The heat matters

The mercury is soaring across the country with several states facing heat-wave conditions. In its recent Seasonal Outlook Update, the India Meteorological Department (IMD) has warned of a warmer than normal temperatures in all meteorological sub-divisions of the country except sub-Himalayan West Bengal and Sikkim.

According to the IMD’s forecast, in the months of April, May and June, the average and minimum temperatures in the Delhi-Haryana region could be at least 1.5° Celsius above normal. For the north-west and central India, the mercury is likely to hover over a degree Celsius above normal.

The IMD has also alerted about a 47% probability of maximum temperature to be above normal in the core heat wave (HW) zone during April to June season. This HW zone covers states of Punjab, Himachal Pradesh, Uttarakhand, Delhi, Haryana, Rajasthan, Uttar Pradesh, Gujarat, Madhya Pradesh, Chhattisgarh, Bihar, Jharkhand, West Bengal, Orissa and Telangana, and meteorological sub-divisions of Marathwada, Vidarbha, Madhya Maharashtra and coastal Andhra Pradesh. Normal to above normal heat wave conditions are likely in the core HW zone during this summer season.

Human-induced change

A heat wave is a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season in the northwestern parts of India. Heat waves typically occur between March and June, and in some rare cases even extend till July. The extreme temperatures and resultant atmospheric conditions adversely affect people living in these regions as they cause physiological stress, sometimes resulting in death.

Heat waves are rising both globally and in India. Numerous studies have documented that human-induced climate change has increased the frequency and severity of heat waves. For instance, a statistical analysis of the Russian heat wave suggests there was an approximate 80% probability that the Russian heat record of July 2010 would not have occurred without climate warming. Further, globally, extremely warm nights that used to come once in 20 years now occur every 10 years.

A 2015 research study published in Regional Environmental Change has warned of intensification of the heat waves around the globe, with potential increase in heat stress and heat-induced mortality in the absence of adaptation measures. “India has a high current exposure to heat waves, and with limited adaptive capacity, impacts of increased heat waves might be quite severe,” reads the study. The authors warn of an increase in mortality due to intensification of heat wave and heat stress condition in India.

“Large regions of southern India, East and West coasts, which are presently unaffected by severe heat waves, are projected to be severely affected after 2070,” concludes the study. Another 2016 research paper, On the Variability and Increasing Trends of Heat Waves over India, says that heat waves have caused more deaths than any other natural hazard in the past in India. For instance, in May 2015, a severe heat wave affected parts of southeastern parts of India (Telangana and Andhra Pradesh) which claimed lives of more than 2,500 people.

Heat waves worsen in cities which are affected due to the urban heat island effect. An urban heat island is an urban area that is significantly warmer than its surrounding rural areas due to human activities. The temperature difference usually is larger at night than during the day. The main reason for the urban heat island effect is change in land use pattern due to urbanisation that replaces natural surfaces (vegetation and moisture-trapping soils) with built surfaces which absorb radiation and release it later as heat. 

According to the United States Environmental Protection Agency (USEPA), climate change will lead to higher temperatures and longer, more severe, and more frequent heat waves; and urban areas, which are already suffering from the heat island effect, will bear the brunt of these harsher heat events. Communities across the world are taking action to reduce urban heat islands, such as increasing tree and vegetation cover, installing green roofs, installing reflective roofs, using cool pavements, and utilising smart growth practices. These strategies can help communities become more resilient to the impacts of climate change.

Urban forests

Simply put, urban forest is a forest or a collection of trees that grows within a city, town or a suburb. In a wider sense, it may include any kind of woody plant vegetation growing in and around human settlements. It is well documented that vegetation has a key role to play in contributing to the overall temperature regulation of cities. Informed selection and strategic placement of trees and green infrastructure can reduce the urban heat islands, and cool the air by anywhere between 2° C and 8° C, reducing heat-related stress and premature human deaths during high-temperature events, claims the Forestry Commission of the UK. Researchers from the Arizona State University, USA found that air temperatures differed by 10° F among neighbourhoods in Phoenix, Arizona during summer afternoons, with a tree-lined neighbourhood much cooler than a barren area featuring high-density housing.

Trees in urban areas provide various ecosystem services that include biodiversity conservation, removal of atmospheric pollutants, noise reduction, mitigation of urban heat island effect, groundwater recharge, prevention of soil erosion, carbon sequestration and recreation. The World Health Organisation suggests an international minimum standard of availability of nine square metre (sq m) green open space per city dweller. However, most Indian cities score very low on this international standard. For instance, in Bengaluru (rural and urban together) the green cover is only 2.17 sq m per city dweller. Chennai is still lower at 1.92 sq m per resident. Per capita green cover in Mumbai is mere 0.635 sq m.

Urban Forestry Scheme is the new thrust area of the Indian government. Last June, the government took up a massive project of tree plantation drive across 200 cities in the country. With people’s participation, it plans to create several urban forests. But while the government promotes plantation of new trees, it must also ensure protection of the existing urban forest, canopies and trees. For instance, in Mumbai, citizens and activists are fighting to protect Aarey forest, where the authorities plan to set up Metro car shed. Similarly, residents of Bengaluru strongly protested against the Steel Flyover Project, which would have led to cutting down of over 800 trees. The project was recently scrapped. 

Various Indian cities are making efforts to create urban forests. Delhi is one such example whose per capita green space is 22 sq m. In Delhi, 7,784 hectare (ha) area of ridge land has been notified as forest. Another 850 ha abandoned and degraded Bhatti mines have been greened through plantations, and soil and water conservation works. Delhi’s forest department has also created over 40 city forests spread over 1,000 ha area.

In a matter of 10 years, Delhi’s green area has increased from 30 sq km to 300 sq km, informs an April 2011 paper published in the International Journal of Environmental Science and Development. Gandhi Nagar, Gujarat has per capita green cover of 30.27 sq m. Urban greenery is built into the city’s master plans. It has an urban forest called Punit Van spread over six ha land. Several such urban forests have been created in other cities of Gujarat.

Experts claim that while creating urban forests, the cities should also understand their own urban biodiversity, for instance, the native tree species and their benefits. City Biodiversity Index can be used for the same. It broadly includes three components – native biodiversity in the city; ecosystem services provided by the native species; governance and management of native biodiversity. In 2012, Hyderabad became the first Indian city to have a City Biodiversity Index which consists of 23 indicators.

Urban forests can be useful in mitigating climate change and in helping cities adapt to higher temperatures and other impacts of climate change. While the government creates new urban forests, it must safeguard the existing vegetation cover.