Title: Impact of Rainfall Variability on Crop Yield and its Relationship with Sea Surface Temperature of Pacific Ocean in Different Agro-Ecology Zone of South Wollo Amhara Ethiopia By Sisaynew Getahun, supervised by Dr Dejena sahlu and Dr Dessalegn chania Agriculture in Ethiopia is the backbone of the economy, because more than 85% of the population is depend on rain-fed agriculture. However, most parts of the country, especially south Wollo is vulnerable to recurrent drought and crop failure due to rainfall variability. This study examines the impacts of rainfall variability on crop yield and its relation to Nino 3.4 SST in different agro-ecology zones of south Wollo, Ethiopia. Rainfall data obtained from the Ethiopian meteorological institute, Nino 3.4 regions of the Pacific Ocean SST were downloaded from NOAA and major crop yield data were obtained from the South Wollo Central Statistical Agency. Mean, Coefficient of variation, precipitation concentration index, and standardized anomaly were employed to describe Crop yield and rainfall variability. INSTAT software used to determine onset and cessation dates of Kiremet season. R-Studio and Mann-Kendall trend test, used trend significance test. Correlation analysis to examine the relationship between rainfall characteristics with SST and crop yields, regression analysis to explain the impact of rainfall variability on crop yield. The analysis revealed that seasonal rainfall is moderate to highly variable in all Agro-Ecology Zones. Correlation between Kiremet rainfalls with SST lag 0, 2 shows negative significance in all Agro-Ecology Zones, and Belg rainfall with SST lag 0, shows positive significance in the Midland area. Rainfall characteristics correlated less to high with selected crop yields (Maize, Sorghum, Teff, Wheat, and Barley) in the study area. The result of Regression revealed that variability of Sorghum crop yield in the lowland area is explained by 88% of Rainfall characteristics. Maize, Sorghum, and Teff crop yield in the Midland area is explained by 69%, 69%, and 53% Rainfall characteristics respectively, Barley and Wheat crop yield in the Highland area is explained by 91% and 75% Rainfall characteristics respectively. Variability of Barley crop yield in the Upper Highland area is explained by 36% Rainfall characteristics. This shows that crop yields are highly variable due to Variability of Rainfall characteristics, so important adaptation strategies will be implemented for the study area to cope with the risks, sustain farming, and improve crop variety. So it is better further study investigated future projection of climate variability in the study area.