Air travellers to the capital in the coming winter months are almost certain to face a harrowing time yet again due to flight uncertainties because of a thick fog, which will not only reduce the visibility but also leave the capital thoroughly cold and damp.

Scouring through volumes of weather data collected in the last 45 years, scientists at the Indian Meteorological Department (IMD) have shown an “alarming rise in fog”, in the capital in the last two decades.

This worrying trend will continue as the causative factors will not disappear in the next three months.

The thickest fog blanket, which generally reduces the visibility to less than 50 mt, was to be seen for only half an hour a day in 1980. But the duration has slowly increased to about one hour in the next 15 years till 1995.
And after 1995 there was a sudden rise in the duration of heavy fog in the capital.

 Now one can expect such heavy fog to stay for at least two to three hours.

“Fog hours of other intensities has also gone up by two to five times. This has caused serious concern to the civil aviation sector, which is experiencing 30 per cent growth in the number of flights,” said Dr Rajendra Kumar Jenamani who published his research in a recent issue of the journal Current Science.

More than 675 aircrafts depart and arrive from the Indira Gandhi International airport with the maximum activity reported at night or early morning when the chances of dense fog is high.

Increase in fog hours
The thick fog blanket remains till the afternoon and sometimes shows no sign of abating for a few consecutive days, he said, adding that on an average fog hours per day has increased by eight hours since 1989.

In 1980, any typical December and January day would have at least two clear hours of more than 5000 mt visibility. But this duration has come to a naught in 2005, the study shows.

For these two peak winter months, the average number of hours with various visibility ranges between 3000 and 4500 mt, has reduced significantly in the last two decades. 

“Similar effects were seen in other cities in northwest India,” Dr Jenamani said, adding that vehicular pollution and moisture available from irrigated farm lands in the vicinity of the capital might be the contributing factors.
Also the capital’s maximum temperature has fallen by two to three degrees Celsius since 1989, which according to the IMD scientist may be because of the fog factor. Due to dense fog, the surface is devoid of sunlight and hence remains cooler.