The two monthly gridded precipitation datasets of the Global Precipitation
Climatology Project (GPCP) (satellite only) and the Global Precipitation
Climatology Center (GPCC) Variability Analysis of Surface Climate
Observations (VASClimO) (raingauge) are compared on a 21-yr period,
January 1979 - December 1999 over land areas. The two datasets are
consistent with respect to the spatial distribution of the annual and seasonal
rainfall climatology over the domain and along latitudinal bands. However,
the satellite generally overestimate rainfall. The inability of the GPCC data
to capture the bimodal rainfall pattern along the Guinea coast could
be an artifact of the interpolation of the rain gauge data. With regards to
interannual variability the satellite and gauge agree reasonably well on the
sign of the anomaly in most cases although the magnitudes are different. For the
northern latitudes the two datasets agreed on the sign of the anomaly 17 out of
the 21 years (81% of the time). The datasets agreed on the sign of the anomaly 11
out of the 21 years (52% of the time) over the Guinea Coast. Most of the years
during which the two datasets did not agree on the sign of the anomaly, were years
with El Nino events. The root-mean-square difference for seasonal rainfall range
between 1.34 to 44.14. The Kendall's tau statistic indicated statistically significant
trends in both datasets separately.  The trends were essentially the same.