Seasonal rainfall variability in southeast Africa during the nineteenth century reconstructed from documentary sources

Analyses of historical patterns of rainfall variability are essential for understanding long-term changes in precipitation timing and distribution. Focussing on former Natal and Zululand (now KwaZulu-Natal, South Africa), this study presents the first combined annual and seasonal reconstruction of rainfall variability over southeast Africa for the 19th century. Analyses of documentary sources, including newspapers and colonial and missionary materials, indicate that the region was affected by severe or multi-year drought on eight occasions between 1836 and 1900 (the rainy seasons of 1836-38, 1861-63, 1865-66, 1868-70, 1876-79, 1883-85, 1886-90 and 1895-1900). Six severe or multi-year wet periods are also identified (1847-49, 1854-57, 1863-65, 1879-81, 1890-91 and 1892-94). The timing of these events agrees well with independent reconstructions of 19th century rainfall for other parts of the southern African summer rainfall zone (SRZ), suggesting subcontinental scale variability. Our results indicate that the relationship between El Nio and rainfall in southeast Africa was relatively stable, at least for the latter half of the 19th century. El Nio conditions appear to have had a more consistent modulating effect upon rainfall during the 19th century than La Nia. The rainfall chronology from this study is combined with other annually-resolved palaeoclimate records from mainland southern Africa and surrounding oceans as part of a multi-proxy rainfall reconstruction for the SRZ. This reconstruction confirms (i) the long-term importance of ENSO and Indian Ocean SSTs for modulating regional rainfall; and (ii) that summer precipitation has been declining progressively over the last 200 years.