Spatio-Temporal Analysis of Rainfall Variability and Meteorological Drought: A Case Study in Bilate River Basin, Southern Rift Valley, Ethiopia

Abstract

Rainfall always plays a deciding role in sustainable agricultural production. This research attends to analyzes variation of rainfall, examine trends of rainfall, evaluate the relationship between ENSO and rainfall variability, and analyzes meteorological drought in Bilate River Basin. The Bilate River Basin includes the portion of SNNPRS regional zones; Hadiya, Kanibate Tembaro, Gurage, Silte, Wolaita, Sidama, and Alaba special woreda and small parts of the South-central Oromiya Regional states. The analysis was done based on historical recorded rainfall data, 26 to 40 years (1974-2013) and ENSO data. Rainfall variability were analyzed through using basic statistics like mean, standard deviation, and coefficients of variation and trend were analyzed by non-parametric Mann-Kendall test methods. From the analysis Butajira both in Belg and Kiremt season rainfall were significant at α=.1, α=.05, α =.01 level with critical statistic table value 1.645, 1.96, and 2.576 respectively. In addition to this, in Shone annual and Belg seasons were significant. In the study area El Niño enhances rainfall activities and La Niña periods lowering rainfall. La Nina episode decrease the amount of rainfall in Belg season and increase the amount of rainfall in Kiremt, while El Nino increase the amount of rainfall in Belg and decrease the amount of rainfall in Kiremt season of the regime. Drought is a natural feature of climate variability in all parts of world. The Standard Precipitation Index (SPI) method was used in this study to analyses major drought characteristics intensity, severity, duration, magnitude, frequency and spatial extents. The highest drought magnitude observed in Sodo when comparing with all seasons which magnitude is-2.1 in SPI-3B and SPI-3K seasons. Next to Sodo is Shone and Hossana its magnitude is-1.88 in SPI-3B seasons. This study could help planners prepare proper forecasting for either long or short-term plans. Encourage to forecasting of El Niño and La Niña periods in each year's. Create awareness about meteorological droughts for society. Geographic Information System were used to generate drought severity maps for Belg and Kiremt seasons of recent eleven years, through using Ordinary Kriging method to interpolation and Coefficients of variations through Thiessen polygon method to interpolation.