A 19th century climate chronology for the Kalahari region of central southern Africa derived from missionary correspondence

Unpublished materials written by missionaries based at London Missionary Society and Wesleyan Methodist Missionary Society mission stations across the Kalahari region have been used as the primary source for the construction of a historical climatic chronology for central southern Africa for the period 1815–1900. Data from these unpublished documents were supplemented by analyses of published material written by various hunters and explorers (as well as missionaries) who travelled beyond the immediate areas of missionary activity. Key features of the climate chronology are the identification of six drought episodes and seven periods of above-average rainfall which affected various parts of the region. Major dry periods occurred in 1820–27, 1831–35, 1844–51, 1857–65, 1877–86 and 1894–99, of which the droughts in 1844–51, 1857–65, 1884–86 and 1894–99 were the most widespread.Wetter periods are identified in 1816–17, 1829–30, 1851–52, 1863–64, 1874–75, 1889–91 and 1899–1900, with the most widely distributed wet conditions occurring in 1889–91. In order to ascertain the reliability of the chronology, the document-derived climate sequence has been compared with available meteorological data for the study area (from Barkly West for the period 1883–1900) and shows good general agreement. The results of this study have been compared with historical climate chronologies for the former Cape Province of South Africa. This comparison reveals that large areas of the southern African subcontinent experienced dry conditions in 1826–27, 1832–35, 1848–1851, 1858–60, 1861–63, 1877–81, 1884–86 and 1894–99, with the dry phases of the early 1850s, 1858–60, 1861–63 and 1894–99 possibly extending beyond the northern border of present-day Botswana. Wetter phases affected much of the subcontinent in 1829–30, 1851–52, 1863–64, 1874–75, 1889–91 and 1899–1900, with 1874–75 and 1889–91 associated with reports of flooding from central Botswana to the eastern Cape. The causal mechanisms of patterns of climatic variability are unclear, but 19th century drought periods in the Kalahari show a close coincidence with the timing of moderate to strong El Ni˜no–southern oscillation events