India’s monsoon is dependent on several factors, including climate change, Indian Ocean Dipole (IOD), El Niño and La Niña, among others. This year, there will be lots of variability in rainfall during the southwest monsoon season due to climate change, which is making weather patterns unpredictable.
El Niño is the phenomenon in which trade winds weaken, as a result of which warm water is pushed back east, toward the west coast of the Americas, where the Pacific Ocean is present. Since warm water is pushed back east due to El Niño, the monsoon in India can be affected.
The periodic cooling of ocean surface temperatures in the central and east-central equatorial Pacific is referred to as the La Niña effect. La Niña causes warm water to be pushed toward Asia.
The El Niño effect is likely to start impacting India from July 2023. According to experts, an El Niño year following La Niña is the worst-case scenario for monsoon deficits.
How a positive IOD can impact India’s monsoon
But certain factors can offset the impact of El Niño for India. These include the accumulation of snowfall over Eurasia and a positive IOD.
Snowfall accumulation over Eurasia is likely to play a compensating role to the El Niño effect for India because the accumulation influences the temperature and pressure patterns over Asia. These patterns can alter the monsoon circulation. Also, heavy snowfall over Eurasia cooled the atmosphere, creating a high-pressure system. This system can strengthen monsoon winds over India.
The IOD is defined as sea surface temperature differences between two poles or dipoles: a western pole in the Arabian Sea, and an eastern pole in the eastern Indian Ocean south of Indonesia. The western pole is located in the western Indian Ocean. Due to the change in temperature gradients across the Indian Ocean, changes occur in the ascent and descent of moisture and air in certain regions. When the western Indian Ocean becomes cooler than the eastern Indian Ocean, a sea surface temperature gradient is created, which can affect the atmospheric circulation and rainfall patterns over the Indian subcontinent. Since the western Indian Ocean experiences higher-than-normal rainfall during a positive IOD event, India can receive increased rainfall.
“The Indian Ocean Dipole (IOD) is a climate phenomenon that affects the sea surface temperature and rainfall patterns over the Indian Ocean. A positive IOD occurs when the western Indian Ocean becomes cooler than the eastern Indian Ocean, leading to a gradient in sea surface temperature across the Indian Ocean. This temperature gradient can affect the atmospheric circulation and rainfall patterns over the Indian subcontinent. During a positive IOD event, the western Indian Ocean experiences higher-than-normal rainfall, while the eastern Indian Ocean experiences drier-than-normal conditions. This can lead to increased rainfall over India and can offset the effects of El Niño, which usually brings drier-than-normal conditions to India,” Dr Anjal Prakash, Research Director, Bharti Institute of Public Policy, Indian School of Business and IPCC Author, told ABP Live.
El Niño affects the sea surface temperature in the Pacific Ocean, which can weaken the monsoon or trade winds, and decrease rainfall over India. But a positive IOD can offset this effect. Increased rainfall over the western Indian Ocean can contribute to increased rainfall over India.
“When El Niño occurs, it affects the sea surface temperature in the Pacific Ocean, which can weaken the monsoon winds and decrease rainfall over India. However, a positive IOD can counteract this effect by strengthening the monsoon winds over India and bringing more rainfall to the region. The increased rainfall over the western Indian Ocean during a positive IOD can also contribute to the increased rainfall over India by creating favourable atmospheric conditions supporting monsoon circulation,” Dr Prakash explained.
He concluded that in this way, a positive IOD can potentially offset the negative impact of El Niño on the monsoon season and help maintain adequate rainfall over the Indian subcontinent.
Neutral IOD condition this year
However, this year, there is a neutral IOD condition, which means that there is no significant sea surface temperature gradient across the Indian Ocean. Also, a neutral IOD condition can have a mixed effect on India’s monsoon. But it may strengthen the monsoon winds, leading to increased rainfall over India.
“This year, there is a neutral IOD condition, meaning there is no significant gradient in sea surface temperature across the Indian Ocean. This neutral condition can have a mixed effect on India's monsoon season. On the positive side, a neutral IOD condition can create a more stable atmosphere over the Indian Ocean, supporting the development and strengthening of the monsoon winds. This can lead to increased rainfall over India and help offset the negative impact of any El Niño conditions,” Dr Prakash said.
However, the negative aspect of a neutral IOD condition is that it can lead to below-average rainfall over the Indian subcontinent when factors such as El Niño or La Niña are unfavourable.
“On the negative side, a neutral IOD condition can also result in below-average rainfall over the Indian subcontinent if other factors, such as El Niño or La Niña, are unfavourable. This could lead to drought-like conditions and negatively impact agriculture and the economy,” Dr Prakash said.
He explained that the effect of the IOD on India's monsoon season this year is uncertain, as it is just one of many factors that can affect the monsoon. Other factors such as El Niño or La Niña conditions, local weather patterns, and atmospheric circulation can also significantly impact the monsoon season.