Unveiling the 'Indian Niño': A New Study Links Ocean Phenomenon to India's Record Heat

The scorching summers of 2023 and 2024 left an indelible mark on India, with temperatures soaring to unprecedented levels, claiming hundreds of lives, and crippling agriculture across vast regions. A groundbreaking study from the University of Maryland has pinpointed a key culprit behind this extreme heat: the 'Indian Niño,' a colloquial term for the Indian Ocean Dipole (IOD). This natural climate pattern, characterized by warmer waters in the western Indian Ocean compared to the cooler eastern part, amplified global temperatures and intensified heatwaves over the subcontinent.

Published in Earth System Dynamics, the research demonstrates how a strong positive IOD event in 2023-2024 contributed significantly to the anomalies, explaining much of the deviation from expected warming trends driven solely by greenhouse gases. For India, this meant prolonged dry conditions, reduced monsoon reliability, and blistering pre-monsoon heat that pushed cities like Delhi and Rajasthan into crisis mode.

What is the Indian Ocean Dipole?

The Indian Ocean Dipole (IOD) is an irregular oscillation of sea surface temperatures in the Indian Ocean, akin to El Niño in the Pacific but confined to this basin. During a positive phase, the western Indian Ocean warms excessively while the eastern part cools, creating a temperature gradient that disrupts atmospheric circulation. This shift suppresses convection over the eastern ocean, leading to deficient rainfall over India and Southeast Asia while boosting it in East Africa.

First identified in the late 1990s by Indian researchers at the Indian Institute of Technology Bombay and IMD, the IOD typically peaks from September to November, overlapping with India's monsoon season. A positive IOD often results in below-normal monsoon rains, exacerbating summer heat by drying soils and reducing cloud cover.

The Historic 2023-2024 Positive IOD Event

The IOD event that unfolded in 2023 was one of the strongest on record, rivaling the 1997 event. It began building in early 2023, coinciding with the transition from La Niña to El Niño in the Pacific. By late 2023, the dipole index peaked, with western Indian Ocean temperatures anomalously high. This persisted into 2024, though weakening by year-end.

According to the study, this pIOD added 0.075°C to global mean surface temperature (GMST) in 2023 and 0.053°C in 2024 relative to 2022 baselines. Combined with other factors like shipping emission reductions and North Atlantic warming, the model captured 93% and 92% of the observed anomalies, respectively—a leap from prior models that overlooked IOD.

How the IOD Fueled India's Heatwaves

In India, positive IOD phases correlate with intensified pre-monsoon heatwaves (March-June). The warmer western ocean enhances subsidence over the subcontinent, trapping heat and inhibiting rain formation. In 2023, despite a slightly above-normal monsoon (106% of long-period average), early summer saw severe heat, with Delhi hitting 49.2°C. 2024 was worse: heatwaves lasted longer, covering northwest, central, and east India, with peaks over 50°C in Rajasthan.

IMD data shows 2024 had 50% more heatwave days than average, totaling ~366 extra hours of exposure per person. Local factors like soil moisture deficits, amplified by IOD-induced dryness, created a feedback loop for extreme heat.

The Human Cost: Deaths and Health Crises

India's 2023-2024 heatwaves were deadly. Official NDMA/IMD figures report ~250 deaths in 2023 and 150-219 in 2024, but independent studies estimate over 700 in 2024 alone, with 40,000+ suspected heatstroke cases. Vulnerable groups—farmers, laborers, elderly—bore the brunt, as outdoor work continued amid 45-50°C temps.

Hospitals overwhelmed; Delhi reported 50+ deaths in May 2024. Climate-attribution research shows warming made events 30% more likely, underscoring the IOD's role in stacking natural variability atop anthropogenic trends.

Agricultural Devastation and Economic Fallout

Agriculture, employing 45% of Indians, suffered immensely. Rabi crops like wheat saw 5-10% yield losses in 2024 due to heat stress during grain filling. Kharif sowing delayed by dry soils. Total labor hour losses: 247 billion in 2024, 66% from farming, costing billions in productivity.

Positive IOD worsened deficits; 2023 monsoon pockets had shortfalls, hitting pulses and maize. Economic hit: ₹10,000 crore+ from crop failures, water scarcity.

Behind the Science: Model and Attribution

The UMD team's energy balance model (EM-GC), trained on 170 years of data, integrates 10+ forcings: GHGs, aerosols, ENSO, IOD index (DMI), solar, volcanoes. A 160k-member ensemble handles uncertainties. Without IOD, 2023 prediction missed by 0.075°C—proving its pivotal role.

Lead author Endre Farago notes: "IOD's omission in standard models left gaps; now we see its global punch."

Global Context and Indian Research Contributions

While global, IOD's Asian warming hit India hard. Indian institutions like IIT Bombay, IISER Pune, and IMD have pioneered IOD-heatwave links. IITM models project 4-7x more heatwave days by 2100 under moderate warming, intensified by frequent strong IODs.

IMD's Heat Action Plans (HAPs) in 50+ cities saved lives, but national scaling needed.

Future Risks: Climate Change Supercharging IOD?

Projections: Warming may boost extreme pIOD frequency 2-3x by 2100, per IISc and IIT studies. Mean IOD amplitude rises, risking compound events with El Niño. India faces 20+ heatwave days/year routinely, with wet-bulb temps nearing limits in coasts.

Mitigation and Adaptation Strategies

• Enhance IMD early warnings, expand HAPs to rural areas.
• Promote heat-resilient crops (wheat varieties like HD-3226).
• Urban greening, cool roofs to combat urban heat islands.
• Research investment: Fund IISER/IIT IOD modeling.
• Global: Cut GHGs to curb baseline warming amplifying IOD.

Stakeholder Perspectives and Calls to Action

Ross Salawitch: "Natural modes like IOD remind us climate is multifaceted; better models aid prediction." Indian experts at IITM echo: Local soil-atmosphere feedbacks + IOD = deadly synergy.

For researchers eyeing climate roles, opportunities abound in modeling IOD impacts.CEEW Heat Impact Report