Influence of South Atlantic Sea Surface Temperatures on Rainfall Variability and Extremes over Southern Africa

Abstract

It is generally agreed that changing climate variability, and the associated change in climate extremes, may have a greater impact on environmentally vulnerable regions than a changing mean. This research investigates rainfall variability, rainfall extremes, and their associations with atmospheric and oceanic circulations over southern Africa, a region that is considered particularly vulnerable to extreme events because of numerous environmental, social, and economic pressures. Because rainfall variability is a function of scale, high-resolution data are needed to identify extreme events. Thus, this research uses remotely sensed rainfall data and climate model experiments at high spatial and temporal resolution, with the overall aim being to investigate the ways in which sea surface temperature (SST) anomalies influence rainfall extremes over southern Africa. Extreme rainfall identification is achieved by the high-resolution microwave/infrared rainfall algorithm dataset. This comprises satellite-derived daily rainfall from 1993 to 2002 and covers southern Africa at a spatial resolution of 0.1° latitude–longitude. Extremes are extracted and used with reanalysis data to study possible circulation anomalies associated with extreme rainfall. Anomalously cold SSTs in the central South Atlantic and warm SSTs off the coast of southwestern Africa seem to be statistically related to rainfall extremes. Further, through a number of idealized climate model experiments, it would appear that both decreasing SSTs in the central South Atlantic and increasing SSTs off the coast of southwestern Africa lead to a demonstrable increase in daily rainfall and rainfall extremes over southern Africa, via local effects such as increased convection and remote effects such as an adjustment of the Walker-type circulation.

Modelling the atmospheric response over southern Africa to SST forcing in the southeast tropical Atlantic and southwest subtropical Indian Oceans

“…These standing waves are known to be important to southern African climate (Mason and Jury, 1997). Similar modulations to these waves were obtained by Williams et al (2008) in AGCM experiments with SST forcing in the central and eastern South Atlantic.…”

Southern African Monthly Rainfall Variability: An Analysis Based on Generalized Linear Models

“…Recent investigations have also considered the Atlantic Ocean as a source of southern African variability, both for southwest cape winter rainfall and for summer rainfall anomalies, particularly over Angola and Namibia (Reason and Jagadheesha 2005b;Reason et al 2006). Williams et al (2008), investigating the association between southern African rainfall and atmospheric and oceanic circulations, identified a combination of anomalously cold SSTs in the central South Atlantic and warm SSTs off the southwestern coast associated with an increase in rainfall extremes over the subcontinent.…”

Atmosphere-land surface interactions and their influence on extreme rainfall and potential abrupt climate change over southern Africa

“…Mean rainfall, averaged over the domain, was firstly compared, then rainfall on a pixel-by-pixel basis was compared to give temporal means. For the definition and identification of daily rainfall extremes, the methodology of Williams et al (2008) is used and therefore will only be briefly described here. The definition used by Samel et al (1999) was slightly adapted, to identify extreme rainfall at the pixel scale as any pixel (on a given day) where rainfall is greater than 1.5% of the climatological total for that individual pixel.…”

“…The issue of scale is an important one for the identification of extreme rainfall changes, with the ability to identify rainfall extremes (be it from observed, satellite-derived or climate model data) increasing when a higher spatial and/or temporal resolution is used (Williams et al 2007(Williams et al , 2008(Williams et al , 2010a. Similarly, in any discussion of land cover changes, there are a number of spatial and temporal scales which should be considered, with lower (i.e.…”

“…Wu et al 2005;RodriguezFonseca et al 2006) and South Atlantic (e.g. Reason and Rouault 2006;Williams et al 2008;Williams et al 2010b). However, in comparison, less work has focused on the influence of land cover on rainfall variability and extremes.…”