Millennial to multi‐decadal variability in the climate of southern Africa

Abstract

Wavelet analysis has been used to determine changes in the variability of southern Africa climate over the last three millennia. The structure of the variability in a 3000-year δ 18 O record has been compared with that in tree ring data for the last 600 years and both to the variability in annual rainfall and runoff during the 20th century. Preferred modes of variability are shown to have occurred in all the data sets. For overlap periods, the variability modes are in phase where the data are for a common seasonal rainfall regime.From the combined proxy and instrumental data it appears that an ∼1500-year oscillation in rainfall variability may have been present during the late Holocene. Considerable variability in South African climate has been shown to reside in the bands 500-800 and 60-120 years. The latter is manifest in stable isotope and tree ring proxy data and in measured rainfall and runoff, and shows a distinctive latitudinal variation over southern Africa. The ∼80-year variability has been present for at least 600 years in the tree ring data and at least 3000 years in the stable isotope data. During the 20th century, the variability in the 60-120-year range was confined south of 20°S in southern Africa.The existence of considerable multi-decadal climate variability in the range 16-20 years has been confirmed south of 15°S. Tree ring data show that the ∼18-year oscillation in climate has been present for at least 600 years. The 500-800-year, ∼80-year and ∼18-year variability has been both frequency-and amplitude-modulated over time, but never to the extent that the variability bands have lost their integrity. Their persistence is a striking feature of southern African climate.The millennial, centennial and multi-decadal variability in climate over southern Africa finds counterparts with temporal variability in similar time ranges reported elsewhere. Spatial teleconnections in variability likewise have been shown to occur. The changes in climate variability over the subcontinent are part of variability changes affecting the Earth system in many other regions.

Tropical systems from the southwest Indian Ocean making landfall over the Limpopo River Basin, southern Africa: a historical perspective

“…These peaks are also present in the positive values of the 24-month Standardized Precipitation Index values calculated for the northeastern interior of South Africa (Rouault and Richard, 2003). The quasi-18-year climate oscillation, according to Dyer and Tyson (1977), is confined to the subtropical latitudes south of 15°S and is clearest in the band extending from 20 to 30°S across the subcontinent (Tyson et al, 2002). This is also shown by the weakness of this oscillation in the rainfall time series at Makoholi in Zimbabwe compared to the South African stations.…”

Western Indian Ocean marine and terrestrial records of climate variability: a review and new concepts on land–ocean interactions since AD 1660

“…South Africa Rain is characterized by interdecadal variability between 16 and 20 years, which is observed in several studies of South African summer rainfall variability (Mason 1995;Krueger 1999;Reason et al 1996;Reason 2002;Reason and Rouault 2002;Tyson et al 2002;Jury et al 2004). Warm (cool) SST anomalies in the southwestern Indian Ocean are associated with increased (decreased) rainfall over central and eastern South Africa on seasonal to interdecadal time scales.…”

“…11a; Holmgren et al 1999;Tyson et al 2002). A lake level record is available from Lake Malawi with annual resolution for the period 1650-1990Owen et al 1990;Johnson et al 2001).…”

“…Tree rings, lake sediment records and laminated stalagmites provide annually resolved proxy data for surface temperature and/or precipitation over the African-Asian landmass for several centuries (Fig. 1b;Holmgren et al 1999;Tyson et al 2002;Verschuren et al 2000;Verschuren 2004;Burns et al 2002;Cook et al 2003;Deser et al 2004;Fleitmann et al 2004;D'Arrigo et al 2005D'Arrigo et al , 2006Therell et al 2006 and references therein). Geochemical parameters in massive coral skeletons from the Indian Ocean are well established in providing monthly to annually resolved time series of changes in SST, salinity and precipitation in the shallow oceans for up to 350 years (Fig.…”

Hydraulic–hydrologic model for water resources management of the Zambezi basin

“…The river is characterized by large natural floodplains attenuating the runoff and large artificial impoundments regulating the flow. The long-term flow series as well as the climate observations reveal inter-annual cycles of high, medium and low runoff with a duration varying from 10 to 80 years (Tyson et al 2002;Jury 2003;Mazvimavi & Wolski 2006). Since the runoff cycles have been reported to be primarily explained by rainfall cycles (Farquharson & Sutcliffe 1998;Beilfuss & Dos Santos 2001), the hypothesis adopted in this study is that a calibrated rainfall-runoff model will be able to reproduce the observed cycles even if not tested over the entire climate cycle.…”