Statistical Analysis Anomalies of Maximum and Minimum Temperature in Cold Period in order to Understand the Effects of Climate Change on Different Regions of Iran

Document Type : مقاله پژوهشی


1 University of Lorestan

2 Atmospheric science & meteorological research center


1 Introduction
Temperature is one of the most important elements in weather and climate forecasting. Therefore studying temperature behavior is important for understanding climate variability that can vary at different spatial and time intervals and local, regional and global scale. The International Climate Change Board (IPCC) has clearly indicated that global temperature trends have increased by about 0.85 ° Cover the period 1880 to 2012. Climate change usually has enormous impacts on people and their temperament, agricultural resources and access to water, especially in areas where their economic activity is dependent on agriculture (as in most parts of Iran). Iran's climate is diverse due to the complexity of the topographic features and the vast geographical extent. Therefore, the effect of major local factors on climate change must be identified.
These results can help confirm the studies of climate models that this also helps in planning for agriculture and water supply, especially for the future. In previous decades, most temperature analyzes focused on average values. In recent year's low-temperature analysis has broadly focused on Changes in the occurrence of extreme temperatures with high frequency, Number of days over different temperature limits, Regional trend of minimum and maximum temperatures and diurnal temperature difference events.
2 Materials and Methods
This article evaluates the monthly mean and seasonal Minimum and maximum temperature variability in autumn (October-December), winter (January-March) and also the cold period (October-March over a 60-year (1951-2010) statistical period. Stations with 60-year statistics included 26 cases. Before using the data, it is synchronized and any possible errors are removed. Changes in mean and variance were tested by conventional methods. Statistical processing was performed using R software. According to World Meteorological Organization methods, Required statistics include mean, coefficient of variation, probability of up and down 20%, standard deviation, daily and monthly temperature and minimum and maximum temperatures in two 30-year(1951-1980),(1981-2010) and 60-year(1951-2010) periods were calculated. Then, using the Mann-Kendall test, the trend of this minimum and maximum temperature over a 60-year period was determined. The patterns of each statistic are plotted and interpreted using the
3 Results and discussion
The results show that the lowest mean temperatures are in the fall, winter, and cold periods in the northwest and north regions and the lowest is in the south and southeast of the country. The lowest coefficients of change in minimum temperatures for autumn, winter, and cold periods are the northern and southern coasts and the eastern and southeastern parts of the country and the southern and central coasts of the country respectively. The highest coefficient of variation is winter in Hamadan and Gorgan and in cold period in Gorgan and Rasht. In the autumn, the coefficient of variation is generally low. In addition, the lowest maximum temperatures occurred in autumn in the northwest and west and in winter in the north and northwest, which coincided with the pattern of maximum coefficient of variation. The years with a high frequency of 20% at the stations under study are synchronized at both minimum and maximum temperatures. But for the 20% lower limit, this coordination is not seen only in the first 30 years of autumn. Also in the last decade compared to the first decade the minimum temperatures during the autumn, winter and cold periods decreased at 8, 4 and 7 stations and at 18, 22 and 19 stations have increased respectively. In the fall, the maximum temperature only declined at three stations, and in the other two periods, all stations showed an increasing trend and the results in a decrease in the diurnal temperature difference.
4 Conclusions
Most of the minimum temperature variability is in the northwest and west and northeast of the country that the reason could be the arrival of different air masses, especially through the northwest and west of the country. But on the north and south coasts of the country, this variability is less due to the moderating effect of the sea. Also, the variability in autumn was higher than winter, which it shows the most active air masses in the winter. The occurrence of the highest maximum temperatures in the southern regions with the lowest coefficient of variation indicates a more uniform temperature conditions than elsewhere. Also, in most parts of the country, the diurnal temperature difference has decreased..


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