Mehdi Feyzolahpour, Neda Kanani,
Volume 0, Issue 0 (3-2007)
Abstract
“Desertification is a form of land degradation in arid, semi-arid, and semi-humid regions caused by climate change and human activities. The purpose of this research is to investigate the desertification situation in the Sirjan Plain region in the period from 1990 to 2023. Desertification in this area threatens human settlements. The purpose of this research is to combine several indicators to evaluate the state of desertification, and for this purpose, several spectral indicators are combined with each other to select the best indicator. In this research, based on albedo, MSAVI and SFI indices, desertification monitoring index (DMI) was proposed and the spatial and temporal distribution of desertification in the west of Sirjan was estimated in 1990 and 2023. To classify the results obtained from the DMI index, Jenks classification methods and quantitative index were used. Based on the results of the Jenks index, it was observed that the areas with very low desertification in 1990 were about 59.7 square kilometers, which decreased to 127.5 square kilometers in 2023, and 47.68 percent of the area has desertification. It has been very little. Areas with high desertification have faced a significant change and have reached 118.6 square kilometers in 2023 from 465.7 square kilometers in 1990. The results showed that Jenks classification method has a higher ability than the quantitative index with an overall accuracy of 82% and a Kappa coefficient of 0.86 in 1990. Finally, it was observed that the albedo index had the highest positive correlation compared to the DMI index. So that the correlation between these two indicators in 1990 and 2023 was estimated at 0.71 and 0.82, respectively.
Mina Daneshvar, Dr Hassan Lashkari, Reza Borna,
Volume 25, Issue 0 (3-2026)
Abstract
Thunderstorms are considered compound atmospheric hazards, as they simultaneously involve several hazardous phenomena such as lightning, strong and gusty winds, intense convective rainfall, and torrential precipitation. Consequently, these storms are often associated with damage to urban infrastructure and environmental impacts. The objective of this study is to analyze the spatiotemporal distribution of thunderstorms across Tehran Province over a 33‑year period corresponding to the last three solar cycles. Owing to its distinctive topographic conditions and geographical location, Tehran Province is regarded as one of the regions prone to the occurrence of this phenomenon. The data used in this research include lightning reports recorded at nine synoptic stations in Tehran Province during the period 1986–2019. To improve the accuracy of thunderstorm system identification, only events that were simultaneously recorded at a minimum of two stations and during at least two six‑hour observation intervals were selected. The analyses were conducted at monthly, seasonal, and annual scales using statistical and spatiotemporal approaches within the framework of three 11‑year solar cycles. Zoning maps of thunderstorm occurrence frequency were also produced for solar cycle 24 using a larger number of stations with an appropriate spatial distribution. The results indicate that the highest frequency of thunderstorms occurs during the spring season, particularly in May. Despite the passage of most precipitation systems during autumn and winter, the lowest thunderstorm activity was observed in winter. Approximately 70% of the systems had a one‑day duration, and more than half of the events were reported only twice per day. Spatially, Imam Khomeini station and, at a regional scale, the southwestern part of the province in most seasons and the northeastern part during summer exhibited the highest frequencies. Considering the economic and infrastructural impacts as well as aviation‑related hazards, the development of thunderstorm warning systems in Tehran Province appears to be essential.
