Central Idea

• With the El Nino phenomenon set to affect the Indian monsoon this year, there is growing optimism surrounding the development of a positive Indian Ocean Dipole (IOD) and its ability to mitigate the effects of El Nino. The IOD, a weaker ocean-atmosphere interaction in the Indian Ocean, has demonstrated limited impacts in the past but holds potential in offsetting the adverse effects of El Nino, particularly in neighbouring regions.

*Relevance of the topic*

*Questions on Indian ocean dipole and El nino and its impact on Indian monsoon have been asked multiple times in previous years.

*Relate this topic with Indian monsoon, and its impact on Indian agriculture as, Rainfed agriculture occupies about 51 percent of country’s net sown area and accounts for nearly 40 percent of the total food production.

The current status of the Indian Ocean Dipole (IOD) and El Nino

• IOD:
• The IOD is currently in a neutral phase. This means that there is no significant temperature difference between the western and eastern sides of the Indian Ocean along the equator.
• However, international climate models suggest the possibility of a positive IOD event developing in the coming months.
• The India Meteorological Department (IMD) has also reported an 80% chance of a positive IOD during the June-August 2023 season. The development of a positive IOD would have implications for weather patterns in the Indian Ocean region.
• El Nino:
• El Nino has already established itself in the Pacific Ocean this year. El Nino occurs when the prevailing wind systems weaken, resulting in reduced displacement of warm waters in the eastern side of the Pacific.
• This abnormal warming of the eastern Pacific can have impacts on global weather patterns, including the Indian monsoon. The presence of El Nino raises concerns about its potential impact on the Indian monsoon rainfall.

Understanding El Nino and IOD

The interplay between the El Nino Southern Oscillation (ENSO) and IOD

• Triggering Mechanism: ENSO events, specifically El Nino, can trigger the development of a positive IOD in the Indian Ocean.
• External Drivers: While external factors such as ENSO can initiate IOD events in some cases, there is evidence to suggest that IOD events can also occur due to local circulations or subsurface processes within the equatorial Indian Ocean.
• Internal Dynamics: IOD events largely develop and mature through internal dynamics, even when triggered by external drivers. They have the potential to exhibit independent existence and can impact weather patterns in the Indian Ocean region.
• Impact on IOD: During El Nino, the Pacific side of Indonesia tends to be cooler than normal, which influences the Indian Ocean side, leading to the development of a positive IOD.
• Mutual Interaction: The circulation patterns of IOD and ENSO can impact each other when both events are strong. The interaction between the two phenomena can influence the intensity and duration of each event.
• Contrasting Associations: Positive IOD events are often associated with El Nino, while negative IOD events are sometimes linked to La Nina. However, this association is not absolute, and IOD events can occur independently or have different associations depending on the specific conditions.
• Combined Impacts: Strong IOD and ENSO events can have combined effects on weather patterns, as their circulation patterns can interact and influence each other.

The impacts of Indian Ocean Dipole

• Rainfall Distribution: IOD significantly influences rainfall patterns in the Indian Ocean region. During a positive IOD, there is increased convection and rainfall along the African coastline and over the Indian subcontinent. Conversely, a negative IOD leads to suppressed rainfall in these regions.
• Drought and Floods: Positive IOD events can bring above-average rainfall to the affected regions, which can alleviate drought conditions and replenish water resources. However, this increased rainfall can also result in flooding and water-related disasters in certain areas.
• Agricultural Productivity: IOD has implications for agriculture as it affects the availability and distribution of rainfall. Positive IOD events can enhance agricultural productivity in the affected regions, while negative IOD events may lead to reduced crop yields and agricultural challenges.
• Fisheries: IOD impacts the productivity of marine ecosystems. During positive IOD, increased upwelling of nutrient-rich waters occurs, which promotes higher fish stocks and benefits fisheries. In contrast, negative IOD can disrupt the marine food chain and impact fish populations.
• Coral Bleaching: IOD influences sea surface temperatures, and prolonged positive IOD events can contribute to increased sea surface temperatures in the affected regions. This can lead to coral bleaching, negatively impacting coral reefs and marine biodiversity.
• Indian Monsoon: IOD can influence the strength and distribution of the Indian monsoon rainfall. Positive IOD events are generally associated with enhanced monsoon rainfall over the Indian subcontinent, while negative IOD events can lead to reduced monsoon rainfall.
• Weather Extremes: IOD can contribute to the occurrence of extreme weather events such as heatwaves, storms, and tropical cyclones in the Indian Ocean region.
• Economic and Social Impacts: The impacts of IOD on rainfall, agriculture, fisheries, and other sectors have direct economic and social implications. These impacts can affect livelihoods, water availability, food security, and overall economic development in the affected regions.

Impacts of El Nino on the Indian monsoon

• Weakened Monsoon Winds: During El Nino, the trade winds that blow from the east across the Indian Ocean weaken. These winds are responsible for carrying moisture-laden air towards the Indian subcontinent, facilitating the monsoon rainfall. With weakened winds, the supply of moisture is reduced, leading to a decrease in rainfall.
• Delayed Onset: El Nino can cause a delayed onset of the Indian monsoon. The normal onset of monsoon rainfall in India is around June, but during El Nino years, the monsoon arrival may be delayed, resulting in a late start to the rainy season.
• Deficient Rainfall: El Nino events often lead to below-average rainfall during the monsoon season in India. The reduced moisture transport and altered atmospheric circulation associated with El Nino result in deficient rainfall across various parts of the country.
• Regional Variations: The impact of El Nino on the Indian monsoon is not uniform throughout the country. Certain regions, particularly central and northern India, are more prone to experiencing below-average rainfall during El Nino years. However, some areas in southern India may receive near-normal or even above-normal rainfall during these periods.
• Drought Conditions: El Nino-induced deficient rainfall can result in drought conditions in affected regions. This can have adverse effects on agriculture, water availability, and livelihoods, leading to crop failures, reduced agricultural productivity, and water scarcity.
• Temperature Extremes: El Nino can contribute to increased temperatures during the monsoon season in some parts of India. The reduced cloud cover and rainfall can lead to heatwaves and higher temperatures, posing health risks and impacting human well-being.

Conclusion

• While the IOD’s ability to counterbalance the effects of El Nino is limited, there is hope that a positive IOD event may develop in the coming months. Past instances, such as the strong IOD event in 2019, have demonstrated the potential of IOD in compensating for monsoon rainfall deficits. As researchers continue to study the interplay between ENSO and IOD, the development of a positive IOD this year would be welcomed, offering some respite from the anticipated impacts of El Nino on the Indian monsoon.

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