Abstract:
Rainfall variability has presented significant challenges to nations worldwide and especially developing countries including Rwanda. The main objective of this study is to determine the rainfall variability and projected change over Rwanda. Data employed in this study include observed rainfall datasets (ENACTS) from 1981 to 2017 obtained from Rwanda Meteorology Agency (Meteo Rwanda) and the Coordinated Regional Downscaling Experiment (CORDEX) model outputs obtained from the CORDEX Africa portal. The study utilized graphical and statistical methods to assess the trend in rainfall variability. To assess the skill of the models in simulating the climate of Rwanda, correlation, absolute mean error, index of agreement and rainfall climatology difference plots analysis were used. The data show that high rainfall are concentrated over the high land and southwestern parts which reduces toward the central parts while the low rainfall amount are observed in the Eastern part of the country during MAM and OND as well on annual time scale.
The trend results from graphical method indicate clear non-uniform rainfall variability over Rwanda. Results from statistical methods show that there is sufficient statistical evidence to conclude that there is a significant increasing rainfall trend over Northern part of the northern province and southern province while there is a non-significant decreasing rainfall trend over eastern, Kigali city, Northern and central western during MAM,OND and annual time scale. The results indicated a coefficient of variation ranging between 20 and 32% during MAM rain season, 18 to 37% during OND rain season and 14 to 31% on annual time scale. Furthermore, results indicate that the north eastern part of the country exhibits a more variable rainfall. The IPSL and CCCma models have revealed a better performance in simulating the of Rwanda during MAM and OND rain season respectively compared to the other models used in study. The projected rainfall change results indicated a projected decrease in rainfall of 5 to 6% over Nyamagabe and Rubavu while other stations will exhibit an increase in rainfall of 2 to 6 % and 1 to 5% under both RCP8.5 and RCP4.5 respectively during MAM rain season. A projected decrease in rainfall of 1 to 5% over Musanze, Nyamagabe, Rubona, Byimana, Kigali and Rubengera under both RCP8.5 and RCP4.5 respectively. Ngoma revealed a decreasing (increasing) rainfall of 1% under RCP8.5 (RCP4.5). Kayonza will exhibit an increasing rainfall of 5% under RCP8.5 and a decreasing rainfall of 2% under RCP4.5 while other stations will experience a projected increase in rainfall ranging from 1 to 5% will be experienced over Nyagatare, Gicumbi and Kamembe under both RCP 8.5 and RCP 4.5 respectively.
