It will be fair to say that many of us are looking forward to the monsoon season this year, eager to put behind us one of the hottest summers ever on record. With each passing year, India has been experiencing more and more instances of severe heatwaves, rendering these months more and more dreadful.
A recent report from the India Meteorological Department (IMD) indicated an increasing trend in the number and duration of heatwaves, based on data from the months of March to June from 1961 to 2020. This year, heatwaves started as early as on March 3, and many areas reported temperatures that were higher than average.
The number of days with temperatures exceeding 30 degrees Celsius has also increased of late. While a temperature of 33 degrees Celsius was recorded between 1961 and 1990 for around 70 days every year, from 1991 to 2022, this temperature was recorded for 89 days a year. It thus became the new normal.
The concept of the ‘new normal’ vis-à-vis climate change refers to long-term changes in weather patterns and climatic conditions that are expected to or have become more frequent because of climate change.
The number of hot days from 1961 to 1990 and from 1991 to 2022
Are weather patterns changing?
Climate change is increasing both the frequency and the intensity of extreme weather events. In India, for one, normal monsoon patterns have given way to, among others, delayed onset, short but intense bursts of rain, and delayed withdrawal. Some weather events have also become drier and others wetter thanks to the effects of climate change on the water cycle, which leads to more evaporation and eventually causes more precipitation. Some areas also experience heavier than normal precipitation while others are becoming prone to unexpected droughts.
The U.N. Intergovernmental Panel on Climate Change’s Sixth Assessment Report warned of prolonged rain-free periods along with excessive rainfall in many parts of the world. In recent decades, India has recorded several such extreme events.
An October 2017 study conducted by the Indian Institute of Tropical Meteorology (IITM), Pune, reported that there was a three-fold increase in widespread extreme events from 1950 to 2015. From June to September 2022, there were variations in rainfall in different parts of India: a significant increase was recorded in central and south India whereas parts of Kerala, Karnataka, and Madhya Pradesh flooded many times. A significant shortfall was also recorded in many parts of Uttar Pradesh, Bihar, Odisha, and the northeast.
High monsoon rainfall variability and continuous warming raise the probability of dry and hot extremes, with profound implications for agriculture, water resources, and India’s overall economy.
There is also a strong connection between land and ocean heatwaves, driven by atmospheric circulation, increase in sea-surface temperature, and feedback mechanisms that exacerbate the intensity and duration of extreme temperatures. For example, when a land-based heatwave occurs, it can enhance evaporation rates and reduce soil moisture, leading to drier conditions. This drier surface, in turn, absorbs more solar radiation, amplifying the heatwave. This feedback can also influence the persistence of heatwaves over both land and ocean environments.
Are marine heatwaves playing a role?
The oceans play a key role in the formation of monsoon winds and in keeping the monsoon alive. When extreme heat warms their waters, the change in temperature can lead to cascading effects, such as marine heatwaves, ocean acidification, sea-level rise, and ice melting faster at the poles.
Marine heatwaves are periods of temperature much higher than the average seasonal temperature in that region. The Indian Ocean recorded six marine heatwaves over a period of 52 days in 2021. They used to be rare in this water-body but today are an annual occurrence.
A low pressure develops over the Indian subcontinent when the land heats up during the summer. The moisture for monsoon rains is thus carried by the winds as they blow in from the Indian Ocean. However, rainfall over the land decreases when ocean heatwaves occur, as the winds are drawn to areas over the ocean instead of land.
In recent decades, oceans have remained warmer for longer periods than normal. In 2022, IITM researchers reported a significant increase in the number of marine heatwaves in recent decades because of warming and a strong El Niño (a phenomenon that describes the unusual warming of surface waters in the eastern tropical Pacific Ocean).
Specifically, they found that from 1982 to 2018, the western Indian Ocean region had a four-fold increase in marine heatwaves (an increase of 1.2 to 1.5 events per decade); the northern Bay of Bengal region followed with a two- or three-fold rise (an increase of 0.4 to 0.5 events per decade).
Earlier this month, the U.S. NOAA announced that another El Nino period had begun this year, with the potential to set new surface temperature highs.
How is climate risk being amplified?
Amplification is what happens when certain climate-related factors and/or events interact with each other or happen at the same time, intensifying or exacerbating the overall risks and consequences associated with climate change. A good example is the warm and dry conditions that have put Canada on course for its worst-ever wildfire destruction this year. Such amplification happens in the form of various feedback loops and interconnected processes in the earth’s climate system. It has greater consequences than ‘just’ individual extremes and is also more complex and challenging to deal with.
The interaction of multiple climatic and non-climatic risks can also increase overall risk. According to a January 2023 study by the School of Geography and the Environment, University of Oxford, the combined consequences of excessive heat and drought are expected to put more than 90% of the world’s population at higher risk, potentially deepening socioeconomic disparities. Such an amplification can occur as a result of an El Niño, prolonged hot days, dry monsoons, and/or ocean heatwaves occurring together, compounding risks across sectors.
Such a combination will also affect water availability, soil moisture, and crop output while increasing food prices and lowering incomes. The co-occurrence of heatwaves and droughts can also lead to wildfires, tree mortality, and a higher risk of thermal power-plant failures. Ultimately, the risks can push sensitive and vulnerable systems over a tipping point, ultimately avalanching into drastic consequences for socio-ecological systems.
Amplified climate risks underscore the urgency of taking proactive measures to mitigate greenhouse gas emissions, adapt to changing conditions, and enhance resilience in both natural and human systems. Identifying compound event hotspots and monitoring them are important to frame suitable adaptation strategies. By understanding and addressing these amplification mechanisms, we will be able to reduce the overall risk associated with climate change and build a more sustainable and resilient future.
Dr. Anushiya J. is a research scientist and leads the Adaptation and Risk Analysis team at the Center for Study of Science, Technology and Policy (CSTEP), a research-based think tank in Bengaluru.
- With each passing year, India has been experiencing more and more instances of severe heatwaves, rendering these months more and more dreadful.
- A recent report from the India Meteorological Department (IMD) indicated an increasing trend in the number and duration of heatwaves, based on data from the months of March to June from 1961 to 2020. This year, heatwaves started as early as on March 3, and many areas reported temperatures that were higher than average.
- Earlier this month, the U.S. NOAA announced that another El Nino period had begun this year, with the potential to set new surface temperature highs.