Rainfall Variability and Trends Analysis in the Sorghum Growing Semi-Arid Rift Valley of Ethiopia

In Ethiopia, 60% of the land is covered by sorghum, and the climate affects the major producing regions. The objective of this work was to assess variability and trends of rainfall in the semi-arid Rift Valley of Ethiopia. 40 years of rainfall data were analyzed for 11 stations. The selected parameters were analyzed for rainfall variability and trend analysis was performed following Mann–Kendall methods. The start and end of the growing season, length of the growing period, and dry spells were analyzed for the stations . The results showed in all the locations was the highest mean monthly rainfall recorded in July, and August then followed by September. Compared to the longest rainy period ( 52.3–70.8% ), the short rainy period ( 19.4–33.2% ) contributes less rainfall to the annual rainfall which was also associated with high inter-seasonal variability (CV ranged from 31.5 to 88%) short rain season. PCI value in studied regions in all stations showed the existence of high concentration in seasonal rainfall distribution. Sen’s slope for NRVE, ERVE, and CRV increases by 0.02-0.81, 0.05-0.71, and 0.02-0.81 mm/yr. in September. Rainfall from 0.31-2.76 mm/yr. decreases to a 0.19-5.12 mm/yr increase in the short and main seasons. Rainfall has increased in some stations (from 0.042 to 3.88 mm/yr.) but decreased in five stations (1.29 to 3.71 mm/yr.). Stations with different rainfall onset and CV (4.9%–16.6%) have varying rainy seasons (24 to 200 days), which affect crop yield. Longer periods lower the risk; it rains every 90 days for crops. Optimize management based on LGP and rainfall variations at stations. Climate change risks crop yields. Consider early crops and rainwater collection.