Analysis of rainfall variability in the northeastern region of South Africa

Abstract

SummaryThe mean monthly and annual rainfall series for 30x30 blocks in the eastern Transvaal-Swaziland region ara analyzed. These series show temporal and spatial characteristics in the regional precipitation regime. Significance is attributed to oscillatory forcings with quasi-periodicities of about 16-20 years and 13-14 months that operate throughout the area. Oscillations near the quasi-biennial cycle are also observed but with less significance. Principal component analysis provides a number of eigenvectors which are identified with changes in the seasonal characteristics of the regional rainfall. The annual cycle clearly dominates over the entire region with January (mid-summer) being the wettest month. The second eigenvector has pronounced loadings in the spring/early summer (November) period and clear spatial responses that are attributed to topographically induced differences in the deep convective processes of the area. Higher principal components are not as clearly defined in their temporal structure. The third eigenvector, however, is attributed partially to synoptic scale forcings which produce different rainfall characteristics over the coastal plains relative to the high inland plateau.

Intra‐seasonal rainfall characteristics and their importance to the seasonal prediction problem

“…Here, local forcing appears to play a crucial role, and a larger proportion of the seasonal rainfall can be attributed to situations where conditions are marginally favourable for localized development of convective rainfall. Kelbe et al (1983) noted the importance of topographical features and diurnal wind circulations in initiating deep convection. In regions such as this it becomes important to separate further the circulation classification to include mechanisms that might suppress rainfall.…”

Topo-edaphic environment and forest plantation disturbance explain patterns of grassland species richness, composition and structure in an agro-ecological landscape, Maputaland, South Africa

“…Contrary to expectation, plant composition corresponded poorly with the modelled water table depth of the primary aquifer (Figure 4). This may have been an artefact of topographic resolution (only 5 m elevation contours were available for the region); however, water-table depth, resulting from regional 18-20 year wet-dry climatic cycles (Kelbe et al 1983) Hempson et al 2015).…”

The Occurrence and Predictability of DR Ough Ts Over Southern Africa

“…Over South Africa, distinctive oscillations have been verified and from the mid-1970s have been used in long-range seasonal forecasting models (Dyer and Tyson 1977, Tyson and Dyer 1978, Louw 1982, Currie 1993. O f greatest significance is an eighteen-to twenty-year oscillation in the northeast part of the country, shown in Figure 8.3 (Tyson 1971(Tyson , 1978(Tyson , 1980(Tyson , and 1986Dyer 1 9 7 5 ,1980a, and1981a;Tyson et al 1975;van Rooy 1980;Vines 1980;Kelbe et al 1983;Lindesay 1984;Currie 1991 and1993;Levey 1993a and1993b). It extends into Zimbabwe (Ngara et al 1983, Makarau andJury 1997) and Botswana (Jury et al 1992) and possibly into southern Zambia.…”