Spatio-temporal trend analysis of precipitation data over Rwanda

This study applies a number of statistical techniques in an attempt to quantify the magnitude, and to determine the significance of trends in the number of rainy days and mean rainfall over Rwanda on a monthly, seasonal and annual timescale. Trend analysis of the number of rainy days (1961-1992) was performed on daily values collected from 25 weather stations and the rainfall trends (1935-1992) were analysed using aggregated mean monthly data from 28 weather stations. The magnitude and significance of trends at 95% interval level derived from the slopes of the regression lines are presented spatially with the help of maps. It was observed that on average, there was a steady decline in the frequency of rainfall across the country. A significant incline was registered mainly over the northern region and the number of rainy days decreased significantly over the eastern and central plateau. The mean rainfall was found to increase sharply in most parts, especially in the regions around Kivu Lake during the short rainy seasons. The central region of Rwanda displayed a diminishing trend in rainfall totals in January and February. At the same time, the wet areas located in the highlands and around Kivu Lake are becoming wetter compared to the rest of the country. The highlands were consequently experiencing more flooding, with the eastern lowlands and the central plateau becoming warmer. These phenomena have an adverse effect on crop production, as they cause failure and/or destruction.