Comparative evaluation of sultry indices in the mid-south of Iran

Abstract

The sultry phenomenon is considered one of the climactic events of south shorelines of Iran which are associated with humidity and high air temperature. The importance and necessity of this phenomenon on the subject of applied studies especially bioclimatology will be regarded if increasing of its severity leads to human discomfort as well as asthma and hard breathing. The main objective of this study was to conduct a comparative investigation into the estimation indices for sultry conditions in the southern half of Iran. To achieve research objectives, the hourly data for partial vapor pressure, air temperature, relative humidity, and wind speed were collected from 12 synoptic stations over a 15-year period (1995–2009). The following five indices were used to differentiate between sultry and non-sultry days: the actual vapor pressure more than or equal to 18.8 hPa (Scharlau criterion), equivalent temperature index (more than 56 °C), physiological deficit index (less than 45 hPa), the approximated heat stress index, and the sultry severity index (Castens-Lancaster criterion). To compare these indices, two quantitative and qualitative criteria were considered. The results obtained from quantitative analysis of these indices showed that the Scharlau and Castens-Lancaster criteria were the most coordinated indices in determining sultry conditions. Suitable coordination was obtained only in half the studied stations for the physiological deficit index of less than 45 hPa. The lowest coordination was between the approximated heat stress index and the equivalent temperature index of more than 56 °C. The results obtained from the qualitative evaluation of the sultry estimation indices showed that the Scharlau criterion was more capable of estimating sultry conditions since it exhibited such characteristics as robustness, tractability, transparency, sophistication, extendability, and dimensionality. In general, the conducted quantitative and qualitative analyses showed that the Scharlau criterion was the most appropriate, homogeneous, and concrete index for monitoring sultry conditions in southern Iran.