Occupational Heat Stress in Outdoor Settings Considering the Regional Climate Change in the Future Decades in Iran

Background and aims: Nowadays, global warming and climate change have become one of the controversial topics that have an impact on the health of individuals and the threat to human life. In recent decades, particular attention has been paid to the issue of environmental change and its impact from different perspectives. Many studies have been conducted to study these effects (generally from a non-occupational perspective) around the world. But from a job standpoint, the probable effects of global warming on occupational health are under reached, although its trend is growing. Outdoor workers are one of the most vulnerable groups of people directly affected by global warming. Climate change and global warming can cause many health problems, one of the most important of which is the development of thermal stresses and related disorders in outdoor occupational exposures.  Iran is a large country with very wide climatic diversity, with 35. 5% of it in complete arid, 29.2% of the arid, 20.1% of the semi- arid, 5% of the Mediterranean and 10% of the Wet climates in the country. Thus, more than 82% of the territory of the country is located in the arid and semi-arid region of the world. The average rainfall is 250 mm, less than one third world-wide (860 mm), and its dispersion degree is very high in the country. Increasing the average temperature can lead to warmer days and longer and more frequent heat waves. This, in turn, can increase the risk of heat-related diseases such as heat stroke, heat cramp, heat exhaustion, etc., and even in advanced cases, causes death. These effects are likely to be different in different regions, based on the sensitivity of the community, the amount and duration of exposure, as well as the ability of individuals to adapt to temperature variations. So, the main objective of this study was to investigate temperature changes in different climates of Iran in the coming decades in order to obtain an adequate understanding of the heat stress state in outdoor environments. Methods: The environmental parameters required in this study were air temperature (ta), wet temperature (tw) and relative humidity (RH) which are determined by calibrated devices. At the same time, the WBGT temperature index was also measured and recorded using the calibrated WBGT meter, Casella model. All measurements were carried out at three times throughout the day, including 9 am, 12 noon and 3 pm, indicating the initial, mid, and final hours of shift work in the studied environments in the country, respectively. In order to cover this study throughout the country, and taking into account all the existing climates in the country, with the exception of areas with cold- dry and cold- humid climates, which often include the western and northwest parts of the country, 9 climatic zones in each country were selected in that country. A total of 495 measurement series of environmental parameters were carried out in nine climates (55 measurements per each climate). All measurements were done in outdoor settings such as open pit mines, asphalt and road workers, farmers, cement factories and shipbuilding industries. The selection of industries and locations was also performed randomly. Selected sites in this study, each representing different climates in the country, included cities of Ahwaz, Bandar Abbas, Rasht, Gorgan, Kerman, Yazd, Sari, Qom and Mashhad. The Arc / GIS 8.0 software was used to generalize the data from a meteorological station to other weather stations in a similar climatic zone, and the environmental parameter values ​​measured at each station were similar to the other meteorological stations in the same climate were linked. Thus, in the GIS information layers, different climate zones were determined using two parameters of air temperature and humidity. In this process, the gathered spot data was converted into regional data. In addition, the long-term data for each climate zone (between 1965 and 2010), including the minimum and maximum daily air temperature, rainfall and sunshine, were used to generalize the data to other similar climate zones. Finally, using the weather behavior of previous periods at the studied stations, the weather conditions between 2011 and 2100 using the LARS-WG model and a coupled atmosphere-ocean general circulation model (HadCM3) for each of the 9 weather stations, simulations were performed. Then, according to the goal of the study that emphasizes the stress on outdoor work space, this model evaluates climate change in different regions based on daily maximum and minimum temperatures up to 2100 at 25-year intervals.   Results: Based on the results, a temperature increase with different intensities is expected in the next decade. In addition, the pattern of variations was almost the same for all stations studied. On the other hand, slight changes in the average daily minimum and maximum air temperature are observed until 2025. These changes were not very different in the spring and summer. After that, by 2075, the temperature increase is observed with a gentle slope, and thereafter, until 2100, no significant changes are observed for most of the stations. However, there is a significant increase in the average daily minimum and maximum temperatures in summer compared to spring. According to the results of the model, the highest temperature rise in 2075 is expected in most parts of the country.  In general, the mean and standard deviation (M ± SD) of expected changes at minimum and maximum temperatures were 1.34 ± 1.41 °C and 1.29 ± 1.40 °C for spring and 2.38 ± 2.44 °C and 2.34± 2.48 °C for the summer, respectively. The respective values, regardless of the season (spring or summer) were1.86 ± 2.05 °C and 1.82 ± 2.07 °C for the minimum and maximum temperature changes, respectively. In general, it can be said that the average temperature of different climates of Iran will increase by about 2 °C until 2100.  The results of the thermal stresses in the nine areas studied, which were simultaneously with other environmental parameters of the study, showed that in the spring, except for climatic zones 5 and 6, which are related to the cities of Yazd and Bandar Abbas, at least at 12 noon, no significant stress was observed in any of the affected areas. However, over time and approaching the afternoon (until around 3:00 pm), many other climatic zones, including sites 2, 7 and 8 (cities such as Ahvaz, Sari and Gorgan) , In addition to sites 5 and 6, will be in a stressed state even in the afternoon.  In other words, in almost all parts of the country, especially in the middle and end of shift work, there is heat stress in the summer or even in many areas in the spring. The lowest WBGT index was 17.5 ± 0.99 °C for the early hours of the morning (in the spring and in the northern regions of the country) and the maximum is 35.10 ± 0.55 °C for noon and evening hours (in the summer and in the southern regions of the country). In general, the analysis of temperature differences and heat stress in different parts of the country also shows that parts of the country that have the greatest impact on climate change are the central and southern regions of the country.  These findings clearly show that many workers, especially those working in outdoor environments, are currently in an environmentally unfavorable condition (regardless of any possible increase in temperature as a result of climate change) and they suffer from the dangers and complications of thermal stress. Considering the objectives of the study as well as the obtaining results about climate change during the current century (about 2 °C), it can be expected that the trend of changes in thermal stress in the country will also change in most parts of the country similar to the trend of temperature changes in the country in the coming decades. Conclusion: Climate change caused by global warming and, as a result, increased heat stress, especially for outdoor workers, is a very important issue that has relatively similar effects in different parts of the world. Based on the obtained results, an increase of about 2 degrees Celsius to the average temperature of the air, regardless of the changes in other parameters affecting heat stress such as relative humidity, air velocity and radiant temperature, can put several parts of the country under thermal stress conditions. In other words, the different areas and external environments that are currently in terms of acceptable thermal stress status will suffer from heat stress due to climate change and rising temperatures in the coming decades. For example, it is expected that the northwest, west, and northern and central parts of the country will be exposed to heat stress.  In addition, most of the southern and central parts of the country, which are currently in heat stress, will be in a worse situation. Therefore, preventive interventions such as open outdoor environments design, shading in industrial areas, designing cool rest areas to reduce exposure to heat, developing work and rest programs, attention to acclimatization to the environment and observing public health programs, can play an important role in reducing the adverse health effects of climate change and the increase in temperature on exposed outdoor workers.