A GIS-based impact assessment of vegetation on rainfall patterns in cross river state, Nigeria

Vegetation dynamics are the phenological metrics variations and transformations in the vegetation of different land cover types over a particular region. This study investigated the spatio-temporal vegetation dynamics employing NDVI, and its response to climate variability (rainfall) between 1988-2018 with the specific objective of determining the rainfall pattern over 40years, determining land use change trend, investigating the annual NDVI trend, and analyzing the correlation between NDVI, land use and rainfall in the study area. The study utilizes annual land use land cover analysis and land use dynamics of the area from the European Sentinel Agency Climate Change Initiative (ESA CCI) at 300m resolution to analyse the vegetative response. Annual NDVI at 250m and 30m spatial resolution from very high-resolution MODIS MOD13Q1, Landsat images, and average annual rainfall for the years; 1988, 1998, 2008, and 2018 were also collected and analysed respectively. The annual Rainfall increased from 1988 to 1998 then decreased steadily from 2008 to 2018. The Av. Mean rainfall is 211.22mm, 239.64mm, 228.83mm, and 220.12mm in 1988, 1998, 2008, and 2018 respectively. Tree-covered areas had shown an increase between 1988 and 1998, then decreased from 2008 to 2018. Cropland increased from 1988 to 2008 with a sharp increase from 2008 to 2018. Grassland witnessed a swift decrease from 1988 to 1998 then steadily from 2008 to 2018. The annual NDVI for the vegetative area (tree-covered, grassland, and cropland) decreased from 1988 to 1998 but increased steadily to 2018. The NDVI of grassland, savanna, and shrubland is more sensitive to climate change than the NDVI of forest and woodland which shows that tree cover decreases while cropland increases. Comparison analysis shows that Rainfall and tree-covered areas have a direct linear relationship while Rainfall and NDVI/Vegetative areas enjoy an inverse relationship.