Geoscience Reference
In-Depth Information
Bolivia, Venezuela, and north-eastern Brazil are
usually affected by drought during an ENSO event;
however, greatest devastation occurs in the western
part of the cell in southern Africa, India, Indonesia,
and Australia. There is a strong coherence in the
timing of both flood and drought on the Nile in Africa,
the Krishna in central India and the Darling River in
Australia. As well, rainfall over parts of Australia,
Argentina and Chile, New Zealand and southern Africa
coincides (Figure 2.10). Most notable are the years
1894, 1910, 1917, 1961 and 1970. There is an even
better correspondence between droughts in India and
'turned off' Walker circulation, or ENSO events. The
severe droughts in India of 1899, 1905, 1918, 1951,
1966, and 1971 all occurred before, or at times when,
El Niño events were at their peak around Christmas or
when the Southern Oscillation index was negative. All
of these years, except for 1951, were also times when
discharges on the Nile, Krishna, and Darling River
systems were either very low, or nonexistent.
A similar relationship can be traced back even further
in Indonesia. This is surprising because most climatic
classifications label Indonesia as a tropical country with
consistent yearly rainfall. Table 2.1 summarizes the
relationship between monsoon droughts and ENSO
events during the period 1844-1983. In Indonesia, over
93 per cent of monsoon droughts are associated with El
Niño events and 78 per cent of ENSO events coincide
with failure of the monsoon. The relationships are so
strong that in Java the advent of an ENSO event can be
confidently used as a prognostic indicator of subsequent
drought. In recent years, both India and Indonesia have
established distribution infrastructures that prevent
major droughts from causing starvation on as large a
scale as they once did; however, the 1982-1983 event
caused the Indonesian economy to stall as the country
shifted foreign reserves towards the purchase of rice
and wheat.
Links to other hazards
(Gray, 1984; Marko et al., 1988; Couper-Johnston, 2000)
The effect of ENSO events and the Southern Oscilla-
tion goes far beyond just drought and flood. They are
responsible for the timing of many other natural
hazards that can influence the heart and fabric of
society. Three culturally diverse examples illustrate this
River discharge
4
2
0
-2
-4
SO index
60
50
40
30
20
10
Area index
Indian floods
and droughts
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
Discharge on Nile, Darling
and Krishna Rivers coincidence
High
Low
Indian floods
Indian droughts
Southern Oscillation index, drought and rainfall indices for India plus timing of coinciding low or high discharges on the Nile, Darling, and
Krishna Rivers, 1890-1980 (based on Bhalme et al., 1983; Adamson et al., 1987).
Fig. 2.10
