VEGETATION RESPONSE TO RAINFALL VARIABILITY IN THE SUDANO SAHELIAN ECOLOGICAL ZONE OF NIGERIA

Abstract

Rainfall variability is an important driver of vegetation shift or dynamics. However, the changes are symmetric and have great multiplying effects on the ecosystem and the general livelihood of man. The study examines the vegetation response to rainfall variability in the Sudano Sahelian Ecological Zone of Nigeria (SSEZ). Rainfall data from the Climate Research Unit (CRU) and the United State Geological Survey (USGS) for satellite imageries for the study areas was acquired for the period of 1981-2018 (37 years). The Interseasonal Rainfall Monitoring Index (IRMI) was used to compute the “actual “or “real” onset and cessation date of the raining season, onset of rains was taken as the pentad within which the index is greater than or equal to 1(≥1) for the first time. The Monsoon Quality Index (MQI) was also used to determine the moisture quality in the study area and the Perpendicular Vegetation Index (PVI) for the analysis of the satellite images at the IR and the NIR. The results revealed that rainfall in the region is highly variable across the ecological zone, the lowest average rainfall is Nguru with an average rainfall of (536mm) and the highest average rainfall is Yelwa (1090.65). The Average Length of Raining Season (LRS) was between 120-140 days, Monsoon Quality Index (MQI) was calculated to determine the quality of rainfall, rainfall in the region ranged from good with value <0.005 and to extremely poor with value >0.02. Satellite imageries analysis shows a change in vegetation dynamic over the years under review. The Normalize Difference Vegetation Index (NDVI) was used to determine the vegetation index, i.e. the vegetation vigour of the region; they were ranked from areas with poor, moderate and healthy vegetation, Maiduguri, Nguru have NDVI value of around -0.2 which signify poor vegetation with average annual rainfall of less than 600mm, Kano and Gusau with NDVI value of 0.0564 which signify moderate vegetation with average annual rainfall of around 800mm and Yelwa and Bauchi has NDVI value of around 0.826whcih shows healthy vegetation with average annual rainfall of more than 1000mm. from the research it was deduced that rainfall is a function of vegetation growth, vegetation can respond positively or negatively to increase or decrease in the quality of rainfall received in a region.