[MA 2026 4] Too Hot to Work: Establishing Safe Work Thresholds amid Rising Humid-Heat in India
University of Amsterdam (Department of Human Geography, Planning, and International Development), Fieldwork in India
Proposed by: Dr. Robbin Jan van Duijne [r.j.vanduijne@uva.nl ]
Introduction
Each additional degree of global warming allows the atmosphere to hold about 7% more water vapor, intensifying humid-heat extremes. In the already humid tropics, this added moisture makes it harder for the human body to shed excess heat through sweating, the body’s primary mechanism for regulating internal temperature. Yet researchers disagree sharply over how much humidity exacerbates heat-related health risks. In climate-controlled chambers, physiologists find that, at a given air temperature, higher humidity makes it substantially harder to maintain a safe core temperature and avoid heat stroke. By contrast, epidemiologists conclude that temperature alone accurately predicts heat-related death rates, with humidity offering little additional explanatory power.
This disagreement poses a serious problem for projecting the impacts of climate change on human health and work. In India, around 200 million people depend primarily on manual agricultural labor, making the country home to one of the largest populations of outdoor workers globally. Agricultural work is physically demanding, minimally mechanized in many regions, and largely conducted during peak heat and humidity in the monsoon season (June–October). These factors place Indian agricultural workers on the front line of exposure to rising humid-heat extremes.
Description of the SRP Project/Problem
The IPCC’s Sixth Assessment Report (AR6) warns of growing evidence that humid-heat increases in the tropics involve non-linear thresholds and tipping points—where small increases in heat and humidity can trigger disproportionately large declines in human performance and health. We have preciously little direct physiological evidence of how real-world manual laborers in vulnerable regions endure sustained humid-heat stress, or when their adaptive strategies begin to fail. Workers often adjust by shifting to pre-dawn or late evening hours to avoid peak humid-heat, taking more frequent breaks, or increasing hydration. But while such strategies can delay the onset of high stress in the body, they have clear limits. Once environmental thresholds are crossed, the body’s compensatory mechanisms can collapse abruptly.
We are planning a large-scale field study among Indian agricultural workers during peak hot–humid conditions, equipping ~60 participants with wearables to monitor their physiological responses while working. The overarching goal of the research, within the student’s Scientific Research Project, is to establish safe work threshold and to examine when and under which conditions these thresholds are being crossed. The findings inform data-driven regulations that prioritize workforce protection but ensure feasible implementation.
Fieldwork logistics will be supported by Prevalence Research, a data collection company based in Lucknow, India, with whom we have collaborated in several projects over the past three years.
We will use new hot-humid events as they arise in the 2026 agricultural growing season and collect physiological measurements from exposed agricultural laborers. In selected hotspots, local agricultural workers are fitted for seven days with multi-sensor wearables that log core temperature, heart rate, sweat loss and activity.
The fieldwork is guided by a Geographical Information System (GIS) of India, in which we included all 650,000 villages of the country, every single agricultural worker in each of these villages, and near real-time hot-humid temperature exposure in each village.
Research questions
The research is guided by the following two overarching research questions:
1. When and where do tipping points occur in human capacity for sustained outdoor labor under hot-humid extremes—beyond which conventional coping strategies begin to fail?
2. Can these thresholds be empirically identified and modeled using physiological data and computational methods?
a. How to measure and monitor the relevant physiological data using wearables, in an accessible way suitable for a rural area in India?
Before traveling to India, the project will begin with a mock data collection campaign in a heat chamber in the Netherlands (at the VU Medical Center or TNO). In this controlled setting, participants will perform simulated agricultural tasks under hot–humid conditions while wearing the same sensors we plan to use in the field. This pilot phase will allow us to test the wearable devices, refine our measurement protocols, and set up a workflow that streams, cleans, and stores the data in an analysis-ready database. Insights from this mock study will directly inform the design, safety procedures, and sampling strategy of the Indian fieldwork.
Expected results
The results of this research are expected to contribute to ongoing debates between physiologists and epidemiologists about the contribution of humidity in heat-related health risks. Using climate projections for the year 2050, we will also know how often hot-humid extremes will arise in the certain regions of India. Combined with our collected wearables data, we will know which places will become increasingly “unworkable”, that is, where hard manual labor will likely no longer be possible in the near future under certain climate scenarios.
Time period, please tick at least 1 time period
o May – November