Regarding a comment on the news report “May in March” published in Republica on March 26, 2010, related to issues of unusually high temperature in Kathmandu last year, a reader suggested reading Urban Heat Island (UHI) effect for Kathmandu Valley rather than jumping to a hasty conclusion about the manifestations of global warming.
UHI effect is the tendency of cities to retain more heat in comparison to their surrounding rural areas, so much so, that temperature differences between them can be as much as 10 degrees.
One major reason for UHI can be attributed to modification of land surfaces by urban development, that uses materials which effectively retain heat. With progressive replacement of natural surfaces composed of vegetation and moisture-trapping soil, replaced by built surfaces composed of non-reflective, water-resistant construction materials from concrete to glass, asphalt and more, the city area can no longer cool itself.
It then intensifies the UHI effect and creates micro-heat islands along the cities called hot spots, which manifests due to poorly vegetated parking lots, non-reflective roofs and asphalt roads.
In this context, the UHI effect does seem to be at play in Kathmandu along with other major urban areas such as Biratnagar, that has developed emerging hot spots in core urban areas. Experts too agree, but without any concrete data, as no or very few studies have been conducted on this issue keeping urban areas of Nepal in mind.
Dr Pitamber Sharma, former Vice- chairman of National Planning Commission and board member of Resources Himalaya, says the rise in annual temperature of Kathmandu has been contributed by UHI. The obvious reasons, he states, are the number of vehicles that have increased drastically, and Green House Gas (GHG) density concentrated in core urban areas with particles suspended in air that tend to trap heat. Coupled with more black topped roads and unnatural construction materials that absorb heat and the drastic change in the use of land.
“Previously, 40 percent of land in Kathmandu valley was agricultural and had more vegetation. The land surface would absorb water and vegetation would transpire so as to keep the area cool,” says Sharma, further adding “The biggest factor in the temperature rise has to be of change in the land use.”
“Even geologically, as Kathmandu is a valley and has a small watershed it cannot easily get rid of its own heat which stays trapped within”, he states. Sharma also mentions about the inversion of temperature in Kathmandu valley. “Due to temperature inversion instead of temperature decreasing with increasing altitude, the temperature here increases along with altitude until it reaches a certain height. This deviation along with heavy air pollution in Kathmandu has resulted in producing harmful winter smog and can also contribute to the UHI effect”, he says.
“The temperature of Kathmandu is increasing at a rate of 0.06 degrees Celsius per year which is relatively higher than other places in Nepal, which is 0.04 degrees Celsius per year,” says Sarju Baidya, Head of Climate division at the Department of Hydrology and Meterorology (DHM). “However, rather than assessing the increase in temperature as global warming, we’ve to consider that it’s also due to the local effect” he adds.
According to Baidya, UHI effect would be a major contributing factor for the increase in heat or climate change in Kathmandu even more than the hyped global warming component. He asserts that if people really want to study climate change and to find out the actual rise in temperature, within the context of Kathmandu, the UHI effect has to be taken into consideration.
As to the reason why no research has been conducted on the issue yet, Baidya says, “Firstly it’s a big effort to study UHI as a gamut of things have to be considered, from population to settlements and land use patterns.” He further adds “the DHM doesn’t have enough man power, only a few those that are limited to their own technical works. Universities and other organizations should be looking into it, but perhaps it doesn’t come at par with priority issues such as sanitation and waste management.”
This year’s edition of UN- Habitat’s Global Report on Human Settlements has also focused on cooling hot cities around the world along with monitoring the GHG emissions. Padma Sundar Joshi, UN Habitat Program Manager for Nepal, however, informs that studying UHI for Kathmandu has not been scheduled in their program..
Madan Lal Shreshta, Academician at Nepal Association of Science and Technology (NAST) and also former director general at DHM, says “UHI effect is manageable or can be mitigated”.
“I think DHM should be technically equipped to carry on image mapping and research for UHI effect in Kathmandu,” says Shrestha, “Unfortunately, whereas a lot of work has been done regarding climate change and urban settlement, the heat island effect which is a manageable environment problem at hand is still neglected and remains an unknown subject” he further opines.
While the rest of the world is trying to cool its hot cities, in Kathmandu it’s still a challenge to find people at NAST, Ministry of Environment, DHM and even universities who possess knowledge about the UHI effect.
He also adds, “Even to get started on the mitigation processes, we need to do some ground works and gather facts. Of course, we can say theoretically that UHI has caused an impact in the warming trend of urban cities but we need to have facts and measure its intensity.”
According to Shrestha, “there is still no means of measurement for energy consumption in Nepal’s cities. As energy consumption and UHI mutually affect each other it’s necessary to keep record of energy consumption level in urban areas.”
But because there isn’t any index on UHI effect and energy consumption in Kathmandu or any other urban area in Nepal, optimum heat management processes can not be undertaken easily.
Senior architect Bibhuti Man Singh opines that the total area of cities may be negligible but as centers for most industrial and anthropogenic activities with rapidly growing population, black topped roads, pavements and no greenery in sight, the cities tend to become heat sinks. As it gets hotter, cities resort to air conditioners or other such alternatives for comfort, which in turn consume more energy and increases heat level.
He further shares, “If buildings are designed properly in the first place, it can help regulate the building temperature to a great extent without much additional costs. This might sound negligible again considering the broader warming trend of an entire urban area but for the building itself, it’s quite substantial and consequently helps to budget the energy consumption as well.”
Green roofs in buildings he says are one of the best ways to counter the effects of UHI, unlike roofs with potted plants, green roofs are a vegetative layer grown on a rooftop, which provides shade and removes heat from the air through evapotranspiration. This reduces temperatures of the roof surface and the surrounding air.
“With just a layer of soil and vegetation growing in the rooftops, the building can be kept cool in the summer as the green roof absorbs heat and doesn’t allow it to enter the building, whereas for winters it also provides insulation,” he states. The architect suggests making maximum use of prevailing wind and natural lights while designing a building that can help lower the usage of energy and the cost.
Singh also stresses on the importance of rainwater evaporation for cooling. “With buildings everywhere, paved roads and lesser open land to retain rainwater, we’re letting it run off into the sewers and there is no evaporative cooling.”
The solutions according to Singh would be to build more parks and add greenery to the city; town planning could be more efficient and may be Kathmandu Metropolitan City (KMC) office can make it compulsory for every colossal building being built to have green roofs.
“If the builders or general people were aware and sensitive, they’d take the initiative,” says Singh. He echoes many of the officials adding, “To make things effective in Nepal, there has to be strong government regulations and equally strong enforcements.”
The feasibility, however, seems questionable as self centered, desirous urban cities aren’t keen on sparing any land for greenery and Kathmandu is no exception, it might even top the list.
The city has been defamed time and again as one of the most polluted places in the world, climbing steep hills in charts measuring environmental problems, health hazard risks, with haphazard settlements and a cripplingly disorganized system. And if the city plans to boil itself in the scorching heat together with rotting air; suffocating smog and diseased people the UHI effect will only speed up the process.
Moreover, with no initiative taken to study “the heat island effect” or getting a thermal-image map of Kathmandu to pin point the hot spots, going on about its impact, formulation of any kind of plans or its mitigation measures may almost seem like a shot in the dark.
It does seem as a better option rather than doing nothing, though.
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