Extremes of the ENSO phenomenon and Indian summer monsoon rainfall

Characterizing every year during the 120 year interval 1871–1990 as a year of El Niño (EN), or Southern Oscillation minimum (SO), or equatorial eastern Pacific sea-surface temperature (SST) warm (W) or cold (C) episode or none (non-events), the corresponding summer monsoon rainfall departures for all India and for the 29 meteorological subdivisions were examined. The best relationship for droughts was with unambiguous ENSOW (El Niño year with SO and W near the middle of the calendar year) and for floods with C (cold SST). The droughts were generally widespread, although Assam and Bengal might have had normal rainfall or even floods when other subdivisions had droughts. In some ENSOW years when all India rainfall was normal, the rainfall in subdivisions was either normal or mixed (droughts in some subdivisions, floods in others). However, droughts and floods occurred during other types of events also, and ENSOW or C were neither sufficient nor necessary. Some floods and droughts were associated with incorrect type (floods during El Niño, etc.), and some occurred during non-events, indicating that factors unrelated to EN, or SO, or W, or C may be more influential in some years. © 1998 Royal Meteorological Society