Relative impacts of ENSO and Indian Ocean dipole/zonal mode on east SADC rainfall

Abstract

ABSTRACT:The current paper is an observational study that investigates the October to December (OND) rainfall variability over the east Southern African Development Community (SADC) mainland region in relation to El Niño-Southern Oscillation (ENSO) and the Indian Ocean dipole zonal mode (IODZM) for the period 1950-1999. An empirical orthogonal function (EOF) analysis of OND rainfall field revealed that the north-south aligned areas of the eastern SADC are located in different covariability regions. This meridionally aligned dipole rainfall anomaly configuration is captured only in the dominant principal component (PC1), making it possible for the opposing rainfall anomalies of the two regions to have a common trigger. However, ENSO which is the standard attribute for regional rainfall variability failed dismally to adequately explain this dipole rainfall anomaly pattern. Instead, there appears to be consistent evidence through statistical techniques which strongly indicates the likelihood of the participation of only the positive IODZM phase events in the creation of the positive dipole rainfall phase (i.e. simultaneous floods over the northeast and droughts over the southeast of the SADC region). Since the negative IODZM phase events can hardly be linked to the reverse rainfall pattern, it implies that the positive and negative rainfall dipoles have fundamentally different causes. Thus, contrary to convectional knowledge, the ENSO association to this dipole rainfall anomaly pattern is by no means robust and could be symptomatic of the well-known ENSO-IODZM connection. Interestingly, however, when analysed over the 31-year overlapping segments, IODZM's once significant independent influence on this dipole rainfall seems to be diminishing gradually as from the early 1990s, whereas that of ENSO is correspondingly being reinforced.

Integrating Dendrochronology, Climate and Satellite Remote Sensing to Better Understand Savanna Landscape Dynamics in the Okavango Delta, Botswana

“…Lag cross-correlations of annual precipitation and the Southern Oscillation Index (SOI) reveal a spatially consistent, but not statistically strong, positive relationship-drought in warm phases of ENSO and excess rains in cold, consistent with previous research [45]. Recent research [42] indicates that, the strength of the association with the ENSO signal in eastern portions of the study area is contingent upon the state of the Indian Ocean Dipole/zonal mode (IODZM) and that the various epochal coupling and uncoupling of these two major atmosphere-ocean forcings, have considerable impact on precipitation variability.…”

“…Mean annual depth of precipitation input to the entire Okavango basin, expressed as deviations from the 50-year median (Figure 4a), indicates the major global climate shift in the mid-1970s identified by many researchers [38][39][40][41][42]. The shift is contemporaneous to changes in circulation of the North Pacific, and the way in which ENSO events evolve, particularly their interaction with the Indian Ocean [40,41].…”

“…Kalahari sands constitute the dominant soils throughout. The inception of a period of reduced precipitation in the late 1970s correlates to a noted shift in global climate and decreased precipitation over much of southern Africa, possibly in connection to a coupling of the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Di-pole [38][39][40][41][42]. Precipitation variability is apparent at three dominant temporal scales; intra-annual, inter-annual and inter-decadal, all of which may well interact in a non-linear fashion.…”

Tailoring seasonal climate forecasts for climate risk management in rainfed farming systems of southeast Zimbabwe

“…About 46% of the variability of de-trended crop yields in Zimbabwe's smallholder farming sector have been ascribed to interannual rainfall variability, with January and February rainfall explaining 66 and 50% of the variability, respectively (Cane, Eshel, & Buckland 1994;Gommes, 2006;Manatsa, Matarira, & Mukwada 2011a). It is estimated that only 37% of Zimbabwe receives adequate rainfall for agriculture (FAO, 2005), yet more than 90% of Zimbabwe's smallholder farmers depend on rainfed agriculture for their livelihood.…”

Exploratory studies into seasonal flow forecasting potential for large lakes

“…As in the studies by Jury (2014) and Siam and Eltahir (2015) the use of climate indices is considered since both the El Niño Southern Oscillation and Indian Ocean Dipole are thought to have a significant influence on rainfall in east and southern Africa (e.g. Saji et al, 1999;Nicholson and Selato, 2000;Jury and Gwazantini, 2002;Manatsa et al, 2011). Since the main aim was to provide insights into possible model structures, the analyses were based primarily on historical datasets derived as part of previous water balance studies as this allowed a more detailed investigation of lake response than would be possible using contemporary datasets.…”