Characterizing Rainfall Variability to Enhance Agricultural Planning in the Eastern Oromia, Ethiopia

Abstract Rainfall variability is one of the major challenges for agriculture in Eastern Oromia, Ethiopia, where smallholder farmers rely mostly on rain-fed systems. This study investigates rainfall patterns, from 1992 to 2024, basically using the dataset from the Ethiopian Meteorological Institute. Rainfall trends and magnitudes were analyzed by using Mann-Kendall test and Sen’s slope, while spatial trends were interpolated with inverse distance weighting in ArcGIS. Onset and cessation dates, the length of the growing period, and dry spells probabilities were examined using Markov chain modelling in INSTAT+. Results showed substantial variation in mean annual rainfall among woredas. Average annual precipitation ranged from 563.6 mm in Mieso to 886.4 mm in Chiro, this is may be largely influenced by local topography and other factors. The annual Precipitation Concentration Index (PCI) was 17.9 in Chiro while 19.8 was found in Babile, indicated a moderate concentration of rainfall. For the Kiremt season, the PCI values ranging from 31.6 in Babile to 37.4 in Chiro, reflecting strongly irregular rainfall distribution during study periods. During the Belg season, the Precipitation Concentration Index values between 35.9 in Mieso to 39.8 in Gurawa, suggesting greater variability than Kiremt season. Onset and cessation date varied across the woredas. Late onset date was observed in the Mieso and Babile (80–90 days), but in Chiro early onset was observed (65–70 days), this shortened the growing periods to 65–81 days. Kiremt started early in Gurawa (150–160 days) and then ran late into Babile (170–180 days) with a stable end around mid-October (285–290 days), and the growing periods were 85–110 days. Dry spell probabilities show that Mieso and Babile are drought prone areas, during the whole study period. These results point toward the need for flexible measures like planting drought tolerant crops, adjusting sowing date, supplemental irrigation, and using soil conservation practices, so as to strengthen resilience in selected woredas of Eastern Oromia.