North India more affected by El Nino

Subject : Geography

Section: Physical geography

Context:

A study suggests that the El Nino Southern Oscillation (ENSO) affects vast regions of India differently.

Details of the study:

Since 1981 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.
The ENSO–ISMR (Indian Summer Monsoon Rainfall) inverse relationship started getting stronger from 1901 to 1940, became stable from 1941 to 1980 and then the relationship has weakened in the recent epoch (1981 onwards).
Consequences:
- The ENSO dominance over the core monsoon zone is weak, which means that seasonal prediction over this region has become less predictable in the recent decades.
- Other factors like Indian Ocean warming should be monitored for the core monsoon zone, due to its impact on the strength of the monsoon trough and the depressions.

Monsoon rainfall in India:

Monsoon rainfall, which accounts for 80% of India’s annual rainfall, is influenced by two broad factors:
- The external one is the impact of ENSO which influences the trade winds and their ability to carry warm, moist air towards India around monsoon.
- The other, internal, is the ‘monsoon trough — an elongated low-pressure area which extends from over Pakistan to the Bay of Bengal.
This trough swings between north and south India through the monsoon bringing rain wherever it is active and is fed on moisture brought in from the Bay of Bengal (and the Arabian Sea to a lesser extent) in the form of low-level cyclones called ‘depressions.’