An Examination of Rainfall Trends in Equatorial Africa Using Newly Created Datasets

Three new rainfall data sets 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 data sets are gridded with spatial resolutions of 2.5 ° and 5.0 ° 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 data sets were produced by and validated by using a period of dense coverage (1947 to 1972) to "calibrate" a spatial reconstruction method, which is then utilized to grid data for the remaining years. The period 1973 to 2010 served as a validation period. The gridded data sets cover each month of the year, six seasons, and annual rainfall and they commence in 1921 and extent through 2014. The gauge-only regional data set covers varied time periods, depending on the geographical region in question. These data sets were used to examine multi-decadal rainfall trends, concentrating on the April-to-June rainy season. There are strong negative trends in eastern and southern portions of the Congo Basin, but positive trends in more western sectors, particularly in the northwest. This pattern of upward AMJ trends in the northwest, downward trends in the south and east prevails over most of the area between 12.5 N and 20 S. Many of the regional time series show a decline in AMJ rainfall commencing sometime in the 1960s, but some show a recovery in very recent years. Results for the other seasons are also presented.

Three new rainfall data sets 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 data sets are gridded with spatial resolutions of 2.5 ° and 5.0 ° 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 data sets were produced by and validated by using a period of dense coverage (1947 to 1972) to "calibrate" a spatial reconstruction method, which is then utilized to grid data for the remaining years. The period 1973 to 2010 served as a validation period. The gridded data sets cover each month of the year, six seasons, and annual rainfall and they commence in 1921 and extent through 2014. The gauge-only regional data set covers varied time periods, depending on the geographical region in question. These data sets were used to examine multi-decadal rainfall trends, concentrating on the April-to-June rainy season. There are strong negative trends in eastern and southern portions of the Congo Basin, but positive trends in more western sectors, particularly in the northwest. This pattern of upward AMJ trends in the northwest, downward trends in the south and east prevails over most of the area between 12.5 N and 20 S. Many of the regional time series show a decline in AMJ rainfall commencing sometime in the 1960s, but some show a recovery in very recent years. Results for the other seasons are also presented.