IMD study finds India's climate zones shifting, ties north India's drying to the Pacific
In one line: Comparing 30-year climate normals since 1951, IMD and IITM scientists find north India drying and the west coast getting wetter, with a North Pacific pattern called the Victoria Mode helping dry the Gangetic plains.
Published 25 October 2026. Written by Pratidin from the reports linked at the end; every fact checked by a separate review before publishing. How we work
A study by scientists of the India Meteorological Department (IMD) and the Indian Institute of Tropical Meteorology (IITM), Pune, published in MAUSAM, IMD's peer-reviewed journal, has redrawn India's climate map for successive 30-year periods from 1951-1980 to 1991-2020 using IMD observations. Climate zones are defined by temperature and rainfall. The study finds that northern regions have trended drier while parts of the south and the west coast have become wetter. In northwest India, the hot semi-arid steppe zone grew from 25.7% to 33.1% of the area between the first and the latest period, and its eastern edge moved from western to eastern Uttar Pradesh.
Other shifts are just as striking. West Vidarbha and Marathwada moved mostly from tropical savannah to semi-arid steppe, while western Saurashtra and Kutch moved from fully arid to semi-arid. In northeast India the tropical savannah zone shrank from about 18% to 12% of the region, and the temperate zone now covers more than four-fifths of it, which the authors link to rising maximum temperatures. Gangetic West Bengal has shifted from tropical savannah to temperate. On the west coast, tropical monsoon zones have expanded in Konkan and Goa, coastal Karnataka and Kerala.
The study names the Victoria Mode, a recurring pattern of warm and cool sea-surface temperature anomalies in the North Pacific that is distinct from the better-known Pacific Decadal Oscillation, as a key driver of drying over the Gangetic plains. In its negative phase it steers moisture away from the region and sets up high pressure over Bengal, suppressing rain. IITM's Rajib Chattopadhyay said rainfall over Gangetic West Bengal and Bihar had been declining for four decades, even before this year's El Niño-linked shortfall, when east and northeast India recorded a deficit of 25.6%. The authors warn of effects on paddy, water and food security, and suggest building ocean patterns such as the Victoria Mode into long-term farm planning.
Prelims facts
- An IMD and IITM study in MAUSAM compared India's climate zones across 30-year periods from 1951-1980 to 1991-2020.
- Northwest India's hot semi-arid steppe zone expanded from 25.7% to 33.1% of the area; its eastern edge moved from western to eastern Uttar Pradesh.
- In northeast India, tropical savannah shrank from about 18% to 12%; Gangetic West Bengal shifted from tropical savannah to temperate.
- Tropical monsoon zones expanded along Konkan and Goa, coastal Karnataka and Kerala.
- The negative phase of the Victoria Mode, a North Pacific sea-surface temperature pattern distinct from the PDO, is linked to drying over the Gangetic plains.
Quick recall
- Which institutions authored the climate zone study reported in October 2026, and where was it published?
- IMD and IITM Pune; published in MAUSAM, IMD's peer-reviewed journal.
- Which 30-year periods did the study compare at its ends?
- 1951-1980 and 1991-2020.
- Change in northwest India's hot semi-arid steppe zone?
- From 25.7% to 33.1% of the area.
- Change in northeast India's tropical savannah zone?
- From about 18% to 12% of the region.
- Climate class Gangetic West Bengal shifted into?
- Temperate, from tropical savannah.
- What is the Victoria Mode?
- A recurring pattern of warm and cool sea-surface temperature anomalies in the North Pacific, distinct from the PDO.
- Where did tropical monsoon zones expand?
- Konkan and Goa, coastal Karnataka, and Kerala.
- East and northeast India's monsoon deficit in 2026?
- 25.6% below normal, the largest regional shortfall.
Prelims practice question
The 'Victoria Mode', recently linked by an IMD study to drying over the Gangetic plains, refers to:
- A pattern of sea-surface temperature anomalies in the North Pacific Ocean
- A cycle of temperature differences between the western and eastern Indian Ocean
- A pressure oscillation over the South Atlantic Ocean
- The seasonal movement of the Inter-Tropical Convergence Zone over Australia
Show answer
Answer: (a) A pattern of sea-surface temperature anomalies in the North Pacific Ocean. The Victoria Mode is a recurring pattern of warm and cool sea-surface temperature anomalies in the North Pacific, distinct from the Pacific Decadal Oscillation. Option 2 describes the Indian Ocean Dipole.
Use this in UPSC Mains: previous-year questions
Recurring theme: Drivers of Indian monsoon variability and shifting climate regions
- How to use this
Use the study to show that monsoon behaviour is changing measurably, while noting that ocean patterns like the Victoria Mode, not only land-use change, drive part of it.
- IMD and IITM found northwest India's hot semi-arid steppe grew from 25.7% to 33.1% of area between 1951-1980 and 1991-2020.
- Rainfall over Gangetic West Bengal and Bihar has declined for four decades, linked to the negative phase of the North Pacific Victoria Mode.
- How to use this
Argue that El Niño explains many but not all unusual climatic events, citing the Victoria Mode-linked decline in Gangetic rainfall.
- East and northeast India's 25.6% deficit in 2026 was linked partly to El Niño.
- IITM scientists said rainfall over Gangetic West Bengal and Bihar had already been declining for four decades, linked to the Victoria Mode.
The IOD is one of the ocean patterns, alongside El Niño and the Victoria Mode, that shape Indian monsoon rainfall.
Mains practice question
India's climate zones are shifting, with the north drying and parts of the west coast getting wetter. Discuss the role of distant ocean patterns in these changes and their implications for agriculture. (150 words)
Model answer
An IMD and IITM study in MAUSAM compared India's climate zones from 1951-1980 to 1991-2020 and found clear shifts.
Observed shifts
- Northwest India: hot semi-arid steppe up from 25.7% to 33.1% of area; edge moved to eastern Uttar Pradesh.
- Marathwada and West Vidarbha: tropical savannah to semi-arid steppe.
- Northeast: tropical savannah down from about 18% to 12%; Gangetic West Bengal now temperate.
- West coast: tropical monsoon zones expanded.
Role of ocean patterns
- Negative Victoria Mode (North Pacific) steers moisture away from the Gangetic plains and builds high pressure over Bengal.
- El Niño years add short-term deficits, such as east and northeast India's 25.6% shortfall in 2026.
Implications for agriculture
- Paddy sowing and harvest windows, groundwater demand and drought risk change.
- Need to include ocean indices in long-range planning, shift crop choices and invest in irrigation efficiency.
Climate zones are moving faster than farm planning; forecasting must look beyond the Indian Ocean.
The basics
Why this matters
School geography teaches India's climate regions as if they were fixed. A new IMD and IITM study shows they are moving within a single lifetime. That matters for crops, water and disaster planning, and it connects Indian weather to oceans far beyond the Indian Ocean.
How climates are classified
Climate zones are drawn from long-term averages of temperature and rainfall, usually over 30 years (a climate normal). The class names used in the study, such as tropical savannah, tropical monsoon, hot semi-arid steppe, arid and temperate, are names found in the widely used Koppen climate classification. Comparing one 30-year normal with another shows how zones shift.
- Warm all year
- Distinct dry season
- Covered much of Marathwada, Vidarbha and Gangetic Bengal
- Hot, with rainfall below what evaporation demands
- Grasslands and dryland farming
- Has spread east across Uttar Pradesh
What moved
The west coast moved the other way: tropical monsoon zones expanded in Konkan and Goa, coastal Karnataka and Kerala.
A driver from the Pacific
India's rain is usually explained with El Nino and the Indian monsoon and the Indian Ocean Dipole. This study adds the Victoria Mode, a North Pacific pattern. In its negative phase it steers moisture away from the Gangetic plains and creates high pressure over Bengal.
- 1North PacificSea-surface temperatures settle into the negative Victoria Mode pattern
- 2AtmosphereCirculation shifts, steering moisture away from the Gangetic plains
- 3BengalHigh pressure builds over Bengal and nearby regions, suppressing rain
- 4GroundRainfall over Gangetic West Bengal and Bihar declines over decades
Why it matters on the ground
The authors warn about paddy sowing and harvest timing, water resources and food security. Their advice is to bring ocean patterns like the Victoria Mode into long-term agricultural planning, rather than reacting only to each season's monsoon.
Go deeper
Why it matters for UPSC
It updates GS1 climate geography (climate regions of India, monsoon drivers), connects to GS3 (agriculture, food security, climate change), and introduces a new term, the Victoria Mode, ripe for Prelims.
The core idea
Climate zones come from long-term temperature and rainfall averages, with class names like those of the Koppen climate classification. When the 1991-2020 map is laid over the 1951-1980 one, semi-arid steppe spreads east in the north and savannah gives way to temperate climate in the northeast. Monsoon variability is usually blamed on El Nino and the Indian monsoon and the Indian Ocean Dipole. The study adds the Victoria Mode as a driver of the Gangetic drying.
Numbers and dates to remember
- Periods compared: 1951-1980 to 1991-2020 (with 1961-1990 in between)
- Northwest India steppe: 25.7% to 33.1%
- Northeast tropical savannah: about 18% to 12%; temperate now over four-fifths
- Rain over Gangetic West Bengal and Bihar declined from 1981 to 2020
- 2026 east and northeast monsoon deficit: 25.6%
Where to go next
- Koppen climate classification: how climate zones are drawn
- Victoria Mode: the North Pacific pattern in the news
- El Nino and the Indian monsoon: the familiar Pacific link
- Indian Ocean Dipole: the Indian Ocean's own see-saw
Go deeper: how much can a distant ocean explain?
What the study adds. Most explanations of monsoon variability focus on the equatorial Pacific (El Nino and the Indian monsoon) and the Indian Ocean (Indian Ocean Dipole). The IMD and IITM study argues that the Victoria Mode in the North Pacific helps explain a slow, multi-decade decline in rainfall over Gangetic West Bengal and Bihar. Earlier research has found that many Victoria Mode events were followed by El Niño, which suggests the patterns interact.
Natural variability or climate change? Shifts in Koppen climate classification zones can come from both. The northeast's move to a temperate zone is tied by the authors to rising maximum temperatures, a warming signal. The Gangetic drying is linked to an ocean pattern that can switch phase. Separating the two matters, because one may reverse and the other will not.
The farm angle. The Gangetic plains and Bengal are paddy country. Less rain and a shifting season change sowing and harvest windows and raise demand for groundwater. Marathwada and Vidarbha moving into semi-arid steppe fits their long history of drought. The west coast getting wetter raises flood and landslide risk.
Policy responses. The authors suggest building ocean indices into long-range agricultural planning. Other possible responses include crop diversification away from water-heavy crops in drying regions, better irrigation efficiency and updated district-level contingency plans.
Caution. The findings are averages over 30-year periods; a single year, such as 2026, says little about trends on its own.
Koppen climate classification
The system behind names like tropical savannah and hot semi-arid steppe
In one line: The Köppen classification divides the world's climates into groups using temperature and rainfall, and the vegetation they support.
The main groups
Köppen used five main groups: A (tropical), B (dry), C (warm temperate), D (cold) and E (polar). Letters are added for rainfall timing and heat. In India, common types include tropical monsoon (Am) on the west coast, tropical savannah (Aw) over much of the peninsula, hot semi-arid steppe (BSh) and hot desert (BWh) in the northwest, and temperate types in the north and northeast.
Why it shifts
Because each class is defined by thresholds of temperature and rainfall, a change in long-term averages can move a place across a boundary. Comparing 30-year normals shows where that has happened.
Why it is in the news
The IMD and IITM study reported in October 2026 found steppe spreading across north India and temperate climate replacing savannah in Gangetic West Bengal.
Where to go next
Victoria Mode
The North Pacific pattern now linked to drying in Bihar and Bengal
In one line: The Victoria Mode is a recurring pattern of warm and cool sea-surface temperature anomalies in the North Pacific Ocean.
How it differs from the PDO
The best-known North Pacific pattern is the Pacific Decadal Oscillation (PDO). The Victoria Mode is a separate pattern of variability in the same ocean. Earlier research found that many Victoria Mode events were followed by El Niño events.
Its link to India
The IMD and IITM study reported in October 2026 found that in its negative phase the Victoria Mode steers moisture away from the Gangetic plains and creates a high-pressure area over Bengal and nearby regions, suppressing rain. The authors link this to a four-decade decline in rainfall over Gangetic West Bengal and Bihar.
Why it matters
It shows that Indian rainfall can be influenced by ocean conditions far outside the Indian Ocean and the equatorial Pacific.
Where to go next
El Nino and the Indian monsoon
The classic Pacific link to India's rain, and its 2026 role
In one line: El Niño is the periodic warming of the central and eastern equatorial Pacific, which tends to weaken India's southwest monsoon.
How it works
In normal years, trade winds pile warm water in the western Pacific. During El Niño these winds weaken and warm water spreads east. The rising air and rain shift east too, and sinking air over the Indian region tends to reduce monsoon rain. La Niña is the opposite, cooler phase.
In 2026
Much of 2026's shortfall was linked to El Niño. East and northeast India recorded the country's largest regional deficit, 25.6% below normal, with Meghalaya 60%, Bihar 32% and Assam 28% short.
Why the study matters here
IITM's Rajib Chattopadhyay said that while much of the 2026 deficit was due to El Niño, rainfall over Gangetic West Bengal and Bihar had already been falling for four decades.
Where to go next
Indian Ocean Dipole
The Indian Ocean's own temperature see-saw that can offset El Nino
In one line: The Indian Ocean Dipole (IOD) is the difference in sea-surface temperature between the western and eastern parts of the tropical Indian Ocean.
Phases
In a positive IOD, the western Indian Ocean (near Africa) is warmer than the eastern part (near Indonesia), which tends to favour the Indian monsoon. In a negative IOD, the pattern reverses. A positive IOD can soften the impact of an El Niño on Indian rainfall.
Exam link
UPSC asked in Prelims 2017 about the IOD, testing that it is an Indian Ocean (not Pacific) pattern and that it can influence El Niño's impact on the monsoon.
Why it is relevant now
Together with El Niño and now the Victoria Mode, the IOD is part of the set of ocean patterns that forecasters and planners need to watch.
Where to go next
Take the 25 October 2026 quiz: 30 Prelims-style questions with answers