- Monsoon Delay: Any discussion of the Indian monsoon delay these days must include mention of the El Nino phenomenon.
- El Nino’s unexpected rise: This year’s monsoon is also moving under the shadow of an El Nino in the Pacific.
El Nino and La Nina: What You Need to Know
- The El Nino and La Nina phases of the El Nino-Southern Oscillation (ENSO) cycle are diametrically opposed.
- ENSO is a naturally occurring occurrence in the equatorial Pacific that involves the interplay of the ocean and atmosphere.
A full comparison between El Nino and La Nina is provided below:
| El Nino | La Nina | |
| Definition | Warmer-than-normal sea surface temperatures | Cooler-than-normal sea surface temperatures |
| Frequency | Every two to seven years | Every two to seven years |
| Duration | Several months to a year or more | Several months to a year or more |
| Impact on winds | Weakens trade winds, leading to changes in patterns | Strengthens trade winds, leading to changes in patterns |
| Impact on rains | Reduces rainfall and can cause droughts | Increases rainfall and can cause flooding |
| Impact on temp. | Warmer-than-average temperatures | Colder-than-average temperatures |
| Global effects | Droughts in Asia and Africa, floods in Americas | Floods in Asia and Africa, droughts in South America |
Impact on India
| El Nino | La Nina |
| Associated with weak monsoons and drought-like conditions in India | Associated with above-normal rainfall and floods in India |
| Sea surface temperature in the equatorial Pacific Ocean rises above normal levels | Sea surface temperature in the equatorial Pacific Ocean drops below normal levels |
| Changes in the atmospheric circulation patterns | Changes in the atmospheric circulation patterns |
| Shift in the location of the jet stream, affecting the strength and direction of the monsoon winds | Increase in the strength of the monsoon winds, bringing more moisture and rainfall to India |
| Results in reduced rainfall, dry spells, and heatwaves, leading to crop failures and water scarcity | Excessive rainfall can also lead to floods and landslides, causing damage to crops and infrastructure |
El Nino and Indian Monsoon
- El Nino and its impact on Indian monsoon: El Nino refers to abnormal warming of surface waters in the equatorial Pacific Ocean, which tends to suppress monsoon rainfall in India.
- El Nino weather patterns Southern Oscillation (ENSO): In the Pacific Ocean, ENSO has three phases: El Nino, La Nina (excessive cooling), and a neutral phase with sea surface temperatures close to long-term averages.
- ENSO includes not just temperature anomalies in sea surface waters, but also atmospheric factors such as changes in sea-level air pressure and wind strength and direction.
- Southern oscillation and the effect of winds: The Southern Oscillation Index monitors the difference in sea-level air pressure between the western and eastern Pacific Oceans, whereas wind patterns play an important influence in ENSO.
El Nino precipitating factors
- Weakening trade winds: When trade winds in the tropical Pacific weaken, it contributes to El Nino by slowing the migration of warm surface waters.
- Changes in ocean current patterns: Changes in ocean current patterns can cause El Nino episodes because they impact the distribution and buildup of warm water in the central and eastern Pacific.
- Changes in atmospheric pressure: Fluctuations in atmospheric pressure patterns disturb the regular circulation associated with trade winds, causing El Nino conditions to develop.
- The presence and behaviour of oceanic Kelvin waves, large-scale waves that transfer warm water eastward, influence the genesis and intensification of El Nino occurrences.
- Interactions with other climatic modes: El Nino can be influenced by interactions and connections with other climate phenomena such as the Indian Ocean Dipole and the Madden-Julian Oscillation, both of which can affect oceanic and atmospheric conditions in the Pacific region.
Measuring the Cycle
(1) Oceanic Nino Index (ONI)
- The oceanic component of the El Nino Southern Oscillation (ENSO) is measured.
- The deviation from average sea surface temperatures in the tropical Pacific Ocean is tracked.
- It assists in quantifying the intensity and length of El Nino and La Nina occurrences.
- A rolling three-month average of sea surface temperature anomalies in certain regions is typically used.
(2) Southern Oscillation Index (SOI)
- ENSO’s atmospheric component is measured.
- The difference in air pressure between Tahiti and Darwin is calculated.
- Positive SOI levels imply that pressure is higher in the eastern Pacific and lower in the western Pacific.
- Negative SOI levels imply that pressure is lower in the eastern Pacific and higher in the western Pacific.
- Reflects the strength and changes in ENSO-related atmospheric circulation patterns.
- The phase and strength of ENSO, as well as its impact on global weather and climate patterns, are assessed.
El Nino’s Economic Impact on Indian Agriculture
- Drought and reduced rainfall: El Nino occurrences frequently result in below-average monsoon rainfall in India, causing drought conditions in various places.
- Crop failure and lower yields: Crop failure or lower yields for major crops such as rice, wheat, pulses, and oilseeds can occur due to a lack of adequate water availability.
- Increased input costs: During El Nino-induced droughts, farmers may need to spend in more irrigation, water management, and supplementary livestock feeding, resulting in higher input costs.
- Price changes: Because of El Nino, crop production may be reduced, causing price swings and potential inflation in food costs.
- Water scarcity and changes in marine habitats can have a severe impact on animal husbandry and fishing activities, hurting the lives of individuals who rely on these industries.
- Rural livelihoods and migration: Economic hardship can have an impact on rural livelihoods, causing more people to migrate from rural to urban regions in pursuit of alternative employment options.
Source: https://indianexpress.com/article/explained/explained-climate/what-is-el-nino-and-how-it-impacts-the-monsoon-8661546/#:~:text=El%20Nino%2C%20as%20is%20commonly,to%20aid%20rainfall%20over%20India.