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

Adewale O Adeyefa,Theophilus O Odekunle

doi:10.5539/jgg.v14n1p9

Adewale O Adeyefa, Theophilus O Odekunle

Open Access

https://doi.org/10.5539/jgg.v14n1p9

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Abstract

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. &nbsp;  The results show that nine years possessed significant positive departures in rainfall versus six years of negative departures significant at &alpha; = 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. &nbsp;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.

Highlights

Climate, a basic and an active factor in the physical environment is constituted by interactions among many elements of which precipitation plays a significant role (Umar & Bako, 2019 and Chinago, 2020)
As noted by Odekunle (2004), extreme events related to the onset of the rainy season in Nigeria can result in a false start to the rainy season and may lure farmers to plant crops early and can spell disaster for farmers if the first rains are followed by a long period of drought
The results indicated that light rainfall contributed an average of 52.8% to the total annual rainfall, during the Significant Years of Positive Departure (SYPD) whereas, an average of 77% contribution to the total annual rainfall occurred during the significant years of negative departures (SYND)

Summary

Introduction

A basic and an active factor in the physical environment is constituted by interactions among many elements of which precipitation plays a significant role (Umar & Bako, 2019 and Chinago, 2020). Rainfall in the tropics is important because it supports life, economic growth, and water supply in general. Significant departures or anomalies from this established mean or normal often comprise extreme weather events, which impact environmental processes (Olaniran, 2004). Such extremes are usually characterised by intense heavy downpours, dry spells within growing seasons, delays in onset and retreat of rainfall, and drastic changes to below or above the values accepted as normal for specific periods of the year. Capable of causing upsets in many important environmental parameters such as the water balance, these rainfall departures possess implications for food security. Knowledge of rainfall characteristics during periods of excessively wet and dry years is required for accurate mitigation planning in agricultural endeavours, the major occupation of the residents of the region

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