Bhubaneswar and Cuttack experience cooler days, warmer nights

Subject :Geography

Section: Physical (Climatology)

Context:

A recent study by researchers from the School of Earth Ocean and Climate Sciences at IIT Bhubaneswar has found that increased urbanisation of Bhubaneswar and Cuttack has led to increased land surface temperature in the last 20 years (2001-2020).

Details:

While there has been an increase in relatively cooler regions over Bhubaneswar and Cuttack during the daytime, the reverse is seen during nighttime.
However, during the night, both cities have been witnessing increased urban heat island effects.
- There has been a clear increase in nighttime temperature leading to 0.75 degree C surface urban heat island intensity (SUHI) during the night in Bhubaneswar and 1.22 degree C increase in SUHI for Cuttack.
As a result, there has been a reduced daytime and nighttime temperature difference.

Study findings:

The urban areas of Bhubaneswar and Cuttack are about 0.75 degree C and 1.22 degree C warmer than the surrounding rural areas, respectively.
Overall, the daytime land surface temperature for Bhubaneswar and Cuttack was over 32 degrees C.
The increase in relatively cooler regions during the daytime has been from 27% and 40% (2001-2010) to 73% and 63% (2011-2020) in Bhubaneswar and Cuttack, respectively.
- This can be attributed to an almost 2.7 and 1.6 times increase in the cooler fractional land cover during the daytime in Bhubaneswar and Cuttack, respectively.
Bhubaneswar and Cuttack are not the only cities that witnessed a drop in daytime land surface temperature.
Reason for deviation in the daytime and nighttime temperature:
- It is not clear why there is a decline in daytime land surface temperature.
- They may be due to an increase in clouds, increased air pollution/haziness, increased vegetation or any other things.
- The warming during nighttime is only affected by heat emitted by the surface.
- Urban areas due to their ability to trap heat emit them slowly leading to a warming pattern above cities.
- The unique geographic location of Cuttack, surrounded by rivers which dries up during pre-monsoon and winter months, exposes the sand beds (creating a desert city-like condition) leading to this phenomenon with more warming in the surrounding regions.

Urban Heat Island Effect (UHI):

Urban heat islands (UHI) occur when cities replace the natural land cover with dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat.
This effect increases energy costs associated with cooling and air-conditioning, air pollution levels, and heat-related illness and mortality.