EL NIÑO AND RAINFALL VARIABILITY IN THE KALAHARI, SOUTHERN AFRICA, 1840-1900

This study uses a range of published and unpublished historical documentary sources to assess the nature of the relationship between El Niño-Southern Oscillation (ENSO) warm events and rainfall variability in the Kalahari region of central southern Africa for the period 1840-1900. Documentary data are used in two ways. Firstly, a chronology of annual rainfall patterns for the Kalahari is presented for the sixty-year study period, from which variations in inter-annual rainfall distribution during wetter/drier episodes and ENSO warm events are identified. Results indicate that, whilst a number of episodes of drought or wetter conditions can be broadly identified across the region, the distribution and onset of periods of above- or below-average rainfall was highly variable. Analyses further suggest that the broad relationship between ENSO warm events and rainfall variability identified for the 20th century, whereby ENSO events are preceded by wetter conditions during the austral summer prior to the ENSO year and succeeded by drought in the following summer, has held for at least the last 160 years. Droughts occur following at least fourteen of the eighteen single- and multi-year ENSO warm events between 1840-1900. Pre-ENSO wetter periods are less common, with only nine of the eighteen ENSO events during the study period preceded by above-normal rainfall. Secondly, the primary documentary data set is analysed to identify high resolution variations in the seasonal distribution of rainfall during ENSO warm events. Seasonal sequences of rainfall/drought appear to have closely followed contemporary patterns, with heavy rainfall commonly occurring late in the pre-ENSO year or early in the ENSO year, with drought at the start of the post-ENSO year. This relationship held most strongly for single-year ENSO events and for the first year of multi-year events, but rainfall conditions were more variable during the later years of multi-year events.