Chennai, Tiruvallur record rise in Urban Heat Island intensity by nearly 3° Celsius

CHENNAI: The rapid pace of urbanisation and the resultant reduction in green cover in Chennai have led to a rise in Urban Heat Island (UHI) intensity by nearly three degrees Celsius in Chennai and Tiruvallur, revealed a study on "Urban Heat Island – Hotspot Analysis and Mitigation Strategies for Tamil Nadu 2024" done by the State Planning Commission.

Urban Heat Island effect is the situation where urban areas remain warmer than the surrounding areas due to the concentration of buildings, roads, and other infrastructure. This is largely due to the transformation of natural ground cover into built surfaces like asphalt, concrete, and buildings.

The report noted a trend of increasing night-time temperatures in Tamil Nadu with a 59 per cent rise in areas experiencing night temperatures of 24 – 26 degrees Celsius. The pattern showed that dense urban areas, particularly Chennai, retain heat overnight, intensifying UHI effect. However, extreme daytime temperatures (46 – 50 degrees Celsius) have decreased by 28 per cent over the past 20 years.

While Thoothukudi recorded the highest daytime temperature in the state, Chennai was affected by increased night-time heat. A temporal analysis for 2013-23 period using landscape indices such as vegetation, built up and water showed that urban expansion heightened UHI effects in Thoothukudi, Chennai, and Madurai, where reduced green spaces and increased construction have raised night-time temperatures.

The projections for air temperature in Tamil Nadu up to 2095 based on representative concentration pathway (RCP) indicated an increase in both minimum and maximum temperatures: 1.3 degree Celsius and 1.4 degree Celsius, respectively, by 2040; 2 degrees Celsius by 2070; and 2.2 degrees Celsius by 2095.

The UHI intensity was determined to understand the impact of climate change and urbanisation on the temperature patterns. Chennai exhibited UHI intensity of about 2.5°C, while other districts like Madurai, Tiruvallur, Chengalpattu, Erode, and Salem recorded values around 2°C.

The intensity increased in 2023, with Chennai, Tiruvallur, and Ramanathapuram reaching values close to 3°C, and districts like Madurai, Thoothukudi, and Virudhunagar recording intensities around 2.5°C.

Planning Commission moots several measures to tackle heat island effect

To mitigate the Urban Heat Island effect, the State Planning Commission report has recommended increasing the urban green cover through forestry and green corridors, adopting cool pavements and reflecting material, and restoring natural heatsinks like waterbodies.

At the building level, it advised adopting climate-sensitive designs and using green roofs and energy-efficient materials.

The commission recommended increasing cooling measures for both indoor and outdoor locations, particularly in high-risk areas, to reduce the incidence of heat-related illnesses and adapt work schedules and provide access to shaded and air-conditioned rest areas with drinking water and rehydration solutions for outdoor and high-exposure workers to mitigate occupational heat stress.

Also, it also advised strengthening healthcare access for both preventive and curative care, with a focus on heat-related health services in urban and rural areas experiencing high temperatures.

Additionally, the commission has recommended the use of multi-dimensional analysis to map heat-vulnerable clusters, factoring in occupational, demographic, and socioeconomic variables to prioritise support in high-risk areas.

Among other recommendations are identifying specific physical and mental health issues linked to heat exposure in different population groups; using thresholds like wet bulb temperature to inform targeted interventions; enhancing monitoring of animal movement and establishing communication strategies to reduce human-wildlife conflict, especially in areas experiencing extreme heat; and conserving wildlife habitats and ensuring essential resources within forest areas to reduce the migration of animals into human settlements, especially during peak heat periods.

RISING RISK:

-- 9 out of 38 districts in Tamil Nadu face risk of drought, 10 are prone to flooding, and 17 are susceptible to heatwaves, and about 11% of the forested area at risk of fire

-- Between 2011 and 2021, Tamil Nadu averaged more than 8 heatwave days annually, and 12 heat-related deaths were reported by June 2023 alone

-- In urbanised regions, the UHI effect intensifies warming trends, with cities like Chennai, Coimbatore, and Madurai experiencing average night-time land surface temperatures of approximately 26°C

-- Since 1981, average maximum summer temperature has risen by 1.5°C, with recent records showing an average summer high of 35.5°C. This increase affects 50% of the State's population, while around 15% experience a surge of 2°C in districts like Tiruchy, Tiruvannamalai, and Vellore. Minimum temperatures have also risen, with an increase of 0.75°C across the State, indicating warmer nights that intensify discomfort and health risks

-- Research by Anna University’s Centre for Climate Change and Disaster Management forecasts a rise in "thermal discomfort" days, expected to grow from 107 days annually (observed between 1985 and 2014) to 150 days per year by 2050