Analysis of past and future intra-seasonal rainfall variability and its implications for crop production in the north eastern Amhara region, Ethiopia

Rainfall is the most important but variable climatic element in semiarid regions. The present study analyzed intra-seasonal rainfall variability, its trends and implications of rainfall change and variability risk on crop production at four stations located in the semiarid North Eastern Amhara Region as in put variables observed (1992-2012) and future projected (2021-2040) daily rainfall data were used. The observed daily rainfall data were obtained from the National Meteorology Agency (NMA) while future daily rainfall data were downscaled for three Global Circulation Models, GCMs (CSIRO-Mk3-6-0, Had GEM2-ES and MIROC-ESM-CHEM) under the 4.5 representative concentration Pathway (RCP) using MarkSim weather generator. After quality control, the rainfall data were subjected to computation of rainfall variability indicator indices such as rainfall totals, rainfall start and end dates, length of growing period (LGP), number of rainy and dry days, and length of dry spells using INSTAT 3.36 software. The analyses of observed data revealed that annual, seasonal Kiremt and Belg rainfall totals were characterized by low amount, short duration, early cessation and high dry spell probabilities for both Kiremt and Belg seasons. The analysis also indicates that the Belg season has been failing increasingly (33-66%) in the region and it is projected to worsen in the future. The projected increasing change in rainfall totals and decreasing change in rainy days indicated that the future Kiremt season will probably experience water logging/flood over the majority stations and this will affect crop production. The GCMs used in the study agreed on reduction of rainfall amount in the Belg season and shortening of the LGS in both the Belg and Kiremt seasons by 2030s at all the studied stations. The implication of the results is that crop production during the Belg season will be risky even for drought tolerant crops as the projected mean LGP in the region will be in the range of 28-54 days only. According to models projection, a combination of early onset of Kiremt and late start of Belg seasons could be advantageous for relatively long maturing and dry spell tolerant crops such as sorghum and millet. Supplemental irrigation from rainwater from month of July and August in which maximum rainfall will be found may be possible for the dry month of September.