Temporal and spatial analysis of thermal stress and its trend in Iran

Abstract

AbstractThe study was conducted to determine thermal stress and its trend in Iran. The atmospheric variables of 304 synoptic stations, including mean temperature, relative humidity, wind speed and cloudiness, for the period 1961–2010, were used to identify the thermal stress conditions in Iran. These data were prepared on a daily basis from the Iran Meteorological Organization. Physiologically equivalent temperature (PET) and standard effective temperature (SET*) were used to identify thermal stress. Also, thermal stress was studied with a simple linear regression method and at a 95% confidence level. The results of the study revealed that in Iran each location can experience different types of environmental conditions throughout the year. At a specified time, thermal stresses of different intensities can be seen. The other results showed that the mountainous regions, especially the highlands of the northwest, along with the Zagros and Alborz mountains, had the highest co‐efficient of variability (> 50%). Also, the southern regions of Iran have both monthly and annual scales with the least co‐efficient of variability (< 20%) in bioclimatic conditions. In general, a diversity of bioclimatic conditions is evident in Iran both temporally and spatially. The other part of the study determined that heat and cold stress and heat comfort had a positive trend (fewer than 60 stations) in parts of Iran, a negative trend in some other parts (more than 50 stations), and no specific trend in the remaining parts (more than 250 stations). Most of the northern stations, especially on the Caspian coast, have been shown to have a positive trend in the event of cold stress. Indeed, extreme bioclimatic conditions (very cold and hot conditions) have been rising in both the southern and northern latitudes of the country. Even in southern parts, a positive trend of cold and very cold conditions can be observed at some stations.