INTRA-SEASONAL RAINFALL CHARACTERIZATION FOR MAIZE AND SORGHUM PRODUCTIONS AT SORO WOREDA OF HADIYA ZONE, SOUTHERN ETHIOPIA

Abstract

Rainfall is the most important, but highly variable climatic resource for planning and management of the agricultural operations which principally affects the cropping calendar, production and productivity. Its variability in occurrence, amount and distribution coupled with high evapotranspiration has historically been the major cause of crop failure and food insecurity. Therefore, this study was conducted to analyze seasonal rainfall variability in terms of intra-seasonal rainfall indices and drought characteristics in Soro Woreda of Hadiya Zone, Southern Ethiopia. Thirty years climatic data (1987-2016) from NMA were used to determine seasonal rainfall variability by using statistical packages and the onset and end of the growing season, length of the growing period using FAO water balance and Reddy models, and INSTAT software. Markov Chain Model was used to analyze the distribution of dry and wet spells in the area. Mean statistical analysis result of observed rainfall data series revealed that long term mean annual rainfall varies ranging from 963 mm with a CV of 16% at Alaba Kulito to1537 mm with a CV of 30% at Hosanna station whereas longer rainy season (Kiremt) rainfall varies ranging from 399 mm with a CV of 31% at Alaba Kulito to 1027 mm with a CV of 19% at Hosanna station and shorter rainy season (Belg) rainfall varies ranging from 334 mm with a CV of 53% at Alaba Kulito to 429 mm with a CV of 39% at Fonko station. The mean onset of the long growing season was found to occur during the first meteorological decade of June and ended during the end of September. Similarly, the mean onset of Belg season was found to occur during the first decade of April at Alaba Kulito and second decade of April at both Fonko and Hosanna. Length of the growing period during the long rainy season (Kiremt) ranged from 133 days with a SD of 11 days and CV of 8.3% at Alaba Kulito to 180 days with a SD of 18 days and CV of 10% at Hosanna. The analysis results obtained from the Markov Chain model indicated that there were higher probabilities of dry spells during Belg, but it was minimal during the Kiremt season. Likewise, based on one, three, six and twelve month time scales analysis, SPI detected some drought events ranging from moderate to extreme in both season. The mean onset and cessation decades for maize was decade 10 and 22 at Alaba Kulito and decade 11 and 23 at both Fonko and Hosanna stations while for sorghum was decade 12 and 25 at Alaba Kulito and 11 and 26 at both Fonko and Hosanna stations. The water requirement of both crops is relatively high at Alaba Kulito following Fonko station and less at Hosanna station. Since maize and sorghum crops are long maturing crops, the seasonal rainfall variability and its implications for the production of these crops revealed that only Belg season rain cannot support most favorable growth of the crops. In general, during the occurrence of prolonged dry spells within the growing season, supplemental irrigation is important for the crops, particularly in Belg season to cope up with the problem of intra-seasonal rainfall fluctuations.