Monitoring the Trend of Iran Cold Extreme based on the Output of the EH5OM Dynamic Model

The growth of industries, and consequently, the excessive consumption of fossil fuels on the one hand, and the increase in the world's population and extensive land-use changes on the other hand, has led to the gradual transformation of the global climate after the industrial revolution. In recent decades, the air temperature has suddenly increased with significant changes in the frequency of cold and hot extremes. This study examines the future extreme minimum air temperature across Iran.

The average daily temperature from EH5OM database was used for assessment of global warming effects on daily minimum air temperature over Iran. EH5OM is one of the CMIP5’s AOGCM models, which uses ECHAM dynamic core with 31 vertical levels (up to near 10 hPa), developed in Max Planck Physics Institute. The simulation results for EH5OM are available from 1960 to 2100 for different IPCC’s emission scenarios. For this study, A1B scenario was chosen, because its fundamental assumption of balanced emphasis on all energy sources (fossil and non-fossil). Previous study shows that the result of this scenario is applicable for analysis of climate change in near future.

The trend of normalized temperature deviation index time series for Iran in the next decades shows a large number of abnormalities. The number of extreme cold days shows a decreasing trend during the study period. In April, most of the country's regions have decreasing trend of frozen events. This downward trend in the western part of the country is more pronounced than the eastern regions, with the highest decreasing trend in the Zagros Mountains. In May, as in April, the negative trend of frozen days covers most regions of Iran, except that in the mentioned period, the decreasing trend of frozen days shows higher values in eastern parts of the country.

The analysis of spatio-temporal patterns of the normalized temperature deviation index (NTD) for Iran during the study period (2015-2050) shows a major abnormality. Frozen days show a significant downward trend in the first half of the year. In winter (except for March) and spring, there is a dominant decreasing trend. Specifically in north-western regions of the country and Zagros Mountains, a significant decreasing trend will be expected in the next decades. Positive trend in the number of frozen days was also projected in some regions of the country, especially for October, November and February in north-western strip and south of Zagros Mountains. This increase in the frozen days during the cold season, may be unexpected at first glance, but with the warming of the ground and climbing the air towards the air, the shape of the polar vortex forms the airflow at high altitudes, resulting in This intense airflow (wind) is created around polar regions, which causes the air to release the cold weather of the polar regions towards the central regions of the planet, which is one of the most important reasons for the shape of cold faults in the decades to come.