Assessment of NDVI variations in responses to climate change in the Horn of Africa

Abstract

The variation of normalized difference vegetation index (NDVI) mainly depends on the change of climatic factors (precipitation and temperature). This study is assessing and analyzing the inter-annual and seasonal change of NDVI in the Horn of Africa (HOA) (1982–2013). The relationship between climatic factors and NDVI values of global Inventory monitoring Modeling System (GIMMS) from 1982 to 2013 was analyzed by means of ordinary least squares, vegetation slope, simple linear regression and correlation coefficients. In addition, the land cover data of the (MODIS) Medium Resolution Imaging Spectroradiometer (i.e. MCD12Q1) are used to assess land-use change from 2001 to 2013 and GIMMS land cover data also applied to extract annual NDVI maximum from 1982 to 2013. The results show that NDVI is proportional to precipitation and inversely proportional to temperature, which precipitation decreased insignificantly while temperature increased significantly for the last 3 decades. In general, NDVI values gradually rise from spring to rainy season and fall steadily from autumn to winter. The NDVI of grassland, savanna and shrub land is more sensitive to climate change than the NDVI of forest and woodland. In grassland, savanna and shrub, NDVI gradients are positive, while in desert areas negative changes are recorded, while forests and woodlands are in transition between stable and positive NDVI gradients. The average NDVI value of each vegetation cover gradually increased from 1982 to 1998 and then slowly decreased from 1998 to 2013 due to precipitation variation. Forest and woodland cover were declined by approximately 0.4% and 1.28% in the past 2 decades. Thus, in the Horn of Africa, land degradation, such as deforestation and desertification, is a serious environmental problem.