Floods and droughts in association with cold and warm ENSO events and related circulation features

Abstract

For the Indian subcontinent. the occurrence of floods and droughts is closely linked with the summer monsoon activity. The phenomenon of El Nino-Southern Oscillation (ENSO) has been established to be one of the major teleconnections of Indian Summer Monsoon. Also the relationship between the circulation features and summer monsoon activity is well documented in the literature. The interaction of F.NSO with monsoon system was known to the seasonal forecasters in India from the days of G. Walker. Northland (1953) summarising these results has remarked that ‘Monsoon has a prolonged influence on the global weather rather than global weather parameters influencing the monsoon’. 1990-94 was a prolonged period of warm ENSO producing weather anomalies in different regions of the globe. Yet during the same period all India rainfall was very close to normal and in fact. 1994 was a year of abundant rainfall for India. The aim of the study is to examine some of these features more critically.

It is observed that ENSO has a modifying effect on the regional scale circulation pattern and possible interactions and/or phase-Locking with the planetary scale circulation pattern. which results into the occurrence or non-occurrence of an extreme event. Also, a qualitative analysis is carried for a period 1960-90 to assess how far the mid-season rainfall deficiency is made up at the end of the season. It is observed that even during drought years, the mid-season rainfall deficiency is made up at the end of the season for a considerable percentage of the total number of cases.