Rainfall Characteristics during the Years of Significant Departures from Normal in the Sudano-Sahelian Ecological Zone of Nigeria

The rationale examining the rainfall characteristics during the years of significant departures from normal in the Sudano-Sahelian Ecological Zone (SSEZ) of Nigeria is based on the devastating effects of extreme weather events and their subsequent implications for agriculture and food security in sub-Saharan Africa. This study designated Significant Years of Positive Departure (SYPD) and Negative Departure (SYND) of rainfall from normal using a Z-score analysis on 39 years of rainfall data (1980-2018) for Sokoto, Kano, Maiduguri, and Nguru.

The results show that nine years possessed significant positive departures in rainfall versus six years of negative departures significant at α = 0.05. The frequency of occurrence of intra-seasonal dry spells outweighed that of wet spells in all the years except in 2000 (Maiduguri), 2012 (Kano and Nguru), and 2016 in Sokoto. Light rainfall contributed almost 60% of the total annual rainfall in the zone with heavy rains comprising 17.6% of the total in SYPD versus only 3% in SYND. The average length of the growing season (106 days) was higher during the SYND than the SYPD with an average of 99 days. Onset and retreat days were mostly recorded during June and September respectively in SSEZ. This study found that SYPD in Sudano-Sahelian Ecological Zone possessed more wet occurrences than dry periods resulting from below-normal rainfall. These wetter occurrences also possess food security concerns because of their timing, while the SYND years portend to drought and possible famine.