Salt Range, Margalla Hills protect capital from heatwaves

Published May 27, 2015
AS the mercury rises in the plains, tourists make for the relatively cooler climes of the Salt Range. — Photo by Khurram Amin
AS the mercury rises in the plains, tourists make for the relatively cooler climes of the Salt Range. — Photo by Khurram Amin

ISLAMABAD: As a strong heat wave continues to take its toll on the Indian plains, Pakistan is not under any immediate threat from the scorching sun, possibly because of the constant inflow of cool winds from Europe and Central Asia.

But Islamabad and the Potohar region are said to be impervious to weather systems that arrive from the east, which bodes well for the cities and towns around the capital.

Media reports from our neighbour to the east put the death toll from the heat wave at around 800 people in the central and south-eastern states.

Even the Indian capital, New Delhi, has experienced temperatures of up to 45 degrees Celsius. On Tuesday night, at around 8pm, weather forecasting websites put the temperature in the Indian capital at 42 degrees with humidity down to a mere nine per cent and a lazy 13km per hour wind.

“Such conditions are akin to standing very close to a tandoor,” an official from the Met Office told Dawn. “However, the situation changes as one starts to move further north towards Pakistan,” he said.

But even in the plains of Punjab, the mercury is rising to alarming levels. Though the maximum temperature in Multan was 41 degrees Celsius during the day on Tuesday, it dropped significantly after sunset and went down to around 26 degrees Celsius at night.

“One major reason for the sharp contrast between maximum and the minimum temperatures in the Multan area is the geography of the region – sand tends to heat up and cool down quite quickly,” the Met official said.

Then, there is the ‘loo’, a strong, hot and dry summer afternoon wind from the west that blows across the plains of North India and Pakistani Punjab, up to Jhelum. This feared phenomenon claims many lives due to heatstroke and dehydration every year.

The Salt Range forms a barrier of sorts, keeping unwanted weather systems away from the Potohar region. The second line of defence are the Margalla Hills of Islamabad. These two ranges not only keep the deadly ‘loo’ at bay, but also help keep temperatures lower than in other parts of the country, during summer months.

“The ‘loo’ blows close to ground level and cannot cross the Salt Range,” the Met official said, adding that this was the main reason why summer temperatures in this region were lower than those on the other side of the Salt Range.

Meteorological data from Tuesday showed that temperatures in Jhelum were at least two degrees Celsius lower than in Mandi Bahauddin, which is the last town before the Salt Range. As one moves further north, the mercury drops four full degrees in Islamabad.

Met Office data shows a difference of six degrees between Mandi Bahauddin and Islamabad, just on Tuesday.

“The Potohar region is comparatively cooler than the plains of Punjab,” the official concluded.

Cool, moisture-laden but low-intensity winds from the north provide relief to the parched capital in the summer months. The dense vegetation over the Margallas and in the Galliyat increases humidity to tolerable levels in areas north of the Salt Range.

While most people think that humidity adds to mugginess, the fact remains that some moisture in the air is necessary for human beings to survive. Very low humidity makes skin itchy and irritable as the body loses moisture.

However, high humidity combined with high temperatures can also be very dangerous, as it prevents perspiration from taking place effectively.

Humidity levels in Lahore were at 10 per cent on Tuesday, which was evident from the faces of the players at last night’s one-dayer between Pakistan and Zimbabwe, but stood at 29 per cent in Islamabad, where the evenings are decidedly more pleasant. Simultaneously, the humidity level in Jhelum was 16 per cent and 13 percent in Mandi Bahauddin, conforming to the pattern indicated by the Met official.

“This difference exists because moisture levels drop as the winds move southwards into the hot areas,” he said.

In winters, the Potohar region is also immune to the dense fog that usually engulfs the plains. This is also thanks to the natural barrier formed by the Salt Range.

“The fog is created due to evaporation of water from the huge water courses in Punjab,” the Met official told Dawn, adding, “As temperatures near the zero-degree mark, the evaporating water condenses to become fog.”

Published in Dawn, May 27th, 2015

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