Issue

Context

The unusually cold December this year could just be another instance of extreme climates becoming more and more frequent, a result of climate change. Across the world, the frequency and intensity of both heat waves and cold waves have increased in the last few years.

About

• Extreme cold temperatures, rainfall and intense fog in the months of December and January are witnessed by north and northwest India.
• Every year, in the second half of December and the first half of January, temperatures routinely drop to 2-4°C at some point of the day in many places in north and northwest India.
• In December, the maximum daily temperature does not rise beyond 16-18°C in most of Punjab, Haryana, Himachal Pradesh and western Uttar Pradesh.
• In Delhi and northern Rajasthan, daily maximum temperatures are usually not over 20-22°C for most of December.
• This has happened only four times in the last 118 years, and the IMD has said this month would most likely become the second coldest December for Delhi since 1901.
• This is already the longest such spell for December since 1997.

How cold is cold/Meaning?

• A cold-day condition is said to prevail when the maximum temperature during the day is at least 4.5°C below normal.
• If the maximum temperature is at least 6.5°C below normal, it is classified as a severe cold day.

Causes for these conditions

• Scientists say there is nothing unusual in the climatic conditions that influence temperatures in this region at this time of the year.
• The cold wave usually arrives from the west, through the Western Disturbance wind system.
• This system is also responsible for causing rains in northern and northwestern parts, after having picked up moisture on its way from the Mediterranean Sea.
• The intensity of the cold also depends on the amount of snowfall that happens in Jammu and Kashmir, Ladakh, Himachal Pradesh and nearby areas.
• They combine in different ways to produce different kinds of winter conditions.
• The frequency and intensity of both heat waves and cold waves have increased in the last few years, and are predicted to increase further. The same is the case with extreme rainfall and drought.
• Flow of north-westerly winds over northwest India that too over much lower levels, further fuelled the chill factor, making the days much colder than normal during December.
• This extended cold spell has been triggered due to low stratus clouds that are blanketed over a large geographical area — between Pakistan, cutting across India and running up to Bangladesh.