Long-term groundwater-level anomalies across Sub-Saharan Africa

Multi-decadal time series of groundwater levels were compiled by the authors from records of observation wells initiated and maintained by government departments and research institutions in nine countries in sub-Saharan Africa. The pan-African collation of these hydrographs was initiated at the 41st Congress of the International Association of Hydrogeologists (IAH) in Marrakech (Morocco) on 14th September 2014. All records were subjected to a rigorous review by the authors during which the integrity, continuity, duration and interpretability of records were evaluated. This process included dedicated workshops in Benin, Tanzania, and Uganda, and records failing these tests were discarded from the analysis. Procedures included taking of the first time derivative to identify anomalous spikes in records commonly associated with errors of data-entry. Where multiple records in same geographic and climate zone were available (e.g. Benin, South Africa) we prioritized records remote from potential areas of intensive abstraction. Statistical clustering of records was also used in the Limpopo Basin of South Africa to identify the representativity of employed records at Modderfontein and Sterkloop.