This PhD thesis provides a major step towards the development of high-resolution climate and river flow records in sub-Saharan Africa. Dendroclimatological methods are employed and adapted to disclose the proxy archive of Juniperus procera trees in Ethiopia. The study entails a quest for annually datable growth rings across the Ethiopian Highlands. The environmental sensitivity of multiple tree ring variables, including ring width, carbon and oxygen isotopes, and minimum blue intensity, is explored. A composite chronology based on ring widths and carbon isotopes is constructed and employed to develop the first annually resolved reconstruction of Blue Nile flow. The results are placed in the wide scope of ongoing Quaternary research efforts in sub-Saharan Africa, potential forcing mechanisms including ENSO and NAO, and dendrochronological theory. In doing so, this work will be a cornerstone foundation of any future research in African dendrochronology.