New analysis by Centre for Science and Environment (CSE) finds big increase in heat index (heat and humidity levels combined) during monsoon
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New Delhi, September 8, 2025: A sharp increase in heat and humidity levels this summer has led to a significant jump in electricity consumption by Delhi and its people, finds a newanalysis by Centre for Science and Environment (CSE).
Even though the summer of 2025 experienced lesser heat waves and was relatively cooler than that of 2024, it was a lot ‘wetter’ due to intense rain. In the pre-monsoon months of March to May, the capital witnessed a moderate heat index range of 31-32oC – the electricity demand remained stable during these months. With the onset of monsoons (June-August), the range jumped up to 46-50oC. Humidity-driven discomfort levels were very high, leading to increased cooling demand and more electricity consumption. “As much as 67 per cent of the daily peak electricity demand in Delhi can be explained by variations in heat index compounded by the lowering of adaptive comfort and changing lifestyles,which is increasing the city’s dependence on mechanical cooling systems,” finds the analysis.
Says Anumita Roychowdhury, executive director-research and advocacy, CSE: “Our study shows how an increase in peak electricity demand is now happening earlier and persisting longer. But Delhi’s deadly dilemma is not only the high heat during the pre-monsoon months, but also the high humidity during monsoon months causing sharp increase in heat index (combination of heat and humidity). This is when the heat index goes beyond the threshold of thermal comfort to surge sharply as cooling devices are switched on across the city. This leads to sharper rise in electricity consumption, which strains grid reliability. Delhi has hit the second highest peak demand for electricity after 2024 summer.”
Roychowdhury adds: “Moreover, warmer nights due to inadequate dissipation of heat accumulated during the dayare causing prolonged heat exposure, increasing public health risks. This needs urgent action. It is imperative to address growing concretisation, inadequate urban greens and waterbodies, lack of thermal comfort in buildings, inadequate cooling shelters, and waste heat from air conditioners and vehicles. These are making our cities hotter, while climate change is making temperature and humidity trends more erratic.”
According to Sharanjeet Kaur, deputy programme manager, urban lab, CSE, “during the monsoon months in 2025, the daytime and nighttime land surface temperatures (LSTs) have risen by about 2.1°C and 3.0°C respectively compared to 2024,while the day-night cooling difference has narrowed down -- thus reducing the cooling window. This is adding to the heat distress. Notably, April 2025 registered higher electricity consumption than April 2024, reflecting a much warmer start to the summer this year.”
Kaur say this new assessment is a continuum of CSE’s earlier analyses in 2018, 2019 and 2020,which had also highlighted the impact of heat stress on electricity demand in the city.
Data and methodology
The study is based on comparative statistical analysis of air temperature, electricity demand, land surface temperature, heat index and humidity condition observed in Delhi from 2021 to 2025. The study’s definition of summer is the period from March to August. It is furthered divided into pre-monsoon (March-May) and monsoon (June-August) as per IMD classification. This is based on publicly available datasets from various national and global agencies.
Time frame of the study: January 1,2021 to August 25,2025. This integrates multiple datasets -- real-time electricity demand, weather observations, land surface temperature, and computed heat index to provide an evidence-based understanding of how Delhi’s power consumption has evolved under intensifying heat stress.
Real time electricity consumption data of 5-minute granularity has been sourced from the State Load Dispatch Center, Delhi. Historical data has been sourced from the Annual Power Supply and Load Generation Balance Reports of the Central Electricity Authority.The weather data including air temperature and relative humidity has been sourced from the CPCB’s CAAQMS network. After careful assessment of quality of available weather data from these stations, 24 stations that have the most consistent data starting from January 2021, were selected and considered. These stations include Alipur, AnandVihar, Ashok Vihar, Bawana, DrKarni Singh Shooting range, Dwarka Sector 8, Jahangirpuri, JLN Stadium, MDC National Stadium, Mandir Marg, Mundka, Najafgarh, Narela, Nehru Nagar, Okhla Phase 2, Patparganj, Punjabi Bagh, Pusa DPCC, RK Puram, Rohini, Sonia Vihar, Sri Aurobindo Marg, VivekVihar and Wazirpur.
These stations are geographically well distributed across in Delhi and cover rural, urban, residential, commercial, and industrial areas within Delhi. Mean of the observations form these stations has been considered representative of weather conditions in Delhi.Freely available MODIS Land Surface Science data from NASA Earth Observations has been used to capture seasonal variations in land surface temperature. Heat index has been used instead of absolute air temperature as a measure of external thermal conditions. Heat index has been computed using formula given the United States National Oceanic and Atmospheric Administration (NOAA) in their National Weather Service Technical Attachment (SR 90-23).
Key findings
Heat stress increases electricity demandfor cooling requirements during summer Summer temperature regime, relative humidity, heat waves and growing heat stress lead to significant increase in cooling demand that impacts electricity demand.During the summer of 2025,power needs jumped by nearly 40 per cent between March and April alone. Peak demand rose by 567 MW (+10.4 per cent), reflecting higher cooling requirements during the warmer-than-usual start to summer.
Energy consumption follows a similar pattern, climbing from about 2,200-2,300 MU in March to well over 4,500 MU in June.
March 2025 recorded a moderate growth of 4.6 per cent in overall energy use compared to March 2024, yet peak power dipped slightly. In August 2025, peak demand rose to 7,050 MW (recorded on 8 August) -- about 2 per cent higher than the previous year.In 2024, the city saw its highest-ever peak of 8,656 MW. Even with wetter conditions in 2025, the June peak still crossed 8,400 MW, showing that early summer cooling needs are now deeply entrenched. In August 2024, peak demand touched 6,890 MW.
Pre-monsoon vs monsoon effect: Worsening of heat index during monsoon
This summer has also demonstrated that relative humidity worsens heat stress,impacting electricity demand. This is reflected in the heat index that determines how it feels like to the human body when relative humidity is combined with the air temperature. It is the “feels-like” temperature which is an important consideration for the human body's comfort.An analysis of heat index from the last five years (2021-2025) shows the impact of this on the city’s power consumption.
During monsoon, high humidity drastically elevates the heat index even when air temperatures are lower. In July and August, Delhi often records heat index values above 46-50°C, creating conditions that are stifling and oppressive. The city’s demand patterns confirm this: electricity consumption remains high well into the monsoon, reflecting how humidity-driven discomfort continues to drive demand. Statistical analysis shows that about 67 per cent of daily peak electricity demand in Delhi can be explained by variations in heat index, while the rest depends on socio-economic and behavioral factors.
This clearly brings out that the power consumption remains steady, as long as the daily heat index remains in the 31-32°C range. During the pre-monsoon period, when humidity levels are moderate, electricity demand begins to climb steeply once the heat index crosses this range. This represents the broad tolerance threshold beyond which residents turn to cooling devices. This is what is largely noticed during the pre-monsoon months (March-May), when Delhi’s heat index generally stays below 40°C.Even though the cooling demand increases during this range, it is not to the extent that is noticed once the heat index crosses the 31-32°C sweet spot.
With the arrival of the monsoon (June-August), high relative humidity pushes the heat index up to 46-50°C even when actual air temperatures are lower. This makes the weather feel much more oppressive and drives a sharper surge in electricity consumption as cooling systems work harder and longer. This explains why demand remains elevated in monsoon months despite rainfall and cloud cover -- the combined effect of heat and humidity keeps the city energy-hungry.
The analysis of August peak demand shows how the city’s electricity stress is no longer confined to May-June alone, but is now spilling deeper into the monsoon months. In August 2025, the average peak demand was about 2 per cent higher compared to August 2024, despite wetter conditions this year. Nearly half of the days in August 2025 (16 out of 31) recorded higher peak demand than the same days in 2024.
The pattern of the demand curve also shows a clear shift. In 2024, it moved within a relatively narrower band, with one clear high point on 22 August (6,890 MW). In contrast, 2025 shows a much more pronounced and sustained upward movement, peaking early on 8 August (7,050 MW) and maintaining higher values across multiple days.
The 2025 curve is less stable and more elevated, reflecting how humidity-driven discomfort during monsoon has extended the duration and intensity of high electricity use. August is increasingly behaving like a peak summer month, with rising demand loads that stretch the grid beyond its traditional summer stress period.
The city’s peak power demand closely mirrors daily weather patterns. The study found that daily peak demand has a strong correlation (0.82) with the heat index. In other words, when the weather feels hotter and more humid, power demand rises almost in lockstep.
A statistical analysis further shows that 67 per cent of the variation in Delhi’s daily peak electricity demand can be explained by how hot and humid it feels outside. The remaining share (about one-third) is influenced by other factors such as economic activity, time of day, or household appliance use.
Warmer nights -- weakening of night-time cooling in the city
This analysis once again confirms that the nights are getting warmer and losing its natural cooling efficiency. The much-needed night-time relief is steadily reducing, especially during the pre-monsoon and monsoon seasons. Despite abundant rainfall this year, cities continue to struggle to cool down at night.
During the pre-monsoon months of March to May, the city once experienced a significant drop of nearly 15°C from day to night, based on the average between 2001 and 2010. In 2025.However, this decline has reduced sharply to just 8.6°C, making a 42 per cent loss in cooling. Night-time land surface temperatures in this period now average 22.8°C, which is higher than the long-term baseline of 20.4°C.
Notably, the 2025 demand peak occurred at night (11:09 PM), a departure from the usual afternoon surges seen in most years. Cooling demand at night is shifting the peak pattern.
During the monsoon season, between June and August, the average night-time cooling of 9.6°C that was observed in the earlier decade, has dropped to only 5.6°C in 2025, again, a 42 per cent decline. Night-time temperatures during this period have touched 30.6°C, which is nearly 6°C warmer than the baseline average of 2001-2010.
Land surface temperature and loss of night-time cooling
Another critical aspect is land surface temperature (LST). During the monsoon months the daytime and nighttime LSTs have risen in 2025 compared to 2024 by about 2.1°C and 3.0°C, respectively. On the other hand, both daytime and nighttime LSTs show a slight decline compared to 2024. But the gap between day and night temperatures has narrowed further by 1.8°C this year. This means that although the city is slightly cooler overall, it is also losing its natural ability to release heat effectively at night.
At the same time, the day-night cooling difference has narrowed by another 0.9°C, pointing to a dual challenge of hotter days as well as warmer nights, with an increasingly reduced cooling window. Between 2001 and 2010, land surface temperatures dropped by nearly 15°C between day and night during pre-monsoon months. By 2025, however, this drop has reduced to just 8.6°C, a 42 per cent decline in nocturnal cooling capacity.
The monsoon shows an equally alarming trend. Between June and August, the historical average night-time cooling of 9.6°C has shrunk to 5.6°C. In 2025, Delhi registered a night-time LST as high as 30.6°C, almost 6°C warmer than the 2001–2010 baseline. Despite abundant rainfall this year, the city is failing to cool at night, intensifying the urban heat island effect.
This weakening of night cooling has severe implications. Scientific studies have shown that rising night-time temperatures are among the most dangerous aspects of climate change because they prevent the human body from recovering from daytime heat stress. In Delhi, this is reflected not only in health risks: dehydration, exhaustion, heat strokes but also in energy use. In 2025, for example, Delhi witnessed an unusual late-night peak demand at 11:09 PM due to cooling demand.
Summer vs winter: Electricity demand shows extreme seasonal swings, with April 2025 setting an early summer surge
Delhi’s electricity consumption continues to reflect a highly seasonal trend, with sharp peaks during the scorching summer months and significant dips through the winter season. Between April 2024 and July 2025, the city’s peak demand touched an all-time high of 8,656 MW in June 2024, with energy consumption peaking at 4,546 MU in the same month.
In contrast, the winter period of November 2024 to February 2025 saw demand fall to nearly half of those summer highs. The peak demand fell to just 4,259 MW in November 2024, marking a 51 per cent decline compared to June 2024. Similarly, energy consumption dropped to 2,041 MU in February 2025, almost 55 per cent lower than the June 2024 peak
Notably, April 2025 registered higher electricity consumption than April 2024, reflecting a much warmer start to the summer this year. In fact, April 2025 demand alone had already reached nearly 69 per cent of the June 2024 summer peak, showing how sharply heat conditions advanced this year.This upward trajectory continued into June 2025, when demand climbed back close to record highs, touching 8,442 MW.
Erratic weather trends impact summer temperature regime
The broader trend over the years showselectricity demand rising year after yearthat is not only impacted by the weather but also the overall economic growth and changing lifestyle.The peak values have frequently crossed 6,000-7,000 MW during 2024 and 2005 summer compared to the previous period of 2021-2023. The demand in April 2025 was higher than April 2024, signaling a hot start to the summer. While 2025 summer has recorded consistently high demand levels, the May-June peak remained slightly below that of 2024. This is explained by the weather pattern. The El Nino-driven summer of 2024 brought hotter, drier conditions, intensifying cooling needs, whereas 2025 saw more rainfall across most months leading to marginal decline in temperature.
Delhi hits second highest peak demand for electricity after 2024 summer
Delhi’s electricity demand touched 8,442 MW on June 12, 2025, at 11:09 PM, marking the second highest peak ever recorded in the city. This was only 2.5 percent lower than the all-time high of 8,656 MW reached last summer on June 19, 2024. Between 2015 and 2025, Delhi’s peak electricity demand has risen from 5,846 MW to 8,442 MW, reflecting a staggering 44 per cent increase in just a decade.
Delhi mirrors the national crisis
Delhi’s experience reflects the national crisis. According to the International Energy Agency (IEA) study of 2023 temperatures have risen steadily in India, advancing the onset of summer forward by at least one month, combined with frequent and intense heat waves. This has led to a growing ownership of air conditioners, and peak electricity demand has grown on an average of 4 per cent annually over the last decade. Cooling demand increases sharply when the average daily temperatures cross 25oC.Peak electricity demand is expected to rise by around 60 per cent from 2022 levels by 2030, with cooling accounting for almost half of this increase.
According to the IEA, every 1°C rise in the average daily temperature above 24°C drives a 2 per cent increase in electricity demand in India.Before 2019, only one in 10 households had access to an air conditioner, while 24 per cent households owned either an evaporative air cooler or air conditioner in 2021. This has increased electricity consumption by 21 per cent between 2019 and 2022. But heat exposed vulnerable sections cannot access adequate means for cooling and require other means to improve thermal comforts of their dwellings.
The way forward
Says Roychowdhury: “Growing heat stress due to climate change is a reality in Delhi and this reflects the growing challenge in other cities and regions as well. There is an urgent need for Delhi and other regions to rethink its approach to managing intensifying summer heat, heat index and the growing electricity burden with both short and long term measures. Electricity demand peaks precisely when people are most at risk from extreme heat. This requires strategies for building resilience. Electricity demand has become a sensitive marker of heat stress. It is necessary to reduce exposure to heat while managing the energy footprint of cooling.”
For more on this, please contact Sukanya Nair at sukanya.nair@cseindia.org / 8816818864.
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