The role of physical geographic parameters affecting past (1980–2010) and future (2020–2049) thermal stress in Iran

In this study, the wet-bulb globe temperature (WBGT) validated biometeorological index is used to monitor and project future human thermal stress in Iran. The meteorological components required to calculate this index include dry and wet temperatures, relative humidity and radiation. To monitor and project thermal stress, data for two time periods are used: (i) baseline data for the period 1980–2010 and (ii) Can-ESM2 model outputs from the CMIP5 model series, which projects values for the period 2020–2049. Four physical geographic factors are used for modeling WBGT frequency; these include station height (elevation), distance from nearest large water body, latitude and longitude. To establish the role of these components on WBGT extreme values, a weighted geographical regression method is used. Findings show that by considering these variables in the form of multivariate weighted regressions, WBGT threshold values are reliably modeled. Based on projected global warming scenarios in coming decades, the threshold of thermal stress occurrence for most regions of Iran shows larger values than those for the reference period. Parameters of latitude, longitude and distance from a large water body will have an incremental impact as contributors to the occurrence of future thermal stress, relative to the reference period. Of these, latitude will have the greatest impact on thermal stress (6.3%), while that for longitude and distance from a large water body will be 2.4% and 1.4%, respectively. However, station elevation will have a reduced impact on thermal stress (by 4.1%).