2-Effect of La Nina-El Nino on Climatic Fluctuations over Major Hydro-ecozones Across India.

Abstract

During boreal summer, the troposphere over southern hemisphere is warming at a faster rate compared to that over northern hemisphere, and the intensity of the general atmospheric as well as the Asian-Indian monsoon circulation shows decreasing trend. Over the equatorial central and eastern Pacific (Nino region), the easterlies are weakening and the SSTs rising, and there is a tendency for occurrence of frequent and intense El Nino than La Nina. Rain-producing weather systems (convergences) are frequent and intense along the western Indian subcontinent, and weaker and infrequent over Indo- Gangetic plains, central India and Bay of Bengal. Consequently, monsoon rainfall is somewhat subdued over Indo-Gangetic plains and central India. The La Nina-El Nino phenomenon provides vital information for extreme rainfall activities across India. To understand effect of the phenomenon on the hydro-ecosystems of the country, difference between La Nina and El Nino years in the parameters of the hydrological wet season (HWS), summer monsoon and wet-dry spells over major/minor/sub-basins have been examined. During El Nino years, climatic condition is considerably adverse over almost the entire hydro-ecosystems across the country compared to that during La Nina years.