The variable nature of the summer monsoon season makes Southern Asia one of the most vulnerable regions to natural disasters associated with climate change, such as droughts and floods. A recent study published in the journal Nature Communications, conducted by researchers at the Indian Institute of Tropical Meteorology (IITM) in Pune, one of the IRD's partners, has revealed that the warming of the Indian Ocean is reducing the intensity of the summer monsoon season and drying up the subcontinent. In a region that is home to a large part of the world's population, dynamic climate modelling represents a major challenge in the prevention of the human and economic consequences of climatic hazards.

When the Indian Ocean heats up, the intensity of the monsoon season reduces

A team from the Indian Institute of Meteorology (IITM) in Pune, one of the IRD's partners, has recently revealed in the journal Nature Communications that the warming of the Indian Ocean, by up to 1.2°C in some areas over the last century, is reducing the intensity of the Indian monsoon season by around 10 to 20% in the country's central, eastern and northern regions.

Scientists made this discovery using an ocean-atmosphere coupled climate model, specially developed by the IITM for making monsoon season forecasts. Thanks to this model, researchers were able to demonstrate that the reduction in rainfall observed over the subcontinent since the 1950s is due to the rapid warming of the ocean. The Intergovernmental Panel on Climate Change (IPCC) anticipates that ocean temperatures will rise further as a result of the greenhouse gas effect.

An increasingly dry subcontinent

The study goes on to explain the reason for the observed reduction in rainfall associated with the Indian monsoon season. The Indian subcontinent has warmed up by only a very small amount during the last few decades, reducing the summer temperature difference between the ocean and the land, which triggers the monsoon winds. This phenomenon is weakening the monsoon season dynamic and is drying up the subcontinent, bringing harmful consequences for agriculture along the Ganges-Brahmaputra-Meghna basins and the Himalayan spurs, an activity requiring extensive irrigation.

Uncertain changes to come

Will India continue to dry up? Projections based on the majority of the climate models used in the IPCC's latest evaluation report do not see this trend replicated in future years. Some anticipate quite the opposite: increased rainfall due to increased water vapour in the atmosphere and a far more noticeable warming of the subcontinent in the future. This divergence between current observations and model-based trends underlines the uncertainties involved when it comes to future climate change in the region, particularly in terms of the water cycle and the monsoon regions.