New Rainfall Datasets for the Congo Basin and Surrounding Regions

This paper describes three new rainfall datasets that have been developed for equatorial Africa. The development relies on acquisition of recent gauge data from the relevant countries and statistical methods to fill in gaps in coverage. Two of the three datasets are gridded with spatial resolutions of 2.5 degrees and 5.0 degrees, and the third is regionally aggregated and based purely on gauge data. The work is based on a total of 1826 gauge records in the analysis sector, of which only several hundred operate in recent years. The gridded datasets were produced and validated by using a period of dense coverage (1947-72) to calibrate a spatial reconstruction method, which is then utilized to grid data for the remaining years. The period 1973-2010 served as a validation period. The validation was carried out by comparing the gridded values with values obtained by simple averaging of station data in grid boxes with an adequate number of stations. This exercise clearly showed that the statistical reconstruction approach based on principal components produced far superior results than those from the more commonly used kriging. The gridded datasets cover each month of the year, six seasons, and annual rainfall, and they commence in 1921 and extend through 2014. In contrast, the gauge-only regional dataset covers varied time periods, depending on the geographical region in question. Records for several regions cover nearly all of the twentieth century and most extend to 2014.