Relief.

Relief is another factor affecting climate in various places on earth.   Rain bearing winds are forced to rise when they blow towards mountains and in the process  they cool and the contained moisture condenses  into  rainfall  on the wind ward sides. Highlands  are  therefore areas  receiving high and reliable rainfall.   These include the mountains of Central Kenya, Southern Tanzania and South Western Uganda.
 
What role do prevailing winds play in a rain shadow
There is the windward side with high rainfall for example east of Drakensberg receives more rain than the western side which is as the leeward.
The leeward sides of mountains are however in the rain shadow and remain relatively dry. Kasese town and adjacent lands are dry partly because of being in the rain shadow cast by Mount Rwenzori. 
The areas do not experience the effects of the westerly winds blowing through Zaire Basin.  Ethiopian highlands have also contributed to the aridity of North Eastern Uganda and North Western Kenya.  When the relatively dry North East Trade winds from the Arabian Desert blow across these mountains,  they lose any little moisture they have on the wind ward side.  These winds descend as very dry air masses  on the southern slopes of the mountains where,  instead of releasing, they absorb moisture.  
 
Diagram showing effect of Relief on rainfall
They therefore play the role of desiccating winds.  This partially explains the semi-aridity in Karamoja/ Turkana land  and North Eastern Kenya.  Similarly, the South East Trade winds bring rainfall  on  the  southern  slopes  of Mountain f Kilimanjaro and descend as dry air on the north western slopes.