by Sagarika Bhatta
On hot days, roof and pavements of urban areas can be (27-50 degree Celsius) hotter than air while surface temperatures in most rural areas remains close to the air temperature. As a result, surface temperatures in the summer can go as high as 12 degree Celsius warmer than the air temperature. This is as a result of Urban Heat Island. Urban Heat Island can cause increases in energy consumption during summer and in consequence, increase in emissions and pollution.
People living in Kathmandu experience changes in settlement, land use, constructions and population growth. According to census, the total population of Kathmandu in 1981 was 422,237. After 30 years, census the total population of Kathmandu city has increased to 1,744,240. The number of households has reached 436,344 within an area of 49.45 km square. This has led to an unplanned rapid urbanized city with no green and open space.
“Unmanaged construction, overly used old vehicles, drastic change in land use, rapid growth in population and urbanization are key reason to Urban Heat Island. I think the concrete (waste) from Earthquake and climate change is adding to the existing choas.” Says Prem Bahadur Bohara, CEO at Climate Alliance of Himalayan Communities.
Temperature in Kathmandu valley has risen from 30C in 2005 to 31C in 2012 to 35C in 2015. In addition, research carried out by “Causes and Consequences of Urban Growth and Sprawl” mentions positive correlation between land surface temperature and impervious surface and clearly indicates temperature increase in the sprawled area. The heat island effect is caused by two factors. First, dark surfaces such as roadways and rooftops efficiently absorb heat from sunlight and reradiate it as thermal infrared radiation. Second, urban areas are relatively devoid of vegetation, especially trees; that would provide shade and cool the air through evapotranspiration.
Urban heat island is created by improper land-use patterns, while global warming has been accelerating the effects. It is a well-known fact that climate change presents challenges in cities like Kathmandu. Climate change and heat island effect impact with each other in two ways. Climate change increases the heat in urban areas while cooling mechanisms help in adapting to the impacts of climate change.
Warmer days are rapidly increasing and experienced in cities like Kathmandu. A city with more green areas, open space, less concrete constructions over land, proper waste management, standard air quality could help in combating climate change and lessening urban heat island effect.
“Proper environmental policy to manage old vehicle, road management and make standards to vehicles, managed construction and green parks in valley are key to the impacts faced. “, says Bohara.
One of the best way to combat the effects can be roof top gardening in congested unplanned urbanized city like Kathmandu. Some other solutions can be increasing vegetative cover, installing cool—mainly reflective—roofs, using cool pavements (either reflective or permeable), and utilizing smart growth practices.
Climate Change Officer at Practical Action, South Asia regional office, Krity Shrestha adds, “ promoting urban greenery, use of gravity water fountains, use of ponds etc can be a solution to lessen the impacts due to urban heat island and climate change as well.”