Drought events are also analyzed in this study based on El Nino and La Nina years (Table 2). For example, in Table 3, we can see that the drought explained by SPI, RDI, and SPEI identified an extreme drought category for Sagure station in the summer and March–August (six months) in 2009 (a moderate El Nino year). Furthermore, during crop growing season (March–August) in 2015 (a very strong El Nino year), Kulumsa and Hawassa are classified as severe drought (based on the SPI and the SPEI) and extreme drought (based on the RDI). The Ziway station, in the summer season of 1987 (the strong El Nino year), was under the extreme drought category. These findings are comparable with earlier research conducted across Ethiopia (Segele & Lamb 2005; Diro et al. 2011). They discovered that El Nino years are related to deficit in rainfall (drought).

Table 2

Selected ENSO years based on the Oceanic Niño Index (ONI) available in the National Oceanic and Atmospheric Administration's (NOAA)

El Nino year
La Nina year
Very strongStrongModerateWeakStrongModerateWeak
1982 1987 1986 2004 1988 1995 1983 
1997 1991 1994 2006 1999 2011 1984 
2015  2002 2014 2007  2000 
  2009  2010  2005 
      2008 
      2016 
      2017 
El Nino year
La Nina year
Very strongStrongModerateWeakStrongModerateWeak
1982 1987 1986 2004 1988 1995 1983 
1997 1991 1994 2006 1999 2011 1984 
2015  2002 2014 2007  2000 
  2009  2010  2005 
      2008 
      2016 
      2017 
View Large
Table 3

The peak negative values for three drought indices (SPI, RDI, and SPEI) in spring, summer, and six-month (March–August) time periods

StationIndexSpring (February–May)
Summer (June–September)
6 months (March–August)
ValueYearValueYearValueYear
Butajira SPI −2.26 2017 −3.00 2017 −2.81 2017 
RDI −2.18 2017 −3.01 2017 −2.78 2017 
SPEI −1.70 2015 −2.21 2017 −1.94 2017 
Ziway SPI −1.79 1999 −3.39 1987 −2.32 1999 
RDI −1.77 1999 −3.32 1987 −2.04 2002 
SPEI −1.64 2015 −2.29 1987 −1.79 2002 
Kulumsa SPI −1.89 2008 −2.23 2005 −1.77 2015 
RDI −1.88 2008 −2.11 2005 −2.06 2015 
SPEI −1.63 2015 −1.70 2014 −1.96 2015 
Sagure SPI −2.16 1980 −2.10 2009 −2.39 2009 
RDI −2.11 1999 −2.12 2009 −2.27 2009 
SPEI −2.14 1999 −2.69 2009 −2.26 2009 
Wulbareg SPI −2.11 2009 −1.96 1981 −1.87 2004 
RDI −2.06 2011 −1.92 1981 −1.81 2004 
SPEI −1.98 2011 −1.88 1981 −1.82 2004 
Hawassa SPI −2.77 2015 −1.91 1993 −1.77 2015 
RDI −2.93 2015 −1.79 1993 −2.09 2015 
SPEI −2.26 2015 −1.74 1993 −1.97 2015 
StationIndexSpring (February–May)
Summer (June–September)
6 months (March–August)
ValueYearValueYearValueYear
Butajira SPI −2.26 2017 −3.00 2017 −2.81 2017 
RDI −2.18 2017 −3.01 2017 −2.78 2017 
SPEI −1.70 2015 −2.21 2017 −1.94 2017 
Ziway SPI −1.79 1999 −3.39 1987 −2.32 1999 
RDI −1.77 1999 −3.32 1987 −2.04 2002 
SPEI −1.64 2015 −2.29 1987 −1.79 2002 
Kulumsa SPI −1.89 2008 −2.23 2005 −1.77 2015 
RDI −1.88 2008 −2.11 2005 −2.06 2015 
SPEI −1.63 2015 −1.70 2014 −1.96 2015 
Sagure SPI −2.16 1980 −2.10 2009 −2.39 2009 
RDI −2.11 1999 −2.12 2009 −2.27 2009 
SPEI −2.14 1999 −2.69 2009 −2.26 2009 
Wulbareg SPI −2.11 2009 −1.96 1981 −1.87 2004 
RDI −2.06 2011 −1.92 1981 −1.81 2004 
SPEI −1.98 2011 −1.88 1981 −1.82 2004 
Hawassa SPI −2.77 2015 −1.91 1993 −1.77 2015 
RDI −2.93 2015 −1.79 1993 −2.09 2015 
SPEI −2.26 2015 −1.74 1993 −1.97 2015 
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