Rainfall variability and trends over Rwanda
Sebaziga Ndakize Joseph.1,2,*, Safaris Bonfils2, Ngaina Ndiwa Joshua3, Ntwali Didier4, Mutai Bethwel Kipkoech5, Safari Kagabo Abdou2,& Rwema Michel2
1Rwanda Meteorology Agency, P.O Box 898 Kigali, Rwanda; 2University of Rwanda P.O Box 3900, Kigali, Rwanda; 3Southern Eastern Kenya University, P.O Box 170, 90200, Kitui, Kenya, 4Rwanda Space Agency, P.O Box 6205, Kigali, Rwanda & 5University of Nairobi, P.O Box 30197, 00100, Nairobi, Kenya
Rainfall is regarded as one of the foundational concepts for comprehending climate variability and/or change. This paper aimed at examining the seasonal and annual rainfall variability and its associated trends over Rwanda between 1981 and 2017. The Coefficient of Variation (CV) was used to determine the rainfall variability. Mann-Kendall test and Sen’s slope estimator techniques were used to detect trends and to quantify the magnitude of change. High rainfall variability was observed over eastern Rwanda, around Kigali city and central plateau, while the south-western, western and the north highland revealed lower rainfall variability. Trend analysis of annual and March-May (MAM) rainfall season depicted a significant decrease of -6.7% over south-western region (Kamembe-Aero station) and -9.8% over eastern parts (Kibungo-Kazo) respectively. A significant increase in trend of 4.3% over North-western (Gisenyi-Aero station) during September-December (SOND) season was also obtained. The rest of the stations registered a non-significant trend on both seasonal and annual time scales. Spatially, areas of Kigali City, eastern and central parts of Rwanda revealed a decreasing trend whereas an increasing trend was observed over the western, northern highland, north eastern and southern region except for the areas towards the south-east. The high rainfall variability and significant nature of changing trends demand that rain-dependent sectors of the economy link climate science and policy in order to make proper planning. With proper climate homogeneity zoning, the agricultural sector in particular needs to develop effective techniques that optimize food production including water use rationalisation.
Key words: Rainfall, Rwanda, Trend, Variability, Rain-Dependent