Urban Growth Fuels Warming In Indian Cities

Cities in India are experiencing warming at nearly twice the rate compared to the rest of the country, according to a recent study.

The study, published in the journal Nature as a brief communication, said climate change is warming the entire region, but the warming rate in most cities is significantly higher than the regional average. The study researchers referred to it as “urbanisation-driven warming”.

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 (NLST) 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 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.

In cities such as Jamshedpur, Raipur, Patna, Indore, Bhilai, Aurangabad, Pune, Dhanbad, Ludhiana and Vadodara, urbanisation contributed more than 50% to overall warming. In particular, urbanisation contributed to 100% of the warming in Jamshedpur.

“The urban contribution is seen to be higher in cities in the eastern and central Indian regions,” the paper said, referring to the amount of temperature increase specifically due to the city’s development and growth or urbanisation.

Explaining the probable reason for this, associate professor of climate science at Indian Institute of Technology (IIT) Bhubaneswar and one of the authors of the study, V. Vinoj said, “This may be due to multiple reasons. One possible explanation could be that these (eastern and central Indian) cities have gained momentum in urban growth in recent years, and hence, the rate of growth at which heat is trapped within these cities is higher than the older cities that are already large, and hence, the rate of growth is smaller. Another possibility is that the regional climate change may be warming at a rate that is lower over these regions.” He emphasised the need for detailed research to explore the actual reason.

Accelerated urbanisation and the risk

Urban areas face significant risks from urbanisation and climate change combined. As cities expand, their altered landscapes lose the cooling effects of evaporation and accumulate heat, leading to the well-known urban heat island (UHI) effect. This phenomenon not only raises temperatures but also impacts other climate factors such as rainfall and pollution levels, the study explained.

The study predicted a substantial increase in infrastructure development due to the projected doubling of the urban population by 2050, alongside economic growth. Extensive infrastructure development is necessary to support this growth, which impacts the emissions scenario which in turn, affects the local and regional climate and environment.

Vinoj said that in recent times, there is a tendency to attribute most changes, especially related to the environment, solely to global warming or climate change. However, the rapid growth of cities is also an important factor contributing to increasing warming. The warming due to local factors such as urbanisation may be mitigated to avoid extremes (here, related to heat).

“Policy makers need actionable information that could be used to allocate the limited financial and other resources to deal with environmental issues,” he said, while highlighting the purpose of the study.

The study pointed out that existing schemes and missions for urban development focus mainly on social and economic development. However, the current scenario of cities calls for city-level climate action plans to address future climate-related challenges. These plans must tackle the specific challenges of each city to achieve the sustainable development goal of creating inclusive, safe, resilient, and sustainable cities.

Reimagining urban development

The study’s findings underline the need for better urban planning, which can help cities minimise the impact of urbanisation on warming. Local-level urban planning can effectively reduce urbanisation-influenced warming, especially in developing cities, though it may not counter climate change-driven warming.

Vinoj explained that urban planning done at a local scale could efficiently address the warming primarily influenced by local urbanisation. In cities where this urban-led warming is higher, city-scale heat mitigation efforts (designing the structure of the city, local emission reduction, energy transitions, incorporation of blue-green infrastructure) will have noticeable results. The mitigation effort in these developing cities will slow down or reverse the urban temperature trend. However, this may not work for cities that are primarily affected by warming related to climate change.

The paper noted that cities where urbanisation has a higher contribution to increased temperature are mostly developing cities. These are cities that haven’t exhausted their natural resources, such as land and have more scope to rethink, redesign, and steer the future path for the city’s growth in a sustainable way, Vinoj said. The paper added that sustainable city planning and adaptation strategies can be more readily implemented in these cities. For example, these cities can be planned to have water bodies, parks, and preserved natural landscapes at suitable locations inside the city to provide thermal comfort, said Vinoj.

The report also underscores the challenge faced by already developed cities (such as Delhi to Hyderabad) noting that these urban centres have depleted their available resources, such as land use. Consequently, they have limited room for city planning without significantly restructuring the existing infrastructure. “Hence, the city action plan for sustainability has to follow a different approach for developed and developing cities,” the paper suggested.

While talking to Mongabay India, Subimal Ghosh, a professor at IIT Mumbai, praised the study and emphasised the urgent need for solutions. Urbanisation and global warming are deadly combinations, he says.

Ghosh said that the time has come for climate scientists and urban planners to collaborate and rethink cities. When it comes to the solution, there are several ways to move forward. One is urban planning, where scientists and planners can explore several models based on available resources. The second is the improved decision-support system. For example, when heavy rainfall or a cyclone is forecast, people are told not to go out. Similarly, heat-related emergencies also need forecasts and warnings, he added.

(Published under Creative Commons under Mongabay-India. Read the original article here)