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.
