Analysis of Historical Monthly, Seasonal and Annual Rainfall Variability (1990–2014) in Machakos Sub County, Kenya

Abstract

Varying climatic conditions with increased uncertainty mainly in rainfall and temperature are salient features in marginal areas globally, adversely affecting farming activities particularly in Africa. Kenya experiences variations of annual rainfall with considerable uncertainty. These variations ranging from below 500mm to above 2000mm annually, cause droughts and floods respectively, affecting farming activities and yields. This study attempts to analyze historical monthly, seasonal and annual rainfall variability in Machakos sub County between 1990 – 2014. Studies on analysis of rainfall variability covered in Machakos have dwelt on broad and expansive areas of Eastern and South Eastern Kenya including Machakos, Kitui and Makueni Counties. Broad studies give generalized information which may not give true and adequate results for some specific areas. This has prompted the need to focus on a smaller area. This study focused on Machakos sub County, a semi arid area, East of Central Kenya highlands. Existing studies in the mentioned areas, mainly cover the period between 1930 - 1990. After this period, very scarce information exists. The main objective of the study was to establish the historical monthly, seasonal and annual rainfall variability in Machakos sub county between 1990 – 2014. Publications from Meteorological Department Nairobi and sub county Agricultural offices, provided rainfall data. Using SPSS, quantitative data was analyzed using descriptive statistics such as Means, Standard deviation and percentages. Inferential statistics using Pearson’s Correlation technique was used to determine relationships between variables. Coefficient of variability, Relative variability and Precipitation Concentration index measured Rainfall Variability. The study established that monthly, seasonal and annual rainfall distribution in Machakos sub County was highly variable, erratic and unpredictable over the 25 years with a CV of 24% and a PCI of 10. There is high temporal rainfall variability (CV of 24% and PCI of 10) in the sub County. Disseminating information on rainfall forecasts, rainwater harvesting for irrigation, proper cattle stocking, a forestation and reforestation programs were highly recommended.