| dc.description.abstract | A three-dimensional numerical model was used in this study to
examine the effects of changes in the surface roughness length on
the meso-scale flow patterns over Kenya.
Three experiments were performed. The first experiment was
performed to test the ability of the model in reproducing the
meso-scale circulations over Kenya. In the second experiment, the
roughness length was uniform over the whole domain (homogeneous
roughness terrain) . In the third experiment, the roughness length
at each grid point was specified according to the terrain
characteristics (heterogeneous roughness terrain). The initial
fields were observations for May 6 1986.
Results of the first experiment showed that the model was able to
give realistic simulations of the meso-scale flow over Kenya. The
model simulated the afternoon sea/lake breezes and upslope flows on
either side of the Kenya highlands. In the morning, the land
breeze and downslope flows from the Kenya highlands were also
simulated. Maximum afternoon low-level rising motion, meso-scale
convergence and precipitation were located over the western
highlands.
Results from the second experiment showed that changes in the
surface roughness had significant impacts on the development of
meso-scale flows over Kenya.The 'simulated boundary layer wind
speed decreased as the surface roughness was increased. The
results further showed enhanced turbulent mixing of the boundary
layer heat and moisture, and increased convective rainfall over
(vii)
the western highlands, when the surface roughness was increased.
Non-convective rainfall contributed relatively less to the total
simulated meso-scale rainfall over Kenya.
In the third experiment, it was found that the simulated
boundary layer wind field compared well with the mean flow patterns
for May. The simulated temperature field indicated high values
over the coastal areas, the lake region and the arid and semi-arid
northern parts of Kenya. Low temperatures were concentrated over
the central highlands. These patterns compared well with the
observed mean patterns for the month. High values of relative
humidity were simulated over the coastal areas and western
highlands in agreement with the observations. Rising motion
accompanied by high meso-scale precipitation was simulated over
western Kenya, while the eastern highlands including the arid/semi
arid areas of northern Kenya were dry. These results compared
-- better with the mean fields and the observed weather patterns for
May 6 1986.
From the results obtained in this study one may infer that
modification of the land surface characteristics through human
activities like deforestation and overgrazing, would have
considerable impacts on the meso-scale weather systems in Kenya.
Such changes would have far r~aching socio-economic impacts.
Proper planning of land use activities is therefore recommended in
order to minimize human induced modification of the surface
characteristics | en |
