Weather is one of the most important natural factors affecting the aviation industry. Although many details of climatological characteristics and long-term changes in some basic meteorological variables such as temperature, wind, and precipitation have been investigated, a few studies have focused on aviation-specific meteorological hazard. The present study analyzes the spatial and temporal variability of thunderstorm (TSTM) and low-level wind shear (LLWS), both of which are aviation hazards. In this regard, ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) has been used to identify areas and airports prone to thunderstorms and low-level wind shear in Iran over a 45-year period from 1979 to 2023.

In order to determine the number of occurrences of hazardous conditions due to TSTM and LLWS, it is necessary to extract a threshold as an indicator of the potential hazard of each phenomenon. The CAPE index is often used to identify thunderstorm-prone environments. The convective precipitation index is also considered. Determining a threshold for LLWS is challenging. A value of 3 knots per 100 feet has been applied in this study. It should also be noted that due to the resolution limitations of the reanalysis data and the parameterization of many processes, the wind shear obtained in this study is mainly the result of synoptic-scale pressure gradients and is not related to local phenomena such as microbursts. Although the defined thresholds have a physical basis, it should be noted that they are merely indicators of a potential situation for hazardous occurrence. Such analyses are subject to probabilistic interpretation and may be accompanied by uncertainty. Therefore, the results obtained should be interpreted with caution.

The results of this study show that the areas located in the northern half, west, southwest and parts of the southern strip of Iran are more affected by the risk of thunderstorms than other areas. Additionally, regions in the east and center of Iran and limited parts of the northwest and west of Khuzestan and a major part of the Persian Gulf are affected by the risk of low-level wind shear formation. In summer, TSTM activity is mainly limited to the northern regions of the country, while in winter, this threat is transferred to the southern regions. The reason for this seasonal shift is that in the southern regions, the arrival of cyclonic systems from the northwest of Iran, along with the moisture transport from the Persian Gulf, leads to the strengthening of convective instabilities and an increase in the occurrence of this hazard. In the northern regions of Iran, during the summer season, the process of evapotranspiration caused by vegetation and local water resources plays a dominant role in providing moisture and, together with the intense heating of the earth's surface, leads to the formation of the TSTM hazard. The largest spatial extent covered by TSTM is observed in the spring season and the maximum hours of occurrence of this hazard are observed in the summer. LLWS has the smallest spatial extent in the autumn and summer seasons. However, in the summer, its maximum values are observed in limited areas of eastern Iran. This is mainly influenced by the activity of the 120-day Sistan winds. Also, in the west of Khuzestan province and a significant part of the Persian Gulf, the maximum occurrence of this phenomenon is observed in this season, which is due to the impact of the dynamic activity of the summer Shamal wind in this region.