Abstract
The impact of topography on heavy rainfall during two rain seasons was investigated in order to explain their mechanisms on rainfall distribution over Rwanda. Weather Research and Forecasting (WRF-ARW) model was used to study two historical cases of heavy rainfall which took place over Rwanda during two rain seasons, March to May (MAM) and September to December (SOND), from April 7 to 9, 2012 (for MAM) and from October 29 to 31, 2012 (during SOND). The control experiment was done with actual topography, whereas sensitivity experiment was carried out with topography reduced by half. Results show that rainfall distribution over Rwanda significantly changes when topography is reduced. The reduction in topography leads to a decrease in rainfall amounts in both MAM and SOND seasons, with varying magnitudes. This reveals the importance of orography in determining rainfall amounts and distribution over the region. The accumulated rainfall amount from WRF underestimate or overestimate rain gauge stations data by region and by season, but there is good agreement especially in altitude below 1490 m and above 1554 m during April and October respectively. The results may motivate modelling carters to further improve parameterization schemes in the mountainous regions.
Highlights
Rwanda is a country with high altitude located in East Africa, where rainfall is the most important climate variable
In order to understand the influence of topography on rainfall over high altitude regions, we examine the mean rainfall in the respective regions for simulations with actual topography and with reduced topography for the
The mean rainfall for CASE-I (a) and CASE-II (b), showing rainfall for simulation with actual topography (WRF_RAT) and with topography reduced by half (WRF_RRT) over high altitude regions of Rwanda
Summary
Rwanda is a country with high altitude located in East Africa, where rainfall is the most important climate variable. The large-scale tropical climate in East Africa is characterized by convergence zones and regional factors associated with complex terrain, several vegetation types, and lakes [1]. It experiences four seasons: two rain seasons and two dry seasons. The main factors influencing Rwanda’ s rainfall are: 1) Subtropical anticyclones; 2) Congo air mass; 3) Inter-seasonal wave variation; 4) The Mascarene, Azores, St. Helena and Arabian high-pressure systems; 5) Regional topography, large water bodies (e.g. Lake Kivu), and large forests. The onset of the short rains in East Africa occurs usually in October and its precipitation exhibits complicated patterns of temporal and spatial distributions where regions have significant different amount of precipitation [1]. This shows the role of using WRF model in weather forecasting in Rwanda which is well known as a country with many high mountains
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
