Weak La Nina to disrupt weather pattern again

Updated on Sep 10, 2021 07:27 AM IST

Despite the cooling influence of La Nina, temperature over land particularly the northern hemisphere except India is likely to be above average during the next three months, the World Meteorological Organisation said.

A flooded road near Pragati Maidan during rains, in New Delhi, on September 2. (PTI)
A flooded road near Pragati Maidan during rains, in New Delhi, on September 2. (PTI)
ByJayashree Nandi, New Delhi

A weak La Nina is likely to emerge between September and November for the second consecutive year, and exacerbate drought in some parts of the world, and heavy rainfall and flooding in others, the World Meteorological Organisation said on Thursday.

Despite the cooling influence of La Nina, temperature over land particularly the northern hemisphere except India is likely to be above average during the next three months, WMO added. South Peninsular India is likely to record below normal temperatures while northwest and central India are likely to record normal temperatures according to WMO’s projections.

La Niña refers to the large-scale cooling of the ocean surface temperatures in the central and eastern equatorial Pacific Ocean, coupled with changes in the tropical atmospheric circulation, namely winds, pressure and rainfall. It usually has the opposite impacts on weather and climate as El Niño, which is the warm phase of the so-called El Niño Southern Oscillation (ENSO).

ENSO has a major influence on weather and climate patterns such as heavy rains, floods and drought. In India for example, El Nino is associated with drought or weak monsoon while La Nina is associated with strong monsoon and above average rains and colder winters.

There is a 60% chance of ENSO-neutral and 40% chance for La Niña conditions in September-November, and equal chances of ENSO-neutral and La-Nina re-emergence in October-December and November-January, according to WMO. The El Niño/La Niña outlook of WMO projects an ENSO-neutral condition again in 2022.

There is a slightly increased probability of above-normal rainfall over India, Australia, eastern and southeast Asia, according to WMO. There is also high probability of above-normal rain over extreme northern parts of Asia, South America, equatorial parts of the Indonesian Archipelago into the Southwest Pacific and up to an area northeast of New Zealand, WMO said in its statement on Thursday.

There is likely to be above normal rainfall activity at over 110% of the so-called long period average or LPA in September, and while this will reduce the current monsoon rain deficiency of 7% over the country, overall monsoon rain (June 1 to September 30) will still be in the “lower end of normal category,” the India Meteorological Department (IMD) said in its monsoon monthly forecast earlier this month. There is currently a 7% deficiency in rainfall with 10% deficiency over central India; 14% deficiency over northwest India; 10% deficiency over east and northeast India and 13% excess over south peninsula.

“All naturally occurring climate events now take place in the context of human-induced climate change, which is increasing global temperatures, exacerbating extreme weather and impacting seasonal rainfall patterns,” WMO said adding that above average temperatures over land areas are expected to be strongest in the northern hemisphere, except for the Indian subcontinent. Normal temperatures are likely over northwest and central India while slightly below normal temperatures are expected over the south peninsula compared to 1993 to 2009 baseline period.

Temperatures are expected to be most above average over the central eastern part of North America, the far northern part of Asia and the Arctic as well as over central and eastern parts of Africa and southern South America.

“Human induced climate change amplifies the impacts of naturally occurring events like La Niña and is increasingly influencing our weather patterns, in particular through more intense heat and drought – and the associated risk of wildfires – as well as record-breaking deluges of rainfall and flooding. We have seen this with devastating and tragic effect in the past few months in nearly all regions of the world. Climate change is increasing the severity and frequency of disasters,” said WMO Secretary-General Petteri Taalas.

“During La Nina years, cold mid-latitude westerlies enter inland. But that is more likely in winter. During the September to November period below normal or normal temperatures are likely because of clouding associated with rainfall. There is global consensus that weak La Nina conditions are likely to remerge in the next couple of months. We have also forecast that above-normal rains are likely in September,” said DS Pai, head of climate and research services at IMD Pune.

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