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Fluvial silts, accumulated in some Namib Valleys, to date are interpreted as records of reduced precipitation in the catchments. Our investigations show that these fluvial silts are slackwater deposits (SWD) which document hydrologic and climatic conditions during the late Holocene that cause extreme flash floods in the valleys. We describe SWDs of some Namibian Desert valleys and present C-14 dates of their ages. The youngest accumulation phase occurred during the Little Ice Age (LIA, ca. AD 1300 to 1850). The biggest flash floods of the LIA, in most catchments, experienced Water levels in the valleys that exceeded the most extreme floods of the last 100 to 150 years. In the northwestern Namib Desert, flash floods of the LIA were more frequent and more extreme than in the central Namib Desert. This may be caused by small shifts of the tropical-temperate-troughs (TTT) in southern Africa and the southwest Indian Ocean that correlate with changes of cosmic ray intensity.