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Climate Change Tracker: India’s variable monsoon rainfall

  • Climate Change is affecting India’s monsoon rainfall
  • There’s a growing trend of differences between excess rainfall areas and areas with deficit rainfall

National Disaster Response Force personnel in flood-hit Wayanad, Kerala.
National Disaster Response Force personnel in flood-hit Wayanad, Kerala. (Photo: AP)

The overriding story of the monsoon in 2018 was the floods in Kerala. As rainfall not seen in nearly a century was dumped on the state, entire regions were washed away in flash floods, with damages totalling 40,000 crore, according to Kerala industries minister E.P. Jayarajan. This year, Kerala has suffered again, along with Karnataka, Maharashtra, Gujarat, Uttarakhand, Himachal Pradesh, Punjab and Assam. And yet, in other parts of the country, rainfall has been severely deficient or is just beginning to catch up in the form of sudden, excessive rain.

According to the India Meteorological Department (IMD), from 1 June-21 August, east and North-East India received 15% less rain than the mean Long Period Average (LPA), while north-west India received 2% less. This is balanced by 13% excess rain in central India and 6% excess in south peninsular India. So while this means that the countrywide monsoon rainfall can be called “normal", this is hardly the case.

This follows a steady pattern. The 2018 monsoon, despite the floods, was deficient overall, with total monsoon rainfall at only 91% of the 50-year average. The 2017-18 Economic Survey reported a 14% fall in agricultural revenue, linked to extreme rainfall shocks due to climate change. In 2014, a paper in Nature by climate scientist Deepti Singh and others had compared rainfall patterns between two periods—1951-80 and 1981-2011—to note that average total monsoon rainfall has declined while rainfall variability in peak months has increased. Although the authors didn’t immediately connect this trend to climate change, Singh did say these changes were “unlikely to happen purely by chance".

The International Centre for Integrated Mountain Development’s (Icimod’s) February Himalayan climate change report forecast an upper limit of 25% increased monsoon rainfall in the next 100 years. Studies elsewhere indicate that climate change-led warming of oceans will create a more moisture-laden monsoon system. However, greenhouse gas emissions as well as the infamous brown cloud over the Gangetic plain—made up of anthropogenic aerosols—absorbs more solar radiation, and results in weak and unpredictable monsoon circulation over the country. Add to this the decrease in forest cover and increase in agricultural land over time, and the result is an unpredictable monsoon.

A 2017 report from the Indian Institute of Tropical Meteorology (IITM) noted that between 1981-2016, the country received 24mm less mean monsoon rainfall than 1871-1980, with the probability of a deficit monsoon the highest in Assam, Meghalaya and eastern Madhya Pradesh.

As greater variability and climate shocks become the new normal, one thing is clear: We can no longer take South Asia’s most dependable weather system, the monsoon, for granted.

This is the first instalment of the Climate Change Tracker, which will present a short explainer on the challenges posed by a rapidly warming planet every week. Follow the series with #MintClimateTracker.

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