Europe's Heat Dome and the Rising El Niño: Why Indian Monsoon 2026 Faces a Below-Normal Forecast — Explained

• Magnitude of the heatwave: Western and central Europe are facing an exceptional heatwave during the last week of May 2026, with daytime maximum temperatures running 10 to 15°C above the climatological norm for this time of year. The normal late-May temperature across Western Europe ranges between 20 and 22°C, but several stations have crossed 35°C — a threshold extremely rare in May. The UK and France registered their highest May temperatures on record, while Italy, Germany, Switzerland, Spain, and Portugal have also reported unusually high readings.

• Geographic spread: The heatwave extends across a broad belt covering Britain, France, the Iberian Peninsula (Spain and Portugal), the Alpine countries (Switzerland, parts of Italy, Austria), and Central Europe (Germany). It is not a localised event but a continent-wide thermal anomaly.

• Why it is unusual: May in Europe is traditionally a transition month between cool spring and summer. The 2026 event has already breached the previous record-breaking summers of 2022 and 2023, when temperatures crossed 40°C over large parts of Europe. The current heatwave is unprecedented not for its absolute peak temperature but for its timing — such extreme heat in May had no precedent in modern records.

• Basic definition: A heat dome is a meteorological phenomenon in which a strong, persistent high-pressure system parks itself over a region for several days to weeks, trapping warm air at the surface like a lid on a pot. While "heat dome" is not a formal scientific term in textbooks, it is widely used to describe high-pressure systems that produce prolonged extreme heat.

• The mechanism step by step: A high-pressure system forms in the mid-troposphere, roughly 7 to 10 kilometres above Earth's surface. Under this high pressure, air sinks (subsides) towards the ground. As the air descends, it gets compressed and warms — a process called adiabatic warming. Simultaneously, the high pressure suppresses cloud formation and precipitation because rising air, which normally causes condensation and rain, is blocked. The result is clear, sunny skies that allow maximum solar radiation to reach the ground. Heat builds up day after day, and because the high-pressure system does not move, the dome essentially "cooks" the region beneath it.

• Role of the jet stream: The jet stream is a narrow band of fast-moving wind in the upper atmosphere (around 10–15 km high) that steers weather systems from west to east in the mid-latitudes. When the jet stream develops large meanders or "Rossby waves," high-pressure systems can get blocked between two low-pressure systems, forming an "Omega block" (shaped like the Greek letter Ω). This blocking pattern is what gives a heat dome its longevity. Many scientists believe that warming of the Arctic — faster than the global average (a phenomenon called Arctic amplification) — has weakened the temperature gradient between the equator and the poles, slowing the jet stream and making such blocking events more frequent.

• Feedback loop: Once a heat dome sets in, the ground beneath dries out, loses soil moisture, and starts radiating more heat back into the atmosphere. This further intensifies the dome. The process is self-reinforcing until the larger atmospheric circulation breaks the high-pressure system.

• Concept of urban heat island (UHI): The urban heat island effect is the phenomenon by which cities and densely built-up areas record significantly higher temperatures than surrounding rural areas. Urban surfaces — concrete, asphalt, glass, metal roofs — absorb solar radiation during the day and release the heat back into the surrounding air, especially at night. Rural areas, by contrast, lose heat more efficiently because of vegetation, soil moisture, and lower built density.

• How it interacts with the heat dome: During a heat dome, dry winds blowing in from arid land regions (in Europe's case, sometimes from the Sahara or interior deserts) further raise air temperatures. Cities such as Madrid, London, Paris, and Berlin trap this incoming hot air, push it through their streets, and re-radiate it from buildings at night, preventing nocturnal cooling. The result is longer "warm nights," which the IMD and World Health Organisation flag as particularly dangerous because the human body cannot recover from daytime heat stress.

• Indian relevance: The UHI effect is well documented in Indian metros — Delhi, Mumbai, Kolkata, Chennai, Bengaluru — where surface temperatures can be 2 to 5°C higher than the surrounding countryside. With India's rapid urbanisation, this is a growing concern for public health, energy demand, and water stress.

• Definition: Climate whiplash, also called weather whiplash or hydroclimate whiplash, describes the rapid swing between two opposite weather extremes — for example, severe drought followed by intense flooding, or unusually cold conditions followed by record heat, with very little recovery time in between.

• The scientific basis: A warming atmosphere can hold more water vapour — roughly 7% more for every 1°C rise in temperature, as described by the Clausius-Clapeyron relationship. This makes the atmosphere act like an "expanding atmospheric sponge," soaking up moisture during dry phases and releasing it as intense rainfall during wet phases. Combined with a wavier jet stream caused by Arctic warming, this is producing sharper transitions between extremes.

• Examples around the world: California experienced years of drought (2011–2016), followed by a record-wet 2016–17, then renewed drought and devastating wildfires by 2024. Mozambique saw prolonged dry spells followed by catastrophic floods in 2026. In Europe, the 2024–25 winter was unusually warm in places, and 2026 is now seeing an extreme May heatwave following a relatively mild April — a textbook climate whiplash.

• Why it matters for India: India has its own version of climate whiplash. In recent years, the country has seen short, intense bursts of monsoon rain causing urban floods (Bengaluru, Mumbai, Delhi), followed by long dry spells. Rajasthan, traditionally arid, has seen unusual excess rainfall episodes since 2020. Disaster managers and agriculture planners now need to prepare for both droughts and floods within the same season.

• Meaning of the name: "El Niño" is Spanish for "The Little Boy" or "Christ Child," a name given by Peruvian fishermen in the 1600s who noticed an unusual warming of the eastern Pacific Ocean around Christmas time, which disrupted their fishing.

• Definition: El Niño refers to the abnormal warming of sea surface temperatures (SST) in the central and eastern equatorial Pacific Ocean, off the coast of north-western South America (Peru and Ecuador). For an event to be classified as El Niño, the SST anomaly must remain at least 0.5°C above the long-term average for at least three consecutive overlapping months. A "Super El Niño" is when the anomaly crosses 2.0°C.

• How it forms — the mechanism: Under normal Pacific conditions, easterly trade winds blow from South America towards Indonesia, pushing warm surface waters westward. This causes cold, nutrient-rich water to upwell along the South American coast (a key reason for rich Peruvian fisheries) and piles up warm water in the western Pacific. The sea level in the western Pacific is about 0.5 metres higher than in the east.

• During an El Niño year, the trade winds weaken or even reverse. The warm water that had been pushed west sloshes back eastward, suppressing the cold upwelling near South America. As a result, the entire equatorial Pacific becomes warmer than normal. This shifts the location of the warm pool — and with it the zone of intense atmospheric convection and rainfall — eastward.

• The Southern Oscillation: The Southern Oscillation is the atmospheric counterpart of El Niño, observed as a "see-saw" of atmospheric pressure between Tahiti (eastern Pacific) and Darwin, Australia (western Pacific). When pressure is high over Tahiti, it is low over Darwin, and vice versa. The Southern Oscillation Index (SOI) is calculated as the difference in pressure between Tahiti and Darwin. The combined oceanic and atmospheric system is collectively called the El Niño-Southern Oscillation (ENSO).

• The discovery story: Sir Gilbert Walker, a British scientist serving as Director-General of Observatories in India in the early 20th century, was tasked with predicting Indian monsoon failures after the catastrophic famine of 1899. He noticed the pressure see-saw between the Pacific and Indian Oceans and named it the Southern Oscillation. The famous "Walker Circulation" is named after him. Later, in the 1960s, Norwegian meteorologist Jacob Bjerknes connected Walker's atmospheric observations with El Niño's oceanic warming, establishing ENSO as a unified ocean-atmosphere phenomenon.

• Definition: La Niña — Spanish for "The Little Girl" — is the cool phase of the ENSO cycle. It is characterised by stronger-than-normal easterly trade winds, cooler-than-average SSTs in the central and eastern equatorial Pacific, and stronger upwelling of cold water off South America.

• Effects: La Niña typically produces wetter-than-normal conditions in Southeast Asia, India (above-normal monsoons), eastern Australia, and southern Africa, while causing drought in the southern United States and South America. The 2022–23 European heatwaves coincided with an unusual La Niña phase, showing that local climate is shaped by more than just ENSO.

• The ENSO cycle: ENSO has three phases — El Niño (warm), La Niña (cool), and Neutral — and cycles every 2 to 7 years. La Niña conditions ended in late 2025, the system passed through a neutral phase in early 2026, and El Niño is now emerging.

• The normal Walker Circulation: The Walker Circulation is a large-scale east-west atmospheric circulation over the tropical Pacific. In a normal year, air rises over the warm western Pacific (Indonesia, northern Australia), flows eastward at high altitude, descends over the cool eastern Pacific (off South America), and returns westward as surface trade winds. This loop creates wet weather in the west and dry conditions in the east.

• During El Niño: The Walker Circulation weakens or even reverses. The warm pool — and with it the rising air and rainfall — shifts eastward to the central Pacific. The western Pacific becomes drier, leading to drought in Indonesia, Australia, and large parts of South Asia, including India. The eastern Pacific (Peru, Ecuador) sees unusually heavy rainfall.

• During La Niña: The Walker Circulation strengthens, intensifying the normal pattern. Warm water and rainfall pile up further in the west; dry conditions deepen in the east. India typically receives above-normal monsoon rainfall.

• Historical correlation: Of 22 major drought years in India between 1871 and 2023, around 13 coincided with El Niño events. Strong El Niño years have suppressed Indian monsoon rainfall in about 70% of recorded cases. Notable examples include the 1877, 1899, 1918, 1965, 1972, 1987, 2002, 2009, and 2015 droughts.

• The physical mechanism: A weakened Walker Circulation shifts atmospheric convection eastward over the warmer central Pacific. This reduces the strength of the monsoon trough over India, weakens the cross-equatorial winds (the Findlater Jet), reduces moisture transport from the Indian Ocean, and increases subsidence (sinking air) over the subcontinent — suppressing rainfall.

• Why the link is not absolute: Despite the strong statistical correlation, El Niño does not always cause drought in India. In 1997, one of the strongest El Niño years on record, India received normal monsoon rainfall — because a strong positive Indian Ocean Dipole (IOD) counteracted the El Niño impact. Conversely, a moderate El Niño combined with a negative IOD produced one of India's worst droughts in 2002. The relationship is probabilistic, not deterministic — a point IMD scientists have repeatedly stressed.

• Definition: The Indian Ocean Dipole, sometimes called the "Indian Niño," is an oscillation of sea surface temperatures between the western Indian Ocean (off East Africa) and the eastern Indian Ocean (off Indonesia and Sumatra).

• Phases: A "positive IOD" occurs when the western Indian Ocean is warmer than normal and the eastern Indian Ocean is cooler. This brings more rainfall to East Africa, India, and the western Indian Ocean coast. A "negative IOD" is the opposite: the eastern Indian Ocean is warmer, and the western side cooler — generally leading to drier conditions over India.

• Significance for India: Positive IOD can offset, and even reverse, the suppressive effect of El Niño on the Indian monsoon. In 2026, the IMD has indicated that IOD is currently neutral and is expected to turn positive towards the latter half of the monsoon season, providing some buffer against El Niño's expected impact. This is one reason why IMD has set the forecast at 90% of LPA rather than a deeper deficit.

• EQUINOO: The atmospheric counterpart of IOD is called the Equatorial Indian Ocean Oscillation (EQUINOO), which refers to the see-saw of pressure and wind between the Arabian Sea and the Bay of Bengal.

• The forecast in numbers: On 27 May 2026, the India Meteorological Department released its second-stage Long Range Forecast (LRF) for the 2026 Southwest Monsoon. Key features:

• Country-wide seasonal rainfall (June–September): 90% of the Long Period Average (LPA), with a model error of ±4%.

• June rainfall: 92% of LPA.

• Below-normal rainfall expected over large parts of the country, especially the central and southern regions.

• An earlier April first-stage forecast had projected 92% of LPA; this has now been revised downward to 90%.

• What "Long Period Average" means: The LPA is the average of monsoon season rainfall over a 50-year reference period (currently 1971–2020). The all-India LPA is approximately 87 cm.

• How IMD classifies the monsoon:

• Deficient: Less than 90% of LPA

• Below Normal: 90–95% of LPA

• Normal: 96–104% of LPA

• Above Normal: 105–110% of LPA

• Excess: More than 110% of LPA

The 2026 forecast of 90% places the monsoon at the border of "below normal" and "deficient."

• Major climate factors flagged by IMD:

• El Niño Southern Oscillation (ENSO): Currently transitioning to El Niño, with a 92% probability of El Niño prevailing during June–September 2026.

• Indian Ocean Dipole (IOD): Neutral now, positive IOD likely later — providing partial offset.

• Northern Hemisphere snow cover: Below-normal Eurasian snow cover during January–March 2026 — generally favourable for the Indian monsoon, providing another mitigating factor.

• Global warming: Long-term warming has added moisture to the monsoon system, potentially producing high-intensity rainfall events even within a "below normal" season.

• IMD heatwave thresholds: According to IMD guidelines, a heatwave is declared based on both absolute maximum temperature and the departure from normal.

• Absolute temperature criteria:

• Plains: Heatwave is considered when maximum temperature reaches 40°C or more.

• Coastal areas: Heatwave when maximum reaches 37°C or more.

• Hilly regions: Heatwave when maximum reaches 30°C or more.

• Departure-from-normal criteria: When the maximum temperature of a station is at or above the threshold:

• Heatwave: Departure from normal is 4.5°C to 6.4°C.

• Severe Heatwave: Departure from normal exceeds 6.4°C.

• Absolute peak criteria: Regardless of departure from normal, if the actual maximum temperature reaches 45°C, a heatwave is declared; if it reaches 47°C or more, it is a severe heatwave.

• To qualify formally, the above criteria must be met in at least two stations in a meteorological subdivision for at least two consecutive days.

• IMD Heat Index: The IMD has launched an experimental Heat Index that combines temperature and humidity to capture the "feels-like" temperature. Categories:

• Green: Heat Index below 35°C — comfortable.

• Yellow: 36–45°C — caution.

• Orange: 46–55°C — extreme caution.

• Red: Above 55°C — danger.

• Why the monsoon matters: The Southwest Monsoon (June–September) accounts for nearly 70% of India's annual rainfall and is critical for kharif crops (rice, sugarcane, pulses, oilseeds, cotton), reservoir storage, hydroelectric generation, and groundwater recharge. About 60% of India's net sown area is rainfed.

• Agricultural impact: A below-normal monsoon directly affects kharif sowing and yields. Crops most vulnerable to deficit rain include rice, pulses (tur, urad), oilseeds (soybean, groundnut), and sugarcane. In El Niño years, India has sometimes imposed export restrictions on wheat, rice, sugar, and pulses to stabilise domestic prices.

• Inflation pressures: Food inflation is a key transmission channel. Lower output of vegetables, pulses, and cereals can push retail food inflation higher. The Reserve Bank of India (RBI) closely monitors monsoon performance because food and beverages account for nearly 46% of the Consumer Price Index (CPI) basket.

• Power sector: Hydropower (around 9% of India's installed capacity) depends on reservoir water levels, which in turn depend on monsoon rainfall. Below-normal monsoons can reduce hydro generation and increase reliance on thermal power, raising fuel costs.

• Rural demand: Agricultural distress translates into weaker rural demand for FMCG, two-wheelers, and consumer durables, slowing overall GDP growth. Past El Niño droughts (2002, 2009, 2015) saw GDP growth slip by 0.5 to 1 percentage point.

• National Action Plan on Climate Change (NAPCC): Launched in 2008, the NAPCC includes eight national missions, including the National Mission for Sustainable Agriculture and the National Water Mission, both directly relevant to monsoon-dependent India.

• Heat Action Plans (HAPs): After Ahmedabad pioneered India's first Heat Action Plan in 2013 (following the 2010 heatwave that killed over 1,300 people), the National Disaster Management Authority (NDMA) issued National Guidelines on Heat Wave Management in 2016 (revised in 2019). Over 25 states and 130 cities have now developed HAPs, focusing on early warning, public awareness, hospital preparedness, and cooling shelters.

• IMD's forecasting upgrades: IMD's dynamical Monsoon Mission Climate Forecasting System (MMCFS) and the seamless forecasting system (in place since 2016) provide forecasts ranging from nowcasting (next 3 hours) to seasonal outlooks. Heatwave warnings are colour-coded (green, yellow, orange, red).

• Agricultural buffer: The Pradhan Mantri Fasal Bima Yojana (PMFBY), Minimum Support Price (MSP) regime, and buffer stocks under the National Food Security Act provide cushioning against monsoon failures.

• Heatwaves intensifying: The IPCC's Sixth Assessment Report (AR6, 2021–22) states with "virtual certainty" that hot extremes have become more frequent and more intense across most land regions since the 1950s, and that human influence is the main driver. Heatwaves in Europe in 2003 (which killed over 70,000), 2022, and 2023 have all been formally attributed to climate change.

• ENSO behaviour changing: Recent research suggests that extreme El Niño events may become more frequent in a warming world. Climate models indicate the eastern Pacific is warming faster than the west, potentially making El Niño-like conditions more common.

• Implications for India: With global warming adding more moisture to the atmosphere, India is seeing greater rainfall variability — periods of intense rain interspersed with longer dry spells. The number of heatwave days has increased; IMD data shows the frequency of heatwave days over India in 2024 and 2025 was significantly above the 1981–2010 average.

• World Meteorological Organization (WMO): A specialised agency of the United Nations, headquartered in Geneva, the WMO coordinates meteorological observations, issues global ENSO updates, and runs the Global Producing Centres for Long-Range Forecasts.

• NOAA Climate Prediction Center (CPC): The US National Oceanic and Atmospheric Administration's CPC issues ENSO advisories and is the most authoritative agency tracking the Pacific.

• European Centre for Medium-Range Weather Forecasts (ECMWF): Based in Reading, UK, ECMWF runs one of the world's most accurate global numerical weather prediction models and provides seasonal forecasts.

• India Meteorological Department (IMD): Established in 1875, the IMD is the national meteorological service of India, under the Ministry of Earth Sciences. It issues Long Range Forecasts for the monsoon in two stages (April and May).

• Intergovernmental Panel on Climate Change (IPCC): Established in 1988 by the UN and WMO, the IPCC produces Assessment Reports on the science, impacts, and mitigation of climate change.