Intensity and spatial extension of drought in South Africa at different time scales

Abstract

The standardised precipitation index (SPI) is an index that allows monitoring the intensity and spatial extension of droughts at different time scales (3, 6, 12 and 24 months). The SPI is linked to the probability occurrence of dry or wet events. The SPI allows monitoring operationally any location with a 30-year time series. It is also used here to do a retrospective analysis of the spatial extension and intensity of droughts in South Africa since 1921. According to this index, the 8 most severe droughts at the 6-month time scale for the summer rainfall region of South Africa happened in 1926, 1933, 1945, 1949, 1952, 1970, 1983 and 1992. There is considerable decadal variability and an 18 to 20 year cycle is only found in the number of dry districts. The total number of wet and dry districts per decade seems to have increased since the 1960s. Drought lasting 3 years is not uncommon for each of the 8 South African rainfall regions defined by the South African Weather Service. Combining the retrospective analysis with real time monitoring could be extremely beneficial in the development of response, mitigation strategies and awareness plans.

A synoptic decomposition of rainfall over the Cape south coast of South Africa

“…Qualitatively, the metrics indicate that the spatial extent of the area receiving rainfall all-year round along the Cape south coast is found within the collective boundaries described in other studies (e.g. Taljaard 1996;Landman et al 2001;Rouault and Richard 2003;Weldon and Reason 2014). Along the coast, the all-year rainfall region is found approximately between 21°E and 27°E, while its northern extent is mostly restricted by the Cape Folded mountain range (Fig.…”

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

“…These years correspond to the peaks in the quasi-18-year cycle as noted and predicted by Dyer and Tyson (1977). 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).…”

On the use of Standardized Precipitation Index (SPI) for drought intensity assessment

“…The SPI-based drought classes proposed by McKee et al (1993), were adopted in this study (Table I), because of their wider applicability to different regions of climatology such as Mexico (Giddings, 2005), Greece (Loukas et al, 2004), Iran (Morid et al, 2006), European Alps (Bartolini et al, 2008), Portugal (Paulo et al, 2005), Europe (Lloyd and Saunders, 2002), Poland (Łabȩdzki et al, 2005), mountainous Mediterranean basin (VicenteSerrano et al, 2004), Slovenia (Ceglar et al, 2008), Colorado, North Dakota, Iowa, Kansas, Nebraska, South Dakota, and Wyoming (Wu et al, 2006), Eastern China (Bordi et al, 2004), Northeast of Thailand (Wattanakij et al, 2006) and South Africa (Rouault and Richard, 2003). As suggested by McKee et al (1993McKee et al ( , 1995, SPI represents wetter and drier climates in a similar way.…”