India’s extreme rain was restricted to a ‘corridor’ during 1901-2019 | Explained Premium

Indian monsoon's stability revealed: Synchronised extreme rainfall events occur along a 'highway' from West Bengal to Gujarat, unchanged since 1901. IMD forecasts rely on El Niño/La Niña, but other global relations can help improve predictions. Network analysis of IMD data reveals dynamics of synchronisation, offering potential to reduce risk from extreme events.

The Indian monsoon has well-known features, such as the onset, the withdrawal, the active and break periods, and low-pressure systems (or monsoon depressions). Every aspect of the monsoon has been affected by global warming. The monsoon onset has been delayed of late as well as being affected by cyclones. Its withdrawal has been affected by Arctic warming.

The total seasonal rainfall has also trended downwards for more than seven decades, due to the differential heating of the land versus the ocean due to global warming. However, this trend has been distributed unevenly through the monsoon season – as manifest in the longer duration but lower intensity of dry spells and the greater intensity of wet spells.

Some researchers have argued that the intense wet spells have become larger in scale, over Central India in particular. The influence of the Arabian Sea and the Bay of Bengal combine to produce dynamic conditions for generating large-scale extreme rainfall events.

While the India Meteorological Department (IMD) has made progress in forecasting extremes, multiple factors can combine to still produce devastating heavy rain events that remain hard to anticipate. We desperately need more improvements in forecasts to reduce losses of life, property, agriculture, and the consequent negative impacts on the country’s economy.

Where does large-scale extreme rain occur?

India’s monsoon forecasts rely heavily on its relation to the El Niño and the La Niña phenomena, although this relation holds only about 60% of the time. We also know of other global relations but translating them to better predictions requires careful modelling experiments. Researchers are also continuing to search for additional process understanding, especially for the high-impact extreme rainfall events.

A new study (of which the author was part) has found that despite all these seemingly disparate changes in different aspects of the monsoon dynamics, a remarkable stationary element exists in terms of where the synchronised extreme rainfall events occur.