Geoscience Reference
In-Depth Information
SOI
NORTH
CHINA
INDIA
KRISHNA
1860
1880
1900
1920
1940
1960
1980
2000
Figure 23.2. Time series representation of the Southern Oscillation Index (1870-
1986), the annual rainfall index for China (1870-1979), rainfall over India in mm
(1871-1985) and discharge in the Krishna River, India, in millions of Ml (1901-
1960). Each series has been standardised with respect to the means and standard
deviations given in
Table 23.1
for the 1911-1960 reference period. Each interval on
the vertical axis represents two standard deviations. The solid curved line shows a
smoothed version of the time series, constructed using a ten-year Gaussian filter,
which suppresses frequencies of less than ten years. (After Whetton et al.,
1990
, and
Williams and Balling,
1996
,
fig. 5.4
.)
informative, especially given the unusually warm global land and sea temperatures
of the last twenty or so years, but to the best of the author's knowledge one has
not been carried out). There is also good evidence that since the 1970s, the links
between Indian monsoonal rainfall and ENSO events have weakened (Kumar et al.,
2006
; IPCC,
2007a
; IPCC,
2007b
), perhaps reflecting changes in the Indian Ocean
Dipole (Ashok et al.,
2001
) or perhaps reflecting the influence of warmer sea surface
temperatures in the northern Indian Ocean and the Arabian Sea. We discuss the Indian
Ocean Dipole in the next section.
Godley (
2002
) extended this type of analysis to the drier parts of Thailand, where
he found that drier-than-average years in northern and central Thailand were El
