Why India’s Monsoon Varies Each Year Explained

In India, monsoon variability is the natural swing in India’s monsoon rainfall, both within a single season, as wet “active” spells alternate with dry “breaks”, and from one year to the next, when the total rain can range from damaging drought to destructive flood. The monsoon is remarkably regular in its arrival and its long-term average, yet no two seasons are alike, and that unevenness shapes crops, water supplies and lives across the country.

Understanding why the rains vary helps explain why forecasters talk about El Nino, the Indian Ocean Dipole and the Madden-Julian Oscillation, and why a “normal” total can hide weeks of drought and days of deluge. Last updated: 2 November 2026. This explainer covers the two kinds of variability, their main drivers, recent examples, and what climate change is doing to the pattern.

Key Takeaways

• Monsoon variability has two layers, the short-term active and break cycle within a season and the longer swings in seasonal totals from year to year.
• El Nino years tend to bring weaker monsoons and La Nina years tend to bring stronger ones, but the link is a tendency and has many exceptions.
• The Indian Ocean Dipole can strengthen or offset the El Nino effect, which is why some El Nino years still delivered good rain.
• The Madden-Julian Oscillation and related slow-moving cycles set the timing of wet and dry spells within a season.
• A season with “normal” total rainfall can still hide long dry gaps and short, intense bursts, which matter as much to crops and cities as the total.
• Climate change is making the monsoon more erratic, with evidence of more extreme rain events alongside longer dry spells.

What is monsoon variability?

Monsoon variability is the difference in monsoon rainfall from one time or place to another, and it appears at several scales: day to day, week to week within a season, year to year, and across decades. It is a natural feature of the monsoon system and not a sign that something is broken.

The monsoon is not a steady rain but a pulsing system. Within each season, rain arrives in surges separated by lulls. Across years, the total varies around the long-term average. And across space, one region can be flooded while another, a few hundred kilometres away, suffers drought in the same season. This patchiness is why all-India averages are only a rough guide to what farmers experience on the ground.

The monsoon’s variability is smaller than that of many other tropical rainfall systems, which is why Indian agriculture has been able to rely on it for millennia. But even a modest percentage swing in the total matters enormously when hundreds of millions of people depend on the rain.

What is intra-seasonal variability, or the active and break cycle?

Intra-seasonal variability is the alternation of wet and dry spells within the monsoon season, commonly described as “active” periods of widespread rain and “break” periods when the monsoon trough shifts and rainfall over much of India weakens. These cycles typically last days to a few weeks.

During an active spell, the monsoon trough sits in its normal position across central and northern India, low-pressure systems move in from the Bay of Bengal, and heavy rain falls over central India and the west coast. During a break, the trough shifts north towards the Himalayan foothills. Rainfall then drops across the plains and central India but rises over the Himalayan foothills and parts of the northeast, sometimes triggering floods and landslides in the mountains while the plains sit dry.

Breaks can last a week or more, and long breaks during sensitive crop stages can hurt yields even if the season later recovers. The interplay between the two spells is why two seasons with the same total can feel very different to farmers.

What drives the monsoon’s wet and dry spells?

The monsoon’s wet and dry spells are driven mainly by slow-moving atmospheric oscillations, the best known of which is the Madden-Julian Oscillation, together with the formation of low-pressure systems over the Bay of Bengal and shifts in the monsoon trough. These systems move rain-bearing disturbances across the Indian region in a pattern that repeats every few weeks.

• Madden-Julian Oscillation (MJO): An eastward-travelling pulse of cloud and rain near the equator with a period of roughly 30 to 60 days; its passage over the Indian Ocean tends to boost monsoon activity.
• Boreal Summer Intraseasonal Oscillation: A northward-moving rain band that travels from the equator towards India with a period of around 30 to 60 days, closely tied to active and break cycles.
• Shorter oscillations: Cycles of roughly 10 to 20 days add to the pattern.
• Bay of Bengal low-pressure systems: Depressions and lows form over the bay and travel west-north-west, delivering heavy rain across central India.
• Monsoon trough: Its position decides whether rain falls over the plains or the Himalayan foothills.

Because these oscillations are partly predictable, extended-range forecasts out to several weeks can offer useful guidance on when active and break spells are likely, an area where the IMD and IITM have invested heavily.

What is inter-annual variability and why do monsoon totals change from year to year?

Inter-annual variability is the change in seasonal monsoon rainfall from one year to the next, and it arises from slow changes in ocean temperatures and atmospheric circulation, especially in the Pacific and Indian Oceans, combined with random weather noise. It decides whether a year is classed as deficient, normal or excess.

The IMD classifies seasonal all-India rainfall against the long period average of about 87 centimetres, and the categories follow percentage bands around that average. Rainfall of 96 to 104 per cent is normal, below 90 per cent is deficient, and above 110 per cent is excess, with intermediate bands for below normal and above normal. A deficient year with a shortfall of more than 10 per cent is generally labelled a drought year.

Sizeable swings happen despite the average being stable. India has had drought years such as 1972, 1987, 2002, 2009, 2014 and 2015, and surplus years such as 1988, 1994, 2019 and 2020. Even in a typical year, the difference between regions can be large, so a national total can hide a drought in one state and a flood in another.

How does El Nino affect the monsoon?

El Nino tends to weaken the Indian monsoon because the warm Pacific Ocean shifts the Walker circulation and encourages air to sink over the Indian region, which suppresses rainfall. A large share of India’s drought years have occurred in El Nino years, but not every El Nino brings a drought.

The relationship runs through the east-west overturning circulation across the tropical Pacific and Indian Oceans. In El Nino, the rising branch of the circulation shifts eastwards to the central and eastern Pacific, while subsidence strengthens over the maritime continent and parts of India. La Nina does the reverse and tends to favour a stronger monsoon. The strength of the connection has varied over time and some studies suggest it weakened in recent decades before partly recovering.

The key lesson is caution. A forecast of El Nino raises the odds of a poor monsoon but does not seal the outcome. Years such as 1997, when a very strong El Nino coincided with a near-normal monsoon, and 2023, when El Nino developed and the season ended below normal with a record-dry August, show that timing and other factors modulate the result.

What is the Indian Ocean Dipole and how does it change the monsoon?

The Indian Ocean Dipole is a difference in sea-surface temperature between the western and eastern tropical Indian Ocean, and a positive phase, with warm water in the west and cooler water in the east, tends to support the Indian monsoon while a negative phase tends to weaken it. It can offset or reinforce the effect of El Nino.

In a positive dipole, enhanced evaporation and rising air over the western Indian Ocean strengthen the cross-equatorial winds and the moisture supply to India. When a positive dipole coincides with El Nino, the Indian Ocean influence has often cushioned the monsoon, as in 1997 and 2019. When a negative dipole accompanies El Nino, the risk of a weak monsoon is greater.

A related feature, the Equatorial Indian Ocean Oscillation, describes the shift of convection between the western and eastern equatorial Indian Ocean and has also been linked to monsoon rainfall. These ocean modes add to the complexity that forecasters must weigh.

Do other factors such as snow cover and the Atlantic Nino matter?

Other factors such as Eurasian snow cover, the Atlantic Nino, Pacific decadal swings and local land and aerosol conditions also influence the monsoon, although their effects are generally smaller and less consistent than those of El Nino and the Indian Ocean Dipole. They are best viewed as additional pieces of a probabilistic puzzle.

• Eurasian snow cover: Heavy winter and spring snow on Eurasia has traditionally been linked to a weaker monsoon, because snowmelt absorbs heat and slows land warming, but the relationship has weakened in recent decades.
• Atlantic Nino: Warm episodes in the equatorial Atlantic have been associated with rainfall effects over India in some studies, with a tendency towards reduced rainfall, though the evidence is still developing.
• Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation: Slow ocean cycles can shift the background state of the monsoon for years or decades.
• Aerosols: Dust and pollution particles can change heating patterns and cloud formation, and have been proposed as a factor in rainfall trends.
• Land use and soil moisture: Irrigation and land-surface changes influence local rainfall and humidity.

Scientists generally describe these as tendencies that change from decade to decade, which is why no single indicator can reliably predict a season.

What do recent monsoon years show about variability?

Recent monsoon years show a wide range of outcomes, including strong and weak seasons, intense local floods and long dry gaps, and they illustrate how an average figure can conceal extreme weather. Each season tells a different story about the drivers involved.

Each year had floods somewhere. Even the weaker seasons produced local extremes, and the stronger seasons had dry regions. This uneven character is the monsoon’s signature.

How is climate change altering monsoon variability?

Climate change is altering monsoon variability by making rainfall more extreme and uneven, with research showing more heavy-rain events and more dry spells within the season, even as the long-term seasonal total shows large natural fluctuation. Projections generally indicate that average monsoon rainfall may increase over the long term, together with greater variability.

Several observed and projected changes stand out.

• More extreme downpours: A warmer atmosphere holds more moisture, so heavy rainfall events have become more frequent, especially over central India.
• Longer dry spells: Breaks and dry spells between rain bursts have also become more common in some analyses.
• Uneven distribution: Rain is arriving in fewer, more intense episodes, raising the odds of floods and flash droughts in the same season.
• Regional shifts: Some parts of central and north India saw a decline in monsoon rainfall in the late twentieth century, partly attributed to aerosols and ocean warming, while others saw increases.
• Future outlook: Assessments by the Intergovernmental Panel on Climate Change indicate that South Asian monsoon rainfall is likely to increase with warming over the long term, with greater year-to-year variability.

These findings come with uncertainty, and attributing a single season to climate change requires careful study. But the direction of change, towards a wetter yet more erratic monsoon, is widely supported.

How do forecasters predict monsoon variability?

Forecasters predict monsoon variability by combining ocean and atmosphere observations with climate models, issuing seasonal outlooks in April and a revised outlook around the end of May, and then monthly and extended-range forecasts during the season. Each layer provides guidance at a different scale.

The IMD’s seasonal forecast draws on statistical relationships and dynamical models such as the coupled model developed under the Monsoon Mission, which is run with the IITM and partners. It considers El Nino, the Indian Ocean Dipole, snow cover, and sea temperatures. Forecasts are issued as probabilities across the rainfall categories, since the exact result is uncertain. During the season, extended-range forecasts out to about four weeks use the MJO and model output to indicate likely active and break spells.

Forecast skill for the seasonal total has improved but remains limited, and skill at local scale is lower still. That is why farmers, water managers and city planners are encouraged to prepare for a range of outcomes and to use district-level advisories during the season.

Why does monsoon variability matter for farmers, water and cities?

Monsoon variability matters because India’s agriculture, water supply and flood risk all depend on when and how the rain falls, not only how much. About half of India’s farmland is rainfed, so a delayed onset or a long break at a critical stage can damage crops even in a year with adequate totals.

• Agriculture: The kharif crops, including rice, pulses, cotton and soybean, are sown with the first rains and need steady moisture; breaks can stunt them.
• Reservoirs and groundwater: Good monsoon years refill dams and aquifers that support the dry season, while poor years strain supplies.
• Economy: Rural incomes, food prices, inflation and power demand all respond to the monsoon.
• Floods and landslides: Short, intense bursts overwhelm urban drainage and trigger hill slope failures.
• Planning: Crop insurance, early warning, drought-tolerant varieties and flexible water management help communities cope.

Bottom Line

The Indian monsoon is a dependable but never uniform system, swinging between active and break spells within each season and between good and poor years over time. El Nino, the Indian Ocean Dipole, the Madden-Julian Oscillation and other factors shape those swings, and a warming climate is adding more extreme rain and more erratic behaviour. Planning for variability, and not just for the average, is the central lesson.

Frequently Asked Questions

What is monsoon variability in simple terms?

Monsoon variability is the way monsoon rainfall changes from week to week within a season and from year to year. Some seasons are wet, others dry, and within each season there are rainy spells and dry gaps. It is a natural feature of the monsoon system.

What causes the active and break cycle of the monsoon?

The active and break cycle is caused mainly by slow-moving atmospheric oscillations such as the Madden-Julian Oscillation and by shifts in the monsoon trough. During an active spell the trough lies over central India and rain is widespread. During a break it moves towards the Himalaya, and the plains turn dry.

Does El Nino always cause a weak monsoon in India?

El Nino does not always cause a weak monsoon, but it raises the chance of one. Many drought years have coincided with El Nino, but some El Nino years, such as 1997, brought near-normal rain. The Indian Ocean Dipole and other factors can offset the El Nino effect.

How does the Indian Ocean Dipole affect the monsoon?

A positive Indian Ocean Dipole, with warmer water in the west, tends to strengthen the monsoon, while a negative one tends to weaken it. A positive dipole can offset the drying effect of El Nino, as happened in some past years. Forecasters track it alongside El Nino.

Is climate change making the monsoon more unpredictable?

Climate change appears to be making the monsoon more erratic, with more extreme heavy-rain events and more dry spells within a season. Long-term projections suggest average monsoon rainfall may rise, but with greater variability. Researchers caution that individual seasons are shaped mainly by natural factors.

Why can a normal monsoon still cause drought or floods?

A normal monsoon can still cause drought or floods because the seasonal total says nothing about the timing and spread of rain. Long dry gaps can damage crops, and intense bursts can overwhelm drainage. Regions also differ, so one area may flood while another stays dry.

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