Spike likely due to increasing sea surface temperatures caused by global warming, say researchers
File photo of 2015 Chennai rains The northeast monsoon is a small-scale monsoon confined to parts of southern peninsular India from October to December. But researchers have found that events of widespread extreme rainfall during the monsoons have nearly doubled in the recent decade compared to the 1980s.
A study published in journal Scientific Reports recorded a 30 per cent rise in precipitation intensity in the recent decade compared to the 1980s, along with a nearly twofold increase in widespread extreme precipitation events.
However, models largely failed to accurately capture the magnitude of observed precipitation during the northeast monsoon.
The two main monsoonal systems of South Asia are the northeast monsoon or the post-monsoon and the southwest monsoon or summer monsoon, which occurs from June to September.
“While various aspects of the southwest monsoon have been extensively studied, the northeast monsoon has received comparatively less attention,” the researchers wrote in their study.
The team analysed the seasonal climatological mean precipitation over the northeast monsoon region using both observations and models between 1980 and 2015.
Their results showed that a roughly 40 per cent increase in extreme events occurred between 1992–2003 and 1980–1991. Also, there was an approximately 50 per cent rise in the recent decade compared to the previous one.
The team also found an approximately twofold or a 100 per cent rise in extreme events in the recent decade compared to the 1980s.
“Our analysis reveals a clear increase in both the frequency and intensity of precipitation in recent decades compared to previous decades,” the paper reads. This increase, it added, may be attributed to climate change.
The researchers said that this spike is likely due to increasing sea surface temperatures caused by global warming. During the study period between 1990 and 2015, the sea surface temperatures have climbed up to 0.5 degrees Celsius per decade, over the entire tropical South Asian region.
Warmer sea surface temperatures lead to an increase in atmospheric water vapour over the southeastern Indian peninsula. Higher water vapour content influences the entire weather, increasing the risk of more frequent heavy precipitation events, the researchers highlighted.
The moisture content has gone up to 30 kilogrammes per metre per second per decade in bands extending from the western Pacific Ocean to the Arabian Sea region in both the northern and southern equatorial tropical regions.
The northeast monsoon coincides with the cyclone season in the North Indian Ocean basin, comprising the Bay of Bengal and the Arabian Sea.
The rainfall in the northeast monsoon season is also affected by cyclonic disturbances that form over the Bay of Bengal, affecting the coastal areas of southeastern peninsular India.
The study has also raised concerns over models. According to the researchers, the models completely failed to replicate some reported widespread, impactful extreme precipitation events in the years 2007 and 2015 over southern India.
In 2015, Chennai received its highest rainfall of 1,929.9 millimetres against its average rainfall of 1,145.46 mm. Of this, the city recorded 1,113.80 mm of rainfall in November itself, according to the National Institute of Disaster Management.
The researchers called for continued improvement in modelling capabilities and addressing challenges associated with simulating extreme precipitation events accurately.
“Understanding the limitations and strengths of these models is vital for making informed decisions related to disaster management, infrastructure planning, and climate change adaptation in the face of increasing extreme precipitation events,” the researchers noted.
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