The significance of this study lies in its integration of station-based sub-daily temperature and humidity data collected over the 2024 Hajj season, combined with forward-looking climate model projections to analyze both immediate and future heat-related risks. According to the data, during several hours in June 2024, heat stress was not merely uncomfortable but outright fatal for extended outdoor exposure, eclipsing survivability thresholds conventionally assumed safe even for well-conditioned individuals. This danger was most acute on June 17, 2024—known as the Day of Arafat—when the combination of extreme heat and humidity rendered prolonged outdoor exposure hazardous for approximately four continuous hours. During this window, natural thermoregulatory mechanisms such as sweating failed to maintain safe core body temperatures, underscoring the life-threatening implications for pilgrims engaged in strenuous rituals under direct sunlight.

Hajj represents one of the five fundamental pillars of Islam and mandates that Muslims who are physically and financially able undertake this once-in-a-lifetime spiritual journey. Pilgrims engage in a consolidated sequence of rituals over five days, collectively requiring extensive physical exertion in outdoor environments. These rituals include Tawaf (circling the Kaaba), Sa’i (walking between Safa and Marwa), standing in contemplative prayer on the plain of Mount Arafat, spending nights outdoors in Mina and Muzdalifah, and performing Rami al-Jamarat, the symbolic stoning of the devil. Each of these rites exposes pilgrims to harsh desert conditions, which are becoming increasingly intolerable due to gradually rising global temperatures and shifting climatic patterns, raising critical questions about the feasibility of safely conducting the pilgrimage in its traditional form.

Among the rituals, the Day of Arafat emerges as the apex of heat exposure risk. Pilgrims spend the entire day standing and praying on an expansive, open plain under minimal shade. This vulnerability is compounded by the extreme physical demands of the ritual and lack of cooling infrastructures, making pilgrims particularly susceptible to heat exhaustion, heatstroke, and other heat-related illnesses. The study highlights that, without urgent measures to adapt both infrastructure and pilgrimage timing, this integral ritual risks becoming a hazardous ordeal or may require fundamental alterations that could erode traditional practices key to the pilgrimage’s spiritual significance.

Current adaptations underway reflect attempts to mitigate heat risks while striving to preserve the pilgrimage’s authenticity. Notable interventions include relocating the Sa’i ritual indoors within climate-controlled environments and the construction of increasingly permanent shelters in Mina to provide respite from relentless sun exposure. While these strategies have indeed improved safety conditions, they simultaneously transform the spatial and experiential context of the pilgrimage, rendering an intricate balance between preserving heritage and safeguarding pilgrim health. The tension between tradition and necessary modernization forms a central challenge for religious authorities and event organizers as climate pressures intensify in the coming decades.

One of the more complex facets outlined in the study is the temporal shift in climate risk profiles associated with the Islamic lunar calendar governing the Hajj. For the next two or three decades, the pilgrimage will primarily coincide with relatively cooler seasons owing to the lunar cycle’s progression through the Gregorian calendar. However, projections indicate that by around 2050, the Hajj will once again fall within the hottest months of the year, potentially exacerbating heat-related dangers dramatically. This cyclical exacerbation underlines a long-term, systemic vulnerability to global warming’s coupled effects of increased ambient temperatures and humidity, threatening to undermine pilgrims’ safety and the feasibility of traditional pilgrimage observances.

Technically, the study employs sophisticated climate modeling techniques that synthesize observational sub-daily meteorological data from key stations surrounding Makkah with ensemble runs from climate prediction models under various emissions scenarios. This methodological rigor allows for granular insights into physiological heat stress dynamics—measured through indices such as Wet Bulb Globe Temperature and heat index values—that directly correlate with human heat tolerance and the risk of heat-related morbidity and mortality. The research underscores that without significant global reductions in greenhouse gas emissions and regional adaptation strategies, the survivability thresholds enshrined in human physiology will increasingly be breached during future Hajj seasons.

The implications of these findings ripple far beyond religious practice, touching on public health, climate justice, and the management of mass gatherings. Hajj, as one of the largest annual human assemblies globally, serves as a potent lens through which the broader societal costs of unchecked climate change become painfully visible. Beyond immediate risks like heat stress and dehydration, escalating temperatures also threaten the logistics, emergency response capacity, and medical infrastructure required to support millions in extreme conditions. The study asserts that fortifying infrastructure and redesigning pilgrim flow management systems, alongside elevating international cooperation on climate mitigation, is paramount for safeguarding both human life and the spiritual integrity of the Hajj.

Moreover, the research challenges the conventional framing of climate change solely as an environmental or economic issue. It posits that climate-induced risks are penetrating deeply into cultural and religious domains, with potentially profound consequences for faith communities worldwide. The necessity of reevaluating religious rites to reconcile them with altered climatic realities signals a new frontier in climate adaptation discourse that balances reverence for sacred traditions with pragmatic health and safety imperatives. In this context, the Hajj pilgrimage epitomizes the critical nexus where climate science, policy, and spiritual practice intersect with urgent ethical considerations.

As a response, the authors fervently advocate for a dual approach emphasizing both aggressive climate mitigation measures and innovative adaptation strategies. Mitigation efforts aimed at limiting global temperature rise are indispensable to reducing future risks once adaptation capacity plateaus. Concurrently, localized interventions such as expanding shaded infrastructure, improving hydration stations, medical preparedness, and disseminating heat risk awareness among pilgrims are crucial immediate steps. This combined strategy is essential not only for protecting millions of pilgrims today but for maintaining the continuity and authenticity of the Hajj experience for future generations, in the face of an evolving and increasingly hostile climate reality.

In summary, climate change presents an existential threat to the Hajj pilgrimage by subjecting participants to perilous heat stress levels that strain human physiological resilience. This research offers a scientifically robust, data-driven prognosis of these escalating risks, elucidating the urgent need for coordinated global action. As the pilgrimage’s traditional calendar advances into hotter periods over the coming decades, the study’s sobering conclusions compel reexamination of deeply rooted practices through the lens of climate resilience. Ultimately, protecting the millions of pilgrims who undertake this sacred journey every year requires transformational thinking at the intersection of science, policy, faith, and human dignity.

Subject of Research: Climate change impacts on human physiological heat stress during the Hajj pilgrimage and future risk projections.

Article Title: Climate Change Threatens the Safety and Tradition of the Hajj Pilgrimage: Heat Stress Risks Exceed Human Survivability Thresholds

News Publication Date: June 2024

Web References: Presented at EGU General Assembly 2026, Session ITS4.19/CL0.10, May 7, 2026, Room 2.17.

Press contact: Asmae Ourkiya, EGU Media and Engagement Manager, media@egu.eu

Keywords: Climate change, heat stress, Hajj pilgrimage, human physiology, heat-related mortality, adaptation, mitigation, mass gatherings, religious practice, climate modeling, heat index, Wet Bulb Globe Temperature

The foundational challenge addressed by the research lies in determining accurate and actionable heat exposure thresholds for outdoor workers. Traditional regulatory approaches have predominantly relied on air temperature (dry-bulb temperature, DBT) measures, which fail to capture the multifaceted nature of heat stress that includes humidity, solar radiation, and wind effects. The WBGT index, by integrating these factors, emerges as a superior metric but is typically complex to measure continuously in sprawling agricultural landscapes. By calculating recommended rest minutes per hour (RMPH) grounded in WBGT climatology modeled via the Weather Research and Forecasting (WRF) system, the researchers provide a compelling method that circumvents the practical challenges of real-time WBGT monitoring.

The study’s methodology intricately considers variables that impact heat exposure and physiological strain, such as geographic location within the ICV, specific work shifts, seasonal variations, worker clothing, acclimatization status, and workload intensity. This comprehensive approach builds on the National Institute for Occupational Safety and Health (NIOSH) criteria, adjusting rest-break requirements to reflect realistic working conditions in California’s diverse agricultural contexts. The coupling of high-resolution WRF regional climate model outputs with occupational health standards allows for the derivation of location-specific and time-sensitive rest break recommendations.

Amid growing awareness of heat-related occupational hazards, governmental agencies have initiated efforts to enhance heat stress monitoring and forecasts. The United States’ National Weather Service recently introduced the HeatRisk forecasting tool, and California’s Office of Environmental Health Hazard Assessment proposed CalHeatScore, both designed to provide localized heat forecasts with health impact considerations. Despite these advances, policy frameworks lag behind, often reverting to simplistic heat indicators and lacking specificity in WBGT-related regulations. Notably, California OSHA’s current outdoor heat illness prevention guidelines rely primarily on ambient air temperature thresholds, a practice that this new research finds inadequate to truly protect farmworkers.

A persistent barrier to WBGT adoption in policy and practice has been the complexity of continuous temperature measurements required, encompassing wet bulb temperature (WBT), black globe temperature (BGT), and dry bulb temperature (DBT). Obtaining such data across vast agricultural expanses is logistically difficult and cost-prohibitive. Furthermore, recommended WBGT-based rest times often exceed typical break durations, raising employer concerns over productivity losses. This study’s approach innovatively utilizes WBGT climatology calculated from WRF outputs, effectively bypassing the need for continuous onsite measurement while ensuring scientific rigor informs work-rest cycles.

The research highlights the nuances inherent in implementing WBGT-based recommendations in real-world settings. Despite the potential increase in rest durations suggested by WBGT criteria, empirical insights indicate that mandated rest breaks may not necessarily hinder farm productivity. However, administrative challenges emerge, notably in the monitoring load placed on peer managers who would be responsible for enforcing dynamic work schedules tied to fluctuating heat stress metrics. The piece-rate payment structures common to farm labor also risk undermining adherence to rest protocols, as workers may prioritize earnings over health safety, underscoring the need for systemic attention to labor practices alongside environmental protections.

Widely accessible hand-held WBGT measurement devices have become more prevalent, though questions remain about their accuracy compared to institutional-grade instrumentation. The study tackles these operational challenges by proposing and validating rest minute schedules derived from WBGT climatology, offering employers and policymakers a practical yet robust framework to enhance heat stress prevention without the hurdles of real-time environmental data collection. This approach represents a balance between scientific exactness and operational feasibility.

Crucially, the researchers demonstrate through comparative analysis that WBGT-based rest break recommendations far exceed those derived from traditional metrics such as dry-bulb temperature or Heat Index (HI), as reflected in both California state protocols and new OSHA proposals. The multiplicity of WBGT thresholds captures a broader spectrum of heat exposure conditions, ensuring more protective measures during hotter parts of the day and season. This finding challenges the adequacy of existing temperature-based guidelines and advocates strongly for the integration of WBGT into formal occupational safety frameworks to better shield farmworkers from heat-related health risks.

The study provides detailed tables of recommended rest minutes stratified by work intensity (light, medium, heavy), acclimatization status, hourly shifts, and seasonal periods, facilitating tailored applications. For instance, tasks such as cutting sugarcane or harvesting dates, classified as “heavy” work, necessitate longer rest durations reflective of the greater metabolic heat produced. This granular approach empowers employers to develop precise, context-sensitive heat mitigation protocols that align with specific crop types and labor demands.

Insight into current farmworker break practices reveals variability in rest frequency and duration, with some experiencing brief 10–15 minute breaks every 2–3 hours in an 8-10 hour day, while others report minimal breaks during shorter shifts. Although commendable adaptation measures exist, such as early shift termination during extreme heat events, adherence to heat-specific break mandates remains inconsistent. Notably, access to shade—an essential component of heat illness prevention—is commonly limited to small, mobile structures offering only overhead protection, sometimes distant from restrooms. This spatial arrangement may inadvertently discourage adequate recovery during breaks, emphasizing the multifaceted nature of occupational heat stress mitigation that encompasses environmental design and workplace culture.

The rest recommendations furnished by the study are intended as supplements rather than substitutes for general labor law rest requirements, such as California Labor Code provisions stipulating breaks irrespective of heat conditions. This layered approach to rest breaks acknowledges the differentiated risks posed by heat stress beyond routine labor rest needs. By focusing rest minute calculations on periods when WBGT exceeds established thresholds, the recommendations target heat-related vulnerability, promoting worker health during periods of elevated environmental stress.

Robustness of the findings is underscored by analyses across different years, comparing 2020 and 2024 WBGT-derived rest minutes, which yielded consistent spatial patterns. This stability suggests that interannual climate variability does not significantly undermine the applicability of the rest minute frameworks. However, the study acknowledges potential limitations related to regional climatic differences, recommending that similar WBGT-based rest break calculations be tailored for other geographic areas, both within the United States and internationally, to account for diverse environmental and occupational contexts.

While WBGT is internationally recognized for integrating key heat stress parameters—temperature, humidity, solar radiation, and wind—it does not fully capture individual factors such as physical fitness, age, or personal heat tolerance. Groups with heightened vulnerability, including pregnant women, older workers, and those with underlying medical conditions, may require more conservative rest protocols than those generally proposed. Additionally, the study’s reliance on monthly averaged WBGT values may not reflect immediate needs during sudden heat spikes, such as rapid-onset heat waves, highlighting an area for further research and real-time monitoring advancements.

The underlying data for WBGT emerged from high-resolution WRF climate modeling previously validated against meteorological station observations within the study region. Despite some inherent model biases—root mean square errors in wet bulb and dry bulb temperatures ranging from 0.7°C to 1.5°C and black globe temperatures from 0.5°C to 0.7°C—the spatial resolution of approximately one kilometer and the consistency with observational data support the credibility of the rest minute recommendations. This demonstrates the feasibility of coupling sophisticated climate models with occupational health guidelines for applied worker safety solutions, paving the way for scientifically informed policy innovation.

In sum, this groundbreaking research confronts a pressing occupational health challenge by integrating meteorological science, physiological criteria, and practical work considerations into a coherent framework for heat-related rest break scheduling. The adoption of WBGT-based guidelines tailored through calibrated climate modeling offers a promising avenue to mitigate the increasing risk of heat illnesses faced by farmworkers as climate extremes become more frequent. By emphasizing precise, localized, and workload-specific recommendations, the work sets a new standard for protecting vulnerable outdoor labor populations amidst the escalating threat of global warming.

Subject of Research: Heat-related rest-break recommendations for farmworkers based on Wet Bulb Globe Temperature (WBGT) in Southern California agricultural regions.

Article Title: Heat-related rest-break recommendations for farmworkers in California based on wet-bulb globe temperature.

Article References:
Parajuli, S.P., Biggs, T., Galvez, N.L. et al. Heat-related rest-break recommendations for farmworkers in California based on wet-bulb globe temperature. Commun Earth Environ 6, 359 (2025). https://doi.org/10.1038/s43247-025-02327-9

Image Credits: AI Generated