CORRELATION BETWEEN MULTIVARIATE ENSO INDEX (MEI) AND PAKISTAN’S SUMMER RAINFALL

Abstract

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.