Preparing effectively for future heat waves in India requires comprehensive strategies that extend beyond short-term disaster plans.

How heat waves will change in India under future climates

Preparing effectively for future heat waves in India requires comprehensive strategies that extend beyond short-term disaster plans.

A recent study analysed future heat waves using observations and model simulations across different climate scenarios: historical, +1.5 °C, and +2.0 °C warmer worlds. It underscored why understanding climate change and predicting future climate events are crucial. Moreso for developing countries like India.

The findings of the study suggest that, while the highest temperatures may not rise significantly, heat waves may last longer and cover larger areas. This poses greater health risks, especially during the monsoon season when humidity is high. Essentially, this suggests that new areas in India may become prone to heat waves.

The study predicts a significant increase in the frequency and severity of future heat wave events compared to past observations. This highlights the need for long-term adaptation strategies beyond current disaster planning efforts. The study does not explore specific adaptation measures. However, it highlights the importance of enhancing climate knowledge to inform effective adaptation policies.

Data used

Researchers obtained observational data, comprising daily maximum and minimum temperatures from 1951 to 2015, from the India Meteorological Department (IMD). This data, collected at a resolution of 1° latitude × 1° longitude, was sourced by interpolating data from 395 stations across India.

In India, “Hot Days” have evolved into “Heatwave” conditions across many regions in the last six decades. Expect increased and prolonged heatwaves in worlds with temperatures rising by +1.5°C and +2.0°C.

Arulalan T
Figure 1. Heat waves over India in the 1.5°C and 2°C warmer worlds
Credit. Climatic Change

Model data

The study utilised data from the HAPPI (Half a degree Additional warming, Prognosis and Projected Impacts) project accessible from the C20C + Detection and Attribution Project. It incorporated simulations from five global models for three time periods: historical (2006–2015), +1.5°C future, and +2°C future. These simulations aimed to assess the impacts of climate change in line with the Paris Agreement.

For the 1.5°C scenario, a weighted multi-model mean derived from the Coupled Model Intercomparison Project Phase-5 (CMIP5) under the representative concentration pathway 2.6 (RCP2.6) provided boundary conditions to all models. Meanwhile, a weighted combination of RCP2.6 and RCP4.5 set the boundary conditions for the 2°C scenario of the HAPPI project. The experiments quantified the impacts on weather-related risks corresponding to + 1.5°C and + 2°C of warming relative to pre-industrial conditions, as mandated by the Paris Agreement.

The five global models allow for the examination of low-probability events. The analysis drew upon the output from the five models, each with 100 members for each experimental scenario. The model outputs were subsequently re-gridded to match the resolution of the IMD dataset and undergo bias correction before analysis. The study authors focused on the March-August period to capture any shifts in heat waves attributable to warmer climates.

Study results

The study compared five global HAPPI model simulations with observations from 2006 to 2015. Overall, the models closely aligned with the observed data, especially regarding the frequency of hot days and heatwave events. However, there were some discrepancies, particularly in regions like the North East and Central India,  where the models exhibited higher mean errors before bias correction. To rectify this, researchers applied bias correction to the HAPPI model outputs, drawing from IMD’s long-term observed temperature dataset.

Hot days transpired across the country, with an average duration of approximately two days. Meanwhile, heatwave and severe heatwave events, lasting around three days, had similar distributions. Observers mostly noted these events in regions like the northern plains and the southeastern coast.

Over the past six decades, there has been a declining trend in the duration of hot days across India. However, researchers observed an upward trend in the northwest and southeast regions. An increase in heat wave duration, particularly in those regions, offset this decline. Moreover, the northwest and southeast regions experienced more frequent and longer hot day events in recent years, indicating a positive trend. Conversely, there was a consistent decrease in event duration and frequency along the eastern edge of the Gangetic plain, possibly due to increased anthropogenic aerosols.

Figure 2. Climate science to inform adaptation policy: Heat waves over India in the 1.5°C and 2°C warmer worlds
Credit. Climatic Change

Future projections of heat waves

Examining large heatwave events with high mortality rates, the study identified six deadly heat wave events between 2009 and 2015. It evaluated their intensity, duration, and spatial extent under present and future +1.5°C and +2°C climate scenarios. It found that the duration and area of these events were likely to increase dramatically in the future, with some grid cells showing durations of up to 30–40 days in the most extreme scenarios.

Analysing future changes, the study found an increasing likelihood of heat events occuring from April to July, especially in May and June, across different temperature rise scenarios. Both +1.5°C and +2°C future scenarios showed an increased probability of heat waves in June and July, coinciding with the peak of the Indian monsoon season and high humidity levels, thereby amplifying the health risks associated with heat events (heat index). The study projected a significant increase in the duration and frequency of future heat events, with shorter events becoming 2–10 times more probable and longer events increasing by a factor of 10–30.

Overall, the highest temperatures during heat waves may not increase significantly. In contrast, the duration and spatial extent of these events are expected to trend upward substantially. This will likely give rise to new heatwave-prone areas in India, posing significant challenges for adaptation and mitigation efforts.

Figure 3. Heat waves over India in the 1.5°C and 2°C warmer worlds
Credit. Climatic Change

Discussion and conclusion

The authors of this study used observations and models to compare past and future heat waves. The models needed adjustments to accurately reflect the observed temperatures, aligning them with real data.

In warmer climates, heat waves will occur more frequently and last longer than they did from 2006 to 2015. Areas that have not experienced many heat waves before may face them in the future. This is especially true during the monsoon season in June and July, when humidity levels rise. The study did not directly examine the impact of humidity. However, it highlights the importance of considering it for healthcare planning during heat waves.

The researchers also studied six deadly heatwaves occurring between 2006 and 2015 to assess potential future changes. They observed more pronounced differences between historical and +1.5 °C climates than those between +1.5 °C and +2.0 °C. The influence of aerosols on temperatures in South Asia could explain this variation.

The study shows that future heat waves will likely cover larger areas and last longer. Already, in 2022, prolonged heat waves affected Northwest India and Southeast Pakistan early in the year. Dealing with these prolonged and widespread heat waves poses significant challenges for many sectors, including health, agriculture, and energy.

Preparing for future heat waves will require long-term adaptation strategies. However, this study did not explore them. This emphasises the importance of having comprehensive climate information to facilitate future planning.

The study also underlines the need for stronger climate science efforts, especially in developing nations like India. Initiatives like the GCF-WMO Climate Science Information for Climate Action can help enhance climate information and prepare for future changes. Ultimately, local expertise in generating relevant climate knowledge will be crucial for effective adaptation planning.

Policy recommendations

A special report by the Intergovernmental Panel on Climate Change (IPCC) for policymakers emphasised the urgency of limiting global warming to 1.5°C. It warned that, without immediate action, achieving this goal may be unattainable by 2030.

Current emissions trajectories indicate that India continues to make a substantial contribution to the climate crisis. This necessitates accelerated reductions, supported by international collaborations, to align with global climate objectives. Despite this, India’s climate targets and actions are still rated as “Highly insufficient” by the Climate Action Tracker.

The recognition of the Right To Be Free From Adverse Effects Of Climate Change report by the Supreme Court of India highlights the need for equitable action. Climate change may impact the constitutional guarantee of the right to equality, particularly traditional activities such as fishing and hunting, which are vital sources of sustenance for people in plain areas of the country. As emissions continue to soar, particularly from major contributors like China, India, and aviation, the time to mitigate climate change rapidly diminishes.

The UN climate agency chief stressed the need for urgent action to curb emissions and constrain the rise in global temperature. He warned that there is a two-year window to implement drastic emissions reductions. India’s leveraging of its extensive road network for tree planting could mitigate carbon emissions and improve local air quality. However, the contribution of individual trees to overall oxygen levels remains limited.

Globally, leaders and individuals must prioritise tree planting initiatives alongside other measures like renewable energy and fossil fuel reduction. Collective action is crucial to addressing anthropogenic climate change and ensuring a sustainable future for all.


Journal reference

Arulalan T, AchutaRao, K., & Sagar, A. D. (2023). Climate science to inform adaptation policy: Heat waves over India in the 1.5° C and 2° C warmer worlds. Climatic Change176(5), 64.

Arulalan T, based in Delhi, India, is currently a Scientist - C at the India Meteorological Department (IMD), Ministry of Earth Sciences, Government of India, bringing experience from previous roles at the National Centre for Medium Range Weather Forecasting (NCMRWF), MoES, the Indian Institute of Technology, Delhi, and NuVeda Learning Pvt. Ltd. Arulalan T holds a Master of Technology (MTech) from 2012 to 2015 in the Centre for Atmospheric Sciences at the Indian Institute of Technology, Delhi.

Krishna AchutaRao is Professor and Head of the Centre for Atmospheric Sciences at the Indian Institute of Technology Delhi in New Delhi, India. Prior to that, he worked at the Lawrence Livermore National Laboratory in California. His research has focused on using climate models to understand how the Earth’s climate is affected by natural as well as anthropogenic factors and how it will impact natural and human systems. His current interests include the attribution of extreme weather events, the changing risk of extreme events under a warming climate, and adaptation to climate change.

Ambuj is the Deputy Director (Strategy & Planning) and the Vipula and Mahesh Chaturvedi Professor of Policy Studies at the Indian Institute of Technology Delhi. He previously was the founding Head of the School of Public Policy.

Ambuj’s interests broadly lie at the intersection of science, technology, and development. His recent work has focused on innovation policy for meeting sustainability and inclusivity challenges, energy innovation policy and strategies (in areas such as biofuels, clean cookstoves, coal power, automobiles, and institutional mechanisms such as climate innovation centres), climate change policy and politics, capacity development, and higher education policy. He was a Senior Research Associate at the Harvard Kennedy School and the Assistant Dean for Strategic Planning at the (now) Harvard Paulson School of Engineering and Applied Sciences before joining IIT Delhi.