The climate of India: Why winters were warm this season?

The temperature readings during the beginning of this winter season were mild, with no significant instances of winter rains and snowfall in November and December last year.

This caused the maximum temperature to remain higher than the usual average. December 2022 was declared the hottest month in the past 122 years, with an average temperature of 21.49 degrees Celsius, surpassing the previous record set in 2008 of 21.46 degrees Celsius.

Although there were some instances of snowfall and rainfall in the western Himalayas at the start of January, the temperatures in February were once again on the rise, breaking records once again.

This trend of higher-than-normal temperatures can be attributed to the lack of rainfall in the past four months, which has been notably low in many regions of northern, central, eastern, and northeastern India during the winter season. This resulted in cold wave conditions in some areas, but overall, temperatures remained high.

While some parts of the southern peninsula experienced rainfall recently due to the formation of low-pressure areas in the Bay of Bengal, the effect was confined to the southern regions only as the low-pressure zones were not strong enough.

The rainfall in other parts of the country has been below average. Here are the overall rainfall statistics for the country.

Meteorologists suggest that the variation in temperature and rainfall is a consequence of alterations in weather patterns. The current winter season has witnessed a decrease in the frequency and intensity of western disturbances.

Western disturbances are instrumental in driving weather conditions and causing winters in regions around Central India and North-West India. Although numerous active western disturbances were observed in January, they did not have any impact on the weather conditions in the Indian plains of Ganga.

In November

During mid-November, the Western Disturbance (WD) typically increases in intensity and frequency in the western Himalayas, and the associated cloud bands move towards lower latitudes, increasing the chances of rainfall.

This period marks the beginning of winter and usually sees one or two episodes of moderate to heavy snowfall and rainfall in the high-altitude areas of Jammu and Kashmir, Himachal Pradesh, and Uttarakhand.

However, in November 2022, there was a lack of snowfall and rainfall in these regions, despite the occurrence of five Western Disturbances.

Only two of these disturbances (November 2-5 and 6-9) led to scattered or isolated precipitation in the hilly states and surrounding plains, while the remaining three WDs (November 13-15, 18-21, and 22-24) were weak and did not have a significant impact on the region.

Meteorologists attribute this deviation from the usual weather pattern to changes in weather patterns.

December

At the start of December, the weather was warm and dry, and there was no sign of winter rains or snowfall in northern and central India.

Throughout the month, seven Western Disturbances were observed, but only one of them (from December 28-30) caused any precipitation in the western Himalayas and nearby areas. The other six disturbances were weak and had no significant impact on the region's weather.

January

The month of January witnessed several active Western Disturbances with high intensity, leading to widespread rainfall and snowfall in North-West India, particularly in the hilly states.

This resulted in a 28% increase in rainfall in the region, while areas around Central India continued to experience a shortage of rainfall due to the low intensity of weather systems in the Bay of Bengal.

During this period, a total of seven Western Disturbances affected Northern India, with four causing rain or snowfall in the Western Himalayan region and surrounding areas.

The last two WDs were particularly active and caused heavy rainfall, along with scattered hailstorms in some areas. However, the other three WDs were weak and had a minimal impact, leaving behind light snow at higher altitudes.

After the passage of these WDs, cold winds from the snow-covered Himalayas resulted in severe cold wave conditions in northern and central India during the first and third weeks of January 2023.

February

During February, the western disturbances continued to be the primary source of precipitation in northwestern India, following a pattern similar to December.

However, the frequent arrival of these disturbances prevented cold northern winds from reaching the region, leading to above-normal maximum temperatures.

Scientists and meteorologists attribute these changes in weather patterns to climate change. A report by the IPCC suggests that heat waves in Asia are likely to increase in frequency due to global warming, and large parts of South Asia, including India, will experience heat stress in the future. It is expected that cold days and nights will become less frequent.

Changing dynamics of Western Disturbance

Western Disturbance is a weather phenomenon that originates in the west and travels through the subtropical westerly jet, causing disturbances in the Indian subcontinent during the winter months.

They usually occur at a frequency of 4-5 per month from December to February. As these disturbances move across the Atlantic Ocean, they accumulate moisture and other characteristics.

As they approach India, they gain intensity and gather more moisture from the Arabian Sea. The Western Himalayas also have an orographic effect on the Western Disturbances and play a crucial role in shaping the monsoon system.

However, due to the increasing global average temperature, the behavior of Western Disturbances has changed.

The way they interact with the Western Himalayas determines the distribution of precipitation in the region, making it important to understand the impact of climate change on these disturbances.

Climate change and its impact on Western Disturbances

Dr. AP Dimri, Director of the Indian Institute of Geomagnetism, has noted that Western Disturbances (WDs) are experiencing structural and dynamic changes due to global warming.

As a result, these disturbances are becoming lighter with increased convection and heat, and tracking in the upper atmosphere.

Dr. Dimri has also observed that not all WDs are dissipating, which means that some days it does not rain during their passage, while there are non-WD days with good rainfall in northern India.

Moreover, the southern proposal of the North Atlantic Oscillation (NAO) can push the subtropical western jet further southward, increasing the probability of more WDs. In a warming scenario, there will be a more stable environment and global connections that can weaken WDs.

Mahesh Palawat, Vice President of Weather Science and Climate Change at Skymet Weather, has mentioned that warming in the Arctic region is one of the primary concerns of global warming. It affects circulation patterns that directly impact the Asian region.

He also explained that the intense Arctic heat wave has pulled weather systems, including WDs, northward, thereby not affecting the weather in India.

High latitudes will become warmer more rapidly

Recent research suggests that as global warming causes high latitudes to warm more rapidly than the overall global temperature, a decrease in temperature gradient could affect total winter snowfall by impacting Western Disturbances (WD).

This phenomenon is called polar amplification and occurs when any change in net radiation balance, such as increased greenhouse gas density, leads to a greater temperature change near the poles compared to the global average.

Furthermore, changes in the frequency, intensity, or flow of moisture related to the monsoon season can have significant impacts on both climate science and extreme events associated with the monsoon.

Future climate scenarios, known as RCP4.5 and RCP8.5, predict a significant decrease in monsoon precipitation in the 21st century. Multi-model ensembles and model interquartile ranges suggest that by 2100, the annual monsoon rainfall could decrease by approximately 6 and 9 years^-1 for RCP4.5 and RCP8.5, respectively.

The Intergovernmental Panel on Climate Change (IPCC) uses representative concentration pathways (RCPs), which are greenhouse gas concentration trajectories that assume no specific climate policies will be implemented, to evaluate future climate change scenarios.

Future climate scenarios during winter months

Different climate scenarios have been proposed, which are expected to occur in the future, based on the level of greenhouse gas emissions.

These scenarios are represented by different Representative Concentration Pathways (RCPs), which predict future climate change outcomes. RCP 4.5 is a moderate scenario where greenhouse gas emissions will peak around the year 2040 and then gradually decline.

On the other hand, RCP 8.5 is a high baseline emission scenario where greenhouse gas emissions will continue to increase throughout the 21st century.

Based on the given data, it is predicted that the frequency of western disturbances will decrease significantly in all future climate scenarios during winter, which will have a major impact.

The four future scenarios (RCP2.6, RCP4.5, RCP6.0, RCP8.5) predict a reduction in annual double-D frequency, with more extreme scenarios indicating a greater increase in strong radiative forcing.

As a result, there is an anticipated decrease in winter rainfall in northern India and Pakistan due to the decrease in western disturbance activity, which is the primary source of winter rainfall in this area.

It is estimated that there will be a reduction of approximately 10%-20% in average winter rainfall in Pakistan and northern India.

La Niña event exacerbates global warming

La Niña is a climate phenomenon that occurs when the central Pacific Ocean experiences cooler than normal water temperatures due to the upwelling of cold water from below the ocean's surface.

This can cause changes in the direction and speed of trade winds, which can affect winter weather patterns in India. Unlike its counterpart, El Niño, La Niña may not have a strong correlation with specific weather features but can still have consequences for weather performance.

The impact of La Niña on winter rainfall in northern India is not entirely predictable, but it is thought to be influenced by factors such as below-normal rainfall and snowfall, lower temperatures during winter, and long cold periods.

However, despite the persistence of La Niña, the years 2021 and 2022 was recorded as the hottest years in history, with the past eight years being the hottest on record globally.

This trend is attributed to increasing greenhouse gas concentrations and accumulated warmth in the atmosphere, which outweighed the cooling effect of La Niña.

In summary, La Niña is a climate phenomenon characterized by cooler-than-normal water temperatures in the central Pacific Ocean, which can affect winter weather patterns in India.

Its impact on winter rainfall in northern India is uncertain but is influenced by several factors. Despite the occurrence of La Niña, global temperatures have been rising due to the increasing concentration of greenhouse gases in the atmosphere.

Hottest years on record

The World Meteorological Organization (WMO) has stated that the hottest years on record globally were the past eight years, from 2015 to 2022. This increase in temperature is believed to be a result of the rise in greenhouse gas concentration and the accumulation of heat.

Although La Niña can cause a cooling effect, it is temporary and not enough to counteract the long-term warming trend that is driven by the excessive greenhouse gases in our environment, according to scientists.

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