Ahead of every monsoon, meteorologists track, with a degree of nervousness, temperatures in the central and eastern Pacific Ocean. Six in ten years, a half degree or more rise — an El Nino — corresponds to diminished rainfall in India. The converse, or a La Nina, is linked to increased rain. A study last week however suggests that this cyclical swing — called the El Nino Southern Oscillation (ENSO) — affects vast regions of India differently.
Since 1981, the study published this week in Scientific Reports notes, monsoon rainfall over Central India — known as the monsoon core zone and where agriculture is largely rainfed — is increasingly getting disassociated from the ENSO with only 10% of droughts or excess rains linked to ENSO fluctuations. On the other hand, the ENSO link to North India was strengthening, with 70% of rainfall fluctuations linked to the ENSO cycle. In southern India, the relationship has remained largely stable.
While past research into monsoon patterns have suggested a “weakening” of the relationship between ENSO and monsoon, the latest suggests that this too has varied since 1901.
