From about 1920, rainfall was measured over the entire Sahel, the number of rainfall stations reaching a peak between about 1950 and 1990, but decreasing since then. In Mali rainfall has been monitored since 1910, with 140 weather stations at maximum during 1960-1985. Currently some dozens of weather stations are operational. A serious problem with using rainfall data from stations in West Africa is the large, and increasing, number of missing values. Satellite technology allows an alternative method of monitoring rainfall.
Available rainfall gauge data on weather stations in Guinea and Mali, located within the Upper Niger Basin and Inner Niger Delta (location see viewer) are presented in the interactive graphs below. The first interactive graph shows the recent RFE (rainfall estimate) compared to satellite derives RFE’s from the period 2001-2016. The second interactive graph show the actual rainfall measurements per station over a long series of years, thus before satellite RFE’s were available.
The reliability of satellite derived RFE’s is depending on several factors. The accuracy of RFE differs per regions. For instance, the accuracy of RFE from the region of Bamako is accurate, while the estimates for the headwaters for Guinea are less accurate (see graphs below). This means that it is very important to continue with ground station measurements.
Comparison of Satellite derived rainfall estimates (RFE’s) with ground station measurements for the region of Bamako in Mali and Kankan in Guinea. The graphs show that the RFE’s in the region of Kankan are generally overestimating rainfall.
Historical rainfall data are published in the annals of the national meteorological organisations, and for Francophone Africa in the past also in the annals of Orstom. These data were summarised for 10-year periods for a number of key stations by the Smithsonian Institution (1920-1940) and the Department of Commerce (uas) (1941-1960). Since 1961, monthly data have been published by the Department of Commerce in the “Monthly Climatic Data for the world”. The latter data can also be downloaded from the National Centers for Environmental Information (NCEI) from the US government. Several institutes and organisations have digitalised the historical meteorological data. A large dataset was collected and made available by the Climate Research Unit (CRU) from the University of East Anglia (uk). Another source is the Global Historical Climate Network, jointly produced by the National Climate Data Center (ncdc) of the Arizona State University (uas) and Oak Ridge National Laboratory (ornl).