Beyond the heat: The mental health toll of temperature and humidity in India
By Manuela Fritz
DOI https://doi.org/10.48550/arXiv.2503.08761
Abstract
Evidence on the heat-mental health nexus remains mixed. I show that this can be partly explained by previous studies focusing solely on temperature while neglecting temperature-humidity interactions. Using a measure that considers both indicators (wet bulb temperature), I assess the causal link between extreme heat and mental health, and its heterogeneity across socioeconomic indicators. I combine self-reported depression and anxiety levels from three Indian WHO-SAGE survey waves with climate data, leveraging quasi-random variation in heat exposure due to survey timing and location. The results reveal that extreme heat increases the risk of depression but not of anxiety. Importantly, these effects are consistently smaller when humidity is not considered. Finally, the study provides evidence that the District Mental Health Program plays a protective role in mitigating adverse mental health effects. The findings suggest that the costs induced by climate change need to account for the economic consequences of deteriorated mental health.
Overview
The paper examines how extreme heat—especially when combined with high humidity—affects mental health in India. While previous research mostly looked at air temperature alone, this study shows that ignoring humidity may lead to an underestimation of the real effects of heat on people’s psychological well-being. The author uses a weather measure called wet bulb temperature (which combines temperature and humidity) to better capture how the weather stresses the human body.
Key Sections
1. Abstract and Main Questions
Objective:
The study aims to determine the link between extreme heat (measured as wet bulb temperature) and mental health outcomes—specifically depression and anxiety—in India.-
Why Wet Bulb Temperature?
Explanation: Wet bulb temperature represents the lowest temperature achievable by cooling through evaporation. Imagine a thermometer wrapped in a wet cloth: if the air is dry, evaporation cools it well, so the reading is much lower than the actual air temperature. In humid conditions, there’s less cooling, so the wet bulb reading is closer to the regular (dry bulb) temperature.
Significance: This measure better captures how humans experience heat because high humidity makes it harder for sweat to evaporate and cool the body.
Research Gap:
Prior studies have mixed results because they typically focused only on temperature. By including humidity, the study seeks to clarify how combined heat and humidity affect mental health.
2. Introduction and Background
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Context of Climate Change:
The paper begins by noting that as the climate changes, people are increasingly exposed to dangerous levels of heat.
In low- and middle-income countries like India, the combined effects of high temperature and humidity can be especially severe.
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Focus on Mental Health:
While many studies have documented that extreme heat can increase physical health risks (like death or illness), fewer have looked at its impact on mental health.
India is a critical case study because not only is the population frequently exposed to heat, but the country also faces challenges in mental health care (e.g., an 80% treatment gap for common mental disorders).
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Why India?
A large share of India’s population works outdoors, has limited access to cooling (like air conditioning), and faces higher humidity—all factors that may amplify the mental health toll of heat.
The rising burden of mental illness in India (with one in seven suffering from such conditions) makes it especially important to understand how environmental factors contribute to mental health issues.
3. Data and Methodology
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Survey Data:
The study uses individual-level data from three waves (2003, 2007, and 2015) of the WHO Study on Global Ageing and Adult Health (WHO-SAGE) in India.
Respondents were asked about their experiences with depression (feeling sad or low) and anxiety (feeling worried) over the past 30 days.
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Weather Data:
Weather information (temperature, humidity, rainfall, wind speed, and air pollution) is matched with the survey data based on the interview date and location.
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Wet Bulb Temperature:
- The author calculates this measure using data on dry bulb temperature (the usual air temperature) along with humidity and air pressure.
- This approach allows the study to assess how the interaction of temperature and humidity influences mental health.
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Empirical Strategy:
The analysis takes advantage of “quasi-random” variation in heat exposure due to differences in the timing and locations of survey interviews.
A common method called temperature bin regression is used to compare individuals experiencing different levels of heat stress, which helps to isolate the effect of extreme heat on mental health.
4. Main Findings
Impact on Depression:
Exposure to extreme heat (especially when measured as wet bulb temperature) increases the risk of severe depression.
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The study quantifies this effect:
- A heatwave lasting two or more days in the 30 days before an interview increases the probability of severe or extreme depression by 24%.
- Each additional day of extreme heat adds a 6% increase in the likelihood of severe depression.
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No Significant Impact on Anxiety:
The research does not find a statistically significant link between extreme heat and self-reported anxiety levels.
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The Role of Humidity:
When only temperature (ignoring humidity) is used, the estimated effects on depression are much smaller or even disappear.
This emphasizes that humidity amplifies the effect of heat on mental health.
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Protective Role of Mental Health Programs:
The study finds that in areas where the District Mental Health Program is available, the adverse effects of extreme heat on depression are notably reduced.
This suggests that effective mental health interventions can help buffer the negative impacts of extreme weather.
5. Implications and Conclusion
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Policy Relevance:
The findings suggest that when evaluating the costs of climate change, it is important to include not only physical health impacts (like mortality or hospital admissions) but also the economic and social costs of deteriorated mental health.
Investing in mental health programs, such as the District Mental Health Program, can mitigate some of the negative effects of extreme heat.
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Methodological Contribution:
By using wet bulb temperature instead of only dry bulb temperature, the study provides a more realistic assessment of how heat stress affects mental health.
This approach could be useful for future research in other regions or countries that face similar climatic challenges.
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Overall Conclusion:
Extreme heat, when combined with high humidity, has a significant adverse effect on mental health in India, particularly increasing the risk of depression.
The study highlights the importance of considering environmental factors comprehensively and shows that policy interventions can play a protective role.
In simple terms, as the climate continues to change, addressing both the direct and indirect effects on health—especially mental health—is essential for protecting vulnerable populations.
Final Remarks
This paper provides evidence that the interplay of high temperature and humidity is an important driver of mental health outcomes. By highlighting how extreme weather conditions increase depression (but not anxiety) and showing that mental health programs can help, the study offers valuable insights for policymakers facing the challenges of climate change.