The difference in air temperature, first discovered by Howard in the 19th century, was termed 'Urban Heat Island' (UHI) by Manley in 1958 whilst his discovery of snowfall patterns between rural and urban areas. Simply put, UHI occurs when cities experience higher temperatures compared to their rural surroundings due to human activities and concentrated infrastructure. Moreover, factors such as dense construction, insulating building materials, and the release of waste heat from vehicles and industry contribute to the formation of UHIs. These areas often suffer from elevated nighttime temperatures as heat becomes trapped by buildings and impervious surfaces. This condition can worsen air and water quality, posing health risks and ecological stress.
Kathmandu Valley (KV) has been experiencing this phenomenon given the temperature rise to 34.4°C on June 10, 2024. The rise in temperature across the country has soared sharply, hampering the lives of people in Terai district. In addition, increased demand for cooling systems has led to brown outs that have been frequent due to poor quality or low voltages. In order to mitigate UHI effects, strategies like green roofs and lighter-colored building materials are used to reduce heat absorption and enhance urban cooling. Addressing UHI challenges requires collaborative efforts from city dwellers, architects, and designers to create more sustainable and resilient urban environments.
Prior research has thoroughly investigated Land Surface Temperature (LST) is an important parameter in the UHI phenomenon (Bajracharya, 2018). First, it is one of the key indicators of surface physical properties and climate. Second, it is sensitive to factors like vegetation and soil moisture, enabling detection of land use/land cover changes such as urbanization and desertification. Lastly, it is valuable for estimating radiation budgets in heat balance studies and as a control for climate models. According to Aryal et al, (2021) Kathmandu, Bhaktapur and Lalitpur administrative units have higher average LST (ranging from 22.1 to 36.9°C in the month of March and June respectively) compared to other administrative units. The average LST was higher in June. LST portrays 2015 as the hottest year during the study period. Also, spatial and temporal evaluation of LST in KV suggests increasing the greener space in the urban areas to minimize surface temperature (Aryal et al.,2021).
According to Mishra et al. (2019) study on UHI in Kathmandu shows a temperature difference of 5°C between forest land and developed land on average in Kathmandu valley. Furthermore, an annual increase of 0-2°C is also noticed in 18 years. Consequently, the valley has also seen a change in weather patterns.
The rise and tremendous growth of population and urbanization has raised the surface temperature globally. The anticipation of the Intergovernmental Negotiating Committee (INC) provides a platform for countries to collectively negotiate agreements to mitigate greenhouse gas emissions, adapt to the impacts of climate change, and stimulate international cooperation on climate-related issues. Governments, scientists, experts, and stakeholders from various sectors are involved and the INC contributes to shaping international climate policy and initiates collaboration.
In Nepal, the Urban Heat Island (UHI) effect has various impacts, presenting opportunities for improvement in the following areas:
Public Health Enhancement: Implementing strategies to address elevated temperatures can help mitigate heat-related illnesses and stress, particularly among vulnerable populations.
Energy Efficiency: Exploring innovative solutions to reduce energy consumption and costs related to increased demand for cooling systems in warmer urban environments can lead to improved energy efficiency.
Water Management and Resilience: Developing better urban water management strategies to mitigate the effects of warmer urban environments on local hydrology and reduce urban flooding risks.
Economic and Social Innovation: Exploring alternative work arrangements and technological solutions to enhance productivity during hot weather can benefit outdoor workers and seasonal businesses. Implementing effective mitigation and adaptation measures is crucial for mitigating the UHI effect and enhancing urban resilience in Nepal. Through Green Infrastructure involving green roofs, parks, and urban forests Nepal can mitigate heat absorption, improve air quality, and enhance urban aesthetics. Consequently, implementing cool roofs, reflective pavements, and energy-efficient building codes can significantly reduce heat retention in urban structures. Sustainable transportation modes and promoting the use of renewable energy sources can play a vital role in reducing emissions and anthropogenic heat. Furthermore, it is imperative to raise awareness on heat-related risks, educating residents on adaptive behaviors, and involving communities in urban planning processes as essential steps in building a climate-resilient urban environment.
Reflecting on Bajracharya (2018) research stated that the Kathmandu valley has a land surface temperature (LST) distribution ranging from 13°C to 34.9°C, with an average of 21.77°C. Additionally, settlements and open spaces exhibit the highest LST, while forests have the lowest. Hence, Nepal must decisively confront the urban heat island effect by embracing sustainable urban development, leveraging innovative technologies, and fostering community resilience. Proactive measures to address rising urban temperatures are essential to create a healthier and more livable environment for all residents. Collaboration across sectors is imperative to build climate-resilient cities capable of thriving in a changing climate landscape.
References:
Aryal, A., Shakya, B. M., Maharjan, M., and Talchabhadel, R. (2021) Evaluation of the Land Surface Temperature using Satellite Images in Kathmandu Valley, Nepal Journal of Civil Engineering, Vol 1, No.1, pp 1-10.
Bajracharya, P. (2018) Estimation of Land Surface Temperature on Land Cover in Kathmandu Valley, Tribhuwan University, Research Gate.
Mishra, B, Sandifer, J. and Gyawali, B.R. (2019) Urban heat island in Kathmandu: Evaluating relationship between ndvi and lst from 2000 to 2018. International Journal of Environment, Vol 8. No. 1, pp.17–29.
