The climate consists of a diverse range of meteorological circumstances extending over an extensive geographical expanse and diverse topography, posing challenges to overarching summarizations. The accumulated typical weather patterns in a specific location spanning an extended duration (30 years or more) are denoted as the climate. Earth exhibits a multitude of distinct climate types. The interplay of several interconnected factors, such as latitude, longitude, altitude, landscape features, proximity to the ocean, and prevailing wind patterns, collectively influences the climate.
Centuries ago, Arab navigators initially coined the term “monsoon” to delineate a pattern of winds that underwent seasonal reversals along the coasts of the Indian Oceans, notably over the Arabian Sea. During the summer, these winds would sweep from the southwest to the northeast, while in the winter, they would shift from the northeast to the southwest. In simpler terms, monsoons represent cyclic winds that change direction completely every six months, forming a predictable seasonal rhythm.
Factors determining the Climate of India
The determinants of a location’s climate can be broadly categorized into two factors:
- Factors related to location and relief
- Factors related to air pressure and winds
Factors related to location and relief
India’s climate is significantly influenced by its latitude. The Tropic of Cancer traverses the nation from the Rann of Kachchh in the west to Mizoram in the east. The southern portion, lying below the Tropic of Cancer, falls within the tropical zone, characterized by consistent high temperatures and minimal daily and yearly fluctuations. The northern part experiences a more extreme climate due to its distance from the equator, leading to wider daily and annual temperature ranges.
2. Himalayan Mountains:
The towering Himalayan range to the north serves as a crucial climate barrier. These mountains shield India from frigid northern winds originating near the Arctic Circle, which sweep across central and eastern Asia. This geographical feature contributes to India’s relatively milder winters compared to regions in Central Asia. The Himalayas also play a role in capturing and releasing monsoon winds, leading to significant moisture deposition within the subcontinent.
3. Land-Water Distribution:
India is bounded by water bodies on three sides to the south and bordered by an extensive mountain range in the north. Water bodies heat up and cool down more rapidly than land, creating varying air pressure zones around the subcontinent. This pressure difference drives shifts in monsoon wind directions.
4. Proximity to the Sea:
The sea exerts a tempering influence on climate. As one moves farther from the coast, this moderating effect diminishes, resulting in regions characterized by extreme weather patterns. This phenomenon, known as continentality, leads to very hot summers and very cold winters.
Elevation also impacts climate. Higher altitudes generally correlate with cooler temperatures. For instance, despite being at the same latitude, Agra experiences a January temperature of 16°C, whereas Darjeeling, located at a higher altitude, records a significantly cooler 4°C.
India’s topography shapes various climate elements, including temperature, air pressure, wind direction and speed, and rainfall distribution. The windward sides of the Western Ghats and Assam receive substantial rainfall during the monsoon months, while the southern plateau remains arid due to its position on the leeward side of the Western Ghats.
These factors collectively contribute to the diverse climate patterns observed across different regions of India.
Factors related to air pressure and winds
The atmospheric conditions that influence India’s climate and its corresponding weather comprise:
1. Surface Air Pressure and Wind Distribution:
The arrangement of air pressure and wind patterns at the Earth’s surface plays a significant role. These factors dictate the movement of air masses and the direction of winds, contributing to the climate variations experienced.
2. Upper Atmospheric Circulation:
The upper layers of the atmosphere are subject to global weather determinants, including the movement of different air masses and jet streams. These upper-level atmospheric processes impact the broader weather patterns observed in India.
3. Inflow of Disturbances and Cyclones:
India’s weather is affected by the arrival of western cyclones, often referred to as disturbances, during winter, and tropical depressions during the southwest monsoon season. These systems create conditions conducive to rainfall, influencing the overall weather dynamics.
These atmospheric conditions collectively shape the climate and weather phenomena experienced across India.
Savanna or Sudan Climate (or Tropical Wet and Dry Climate)
The savanna or Sudan climate emerges between equatorial rainforests and arid trade wind-dominated deserts. This climate type is confined to the tropical regions, specifically within the Tropics of Cancer and Capricorn. Its most notable manifestation is in Sudan, where the contrast between dry and wet conditions is particularly pronounced, giving rise to the name “Sudan climate.”
Encompassing significant portions of Africa (including Kenya, Nigeria, and Gambia), Australia, South America (particularly the Brazilian highlands), and India, the Savanna Climate exhibits distinctive attributes. Notably, it sets itself apart from other global climates due to its distinct dry season occurring during winter. Rainfall is primarily concentrated in the summer months. The prolonged dry season often leads to the decline of vegetation and the drying up of water bodies, prompting migratory behaviors in animals.
The savanna or Sudan climate occupies the transitional space between equatorial forests and arid trade wind-influenced deserts. Its primary occurrence is within the tropical latitudes on both sides of the equator. Particularly well-developed in Sudan, where distinct wet and dry seasons prevail, it’s aptly named the “Sudan climate.”
This climate extends over substantial portions of Africa (including regions like Kenya, Nigeria, and Gambia), South America (such as the Llanos grasslands within the Orinoco river basin), Australia, and India.
Monthly temperatures in lowlands exhibit a range of 20 to 32 degrees Celsius, expanding with increasing distance from the equator. The annual average temperature hovers around 18 degrees Celsius.
Peak temperatures occur in April in the northern hemisphere and October in the southern hemisphere, right before the onset of the rainy season. Notably, the hottest month is not during the summer solstice in June.
During the rainy season, cloud cover causes temperature declines. Summers can witness midday temperatures surpassing 37 degrees Celsius. Clear skies, however, lead to temperature drops below 10 degrees Celsius even in the hot season, resulting in occurrences of night frost. This climate’s hallmark is its remarkable diurnal temperature variation.
The savanna climate experiences distinct wet and dry seasons. In the northern hemisphere, the hot and humid period spans May to September, while the remainder of the year remains cool and dry. For instance, in Nigeria’s Kano, situated at an elevation above sea level, over 80 centimeters of annual rain occurs, with a major portion during summer.
Conversely, in the southern hemisphere, the rainy season prevails from October to March. As one moves away from the equator towards desert edges, both the length of the rainy season and total annual rainfall decrease substantially.
The region’s prevailing winds, referred to as trade winds, bring rainfall to coastal areas. These easterly winds move from east to west, contributing to higher rainfall along eastern coasts.
During summer, when the Intertropical Convergence Zone (ITCZ) positions over arid deserts, trade winds are strongest. Over coastal areas, they deposit moisture, but as they proceed inland, they become comparatively dry.
In West Africa, these easterly trade winds blow offshore, introducing dry, dusty Saharan winds known as “the doctor” or “Harmattan.” Although detrimental to crops, Harmattan also brings cooling effects by increasing evaporation, offering relief from humidity.
Trade winds are instrumental in creating the region’s distinct alternating wet and dry seasons. Onshore trade winds induce summer rainfall, while off-shore winds maintain dry conditions during winter.
The savanna predominantly comprises tall grass and sparse trees, often referred to as “parkland” or “bush-veld.” The tree density is highest near riverbanks and decreases further away from the equator.
Deciduous trees are common, shedding leaves during the cool, dry months to conserve water. Acacia is a characteristic example. Some tree species possess wide trunks functioning as water reservoirs to endure dry spells, such as bottle trees and baobabs.
The grass in this region can grow remarkably tall, up to 6-12 feet, with elephant grass reaching 15 feet. Dense grass with deep roots adapts to water scarcity, becoming dormant in dry periods and flourishing during rainy seasons. Closer to deserts, grasses give way to thorny shrubs.
The savanna houses numerous large terrestrial species, primarily categorized into herbivores and carnivores. Iconic herbivores include zebras, giraffes, elephants, and antelopes. Herbivores employ either speed or camouflage to evade carnivores.
Carnivores in this region encompass lions, hyenas, leopards, and other formidable predators equipped with powerful jaws and teeth for hunting.
Reptiles like crocodiles, monitor lizards, and giant lizards inhabit rivers and marshy zones. Additionally, the savanna is home to rhinos and hippos.
Seasons in India
The Indian subcontinent spans significant latitudinal extents, resulting in diverse climatic conditions from Kashmir to Kanyakumari. Meteorologists, however, classify the following four distinct seasons:
1. Winter Season
2. Summer Season
3. Rainy Season
4. Retreating Monsoon Season
The Cold Weather Season (Winter):
The cold weather season spans from mid-November through February in northern India, with December and January being the coldest months. Temperature diminishes generally from south to north during this period. Days carry warmth while nights bring coldness. Frost is commonplace in the north, and the higher Himalayan slopes experience snowfall. However, the peninsular region’s proximity to the sea and the equator results in an absence of a well-defined cold season. Coastal areas exhibit minimal seasonal temperature shifts.
The Hot Weather Season (Summer):
As the sun progresses northwards toward the Tropic of Cancer, temperatures surge in north India. April, May, and June constitute the summer months in the north. March witnesses the highest temperatures, peaking at around 38°C on the Deccan plateau. Gujarat and Madhya Pradesh record temperatures of approximately 42°C in April, while the northwestern part of the country reaches 45°C in May. Peninsular India experiences milder temperatures, ranging from 20°C to 32°C, due to oceanic influences. Altitude maintains the Western Ghats hills’ temperatures below 25°C.
The South-West Monsoon Season/Rainy Season:
With the advent of June, rising temperatures intensify low-pressure conditions in the northwestern plains. This attracts the Southern Hemisphere’s southeast trade winds from the Indian Ocean. The trade winds cross the equator and adopt a southwesterly direction, referred to as the south-west monsoons. As they traverse the Bay of Bengal and the Arabian Sea, these winds gather abundant moisture from equatorial warm currents. The monsoon’s arrival, accompanied by thunder, lightning, and precipitation, is often called the “break” or “burst” of monsoons. Coastal regions experience this burst in early June, while inland areas might witness it in early July.
The monsoon advances in two branches:
1. Arabian Sea Branch:
This branch bifurcates into three parts:
– One segment encounters the Western Ghats, triggering ascent and causing heavy rainfall on the windward side and coastal plain.
– Another section impacts the Narmada and Tapi river valleys, bringing rainfall to central India.
– A third portion reaches the Saurashtra Peninsula, Kachchh, Rajasthan, and Punjab, resulting in limited rainfall.
2. Bay of Bengal Branch:
This branch strikes Myanmar and Southeast Bangladesh before entering West Bengal and Bangladesh. It bifurcates into:
– A westward-moving branch along the Ganga plains, extending to Punjab.
– A north and northeast-bound branch along the Brahmaputra valley, causing heavy rains.
The Retreating Monsoon Season:
In October and November, as the sun moves southward, the monsoon trough over northern plains weakens and is replaced by a high-pressure system. The south-west monsoon winds recede gradually, yielding to a transition from the rainy season to the dry winter period. By early October, the monsoon withdraws from the northern plains, leading to clear skies and rising temperatures. The withdrawal is accompanied by the “October heat,” characterized by high temperature and humidity. The low-pressure trough relocates to the Bay of Bengal in November, coinciding with cyclonic depressions originating over the Andaman Sea. These cyclones often impact India’s eastern coasts, especially densely populated deltas like Godavari, Krishna, and Kaveri. They can also reach Bangladesh, West Bengal, and Odisha, resulting in substantial damage.
Monsoons are a complex meteorological phenomenon that affects a vast tropical region, roughly stretching from around 20°N to 20°S latitudes.
Understanding the intricate mechanism of monsoons in India involves delving into several key factors:
1. Land-Water Temperature Dynamics:
The variation in heating and cooling rates between land and water surfaces creates differences in air pressure. Land heats up and cools down more quickly than water, leading to the movement of air from regions of high pressure (over oceans) to regions of low pressure (over land).
2. ITCZ and Monsoon Trough:
The Intertropical Convergence Zone (ITCZ) is an area near the equator where trade winds from the Northern and Southern Hemispheres meet. During summer, this zone shifts northward, positioning itself over the Ganga plain in India, typically around 5°N of the equator. This northward shift is referred to as the monsoon trough and marks the onset of the monsoon season.
3. High-Pressure Area:
To the east of Madagascar, approximately around the 20°S latitude, a high-pressure zone forms over the Indian Ocean. The intensity and position of this high-pressure area have a significant impact on the behavior of the Indian monsoon.
4. Tibetan Plateau and Vertical Air Currents:
The Tibetan plateau, situated at a considerable altitude, undergoes intense heating during summer. This heating results in the formation of a low-pressure system at about 9 kilometers above sea level. As a result, strong vertical air currents are established, which play a crucial role in the circulation of air masses and the initiation of monsoon flows.
5. Influence of Jet Streams:
Jet streams are high-speed air currents in the upper atmosphere. Both the movement of westerly jet streams from west to east and the tropical easterly jet streams from east to west impact the overall monsoon patterns in India. These high-altitude air currents influence the behavior of the lower-level monsoon winds.
6. Southern Oscillations and El Niño:
- Southern Oscillations (SO):
The pressure conditions over the southern oceans, particularly the eastern south Pacific and the eastern Indian Ocean, undergo variations. These fluctuations are known as Southern Oscillations. The pressure pattern normally has high pressure in the eastern Pacific and low pressure in the eastern Indian Ocean, but it can reverse in certain years.
- El Niño:
SO patterns lead to an El Niño phenomenon. El Niño refers to the development of a warm ocean current along the coast of Peru in the eastern Pacific, temporarily replacing the cold Peruvian current. This phenomenon increases sea surface temperatures and weakens trade winds, which in turn affects monsoon patterns. El Niño is a key factor in forecasting long-range monsoon rainfall.
7. Pressure Difference Indicator:
The difference in atmospheric pressure between two locations, specifically Tahiti in the Pacific and Darwin in northern Australia, serves as an indicator of monsoon intensity. A negative pressure difference suggests below-average and delayed monsoon conditions.
8. El Niño Impact:
El Niño’s occurrence can lead to a delay in the onset of the southwest monsoon in India. In the past, El Niño events have disrupted the timing and distribution of monsoon rainfall.
Collectively, these factors interact to create the intricate monsoon phenomena observed in India, influencing temperature, precipitation, wind patterns, and overall weather conditions.
Monsoon Onset and Withdrawal Dynamics
Monsoon winds exhibit pulsating characteristics, unlike the steady trade winds. Their behavior is influenced by various atmospheric conditions, especially as they traverse warm tropical regions. In the southern Indian Peninsula, the monsoon typically spans 100 to 120 days, commencing in early June and retreating by mid-September.
Monsoon Burst and Fluctuating Rainfall:
The monsoon’s arrival is marked by a sudden surge in rainfall that continues for several days, known as the “burst” of the monsoon. This phenomenon is distinct from pre-monsoon showers and brings alternating wet and dry spells during its course.
Onset of Monsoon:
The monsoon typically reaches the southern tip of the Indian Peninsula in the initial week of June. Upon reaching this point, it bifurcates into two main branches: the Arabian Sea branch and the Bay of Bengal branch, both advancing rapidly.
– The Arabian Sea branch progresses northward along the Western Ghats, reaching Mumbai around the 10th of June. It subsequently covers regions like Saurashtra-Kuchchh and the central Deccan Plateau.
– The Bay of Bengal branch reaches Assam during the first week of June, and then it turns westward due to mountain ranges, thereby providing rainfall to the Ganga Plains.
– These two branches converge once again over the northwestern portion of the Ganga Plains. Generally, Delhi receives rainfall by the end of June, primarily from the Bay of Bengal branch. By the first week of July, the monsoon embraces western Uttar Pradesh, Punjab, Haryana, and eastern Rajasthan.
Withdrawal of Monsoon:
The retreat of the monsoon is a gradual process. It initiates in the northwestern states by early September. By mid-October, the monsoon completely withdraws from the northern half of the Indian Peninsula. The withdrawal from the southern half is comparatively swifter. By early December, the monsoon has withdrawn entirely from the remaining parts of the country.