The present paper deals with the Influence of El Nino event on the summer
monsoon rainfall over Pakistan. The correlation between monthly rainfall of
summer monsoon season and bi-Monthly Multivariate ENSO Index (MEI) has
been calculated to see the influence of El Nino on the summer monsoon rainfall.
While study the correlation’s with the ENSO events out side the Pacific Ocean
MEI is more appropriate than other indices like Southern Oscillation Index (SOI)
as MEI integrates complete information on ENSO viz. six oceanic and
meteorological variables over the tropical Pacific. The results of the study show
that there is a tendency of reduction in summer monsoon rainfall over Pakistan
during El Nino years. The deficiency in %rainfall is statistically significant up to
90 %level during July and September months. It is interesting to note that
Pakistan receives more than normal rainfall during summer monsoon season in
the immediate following year after the El Nino event.
Since topography plays an important role in the frequency, intensity and
distribution of rainfall, correlation analysis is also performed for northern and
Southern Pakistan region. Over Northern Pakistan the reduction in % rainfall
departure is significant during July and September during El Nino years.
Whereas in case of Southern Pakistan, July and August rainfall show significant
reduction during El Nino years.