20th century droughts in southern Africa: spatial and temporal variability, teleconnections with oceanic and atmospheric conditions

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Abstract

Southern African rainfall does not show any trend to desiccation during the 20th century. However, the subcontinent experienced particularly severe droughts in the 1980s and at the beginning of the 1990s and the magnitude of the interannual summer rainfall variability shows significant changes. Modifications of the intensity and spatial extension of droughts is associated with changes in ocean–atmosphere teleconnection patterns.

This paper focuses mostly on the well-documented 1950–1988 period and on late summer season (January–March). A principal component analysis on southern African rainfall highlights modifications of the rainfall variability magnitude. The 1970–1988 period had more variable rainfall, and more widespread and intense droughts than the 1950–1969 period.

To investigate the potential modifications of the associated ocean–atmosphere teleconnection patterns, a composite analysis is performed on sea-surface temperature (SST) and National Center for Environmental Protection (NCEP) atmospheric parameters, according to the 5 driest years of both sub-periods. Significant changes are shown in ocean–atmosphere anomaly patterns coincident with droughts for both sub-periods. The 1950–1969 droughts were associated with regional ocean–atmosphere anomalies, mainly over the southwest Indian Ocean region. In contrast, during the 1970–1988 droughts near-global anomalies were observed in the tropical zone, corresponding to El Niño–Southern Oscillation (ENSO) phenomenon.

Within the whole century, significant correlations between Southern Oscillation Index (SOI) and southern African Rainfall Index (SARI) were found in the periods (1900–1933 and 1970–1998) when SOI and SARI experienced high variability, and when southern Africa was affected by intense and extended droughts. During periods of low SOI (1934–1969), correlations became less significant and droughts were less intense and widespread. Copyright © 2001 Royal Meteorological Society

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