After facing tremendous heat this year, now the countrymen may have to face severe cold as well. This summer, more than 40 thousand suspected heatstroke cases were registered in the country, while many people also died across the country. Now the Indian Meteorological Department (IMD) in its forecast released on September 2 said that this time people may have to face severe cold as well. IMD has blamed the weather-related ‘La Nina’ pattern for this.

In fact, many global weather agencies including IMD had predicted that La Nina could start from July-August. But all these predictions have proved wrong. Due to the delay in La Nina, IMD has predicted that the country may witness severe cold. In such a situation, let us understand how the phenomenon of La Nina can act as a factor behind severe cold, and why the predictions of all those agencies proved wrong?

First of all, what is La Nina?

La Nina is a climate pattern that is part of the three phases of the El Nino Southern Oscillation (ENSO). The others are El Nino and the neutral phase. El Nino and La Nina are two opposing climate patterns, while the neutral phase involves neither El Nino nor La Nina.

ENSO is characterised by changes in the temperature of the central and eastern tropical Pacific Ocean as well as changes in the air pressure above it in the atmosphere. This pattern alternates between warm and cool phases known as El Niño and La Niña and the cycle occurs irregularly every two to seven years.

The warm phase is called El Niño, or ‘the little boy’ in Spanish, while the cool phase is called La Niña (little girl in Spanish).

La Nina is a phenomenon that plays an important role in global climate change. To put it simply, our Earth rotates from ‘West to East’ and because of this, tropical winds travel from ‘East to West’. Understand it this way that when someone travels in a car, he feels that the wind is blowing from the opposite direction.

However, these winds are called trade winds. These winds play an important role in climate events like El Nino and La Nina.

Actually, these trade winds in the Pacific Ocean push the warm water currents present on the coast of Peru (a Latin American country) towards Australia. Now a question arises here that why do these winds push only warm water currents. Since the volume of warm water currents is less than that of cold water, it remains above the surface. When the trade winds push the warm water forward, cold water comes from below and takes its place. This is called ‘upwelling’.

Now when this warm water reaches Australia carrying moisture from the sea, it starts evaporating and rising upwards, and due to this a low pressure area is formed there. There is a rule in geography that winds travel from ‘high pressure to low pressure’. When low pressure starts forming in Australia, winds from all sides try to fill that space. In the same sequence, trade winds in the Indian Ocean also move forward carrying moisture from the sea and there is good rainfall in other Asian countries including India. In this situation, monsoon is considered to be strong.

Anyway, this is the situation of La Nina. But when the opposite happens, it is called El Nino. In this, the trade winds are not strong enough to push the warm water current forward. Due to this, a low pressure area is formed on and around the coast of Peru. As a result, there is heavy rainfall in Peru and its surroundings and bad monsoon conditions are created in continents including Australia and Asia. Due to this, while incidents like forest fires are seen in Australia, drought conditions are created in countries like India.

What did global agencies predict?

When one of the most powerful El Niño events ever recorded ended in June this year, ENSO entered a neutral phase. After this, many major global weather agencies initially predicted that La Niña conditions would begin around July. But by mid-July, it became clear that La Niña would be delayed. According to reports, the US-based National Oceanic and Atmospheric Administration (NOAA) had then said that the transition of ENSO from neutral to La Niña phase would happen between August and October.

Apart from this, Australia’s Bureau of Meteorology (BOM) also maintained more or less the same forecast, and predicted a post-July period for the La Nina event. The Indian Meteorological Department (IMD) also believed in its first stage long range forecast released in mid-April that La Nina conditions would arise in the latter half of the monsoon (June-September). Another most important thing in it was that due to La Nina, more rain was expected in the months of August and September.

Why did the initial estimates prove wrong?

Anjali Marar, Science Communicator at Raman Research Institute, writes in the Indian Express that there is no single reason behind the predictions not being correct. Apart from this, while almost all the predictions miscalculated the time of onset of La Nina, they were largely accurate about its comparatively weak intensity.

In fact, one of the main reasons given by weather modelers and meteorologists for their inaccurate predictions of La Niña is its severity. Weather models can better capture signals in cases of strong La Niña (or El Niño) phases rather than weak La Niña (or El Niño) phases. In addition, there are other factors that influence surface and subsurface conditions in the Pacific Ocean.

In particular, these include inter-seasonal variability in the atmosphere, wind and pressure, which is directly linked to the movement of the Madden Julian Oscillation (MJO). The MJO is a marine-atmospheric phenomenon that affects weather patterns around the world. It is an eastward moving band of winds and clouds that bring rain. The interaction of different weather systems sometimes makes forecasting difficult.

According to the National Ocean and Atmospheric Administration (NOAA), the US weather regulatory body, ENSO-neutral conditions currently prevail in the Pacific Ocean. The latest forecasts suggest that initial signs of the onset of La Nina will emerge in late September or early October. La Nina will peak in November, and is expected to persist throughout the winter in the Northern Hemisphere.

This year it could be extremely cold!

Pointing to the late onset of La Nina (September), the IMD has forecast that the country may experience severe winter this year. According to an IMD announcement on 2 September 2024, severe winter is expected due to La Nina. The intensity of winter is expected to vary in different regions of India. Particularly cold conditions can be seen in hilly states like Himachal Pradesh, Uttarakhand and Jammu and Kashmir, where temperatures may possibly drop to 3 degrees Celsius.

In addition, the combination of extremely cold weather and increased rainfall may impact agriculture, especially in areas that depend on winter crops. The IMD has urged citizens to prepare for the coming winter by having adequate heating, stocking up on essential supplies, and staying updated on weather reports. The IMD is closely monitoring the situation and will continue to issue updates and advisories.