Explained: Why Is The Indian Monsoon Erratic In Nature?

The Indian Monsoon is a weather phenomenon that affects the livelihoods of millions of people in South Asia. It's characterized by seasonal winds that bring heavy rainfall to the Indian subcontinent, essential for agriculture and water resources. The summer, or southwest, monsoon, which occurs from June to September, accounts for 70 per cent of India's annual rainfall and is crucial for its agricultural economy.

However, the Indian Monsoon is known for being erratic and uneven. Several complex factors contribute to this variability:

1. Complex Atmospheric Factors
a. Inter-Tropical Convergence Zone (ITCZ)
The ITCZ is a belt of clouds forming near the equator where winds from the northern and southern hemispheres meet. This zone moves north and south with the seasons. During the Indian Monsoon, the ITCZ shifts towards India, bringing rain-bearing clouds. The movement of the ITCZ is influenced by various oceanic and atmospheric conditions, leading to changes in rainfall patterns.

b. Pressure Gradients
Differences in air pressure play a significant role in monsoon activity. High pressure over the Indian Ocean and low pressure over the Indian subcontinent create a pressure gradient. Air moves from high-pressure areas to low-pressure areas, bringing moist air from the ocean to the land, causing rain.

c. El Nino-Southern Oscillation (ENSO)
ENSO is a climate pattern involving changes in ocean temperatures in the Pacific Ocean. El Nino refers to the warming of these waters, often leading to weaker monsoons and less rain in India. Conversely, La Nina refers to cooler Pacific waters, usually resulting in stronger monsoons and more rain. These temperature changes affect global weather patterns, including the Indian Monsoon.

2. Variability of the ITCZ
The position of the ITCZ fluctuates, affecting the onset and intensity of the monsoon. Its movement, influenced by oceanic and atmospheric conditions, can be unpredictable. When the ITCZ moves towards India, it marks the start of the monsoon and brings rain. However, this movement can vary, leading to erratic rainfall patterns. Some years may see heavy rains, while others experience less, depending on the ITCZ's position.

3. Monsoon Trough
The monsoon trough, an extension of the ITCZ, also fluctuates, causing changes in rainfall distribution and intensity. This trough moves north and south, influenced by weather conditions in the ocean and atmosphere. Its position affects where and how much it rains. If the trough moves towards a particular area, that area receives more rain; if it moves away, the area receives less. This movement leads to variations in rainfall patterns across different regions.

4. El Nino and La Nina Events
These oceanic phenomena disrupt normal weather patterns, leading to droughts or excessive rainfall in different parts of India. El Nino often causes weaker monsoons, leading to less rain and potential droughts. La Nina typically results in stronger monsoons, causing excessive rainfall and potential flooding. These events make the monsoon unpredictable, with some years experiencing too little rain and others too much.

5. Indian Ocean Dipole (IOD)
The IOD refers to temperature anomalies in the Indian Ocean. It has two phases: Positive IOD, where the western Indian Ocean is warmer, leading to more rain in India, and Negative IOD, where the eastern Indian Ocean is warmer, leading to less rain in India. Variability in the IOD affects monsoon rainfall, contributing to its erratic nature. A positive IOD can enhance the monsoon, while a negative IOD can suppress it.

6. Topography
India's diverse topography, including mountains, plateaus, and plains, influences local weather patterns, leading to spatial variations in rainfall. Mountains, like the Himalayas, cause moist air to rise and cool, resulting in rain on the windward side and dry conditions on the leeward side (rain shadow effect). Plateaus and plains also affect how much rain different areas receive, causing uneven distribution of rainfall.

7. Urbanisation and Land Use Changes
Rapid urbanisation and changes in land use alter surface temperatures and atmospheric dynamics, affecting local weather patterns. Cities, with their concrete surfaces, become hotter than natural areas, creating the 'urban heat island' effect. These changes can disrupt air movement, influencing cloud formation and rainfall patterns. As a result, the monsoon becomes more unpredictable, with some areas experiencing too much rain and others too little.

8. Climate Change
Global warming alters atmospheric circulation patterns, sea surface temperatures, and moisture content, potentially exacerbating the variability of the Indian Monsoon. Changes in air movement, ocean temperatures, and moisture levels due to global warming can make the monsoon more variable and unpredictable. This leads to changes in the timing and strength of the monsoon, causing heavier rains in some areas and droughts in others.

9. Feedback Mechanisms
Changes in land cover, such as deforestation or afforestation, create feedback loops that modify regional climate patterns. Deforestation makes areas hotter and drier, leading to less rain, while afforestation can make areas cooler and moister, leading to more rain. These feedback loops can significantly alter local climates, making the monsoon more erratic.

Monsoon Forecast for 2024
According to the Indian Meteorological Department (IMD), the average June rainfall for the country is likely to be below normal, defined as less than 92 per cent of the Long Period Average (LPA) of 16.69 cm. The forecast suggests normal to above-normal rainfall over most areas of the southern peninsula and some parts of Northeast India. However, below-normal rainfall is expected in many areas of Northwest and adjoining Central India, as well as some parts of Northeast India.