Empirical Orthogonal Function analysis can be extracted variance of monthly mean
rainfall from a total of 80 stations throughout all areas of Thailand. The rainfall
variability was extracted into a quite signi¯cant measured by the ¯rst four modes,
which explains 79.77% of the total variance, with each mode contains 57.64%,
12.94%, 6.31% and 2.88% of the total variance respectively (Fig. 4). The princi-
pal component between the ¯rst four modes of monthly mean rainfall anomalies,
which are able to account for 79.77% of the total variance and DMI covering a
10-year period from the year 1979 to 1988, are shown in Fig. 9. The strong positive
IOD occuring in the years 1982 and 1987 is in contrast correlation with the ¯rst
four modes of rainfall. In addition, the strong negative IOD in the year 1980 is in
contrast correlation with the ¯rst four modes of monthly mean rainfall anomalies
such that temperatures are less, rainfall is higher. Next, the result of the ¯rst four
modes of monthly mean rainfall anomalies from 1989 to 1998 represent the contrast
correlation between DMI in the years 1991, 1994, and 1997, which is the near of a
strong positive IOD, such that as high temperatures, low rainfall. But in the years
1992, 1996 and 1998, which is the year of strong negative IOD represents the year
of low temperatures, high rainfall (Fig. 10). Fig. 11 shows the contrast correlation
between DMI and the ¯rst four modes of monthly mean rainfall anomalies in the
year 2006, which is explained by high temperatures, low rainfall.