Validation of the abrupt change in GPCP precipitation in the Congo River Basin

Abstract

AbstractThe Global Precipitation Climatology Project (GPCP) monthly precipitation exhibits a significant negative trend during 1979–2004 over southern tropical Africa from the Congo River Basin to the east coast. This trend appears as a more than 20% drop beginning in 1992 in the 6‐year and 9‐year averages of the areal mean GPCP satellite‐gauge precipitation, whose magnitude is largely determined by the gauge analyses. This paper's analysis of satellite precipitation estimates, gauge precipitation analyses, and gauge coverage information suggests that the negative precipitation trend is only true in part of southern tropical Africa but the magnitude is much smaller than that calculated from the GPCP. In the eastern portion of the region, the precipitation drop in the GPCP is confirmed by the satellite‐only estimates but the decrease of more than 16% is amplified by a change in gauge coverage. In the western portion of the region, basically the southern Congo River Basin, all gauge dependent products show a negative precipitation trend, which is much larger in the GPCP merged satellite‐gauged data set, but not supported by the satellite‐only precipitation estimates. In this study we conclude that for the Congo River Basin, where both the mean precipitation and its spatial gradient are high, the spurious negative trend detected in the GPCP precipitation is caused by a significant change in local gauge coverage and the methodology used by the GPCP to merge satellite and gauge data during the analysis period. Copyright © 2009 Royal Meteorological Society