For rain-deprived Karachi, possible respite in nurturing trees

Vast expanse of vegetation helps form clouds and make them rain

KARACHI: Trees are fast disappearing from Karachi’s landscape to make way for billboards selling lawn suits and crispy burgers and as we lose our source of shade and oxygen, we also reduce our chances of inviting rain during hot summer days.

Rain occurs when water from the earth surface evaporates, moves up in the sky, cools down to form clouds and falls back when the cloud becomes too heavy to stay afloat. Experts say trees play a role in forming clouds and making them heavy enough to rain.



Muhammad Tahir Qureshi, a senior adviser of coastal ecosystem at International Union for Conservation of Nature (IUCN), says trees help cool down the overall temperature which in turn helps formation of clouds.



An environmental expert at WWF-Pakistan, Saeedul Islam, says trees also play a role in making clouds heavy by exporting more water into the atmosphere through the process of transpiration.

“As this water from tree is in gaseous form, it freely spreads and interacts with moving clouds. This combining of water vapours from trees with water vapours of clouds makes the mass heavy and leads to rainfall,” Islam explains, quickly adding this process takes place only with the help of large number of grown trees and not small amount of vegetation.

“This is the reason why we have heavy rainfall in our northern areas; they have thick forests which make air moist and cause rain,” he says, stating that if Karachi can nurture thick trees in a big number — at least one-fourth of total area — the city can have better rainfall.



Rainfall in Karachi

IUCN’s Qureshi says Karachi used to have regular winter and summer monsoons with very little rainfall in the colder months but thundering downpour from June to September. “In the 1950s, when I was growing up, I remember having to write an essay on ‘Karachi ki toofani barishain’ because that’s how intense and regular they were,” Qureshi quips, stating that now for the last 15 to 20 years, as per meteorological data, the city’s monsoon pattern has become erratic and irregular.

“Sindh coast would witness 200mm rainfall per year in the past but now it is hardly 50mm. Earlier, when it would rain in Karachi, areas from one corner of the city to another would be wet but now we see that if there’s rain in Nazimabad, DHA remains dry,” he says, highlighting the inconsistent nature of rainfall in Karachi.

Qureshi says according to 1892 data, 150 million acre-foot (MAF) Indus water would discharge into the Arabian Sea from Kotri Barrage alone. “This abundance of water supported our mangroves but now the total water for entire Pakistan, as per a mid-1990s report, stands at 206MAF,” he states.

The IUCN expert says Karachi’s two flowing rivers — Lyari and Malir — also nurtured thick vegetation around their path but rapid growth and industrialisation destroyed the natural environment.





Trees, our lifeline

Rafiul Haq, founder of Coastal Restoration Alliance for Biodiversity, says trees are not a luxury but a necessity as they are a  major contributor of the oxygen we breathe. “One person’s need for oxygen for 24 hours is covered by seven trees; by this calculation, we need 140 million trees for the estimated 20 million people that live in the city,” Haq states.

“Thankfully we have 420 trees per person spread across the world as well as plants in sea producing oxygen to help us keep breathing,” he adds. Haq laments that while we aspire to build high-density areas with tall buildings in Karachi, we don’t ever consider having high-density forests for our benefit. “One of the Millennium Development Goals is to build resilient cities which is basically a society’s capacity to cope with disasters and return back to life. Trees play a very important role in achieving this goal,” he shares.

Published in The Express Tribune, July 10^th, 2016.