Investigating Minimum and Maximum Temperature Anomalies during Warm Seasons to Reveal Warm and Cool Spell over Iran

Temperature is one of the most important parameters of the climate, which is the source of many physical, chemical and environmental changes. Regional assessments of these changes and their understanding of the process in different climatic zones are essential because they can help identify the severe climatic events and their impact on environmental systems and risk management. The importance of the issue and uncertainty about future changes will require us to know why and how the temperature changes affect climate conditions in the future. For this reason, the study of climate events has become a special issue. changes in the average of minimum and maximum temperature have become more intense in recent decades; thus directly or indirectly through the expansion of the growth season of pests and pathogens, increased drought in the spring and soil erosion, etc., can be plant, animal and human life Threatened Hence, the accurate analysis of changes in spatial-temporal patterns is the minimum and maximum temperature for establishing ecosystem management strategies. The geographic location of Iran and the wide range of deserts and dry lands with mountainous areas make its ecosystem vulnerable to slight changes in temperature. Because temperature variations and affect on limit plant growth, it can challenge their stability and flexibility. In this research, by selecting 26 synoptic stations, the required statistics including mean, coefficient of variation, estimation of high and low probability of 20% for two 30-year periods (1951-1980) and (1981-2010) and two 10-year periods (1951-1960) and (2010-2001) and a 60-year period (1951-2010) were calculated using R software. Then, using the Mann-Kendall test, the two parameters were calculated for the period of 60 years. In the next stage, the patterns of each of the stories were mapped using the IDW method in GIS software and were then interpreted. The pattern of the average of maximum, minimum and their coefficient of variation shows in the spring, summer and warm period associated with tittle variations. The coefficient of change in the western and northern parts of the country is more variable. The southern half is modest in all three periods. The average of the maximum and minimum temperatures of most stations in the periods 1981-2010 and 2001-2010 has increased. The increase in the mean temperature of the maximum temperature is slower, which reduces the range of temperature changes overnight. The Midwest has the highest average and minimum temperature difference, which is consistent with the results of the difference between the average temperature of the minimum and maximum periods (1960-1951 and 2010-2001). The highest increase was observed in the average temperature of Ahwaz, Tehran, Mashhad, Shiraz and Shahrood cities. The probability of 20%, which is higher than the average maximum temperature, and 20%, which is below the mean minimum temperature showed that the frequency and intensity of the hot and cold periods increased during in 1981-2010.
The difference between the average minimum and maximum temperatures 2001-2010 and 1951-1960 showed that except for Urmia, Hamedan, Shahrekord, Khorramabad and Bandarabbas, the remaining stations experienced this increase in spring. In summer, the stations of Urmia, Shahrekord and Kerman, the rest of the stations for the last 10 years have experienced a rise in the average temperature. Data reconciliation using the Mann-Kendall test for the period 1981-2010 showed that average minimum temperature of 21 stations during spring, and 22 stations in summer was significant. The average temperature of the two stations of Shahrekord and Khorramabad in spring, as well as Urmia and Shahrekord in summer have a significant decrease. The average temperature of spring and summer is also increasing and decreasing. The rate of increases the average temperature of spring and summer months more severely than the average temperature increase, thereby reducing the range of temperature changes (DTR). The average temperature pattern and its coefficient of variation in spring, summer and warm periods in the western and northern parts of the country are more variable than the rest of the regions. The highest coefficient of variation in the northwest, west and the Caspian basin is related to Anzali, Urmia and Zanjan stations, which seems to be influenced more by northern cold weather and roughness conditions. The southern half of the country has notable changes in all three periods indicating that the regime is still stable in spring and summer temperature variations in the region. It is concluded that in these sections, when the northwest adjacent high-lying area is displaced to the central and northern parts of Iran, these areas are affected by the flow of tropical regions increase in the average of maximun and minimum temperature of most stations in the north-west and west in the second period can be explained by changes in land use, urban expansion, population growth, and consequently, the increase of greenhouse gases and thermal systems and the station's displacement, which can change the climate create an area. It also seems that in the second period, the impact of the northern currents reduced to the first period, and the same has been added to the effects of systems with a southern source and high-altitude hegemonic sovereignty. The increase in mean temperature in the second period was lower in most of the stations than in the first period in summer, which seems to be due to the decrease in the frequency of relatively cold air invasion and also the convective systems. The relative disparity in the north and west of the country is due to the height and direction of roughness. The increase in minimum temperatures in stations like Tehran, Rasht, Mashhad and Tabriz in the northern half of the country is more than 2 degrees in the spring. Although in the spring, the northern part of the country has not yet been influenced by the tallest grassroots dominance. Therefore, such an increase in the average of the minimum temperatures of these stations can be justified in view of the abovementioned cases in the increase of the average maximum temperature. The average temperature increase in summer is slower but is faster regarding the mean minimum temperature; therefore, the range of average mainimin and maximum is declined. Study of 20% above and below average of the maximum and minimum temperature of spring and summer in the two 30 years’ period indicate that frequency and occurrence of the hot spell during the second 30-year period is more than firs 30-years period. The average maximum temperature in spring has a direct effect on the average summer temperature, and therefore, on the experience of the maximum temperature corresponding to spring. The study of the average minimum temperature is also consistent with global warming and confirms the occurrence of climate change in Iran. The mid-term maximum temperature also indicates an increase in most of the stations. According to what mentioned above, hot nights can increase the risk of terrain events in the country as a result of reducing the range of temperature changes during night, and as a result, can increase the vulnerability of the people to economic, social and environmental problems.