Urban growth leading to warmer cities

A recent study published in the journal Nature as a brief communication, as highlighted by a Mongabay-India report, finds that cities in India are experiencing warming at nearly twice the rate compared to the rest of the country. The study’s analysis shows that show that urbanization alone has led to an overall 60% enhancement in warming in Indian cities, with eastern Tier-II cities leading the way. Such a difference in the urban contribution to warming over cities across India calls for a differential approach to combat urban warming effectively.

Titled ‘Urbanization and regional climate change-linked warming of Indian cities’, the study says that urbanization is one of the most visible and irreversible human interventions modifying land use and land cover and is a key driver of socioeconomic change. Despite accounting for only ~1% of the land, cities house more than half of the world’s inhabitants. Global forecasts indicate that the urban population share will reach 68% by 20501. The ongoing unplanned and rapid urbanization has posed a substantial threat to the natural environment and caused a range of socioeconomic issues.

Urban areas are highly vulnerable to the compounding effects of both urbanization and climate change. Changed urban landscapes no longer benefit from evaporative cooling but accumulates heat leading to the well-known urban heat island effect, which subsequently affects other climate parameters (like rainfall, pollution, etc.). Urbanization and associated energy demands also lead to the production of greenhouse gases and emissions. Furthermore, due to the dense population and infrastructure of urban areas, they face climate-change impacts such as heatwaves, extreme weather events and flooding.

The study points out that Indian cities are increasingly central to such discussions. With a projected doubling of the urban population by 2050 (reaching over 800 million urbanites), India is expected to witness the largest urban growth globally1. In addition, India is also projected to be the fastest-growing major economy in the world, with the projected highest growth in energy demand by 2050. To support this scale of expansion, substantial infrastructure development will occur, further deteriorating the emission scenario and affecting the local and regional climate. India is the seventh most profoundly impacted nation by climate-related extreme weather phenomena, according to the Global Climate Risk Index 2021. Also, studies indicate that India will be one of the most vulnerable countries to the impact of climate change, with its cities at the forefront. Consequently, given the scale and scope of urbanization (both ongoing and projected) and exposure to climate-change-related risk, the synergistic effect of the two will make Indian cities particularly vulnerable.

Stating that cities are both the harbingers of future climate change, the study says that they are one of the critical global systems that can speed up climate action. Accordingly, for Indian cities, the timely consideration and strategic implementation of policies targeting climate resilience are imperative. Although national urban missions are already underway and primarily focus on social and economic upliftment while targeting pressing local development needs, comprehensive city-level climate-action plans are the need of the hour. To achieve this, more detailed studies on various facets of urbanization in India are needed to enable individual cities to develop tailored climate action plans to achieve the sustainable development goal of ‘making cities inclusive, safe, resilient and sustainable’.

As the MI report highlights, the study found that cities in India are warming at an average rate of 0.53°C per decade, with urbanisation contributing 0.2°C. It means, urban areas are experiencing 37.73% more warming (decadal trend), linked to urbanisation, relative to the surrounding non-urban areas, significantly contributing to the overall increase in temperature in cities. Researchers used satellite data to trace urban boundaries and used Nighttime Land Surface Temperature data from 2003 to 2020 to estimate the warming levels. They compared city temperatures with surrounding non-urban or rural areas, assuming that warming in rural areas is largely driven by regional climate change and warming in urban areas is caused both by regional climate change and local effects of urbanisation. This comparison helped the researchers understand the contribution of urbanisation to the overall warming in cities.

The researchers ranked 141 cities in the study based on warming attributed to climate change (regional effect) and urbanisation (local effect). The cities were selected based on population exceeding one million, as per 2011 census, and that experience the highest impact of urbanisation-driven warming. The top ten cities, ranked based on the increase caused by urbanisation, include Pune, Raipur, Jaipur, Ahmedabad, Patna, Nashik, Ludhiana, Lucknow, Bengaluru and Vadodara.