Climate Part 4: Seasons of India (Winter, Summer, Monsoon, Retreating)

Background and Historical Context

The four-season scheme is the calendar against which Indian agriculture, water management, disaster preparedness, and tourism are organised, and it is the analytical frame through which UPSC tests the candidate's grasp of climate. The rabi cropping cycle (wheat, mustard, gram) depends on cold-weather rainfall delivered by western disturbances. The kharif cycle (rice, cotton, sugarcane) depends on the southwest monsoon. The retreating-monsoon cyclone window is the dominant climate-hazard regime for the Tamil Nadu, Andhra Pradesh, and Odisha coast. UPSC Prelims has tested season-specific phenomena (jet streams, cyclones, monsoon onset, western disturbances) in 2020, 2017, 2015, and earlier years; Mains GS-I covers the integration of seasons with the monsoon mechanism and GS-III covers the disaster-management response.

What is the significance of mastering the four-season scheme? The seasons are the operational expression of the monsoon system, not separate phenomena. The cold-weather northwestern winter rainfall, the hot-weather heat-low formation, the southwest-monsoon Inter Tropical Convergence Zone migration, and the retreating-monsoon Bay of Bengal cyclones all link to the broader pressure-wind-jet-stream architecture treated in the earlier parts of this series. Reading the seasons in sequence reveals the cause-and-effect chain that produces India's lived climate.

The National Disaster Management Authority aligns its hazard calendar to the four-season scheme: heat-wave red alerts in the hot-weather window, flood preparedness in the southwest-monsoon window, cyclone warnings in the retreating-monsoon window, and cold-wave alerts in the cold-weather window. The IMD colour-coded warning system (green, yellow, orange, red) and the NDMA cyclone-preparedness framework are seasonally calibrated. The IPCC AR6 South Asia chapter projects amplification of the monsoon variability and the heat-wave frequency under continued warming, with first-order implications for the kharif and rabi cropping cycles.

Introduction: The Four-Season Scheme of the India Meteorological Department

The IMD four-season scheme and its climatological rationale

The India Meteorological Department recognises four seasons in the Indian climatic year, in this order: the cold weather season from December to February, the hot weather season from March to May, the southwest monsoon season from June to September, and the retreating monsoon season over October and November.

The scheme is climatological rather than astronomical, fixed not on solstice or equinox dates but on the seasonal reversal of pressure, wind, and precipitation that defines the monsoon system. The cycle is asymmetric, reflecting how a continental landmass and a tropical ocean interact under shifting solar insolation.

The four seasons are not abstractions imposed on the year. Each is a coherent meteorological regime with its own pressure pattern, wind direction, temperature distribution, and rainfall behaviour. Reading them in sequence shows why India's climate is described as tropical monsoon and why almost three quarters of annual rainfall arrives in a single four-month window.

Cold Weather Season: December to February

Temperature, pressure, and wind regime

Although cold conditions begin to set in by mid-November in northern India, the cold weather season proper runs December to February, with December and January the coldest months. The mean daily temperature stays below 21 degrees Celsius across most of the northern plain, and night temperatures occasionally drop below freezing in Punjab and Rajasthan.

The Peninsular region develops no comparable cold season because the moderating sea and proximity to the equator hold coastal temperatures around 26 to 32 degrees Celsius through the year. Mean January maximum temperature at Thiruvananthapuram, for instance, is about 31 degrees Celsius.

Three factors explain the severe cold in north India. Continental interiors in Punjab, Haryana, and Rajasthan lie far from the moderating sea. Snowfall in the Himalayan ranges triggers cold-wave conditions across the adjoining plain. Around February, cold winds from the Caspian Sea and Turkmenistan bring further cold spells and dense fog over the northwestern districts.

Surface pressure is feebly high over the northern plain because the sun is overhead in the Southern Hemisphere. Isobars of 1019 millibar and 1013 millibar pass through northwest India and the far south respectively, generating light winds of 3 to 5 kilometres per hour that blow outwards from the northwestern high to the southern Indian Ocean low.

Western disturbances and the northwestern winter-rainfall regime

The cold weather season is the only window in which northwestern India receives systematic rainfall, and that rainfall is critical for the rabi cropping cycle covering wheat, mustard, and gram. UPSC Prelims has tested the western-disturbance mechanism and the geography of winter rainfall, and Mains GS-I asks candidates to integrate the regime with the broader monsoon picture.

Winter winds travel from land to sea and carry almost no humidity, so most of India stays dry in this season. The exception is the chain of weak temperate cyclones called western disturbances that originate over the eastern Mediterranean and travel eastward across West Asia, Iran, Afghanistan, and Pakistan, gathering moisture from the Caspian Sea and the Persian Gulf en route.

The westerly jet stream at 9 to 13 kilometres altitude steers these systems into the northwestern Himalayan and plain regions, producing modest but agronomically vital winter rainfall. Average winter rainfall is around 53 millimetres in Delhi, 25 millimetres in Punjab, and 18 millimetres in Bihar, decreasing from west to east in the plains and from north to south in the mountains. The same systems deliver winter snowfall to the lower Himalayas that sustains river flow into the following summer.

• Northwestern winter rainfall: Western disturbance-driven rainfall over Punjab, Haryana, Delhi, western Uttar Pradesh; meagre amount but essential for rabi crops.
• Lower Himalayan snowfall: Winter precipitation as snow that sustains Himalayan river flow during the following summer.
• Central and southern Peninsular winter rainfall: Central India and the northern Peninsula receive occasional winter rainfall from extended western disturbance tracks.
• Northeast monsoon Tamil Nadu coast: October-November retreating monsoon crossing the Bay of Bengal picks up moisture and produces torrential rain on the Tamil Nadu coast, southern Andhra Pradesh, southeast Karnataka, and southeast Kerala.

Hot Weather Season: March to May

Temperature pattern and the northward heat-low migration

Why the hot-weather season is the monsoon pivot. The hot weather season sets the stage for the southwest monsoon by building the thermal low over the northwestern subcontinent that draws moist maritime air across the equator. The seasonal heating reorganises pressure across the Indian Ocean basin and is the immediate cause of the wind reversal that defines the monsoon.

As the sun shifts northward toward the Tropic of Cancer in March, temperatures rise rapidly across north India, and April, May, and June form the summer months. In March the highest day temperature reaches about 38 degrees Celsius over the Deccan Plateau. In April temperatures of 38 to 43 degrees Celsius appear over Gujarat and Madhya Pradesh. In May the heat belt migrates further north and temperatures near 48 degrees Celsius are not uncommon in the northwestern plain.

The hot weather stays mild in south India because of the moderating influence of the surrounding oceans, with temperatures between 26 and 32 degrees Celsius across the peninsula and below 25 degrees Celsius in the Western Ghats hills. Coastal isotherms run parallel to the coast, showing that temperature does not fall from north to south on the peninsula but instead rises from the coast inland.

Local pre-monsoon weather phenomena

Several named pre-monsoon phenomena mark the late summer. Loo winds are strong, dry, hot, dust-laden surface winds that sweep the northern and northwestern plain in May and June, raising temperatures and creating dangerous heat-wave conditions. Kalbaisakhi, also called Norwesters, are violent thunderstorms over West Bengal, Assam, and Odisha in April and May that deliver short, intense rainfall and damaging hailstorms.

Mango showers are pre-monsoon thunderstorm rains over the Kerala and coastal Karnataka coast that help ripen the mango crop. Cherry blossom showers over the Karnataka coffee tracts and Bardoli Chheerha over Gujarat are the regional pre-monsoon-shower analogues.

• (a) The thermal low over northwestern India is the seasonal-circulation pivot that draws maritime air northward.
• (b) Loo winds at 45 to 48 degrees Celsius establish the heat-wave health-emergency window that the NDMA escalates to red-alert each May.
• (c) The pre-monsoon thunderstorm sequence (Kalbaisakhi, Mango showers, Cherry blossom showers) provides the only rainfall outside the southwest-monsoon window for peninsular agriculture.

Southwest Monsoon Season: June to September

ITCZ migration, easterly jet onset, and the burst of the monsoon

Distinguishing features of the southwest monsoon emerge from the seasonal reorganisation of pressure and wind aloft. By mid-July the Inter Tropical Convergence Zone migrates northward to 20 to 25 degrees North over the Gangetic plain, where it forms the monsoon trough. The westerly jet stream withdraws south of the Himalaya, and an easterly jet stream sets in along 15 degrees North with peak speeds near 90 kilometres per hour, held responsible for the burst of the monsoon.

• (i) ITCZ migration to 20 to 25 degrees North creates the monsoon trough that draws the maritime tropical airmass northward across the equator.
• (ii) Easterly jet stream onset at 15 degrees North is the upper-air signature of the burst.
• (iii) The southwest monsoon is a continuation of the southeast trades, deflected to a southwesterly direction by the Coriolis force after crossing the equator between 40 and 60 degrees East longitude.

Onset dates, the two branches, and rainfall distribution

The southwest monsoon sets in over the Kerala coast on 1 June, reaches Mumbai and Kolkata between 10 and 13 June, and covers the entire subcontinent by mid-July. Two rain-bearing systems together produce the monsoon rainfall pattern. The Arabian Sea branch brings heavy orographic rainfall to the windward Western Ghats and skirts the Indo-Gangetic plain.

The Bay of Bengal branch drives tropical depressions inland over the plains of north India and the Northeast, where the Khasi-Jaintia-Garo hills generate some of the world's heaviest rainfall at Mawsynram and Cherrapunji. The intensity of rainfall over the west coast depends on offshore meteorological conditions and the position of the equatorial jet stream along the eastern African coast.

• Arabian Sea branch: Windward Western Ghats receives orographic rainfall; the rain shadow east of the Ghats receives little.
• Bay of Bengal branch: Khasi-Jaintia-Garo hills produce extreme rainfall (Mawsynram, Cherrapunji); the branch drives tropical depressions inland over Bihar, Jharkhand, and the Indo-Gangetic plain.
• Frequency of Bay-of-Bengal depressions: Year-to-year variation in depression frequency and track determines the spatial pattern of monsoon rainfall over the subcontinent.

Break in the monsoon: dry spells and their causes

A break in the monsoon denotes a dry spell of one or more weeks during the active monsoon period. Breaks are common and their causes differ by region. In northern India, rains fail when rain-bearing storms are infrequent along the monsoon trough or the trough shifts off its usual position.

Over the west coast, dry spells coincide with days when winds blow parallel to the coast and do not strike the Western Ghats. Break timing carries crop-failure consequences because rice and oilseeds at the tillering or flowering stage are highly water-sensitive.

Retreating Monsoon Season: October and November

Withdrawal pattern and the October heat

Observable outcomes in the retreating phase include the gradual southward shift of the ITCZ, the steady weakening of low pressure over north India, and the transition to a clear-sky regime. The withdrawal begins from the northwestern margin in early September and reaches the southern tip by mid-October.

Land surfaces stay humid because the soil is still saturated, and high temperature combines with humidity to produce the muggy oppressive weather popularly called the October heat. By early November cooler weather sets in across most of the country as the surface pressure pattern begins to revert.

• (a) Gradual ITCZ southward shift and weakening of the north-India low pressure mark the withdrawal.
• (b) October heat refers to the high temperature plus high humidity that produces oppressive surface conditions despite the ending of the rains.
• (c) By early November the surface pressure pattern reverts to the cold-weather configuration, setting the cycle for the next season.

Northeast monsoon and Bay of Bengal tropical cyclones

The retreating-monsoon season delivers the northeast monsoon rainfall over the Tamil Nadu coast, southern Andhra Pradesh, southeast Karnataka, and southeast Kerala. As the northeast trades cross the Bay of Bengal they gather moisture and produce torrential rainfall on the south Indian east coast.

The same Bay of Bengal also generates the tropical cyclones that strike the Tamil Nadu, Andhra Pradesh, and Odisha coast with high wind velocity and heavy rainfall. The IMD colour-coded cyclone warnings (green, yellow, orange, red) are calibrated to landfall intensity, evacuation thresholds, and the NDMA cyclone-preparedness framework. The cyclones of October and November form the dominant climate-hazard window for the east coast and have shaped the Andhra Pradesh and Odisha disaster-resilience policy.

Synthesis: Why the Four-Season Scheme is Exam-Foundational

Cross-links to Parts 1, 2, 3 and to the Western Disturbances entry

The four seasons are not isolated phenomena. Each is the lived expression of the six controlling factors covered in Climate Part 1, the pressure-wind-jet-stream framework of Climate Part 2, and the dynamic monsoon mechanism explained in Climate Part 3.

The cold-weather western-disturbance regime is treated in detail in the dedicated Western Disturbances resource. Together these pages supply the integrated framework that UPSC candidates need for Prelims pressure-and-wind questions and Mains GS-I geography answers on Indian monsoon variability.

Sources

• NCERT Class 11 India Physical Environment, Chapter 4 (Climate)
• India Meteorological Department (IMD) seasonal outlook archive
• Indian Institute of Tropical Meteorology (IITM), Pune
• NOAA Climate Prediction Center monsoon page
• Wikipedia: Climate of India
• Wikipedia: Monsoon of India
• Wikipedia: Western disturbance
• Wikipedia: Northeast monsoon