The effect of the Indian Ocean Diople (IOD) on the seasonal rainfall patterns of Uganda: A case study of the Lake Victoria Basin
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Rainfall is one of the major climatic elements with a high spatial and temporal variability on a global scale. In East Africa, particularly in Uganda, a number of factors affect and influence the variability of the rainfall. These factors can be global such as Sea Surface Temperatures, Inter Tropical Convergence Zone, monsoons or can be local such as Land and sea breezes, topography and vegetation among others. This study focused on the effect of the Indian Ocean Dipole on the seasonal rainfall patterns of Uganda particularly the Lake Victoria Basin. The overall objective of the study was to determine effect of the IOD on the seasonal rainfall patterns of the LVB. The data used in the study included gridded rainfall data from Global Precipitation Climatology Center and Indian Ocean Dipole in terms of the Dipole Mode Index from National Oceanic and Atmospheric Administration from 1982 to 2012. Graphical displays, spatial analysis and correlation analysis were the methods used to achieve the specific objectives. The graphical analysis showed that the September to November rainfall season has a higher variability than the March to May season. However, both seasons indicated a decreasing trend in the rainfall patterns. The seasonal spatial analysis indicated rainfall increasing eastwards of the basin for the first 20 years (from 1982 to 2002) and later decreased during the March to May season. The September to November season on the other hand showed a decrease in the in spatial patterns throughout the entire period of the study. The correlation analysis between the Indian Ocean Dipole and March to May season indicated no significant correlation where all stations showed R-values < -1 and P-value > 0.5 on average. However, correlating the Indian Ocean Dipole with the September to November season, two of the stations (Entebbe and Kampala) indicated a positive significant correlation with R = 0.5 and P = 0.001. The findings revealed that however much only two stations of the four used in the study showed a correlation with the Indian Ocean Dipole, this still indicated the Indian Ocean Dipole has effect on the rainfall especially on the September to November season.