资源环境科技发展态势分析平台

Recent and historical austral summer and winter rainfall characteristics have been widely investigated across southern Africa. However, a notable gap of knowledge remains for the Namibian region. This article presents the first extensive 19th century (1845-1900) hydro-climate history for central Namibia, derived from documentary evidence. Unpublished and published data sources were scrutinized in various archives and libraries in Germany, Switzerland, Namibia and South Africa. Missionary Carl Hahn's detailed diaries are the most valuable source of information for the earliest period until 1859. Other important sources of information include the Rhenish Missionary Society (RMS) annual reports and monthly 'Berichte' (news), station chronicles, official annual reports for the colonial period (1894 onwards) and letters/diaries by traders, travellers, etc.

Climate information was transcribed, translated and organized chronologically. Using a five-point categorization system ranging from very wet (+ 2) to very dry (-2), each year was classified according to overall rainfall conditions during the rain season. A portion of the chronology is compared with instrumental rainfall data for Okahandja, Windhoek and Rehoboth and confirms good agreement. Possible associations between El Nino-Southern Oscillation (ENSO) phases and subsequent austral summer rainfall conditions are explored for central Namibia. Wetter years (42%) are over-represented in comparison to dry years (38%) during the second half of the 19th century in central Namibia, with a high percentage (42%) constituting either extremely wet or extremely dry years. Inter-annual rainfall variability between 1845 and 1900 seems more pronounced than elsewhere in southern Africa during this period. Extreme to very strong and prolonged El Nino (e.g. 1876-1878) and La Nina (e.g. 1865-1866) phases account for rare hydro-climatic synchronicity between southern African sub-regions and between continents of the Southern Hemisphere.