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One of the external factors responsible for the interannual variability of Indian summer monsoon rainfall (ISMR—June through September) is the El Niño phenomenon. About half of the droughts over India have been related to this phenomenon. Other external factors, such as the Eurasian snow, also affect the year-to-year variability of the ISMR. It is believed that in such cases, the ISMR becomes locked into its own internal dynamics.