Climate of India

Analysis

India's rainfall distribution is exceptionally diverse, a direct consequence of its unique physiography and the interplay of various atmospheric phenomena. While the Southwest Monsoon is the primary rain-bearing system, contributing over 75% of the country's annual precipitation, other seasonal rainfall mechanisms are vital for specific regions and agricultural cycles.

During the Cold Weather Season, the Western Disturbances are crucial for the rabi crops in Northwest India, providing much-needed moisture. These disturbances, originating in the Mediterranean, travel eastward with the westerly jet stream, bringing light to moderate rainfall and snowfall in mountainous regions. Simultaneously, the retreating northeast monsoon picks up moisture over the Bay of Bengal, delivering significant rainfall to the Coromandel Coast (Tamil Nadu, parts of Andhra Pradesh), which receives its primary rainfall during this period, contrasting sharply with the rest of India.

The Hot Weather Season, though generally dry, is vital for pre-monsoon agricultural activities. The localized convectional thunderstorms, such as Norwesters (Kal Baisakhi) in Eastern India, provide relief from heat and are crucial for jute and rice cultivation. Mango Showers in the south aid coffee and mango crops. These localized phenomena highlight the micro-climatic variations even within a broad seasonal classification.

The Southwest Monsoon's distribution is highly uneven. The Western Ghats receive torrential rainfall on their windward side (e.g., Mawsynram and Cherrapunji in Meghalaya are among the wettest places on Earth due to orographic lifting by the Bay of Bengal branch). Conversely, the leeward side of the Western Ghats and regions like Rajasthan and parts of Gujarat experience rain shadow effects, leading to aridity. The 'breaks in the monsoon', periods of reduced rainfall, are also significant, often linked to the shifting position of the monsoon trough and can lead to mid-season droughts.

The Retreating Monsoon Season is characterized by the formation of tropical cyclones in the Bay of Bengal. These cyclones are vital for the rainfall of the eastern coastal states but also pose significant risks of floods, storm surges, and destruction, particularly in Odisha, Andhra Pradesh, and Tamil Nadu. The frequency and intensity of these cyclones are critical factors in the region's annual rainfall and disaster management.

Comparison Table: Seasonal Rainfall Characteristics

Case Study: Tamil Nadu's Unique Rainfall Pattern

Tamil Nadu stands out for receiving the bulk of its rainfall during the retreating monsoon season (October-November) and the cold weather season (November-December), primarily from the Northeast Monsoon. While the rest of India relies on the Southwest Monsoon, Tamil Nadu lies in the rain shadow region of the Western Ghats during this period. The northeast winds, after picking up moisture from the Bay of Bengal, bring significant precipitation to the state. This unique pattern makes Tamil Nadu highly vulnerable to Bay of Bengal cyclones during these months, which contribute substantially to its annual rainfall but also cause widespread damage.

Mains Hooks

• Agricultural Vulnerability: Discuss how the variability and distribution of rainfall directly impact Indian agriculture, leading to issues like droughts and floods, and influencing crop choices and food security.
• Water Resource Management: Analyze the challenges in water management given the highly seasonal and concentrated nature of rainfall, emphasizing the need for robust irrigation systems, rainwater harvesting, and inter-linking of rivers.
• Disaster Management: Examine the preparedness and response mechanisms for monsoon-related disasters such as floods (e.g., Bihar, Assam), droughts (e.g., Marathwada, Rajasthan), and cyclones (e.g., Odisha, Andhra Pradesh).
• Climate Change Impacts: Discuss how global warming is altering monsoon patterns, leading to increased frequency of extreme rainfall events, prolonged dry spells, and changes in cyclone intensity, posing new challenges for India's climate resilience.

Recent Developments

The Indian Meteorological Department (IMD) continuously monitors and forecasts monsoon behavior, incorporating advanced models and satellite data. Recent years have seen increased focus on the impact of global phenomena like El Niño and La Niña on the Indian monsoon. While El Niño is generally associated with weaker monsoons and drought conditions, La Niña often brings stronger monsoons. However, the IMD has stated that the impact of other oceanic activities (like specific cyclones in the Indian Ocean or typhoons in the Pacific) on the Indian monsoon is not always scientifically supported or significant. There's a growing concern about the increasing frequency of extreme rainfall events and cloudbursts, even as overall monsoon rainfall might remain normal, indicating a shift in rainfall intensity and distribution due to climate change.

Analysis of Modern Monsoon Theories

Modern theories move beyond the simple thermal contrast to explain the complex, dynamic nature of the Indian Monsoon, integrating atmospheric circulation at various levels.

1. Air Mass Theory

This theory views the monsoon as a large-scale interaction of distinct air masses. The Southwest Monsoon is essentially the northward displacement of the moist, maritime equatorial air mass (South-East Trade Winds) after crossing the Equator, where they are deflected rightwards by the Coriolis effect. These displaced trade winds become the southwest monsoons when they blow over the Indian subcontinent. The boundary where these moist monsoons meet the drier continental air masses is the Monsoon Front (ITCZ), where significant rainfall occurs.

2. Jet Stream Theory

This is the most accepted modern theory, emphasizing the role of upper tropospheric winds.

• Role of Sub-Tropical Westerly Jet (STWJ):
  • During winter (March-May), the STWJ blows south of the Himalayas, creating a high-pressure belt over Northwest India. This position inhibits the development of the summer monsoon cell.
  • As summer approaches (late May to early June), with the apparent northward movement of the sun, the STWJ weakens and shifts northward, moving to the north of the Himalayas (over the Tibetan Plateau). This shift is critical as it removes the blocking effect, creating favorable conditions for the monsoon onset.
  • The sudden shift of the STWJ is often linked to the 'burst' of the monsoon.
• Role of Tropical Easterly Jet (TEJ):
  • Following the northward shift of the STWJ, intense heating of the Tibetan Plateau creates a strong high-pressure zone in the upper troposphere (around 8 km altitude).
  • This high-pressure leads to the formation of the Tropical Easterly Jet (TEJ), which flows from east to west over Peninsular India (between 8°N and 35°N latitudes).
  • The TEJ strengthens the low-pressure system over the Indian subcontinent and is associated with the guiding of tropical depressions from the Bay of Bengal and Arabian Sea, which are major sources of monsoon rainfall.

3. Role of the Tibetan Plateau

The Tibetan Plateau acts as a 'heat engine' during summer. Its immense elevation (average 4,500m) and intense solar heating create a significant thermal contrast with the surrounding atmosphere. This leads to:

• Strong convective updrafts, drawing air from below.
• Formation of a high-pressure cell in the upper troposphere, which is crucial for the genesis and maintenance of the TEJ.
• The plateau's heating also contributes to the northward shift of the ITCZ.

4. Seasonal Shift of the ITCZ (Monsoon Trough)

• The ITCZ is a zone of convergence of trade winds and is characterized by low pressure, ascending air, and heavy rainfall.
• During the summer (July), the ITCZ shifts northward, extending into the Indo-Gangetic Plain and often referred to as the Monsoon Trough. This position (NITCZ - Northern ITCZ) is the zone of maximum cloudiness and rainfall for India.
• During winter (January), the ITCZ shifts southward (SITCZ - Southern ITCZ), resulting in dry conditions over most of India.

Comparison Table

Mains Hooks

• Agricultural Impact: The reliability and intensity of the monsoon directly affect agricultural productivity, food security, and rural livelihoods in India. Monsoon variability (e.g., delayed onset, prolonged break, uneven distribution) can lead to droughts or floods.
• Economic Significance: Monsoons influence GDP growth, inflation (especially food prices), and water resource management (hydro-power, irrigation, drinking water).
• Climate Change: Understanding monsoon mechanisms is crucial for predicting how climate change might alter monsoon patterns, leading to more extreme weather events.
• Disaster Management: Accurate monsoon forecasting is vital for flood and drought preparedness and mitigation strategies.

Recent Developments

Ongoing research continues to refine monsoon understanding, incorporating factors like the Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO). A positive IOD often correlates with a good Indian monsoon, while El Niño events are frequently associated with weaker monsoons. These teleconnections highlight the global influences on India's regional climate system.

Analysis: Interplay of Climate Drivers and Extremes

The Indian climate is a complex system influenced by both global teleconnections and regional dynamics. The El Niño-Southern Oscillation (ENSO), encompassing both El Niño and La Niña, is the most significant global driver. El Niño involves a weakening of the Walker Circulation, leading to subsidence over the western Pacific and Indian Ocean, thus suppressing monsoon rainfall. Conversely, La Niña strengthens the Walker Circulation, promoting convection and enhancing monsoon activity. However, the relationship is not always straightforward; other factors can modulate ENSO's impact.

The Indian Ocean Dipole (IOD) acts as a regional modulator. A positive IOD, characterized by warmer western Indian Ocean waters, can sometimes mitigate the negative impact of an El Niño event on the Indian monsoon, leading to near-normal or even above-normal rainfall despite El Niño conditions. This highlights the importance of considering multiple climate indices for accurate monsoon forecasting. The Monsoon Mission, launched by the Ministry of Earth Sciences (MoES) in 2012, aims to improve seasonal and intra-seasonal monsoon forecasts by developing a seamless prediction system that incorporates these complex interactions.

Specific Extreme Events and Their Drivers

Heat Waves

Heat waves in India are becoming more frequent and intense. Recent research suggests a strong correlation between extreme summer heat events and the presence of anticyclones, which lead to clear skies, increased solar radiation, and sinking air that warms adiabatically. The Urban Heat Island (UHI) effect further amplifies temperatures in urban areas due to increased sensible heat release, reduced evaporative cooling, and higher heat storage capacity of artificial surfaces. The MOES report (2020) notes a significant increase in the frequency, intensity, and duration of heatwaves over India.

Lightning

India records a high number of lightning strikes and associated fatalities. While the exact mechanisms linking climate change to lightning are still being studied, warmer temperatures and increased atmospheric instability are generally associated with more vigorous convective activity, which in turn can lead to more frequent and intense lightning. Regions like Bihar, Uttar Pradesh, and Odisha are particularly vulnerable.

Changing Western Disturbances

Western Disturbances are vital for winter precipitation in North India, supporting rabi crops like wheat. However, their patterns are changing. Some studies indicate a decrease in their frequency but an increase in their intensity, leading to more concentrated heavy snowfall or rainfall events. This impacts water security in the Himalayan region and can trigger events like flash floods or avalanches.

Landslides in the Himalayan Region

The Himalayan range is highly susceptible to landslides due to its young, fragile geology and steep slopes. Extreme rainfall events, often a consequence of changing monsoon patterns and intensified WDs, are primary triggers. Anthropogenic factors like deforestation, unscientific construction, and road building further exacerbate the risk. The Hindu Kush Himalayas have experienced significant warming, leading to glacier retreat and permafrost thawing, which destabilizes slopes and increases landslide vulnerability.

Mains Hooks and Recent Developments

Mains Hooks:

• Disaster Management: The increasing frequency of extreme events necessitates robust early warning systems, disaster preparedness, and response mechanisms. The role of the National Disaster Management Authority (NDMA) and state agencies is critical.
• Climate Adaptation: India needs to implement climate-resilient agriculture, water management strategies (e.g., rainwater harvesting, micro-irrigation), and climate-proof infrastructure.
• Policy Implications: Understanding climate variability is crucial for formulating policies related to food security, water resources, energy, and public health.
• International Cooperation: India's vulnerability to climate change makes it a key player in international climate negotiations and a recipient/contributor to climate research.

Recent Developments (MOES Report, 2020):

• Temperature Rise: India's average temperature rose by 0.7°C between 1901 and 2018, projected to increase by 4.4°C by the end of the 21st century under a business-as-usual scenario.
• Rainfall Patterns: A significant decrease in seasonal summer monsoon rainfall (by 6% from 1951 to 2015) has been observed over the Indo-Gangetic Plains and Western Ghats.
• Droughts: Both the frequency and spatial extent of droughts have increased significantly during 1951–2016.
• Sea Level Rise: The North Indian Ocean (NIO) experienced a sea-level rise of 1.06–1.75 mm/year (1874–2004), accelerating to 3.3 mm/year (1993–2017), comparable to the global mean.
• Cyclones: A significant reduction in the annual frequency of tropical cyclones over the NIO basin has been observed since the mid-20th century, though there is concern about increasing intensity of individual cyclones.

These trends underscore the urgent need for comprehensive climate action and adaptation strategies across all sectors in India.