TITLE:
Changes in Vegetation and Rainfall over West Africa during the Last Three Decades (1981-2010)
AUTHORS:
Adama Bamba, Bastien Dieppois, Abdourahamane Konaré, Thierry Pellarin, Ahmed Balogun, Nadine Dessay, Bamory Kamagaté, Issiaka Savané, Arona Diédhiou
KEYWORDS:
Decadal Variability, NDVI, Re-Greening, Rainfall Recovery, Significant t-Test
JOURNAL NAME:
Atmospheric and Climate Sciences,
Vol.5 No.4,
September
14,
2015
ABSTRACT: The decadal variability of rainfall and
vegetation over West Africa have been studied over the last three decades,
1981-1990, 1991-2000 and 2001-2010 denoted as 1980s, 1990s and 2000s,
respectively. Climate Research Unit (CRU) monthly precipitation and Normalized
Difference Vegetation Index (NDVI) from the National Oceanic and Atmosphere
Administration (NOAA), all covering the period 1981-2010 have been used. This
study aimed to assess the changes in the land surface condition and the
spatio-temporal distribution of rainfall over West Africa region. The
relationship between rainfall and vegetation indices over this region was
determined using Pearson’s correlation. Also, the decadal comparison between
rainfall and NDVI over the region was based on the significant t-test and the
Pearson’s correlation. Results showed that significant return to wet conditions
is observed between decade 1980s and decade 1990s over West Africa, and also
during decade 2000s with the exception of central Benin and the western Nigeria.
Meanwhile, a regreening of the central Sahel and Sudano-Sahel regions is noted.
From 1990s to 2000s, this regreening belt is located in the South and the
coastal areas: the Guinea Coast, Sudano-Guinea and western Sahel regions. A
northward displacement of this re-greening belt is also detected. Thus, a
linear relationship occurs between rainfall and NDVI in the Sudanian savannah
region, but it is not the case in the rest of West Africa. This may suggest
that the re-growth of vegetation in the Sudanian savannah region may be linked
to rainfall supplies. Therefore, re-greening over Sahel region in 1990s is
related to rainfall recovery. However, this re-greening was not sustained in
the decade 2000s due to a slight decrease in rainfall.