The Indian summer monsoon may change under the impact of global warming, potentially returning to conditions similar to the mid-Pliocene era, according to research by the National Institute of Technology–Rourkela (NIT-R) in collaboration with IISER-Mohali. The mid-Pliocene occurred around three million years ago. In scientific terms, it is a period in Earth’s history when temperatures were 2–3.2 degrees Celsius higher than today. The Earth is expected to experience similar warming by 2100. According to the Encyclopaedia of Paleoclimatology and Ancient Environments, the mid-Pliocene was very similar to the modern world.
Findings of the study titled ‘Assessing the Changes in Indian Summer Monsoon in Warm Climates: Mid-Pliocene and Future Projection by the End of 21st Century’ by Prof Nagaraju Chilukoti, Dr Karishma Dahiya and Prof Raju Attada, project a stronger future monsoon over the Indian subcontinent under a global warming scenario. The study was published in the International Journal of Climatology.
Amid rising global temperatures due to climate change, there is a contradiction in the results of various global studies. While some suggest that rising temperatures may reduce rainfall, others indicate that monsoon rainfall could become stronger.
To bridge this gap, the study analysed how the monsoon behaved during warmer periods in Earth’s past to understand how it might behave in the future.
The study showed that monsoon rainfall over India was higher during the mid-Pliocene, and a similar increase is expected in a warmer future climate. However, the reasons behind the increase in rainfall differ in the two cases. In the mid-Pliocene, stronger winds and more active atmospheric circulation led to increased rainfall. In the future scenario, the increase is expected because a warmer atmosphere can hold more moisture.
It also found that though monsoon precipitation rate will increase in a future warm climate, the rate of increase is slightly lower compared to the past warm climate. The research team next plans to study the influence of large weather systems forming far north of India on rainfall patterns in the region.
Explaining the findings, Chilukoti, an assistant professor in the Department of Earth and Atmospheric Sciences at NIT-R, said the team observed that a warmer climate will likely increase moisture in the atmosphere over the Indian Ocean and the Indian landmass, which could strengthen the movement of moisture toward India.
“The team noted that the peak monsoon rainfall month may shift from July to August. These findings are important for climate preparedness, agriculture, and water management in India and nearby regions,” he added.
The study found that the simulated moisture over the Indian region is higher in a future warm climate compared to the mid-Pliocene period. Similarly, enhanced surface and tropospheric temperatures in the region were observed.
“From a dynamical perspective, large-scale low-level wind circulation changes and convection over the Indian subcontinent are simulated to be stronger in the mid-Pliocene compared to the future warm climate. Moisture budget analysis reveals that during the past warm climate, both thermodynamic and dynamic components contributed to intensified Indian summer monsoon conditions,” the study added.
The study used the mean of six models from the Coupled Model Intercomparison Project Phase 6. Variables such as precipitation, surface air temperature, precipitable water, vertical wind, and zonal and meridional winds were analysed. The mid-Pliocene and projected future climate (2071–2100) under a high-emissions scenario were examined. For past periods, the last 100 years of datasets were considered, whereas for the future, 30 years of data were used. Dahiya is a research graduate with NIT-R while Prof Attada is an associate professor with Department of Earth and Environmental Sciences of IISER Mohali.