and accumulated rainfall and stream
flow in rainy season data was carried out and
tested by using the Pearson correlation
method. Then, the index giving the highest
correlation was selected. The SOI is the
highest correlation as shown in Table 1, thus
it was a selected for using to study the impact
of ENSO on rainfall and stream flow
anomaly in UPRB. The SOI is the ENSO
index measured based on the difference of the
atmospheric pressure above sea surface
between Darwin and Tahiti in the Pacific
Ocean. It is in agreement with the research’s
result of Singhrattna et al. (2005) that SOI
shows a strong correlation with monsoon
rainfall during the concurrent season and also
one or two seasons prior. The method to
classify ENSO phase (El Niño, La Niña and
Normal) used by NOAA and the three
monthly running mean (three-mrm) which is
calculated by the 3 months moving average of
the SOI is used in this study.