Indian Ocean Dipole – Artifex.News

Why is the Indian Ocean Dipole in the news | Explained

admin — Wed, 01 Jul 2026 05:19:00 +0000

A woman walks along the promenade on a rainy monsoon day, at Marine Drive in Mumbai. File
| Photo Credit: PTI

In the monsoon of 1997, the Central Pacific was running one of the fiercest fevers in its recorded history in the form of an El Niño so violent that, by every rule of thumb, India ought to have stared at one of its worst droughts. However, in the greatest of meteorological surprises, June-September monsoon rainfall ended up being surplus, about 2% above normal. The Director-General of the India Meteorological Department (IMD), Mrutyunjay Mohapatra, observes that it has “happened only once ever.” The agent of that escape sat not in the Pacific but in India’s backyard sea and is called the Indian Ocean Dipole (IOD). With a ‘Super El Niño’ forecast for this year, it is an open meteorological question if a 1997 situation could recur. Currently, the monsoon is running a 40% deficit in India, with the IMD expecting June-September rain to be 90% — a tad above ‘deficient’ –of the long-period average.

What exactly is the IOD?

The equatorial oceans and the air directly above them are two layers in endless conversation, forever trading moisture. Where the sea surface is warm, it breathes water vapour upward; the moist air rises, cools, condenses into clouds, and falls back as rain. Where the surface is cool, the air sinks dry, and the sky withholds. The Pacific runs the largest version of this engine. Trade winds drag sun-warmed water and heap it near Indonesia, where the air ascends in towering rain, drifts back east at altitude, and subsides over the cool eastern Pacific off South America.

This is a vast east–west loop called the Walker circulation, whose rising western limb helps pump moist air towards South Asia. Every few years, the loop wobbles. This is the El Niño–Southern Oscillation (ENSO): in an El Niño, the central and eastern Pacific warm, the trade winds slacken, and the column of rising air slides eastward, leaving cool air to settle over the Indian Ocean and starve the monsoon; La Niña tilts it the other way and feeds the rains.

The Indian Ocean keeps a smaller engine of its own. Imagine it as a long, shallow bathtub of warm water with a slow seesaw running its length, called the IOD. In a positive phase, the western end of Africa warms while the eastern end, off Sumatra, cools; air rises over the warm western water, clouds gather, and the winds that feed the monsoon are given a westward shove towards the subcontinent. In a negative phase, the seesaw tips the other way and the rains are starved at the source. A neutral phase, as is likely this year, leaves the tub level and the monsoon to its own devices. These three phases are the dipole’s whole repertoire, and it cycles through them every year, El Niño or no El Niño.

When was this discovered and by whom?

Unlike the ENSO, the dipole is a young discovery. In 1999, a team led by N.H. Saji, with the Indian scientists B.N. Goswami and P.N. Vinayachandran among them, described it for the first time in Nature, showing that this east–west seesaw accounted for roughly an eighth of all temperature variability in the Indian Ocean and ran on its own engine, independent of the ENSO in the Pacific. Nevertheless, they engage in a complicated tango.

An El Niño often coaxes a positive dipole into being even as it throttles the monsoon, which is why 1997 could host both at once. The question that matters for India’s monsoon this year is whether the IOD can counter El Niño. “The El Niño,” Mohapatra puts it, “is like the big brother, and the IOD cannot fully compensate.” Only when the dipole turns strongly positive does its convergence over the Bay of Bengal cancel the subsidence that El Niño imposes, as it did in 1997. In most El Niño years, it stays quiet, and six monsoons in ten arrive depleted.

There is a third, faster hand on the scales. The Madden–Julian Oscillation — a pulse of cloud and rain that Roland Madden and Paul Julian identified in 1971, conventionally tracked through eight phases as it marches eastward across the tropics every 30-60 days and ignites over the equatorial Indian Ocean — governs the monsoon’s intraseasonal rhythm of active and break spells, and can itself nudge the dipole into life. The dipole is measured, meanwhile, by the Dipole Mode Index: the difference in sea-surface temperature anomaly between the western and south-eastern reaches of the basin, reckoned positive when the west runs warm.

Will the dipole come to monsoon’s rescue this year?

With the present evidence, no. The IMD’s models, and most others, forecast a neutral dipole across the four monsoon months; the Australian Bureau of Meteorology allows a slim chance of a positive turn late in the season, in August or September. But a level seesaw lends the rains nothing, and a positive phase arriving that late and that faintly would be too weak to blunt an El Niño.

Published – July 01, 2026 10:38 am IST

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Razor’s edge: On the progress of the southwest monsoon

admin — Wed, 24 Jun 2026 19:47:00 +0000

The southwest monsoon deficit nationwide has increased from 35% to 43%; the winds’ northward advance was stalled near Mumbai; and both the U.S. NOAA and the India Meteorological Department (IMD) expect a moderate-to-strong El Niño this year. The El Niño suppresses the vertical air movement needed for rainclouds to form while a warming Pacific is weakening the trade winds that bring moisture to the subcontinent. The Madden-Julian Oscillation is also in an unfavourable phase and the Indian Ocean Dipole currently cannot offer a buffer. Further, while northwest India has received 5% more rain than normal, central India and the northeast face deficits of 63% and 43%, respectively. But with two-thirds of the seasonal rainfall historically arriving in July and August, the monsoon may still recover and salvage the season. Together with reservoir storage at 30.4% of capacity, compared with 25.1% during previous El Niño years, there is no reason for alarm yet. However, the effects for agriculture are more concerning. The Agriculture Ministry has already prioritised 111 districts out of 315 vulnerable ones based on their irrigation coverage. Extreme heat has been reducing farm labour productivity. High heat and rain shortfall have sown anxiety over the cardamom harvest in Idukki, a fate that bodes ill for other plantation crops in the Western Ghats.

Both the kharif sowing window for rice, pulses, and oilseeds and the availability of fertilizers could come under pressure, the latter due to Chinese export curbs and tensions in West Asia, heightening the risks of lower soil moisture and higher input stress. Retail food inflation was 4.2% in April; further deficits will especially threaten vegetables and pulses, complicating the monetary policy. The fundamental problem is the way India has built its rural economy around the assumption of reliable rainfall delivery. No adaptation strategy can indefinitely outpace unchecked warming, so limiting future warming should amount to reducing the extent of exposure. The ideal sustainable strategies are to switch from rain-centric to water-centric organisation, reduce dependence on water-intensive crops, and improve resilience. Pathways for the first two have already been outlined. On the last, while the Agriculture Ministry’s extant contingency plans reflect the need for adjustable sowing windows and alternative seed varieties, the principal variable remains implementation at scale. Second, the government should consider a new authority to coordinate inter-State water use and cropping changes based on extended El Niño forecasts, eliminating the cropping governance currently fragmented between the Agriculture and Jal Shakti Ministries, and the IMD.

Published – June 25, 2026 12:10 am IST

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From Western disturbances to El Niño, climate change is affecting India’s food security

admin — Mon, 11 Sep 2023 10:00:00 +0000

There has been a series of disruptive weather and climate phenomena in India this year, demonstrating the complexity of our precipitation system.

There was the Western disturbance, which usually brings much-needed moisture from European seas to the western Himalaya and parts of northern India in the winter and spring. But this year, the Western disturbance lived up to its name and remained active late into the summer, snapping at the heels of the southwest monsoon.

An El Niño phase

The widespread destruction of infrastructure and loss of life due to landslides and flooding in the western Himalaya and northern India raised concerns about the sustainability and resilience of our development projects in the mountains and floodplains. Between July 5 and July 20, the affected area was estimated to be between 2,124 and 7,362 sq. km. The population affected was potentially more than 25 lakh.

Climate-linked warming is likely to weaken winter precipitation from the Western disturbance and shift it to more intense rain events. If this happens later into the summer, its consequences will be of great concern.

Soon after this came evidence that an El Niño phase of the quasi-periodic El Niño Southern Oscillation (ENSO) – a phenomenon in the eastern and central tropical Pacific Ocean – was intensifying and likely to affect the southwest monsoon.

Not all El Niño events have adverse effects on the southwest monsoon because the latter is driven by many ocean-atmosphere-land processes. But the relationship between the two entities has been changing over time. When an El Niño affects the southwest monsoon, another ocean-atmosphere phenomenon in the Indian Ocean – called the positive-phase Indian Ocean Dipole (IOD) – could balance the consequences.

Dynamic regression models have suggested that 65% of the inter-annual variability of the southwest monsoon, over many decades, can be attributed to the combined effects of ENSO and the IOD.

El Niño and food security

Agriculture depends on two types of water. Green water is rain-fed soil moisture tapped by food and cash crops, eventually transpiring into the atmosphere. Blue water is the water in rivers, lakes, reservoirs, and groundwater, which is the basis for irrigation in agriculture, apart from drinking and industry use supply, and to maintain ecological flows in rivers.

The El Niño and other climate phenomena affect rainfed agriculture in many ways, from delaying the start of rains, and affecting sowing, to hot temperatures that may negatively influence plant growth and soil moisture.

Despite investments in dams, reservoirs, and irrigation systems, around half of the cultivated area in India depends on green water, not blue water. Our daily diet in India – from cooking oil to diverse foods – also requires 3,268 litres of water per person per day on average, subject to regional variability. Some 75% of this footprint is green water, demonstrating the importance of rainfed agriculture to our food and nutritional security.

Even in irrigated areas, many dominant crops require green water to different extents. For example, in kharif season, rice paddy under irrigation uses green water to the tune of 35%. Many staple crops like tur dal, soybean, groundnut, and maize also rely considerably on green water at this time. In the 2015-2016 El Niño year, soybean production in India declined by 28% from the 2013-2022 average.

We have just emerged from one of the warmest and driest Augusts in many decades, and hope that the IOD or other phenomena will help reduce the impact of the El Niño on India’s agriculture, farmers, food security, food inflation, and conflicts over water-sharing between States.

El Niño and the northeast monsoon

At the end of the southwest monsoon, the blue water stock in our reservoirs and groundwater will partially determine the fate of the rabi crops sown in winter and the overall water security. Contributions of green water from the northeast monsoon in southeast India and the Western disturbance in the north will play significant roles as well.

Studies have found that 43% of heavy rainfall events in the northeast monsoon (including the 2015 Chennai floods that caused widespread devastation) coincided with an El Niño. We will be closely watching the rabi crops in 2024, which bank heavily on blue water or irrigation during the summer months, along with our overall water security.

Consider Central India’s highlands, encompassing 36 districts in the states of Madhya Pradesh, Chhattisgarh, and Maharashtra, which are emerging as climate change hotspots critical for our water, food and ecological security. It includes 17 urban centres with populations over a lakh and the headwaters for five of India’s 10 major river basins. The basin precipitation ranges from 699 mm in the west to 1,380 mm in the east, with an average of 987 mm per annum.

This region experiences significant and perennial water stress, driven largely by rabi irrigation with blue water. As a result, some 70-78% of the landscape experiences water stress for four or more months in a year.

Of the 17 urban centres, 11 face water stress for six to eight months, with Nagpur enduring water stress for the longest duration.

Persistent uncertainties

The amount of monsoon precipitation has been declining since the 1950s, attributed by some climate scientists to the reduction in land-sea thermal gradient, in turn due to warming of the seas. However, indications of increased frequency of intense rain events and greater heat and moisture stress for people and ecosystems align with predictions of warming’s impact on the atmosphere’s water-holding capacity and acceleration of the hydrological cycle. These events increasingly interact with hydrologically incompatible land-use and built infrastructure, resulting in high exposure and vulnerability to disasters.

Global climate models and their regional equivalents have failed to simulate these observed trends in precipitation, increasing the uncertainty in future projections. However, climate modellers are trying hard to improve the models. Given the persistent uncertainties, we should base our adaptation plans on the idea that current trends will continue: more-frequent intense rain, summer heat and moisture stress, and declining monsoon precipitation in some parts of the country. It is possible that as warming continues, total rainfall in parts of India may increase but the share of extreme rain events may go up. When this tipping point will transpire is uncertain.

Attributing specific extreme rain events to climate change or natural dynamics in our complex climate systems, or both, is challenging for climate scientists. But mounting evidence suggests that a warming atmosphere is amplifying many natural dynamics within our complex climate systems.

How we respond

In terms of agriculture and food security, there is now an emphasis on reducing dependence on water-intensive crops, with millets being the crops of choice. Shifting to less water-intensive crops may reduce vulnerability of our food systems to phenomena like El Niño. One estimate suggests that more than 30% of blue water savings from such shifts, with some gains in protein and micronutrients but a slight reduction in calories. However, water saved in this manner may not necessarily help recharge our depleted aquifers or restore ecological flows in our rivers: new demands for the saved water quickly emerge unless appropriate policies are in place.

There are several adaptations and alternative crop strategies available now, thanks to the work of our farmers and agricultural scientists. They include shifting to millets and alternative varieties of dominant cereals and advisories to farmers to switch to crops with shorter growing cycles. The government, both at the Centre and in States, along with farmers, now benefit from forecasts of phenomena like El Niño and their impact on the monsoon and improvements in short-term weather forecasts and early warning systems for both intense rain and dry spells.

Based on decades of experience, it is clear that alternative short-term and long-term management of our dams and reservoirs is required to reduce the risk of dam-based flood disasters and ecological damage to aquatic ecosystems.

How we respond as a society and in terms of governance to the water and climate change crisis, which links food, water, and ecological security through diversifying our agro-food systems, a lower dependence on blue water, rejuvenating our rivers, and sustainable water-sharing between humans and nature will to a great extent determine the well-being of 1.4 billion people.

Jagdish Krishnaswamy is dean, School of Environment and Sustainability, Indian Institute for Human Settlements (IIHS), Bengaluru. The author acknowledges Kiran M.C., Geospatial Lab, IIHS for his contribution to this article.

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