SUB-SEASONAL TO SEASONAL RAINFALL VARIABILITY AND ITS IMPACT OF ON CROP PRODUCTION IN THE NORTH WOLLO AND WAG HEMRA ZONES, AMHARA REGIONAL STATE, ETHIOPIA

Abstract

Rainfall variability directly or indirectly influences the quality and quantity of agricultural crop production. This study aimed to evaluate rainfall variability starting from sub-seasonal time scales and investigate its influence on rain-fed wheat and sorghum yield production in the North Wollo and Waghemra zones of Ethiopia. Specifically, the study focused on assessing the characteristics of the onset, cessation, length of the growing season, dry spell probabilities as well as spatiotemporal variability including extreme rainfall events. To achieve these objectives, observed daily rainfall data were collected from the Ethiopian Meteorological Institute (EMI) for the periods of 1990 to 2020. The yield data of wheat and Sorghum from 2007 to 2018 was obtained from the annual agricultural survey database of the Ethiopian Statistics Services (ESS) and the Amhara Region agriculture offices in the North Wollo and Wag Hemra zones. Access the rainfall variability, rainfall data were analyzed using the coefficient of variation (CV), precipitation concentration index (PCI), and standardized rainfall anomaly. The modified Mann–Kendall trend test and Sen's slope estimator were used to analyze rainfall trends. The seasonal meteorological drought was evaluated using a standardized precipitation index (SPI). The rainfall variability and crop yield relationship was accessed using the correlation function. The results showed that sub seasonal and seasonal rainfall in the area are highly variable and non-uniform. June and September are highly variable months of the main rainy season having a higher CV, mostly greater than 30 %. The Kiremt (June to September) seasonal rainfall showed an increasing trend at Amdework, Sirinka, Debrezebit, Sekota, Woldia, Geregera, Gobiye and Robet stations by 3.4, 1.2, 7.10, 3.3, 8.2, 1.3, 2.2, and 5.6 mm per year. On the other hand, the drought occurrence has increased in many stations during the study period. The rainfall features such as onset date, cessation date, length of growing period, and probability of dry spells are highly variable, making agricultural decisions highly uncertain. Moreover, wheat and sorghum crop yields have a strong correlation with these rainfall features. This implies that the timing and distribution of rainfall highly dictate crop production in the study area. The inclusion of tailored sub-seasonal forecast information in the agro advisory is recommended.