.

GRACE-gridded monthly data for 2006 and 2015 was acquired to carry out spatial-temporal analysis of
Terrestrial Water Storage (TWS). This analysis was carried out with a view to estimating and assessing the
total water storage change between the two dates. The data was post-processed for north-south trending
errors, glacial isostatic adjustments and other non-hydrological effects; the time-variable gravity fields were
then converted to TWS variations. Multiband raster data for 2006 and 2015 were created by using composite
bands function in ArcGIS 10.5 and re-projected to World Geodetic System (WGS) 1984. Water storage trends
were generated by fitting a time series using least squares methods to determine the slope at each grid value
and re-sampled to bilinear interpolation. The TWS for 2006 varies from – 10.58 mm to 47.14 mm with the
mean and standard deviation of 9.86 mm and 10.10 mm respectively. While the spatial variability in TWS for
2015 ranges between - 27.51 mm and 64.03 mm, with 17.54 mm and 20.73 mm as the mean and standard
deviation. The water thickness change between 2006 and 2015 over West Africa varies between -43.36 mm
and 56.29 mm, having 7.66 and 22.18 as the mean and standard deviation respectively.
The study concluded that variable water storage change in terms of gain occurred across the central portion of
West Africa trending east-west direction and to the south, while mutable storage deficit took place at northeast,
south-east, south-west and north-west between 2006 and 2015.