La Nina as a contributor to severe heat waves in the country
- In most years, meteorologists consider the La Nina to be a friend of India
- This year, however, the La Nina is being blamed for worsening perhaps the longest spell of heatwaves from March to April in north, west and Central India.
- This phenomenon is associated with below normal sea surface temperatures in the eastern and central Pacific Ocean which makes the summer monsoon wetter and the winter colder
- During a La Nina winter, a north-south pressure pattern sets up over India and normally this influences the trade winds that bring rains to India.
How La nina has contributed to the heatwaves
- The north-south pressure pattern has been persisting over India, with La Nina extending its stay over the Pacific.
- This has impacted the weather over India, which has been seen even during 1998-2000 when La Nina had persisted for three years.
- While land temperatures over India begin rising in March, they are usually punctuated by western disturbances, or moisture from the Mediterranean region that fall as rain over north and western India.
- For these currents to make it as far as India, they need a significant difference in temperature between Europe and the latitudes over India.
- Partly due to La Nina, this temperature difference was absent and so the western disturbances that came to India were weak with hardly any rain.
Report of the Ministry of Earth Sciences regarding Heat waves
- According to a 2021 report by the Ministry of Earth Sciences, ‘Assessment of Climate Change over the Indian Region’, all India averaged frequency of summer heatwaves is expected to rise to about 2.5 events per season by the mid-21st century, with a further slight rise to about 3.0 events by the end of 21st century under current trajectory of greenhouse gas emission.
Prelims take away
- La Nina
- Conditions to declare Heat waves