El Niño’s impact on monsoons over central India, the core monsoon zone, has weakened in the past three decades1. This means the impact of climate change, including warming of the Indian Ocean, is more pronounced in this region.
Scientists at the Indian Institute of Tropical Meteorology in Pune examined the changing relationship between El Niño Southern Oscillation (ENSO) and Indian summer monsoon rainfall from 1901 to 2018.
The ENSO cycle occurs every five to seven years when the central and eastern parts of the tropical Pacific Ocean switch between warm El Niño and cool La Niña. There is also a neutral phase when the waters are near their average temperature.
The relationship between ENSO and monsoon rainfall has been inconsistent over the past century. The results show that monsoon trough and depression are the primary cause of rainfall variability over central India where agriculture is mainly rain-fed, surpassing the role of ENSO.
South India's rainfall is consistently influenced by both ENSO and monsoon trough strength, while north India's rainfall is increasingly influenced by ENSO and the impact of the monsoon trough and depression is decreasing.
Understanding the differing regional ENSO–monsoon relationship is important for improving monsoon forecast skills, the researchers say.