Wavelet Analysis of Hydroclimatic Teleconnections and Precipitation Variability over Ethiopia

Abstract

Atmospheric variables like precipitation and stream flow are significantly influenced by various climatic factors and large-scale atmospheric circulation patterns. Investigations into the variation of rainfall by different large-scale oceanic impacts are very fundamental for the economy and climatic maintenance of the country. The study examines the variability of precipitation over Ethiopia through the analysis of monthly and annual rainfall data at five stations in the north, east, west, south, and central parts of Ethiopia from 1987 to 2017 for 31 years. Standardized precipitation ratio (Ip) and wavelet analyses were applied to examine the spatiotemporal variability of precipitation and to determine the effect of oceanic fluctuations on rainfall variability. The calculated standard precipitation index (Ip) indicates the year-to-year variability of rainfall over Ethiopia, which lies between 3.2 and -2. The continuous wavelet technique applied to the yearly time series of precipitations over five stations in Ethiopia reveals short- and long-term periodicities like 2-3, 3-5, and 6–10 years at different time periods. The oceanic indices reveal long-term oscillations like 2-3, 3-5, 6–10, and 8–13 years over different time periods. The rainfall and oceanic fluctuations show similar periodicity in some parts of Ethiopia. Our analysis reveals that the northern part of Ethiopia is negatively affected by Nino-4 during 1992-2003 with a flood event (wet 2.5) around 2001, the southern part is negatively affected by NAO during 2009-2016 with a severe drought (dry -2) in 2014/2015, the western part is negatively affected by SOI during 1992-2005 with two severe droughts observed around 1994/1995 (dry -1.8) and 2003 (dry -2), the eastern part is negatively affected by MOI during 1995-2000 with a drought around 2000/2001, and the central part is negatively affected by Nino-4 during 2002-2010 with a drought (dry -1.3) around 2004/2005.