Mengistu, Gizaw (PhD)Gebremariam, Temesgen2018-07-042023-11-092018-07-042023-11-092011-06http://10.90.10.223:4000/handle/123456789/6441The study compared the performance of four di erent cumulus parametrization schemes in the ICTP's Regional Climate Model RegCM4 for the period 1989-2008 over the Horn of Africa. The Horn of Africa has been delineated in to 12 homogeneous region based on clustering method that minimizes a sum of dissimilarities. Grell-FC scheme best captured the mean climatology. Within the 12 clustered regions positive/negative precipitation biases are obtained in Emanuel/Grell-AS and Kuo convective schemes while intermediate values closer to zero are obtained in Grell-FC. Grell-FC scheme is then selected for customization over the Horn of Africa. To improve the simulation of rainfall using the selected Grell-FC scheme, several sensitivity experiments are performed by adjusting the minimum and maximum precipitation e ciency, the minimum and maximum shear e ect on precipitation e ciency, the minimum and maximum convective heating and the available buoyant energy removal time scale. Setting the minimum and maximum shear e ect on precipitation e ciency to 0.10 and 0.30 respectively improve the correlation, which implies a better simulation of precipitation. Setting the minimum and maximum convective heating to -150 and 400 respectively minimize the positive bias over most of the regions. 17 years long period run revealed that using the new values of shear e ect on precipitation e ciency improve the correlation and representation of the inter-annual variabilityenModeling over the Horn of AfricaThesis