affect agricultural production resulting in low yields. Rainfall in Mumias Sub County varies from season to season or year to years such that, between 1982 and 2012 Mumias experienced an increase in annual rainfall amounts. This variability of rainfall had an effect on sugar cane production. Thus, there was need to examine the effects of variation in total seasonal and inter annual rainfall amounts on sugar production in Mumias Sub County, Kakamega County Kenya. Therefore, the purpose of this study was to examine the effects of rainfall variability on sugar cane production. The specific objectives were to: determine historical trends in seasonal, inter annual rainfall amounts and sugarcane yields between 1982 and 2012; establish the effects of variations in seasonal and annual rainfall amounts on sugarcane biomass yields; and assess effects of variations in inter annual rainfall amounts on sugar quantity. Descriptive Cross-sectional research design was adopted. Secondary data were obtained using document analysis to extract information from Mumias Sugar company annual reports on sugarcane biomass yields and sugar quantity yields. Data on total seasonal and inter annual rainfall amounts was obtained from records at Mumias synoptic weather station. Quantitative data on seasonal and inter annual rainfall variability, sugarcane biomass yield, sugar quantity were analyzed using trend analysis, simple linear regression and coefficient of variation. A line graph result show the variability trend at seasonal scale was (positive slope=2.51 for “long rains” and slope=3.85 for “short rains” implying increasing trends). The variability at inter annual rainfall scale was a positive slope=7.98 and a mean coefficient of variation of 0.2(20%) was obtained which suggests low inter- annual rainfall variability. The variations in seasonal and inter annual rainfall were found to be 83.17 % and 67.7% respectively within the study period implying a high level of temporal rainfall variability. The linear regression results show that 55% (r²=0.55) of variation of sugar cane biomass yields can be explained by total seasonal rainfall whereas61% (r²=0.61) of variation of sugar quantity can be explained for by total annual rainfall amounts. In addition 55 % (r²=0.55) of variation in sugar quantity (sucrose content) can be explained by inter annual rainfall variability. It can be concluded that total seasonal rainfall and total annual rainfall amounts affect variation of sugar cane biomass yields and sugar quantity. The study recommends that, due to the high level of temporal rainfall variability that affects sugarcane yields, the departments of agriculture and meteorology to provide farmers with information on rainfall trends so that sugarcane farmers can plan their agronomic activities in accordance with variations in rainfall amounts.