Kolkata, 7th May 2024: The month of April witnessed an unprecedented phenomenon: a relentless heatwave that shattered records and wreaked havoc across Kolkata. In the recent years, there has been a noticeable shift towards a drier summer with loo-like conditions more commonly associated with western India. This unprecedented summer and its consequences are proving unbearable for the region. SwitchON Foundation has showcased the temperature trends, elucidated the underlying factors driving the prolonged heatwave, and has also put forth the forecast for the upcoming days.

April 24 Temperature Saga

Source: Regional Meteorological Centre Kolkata Media (A Public Whatsapp Channel of RMC Kolkata)  https://whatsapp.com/channel/0029VaD6VGS3QxS9vKh3e13C 

Retrieved on: 1st May 2024

As per IMD Data, 

• On the last day of the month, Kolkata experienced the highest-ever temperature (43°C) in the past five decades. This temperature was more than 7.4°C than the normal temperature, which denoted a severe heat wave condition in the city. 
• The lowest minimum temperature this month was 24.7°C, which was also +0.9°C deviation from normal, which was recorded on 12th April. 
• For the 9 days in April, the mercury of Alipur crossed the 40°C mark this year.

Concerning Temperature Trends between 2019 and 2024

The SwitchON Foundation’s previous study emphasised that respondents unanimously expressed growing discomfort due to the increasing severity of heat waves over the years. A similar trend is evident from the temperature dataset acquired from weatherspark.com on the first of May 2024. 

Data Source: www.weatherspark.com 

• The maximum temperature has increased by 6℃ from 2019 to 2024 for April in Kolkata. 
• Kolkata’s minimum temperature has also increased by 5℃ from 2019 to 2024 during April.
• Frequent rise and drop of temperature was noticed in 2019 than in 2024
• The temperature graph is noticed to start at a higher mercury level and also end at the same course. 
• The higher temperatures are noticed to be experienced in the final days of April in both years. Similarity prevails only in this course between 2019 and 2024.

An increasing number of hot days in April 

Data Source: www.weatherspark.com 

• In 2024, 90% of days have experienced higher maximum temperatures than in 2019 in the month of April. 

• Only 7% of days were with lesser maximum temperatures than in 2019
• Only 6% of days during April 2024, was the minimum temperature lesser than in 2019
• Whereas 93% of days experienced higher minimum temperatures this year than in 2019 during April in Kolkata.

Average Maximum temperature in April

Data Source: www.weatherspark.com 

• April, being the summer month in Bengal, has experienced upward growth in the average maximum temperature over the years, from 35℃ in 2019 to 38℃ in 2024. 
• Simultaneously, tthe daily average maximum temperature in April has gradually increased from 30℃ in 2019 to 33℃ in 2024 
• April is becoming a vulnerable month year by year.

Reasons

• Absence of Trigger Mechanisms: The lack of systems capable of initiating thundershowers has contributed significantly to the parched conditions. Without triggers such as cyclonic circulations or trough lines, which typically indicate rain, the city is experiencing a dearth of precipitation.
• Insufficient Moisture Incursion: Typically, nor’westers in Kolkata during April and May are fueled by abundant moisture incursion from the Bay of Bengal. However, this year, moisture levels at lower levels are notably low due to prevailing dry westerly-to-northwesterly winds, hindering the formation of thunderclouds.
• Limited Heating and Convection: While heating and convection are vital for pushing moisture into the upper atmosphere to form thunderclouds, these processes are not occurring as robustly as expected. This limited atmospheric instability further hampers the development of thundershowers.
• Below-Average Rainfall: The observed rainfall in April falls significantly below the mean total, with only one recorded rainy day and minimal precipitation compared to the historical average. The absence of squalls further underscores the anomalously dry conditions experienced in the city this April. In 2024 April, Kolkata received rainfall solely on April 7, with a meagre 0.5 mm recorded by the Alipore Met Office. In contrast, April 2023 witnessed rain on four occasions, accumulating to 50 mm. Notably, three of these rainy days occurred towards the end of the month of 2023.
• Man-made reasons: Research shows that studies conducted by the universities across Bengal have shown that the annual mean land surface temperature of Kolkata has increased by 4.72℃ in the last thirty years due to the loss of vegetation in the city and subsequent increased built-up spaces, which finally led to urban heat island effect in the city.

Forecasts

According to IMD data spanning from May 2011 to 2022, the highest temperature of 41.5℃ was documented in 2014.

Source: www.internal.imd.gov.in/pages/city_weather_main_mausam.php 

Retrieved on: 6th May 2023

• After a prolonged heatwave days Kolkata is going to experience a sigh of relief this week between 6th to 12th May. As per IMD, Kolkata is going to face thunderstorms with heavy to light rain and cloudy sky all week long
• Maximum temperature will range between 36℃ to 33℃
• Minimum temperature will range between 28℃ to 25℃
• A detailed weather forecast for May can be seen from the Weather Channel monthly weather forecast

Source: www.weather.com

Conclusion 

In conclusion, Kolkata’s recent temperature saga underscores the urgent need for proactive measures to mitigate the adverse effects of escalating heat waves, particularly on vulnerable communities. The unprecedented rise in temperatures, coupled with inadequate infrastructure and urbanization, amplifies the suffering of marginalized populations, especially during night-time. As voices from the slums resonate with calls for relief and support, stakeholders must heed their pleas and implement strategies that prioritize both short-term relief and long-term resilience. Only through concerted action and compassion can Kolkata hope to navigate the challenges posed by climate change and ensure a more equitable and sustainable future for all.

Please note that both datasets (IMD and weatherspark.com) were analyzed separately, without direct comparison between them.

Media Dossier

Online Articles: The Indian Express | Ei Samay

For more information please contact Gargi Maitra (8336919233)