Revealing the structure for the trend of maximum temperature average in Isfahan Province during the recent half- century

Changing climate and increasing temperature is considered as one of the important bio-environmental problems for the human being which has dedicated various studies to itself during the recent years. Increasing the average temperature of the earth and its changes is an indication of the climate changes which has been considered in all the theories of climate change.(Ibrahimi & Colleagues, 1384: 5). Studying the temperature changes and its role in the world heating due to freeing greenhouse gases in the atmosphere has been the dominant field of climate studies during the recent decades. Almost all of these studies in regional and world criteria approve increasing temperature during the past century. Even though this increase has not been similar in all the points and negative procedures have also been reported in some areas (Movahedi & Colleagues, 1384:15). In this regard, the role of maximum temperatures is evident in increasing evaporation and respiration, decreasing the surface and underground waters, development of types of diseases, firing forests, the process of melting glacials and creating drought and lack of water (low raining)in other areas (Husseini, 1388: 3). 1- Materials and Methods In the direction of performing this research, the statistics for the average of maximum temperature of 8 synoptic stations and 8 climatology stations with appropriate distribution in the province and 4 synoptic stations and also 1 climatology station for suitable coverage and for more accuracy of the calculations out of the province were used (Figure 1). In the studies for climate change, the long term statistical period is considered for ensuring from the authenticity of the obtained findings. For this purpose, the 50-year statistical period was determined in this research during the years 1961-2010. At first, the data were measured by the tests of Anderson – Darling and Ryan – Joiner and after making sure of their abnormality, the non-parametrical test of Mann- Kendall was selected for calculating and analysis of the trend. Also the tests of Chi-Square and Kolmogorov- Smironov were used for making sure of harmonious data. Following that, the data were arranged in a matrix with the dimensions of 21 x 600 and they were changed to the pixel data with the dimensions of 5x 5 km through programming in Software of Surfer and by the method of Kriging in station data. Then they were set in a matrix with the dimensions of 4260 x 600 and by Matlab Software monthly trend of each pixel was calculated 95 % in a significant level using Mann- Kendall Test and their regionalization was performed by ArcGis Software. 

The inferred results from studying the procedure make it clear that during January the whole province consists of the region without any trend and no trend has been observed in any one of the stations under study. During February, only Isfahan station had an increasing trend and other locations of the province lack the trend. With beginning of March, the locality for the region of increasing procedure has been transferred to the north of the province and it covers the stations of Badrud – Natanz and Kashan, and each year it increased 0.023 Centigrade Degrees. Other locations of the province still has no trend. During April and with warming weather, the region for the increasing procedure reaches to its climax throughout the year to the extent that it covers 52.2 % (2225 cells) or in other words half of the province area and it is being increased with the rate of 0.044 Centigrade Degrees per year. After April, the area of the regions which had increase in maximum temperature decreased and it reaches to 5.1 % in June from 52.5 % in April. During May, the increasing trend is transferred to south of the province and only a small part of northern areas in the province consist of the increasing trend region. With beginning of June, decreasing trends also are manifested in the province so that reduction in the rate of 0.005 Centigrade Degrees per year and 0.25 Centigrade Degrees during the past 50 years has occurred. After that from July to October, the extent of the increasing trend region is added in a manner that during the past 50 years, 0.35 % Centigrade Degree increase in July reaches to 0.55 % Centigrade Degree increase in October. During July, the decreasing trend region is reduced and it is limited to the western sides of the province. In September and coincident with the end of Summer, the regions with trend, are limited to the north west and west of the province. During this month, increasing trend has occurred in north and south-west of the province and decreasing trend has occurred in the western areas of the province consisting Meimeh Station. In this month the temperature has increased in the rate of 0.15 Degrees during the past half century (0.003 Degrees per year). During October and with beginning of Autumn, the decreasing trend region is reduced and it is limited to the Natanz station and increasing trends are more manifested so that it is increased 0.011 Centigrade Degrees per year. In November increasing trend region has been reduced very much and it is limited to Najaf Abad station at south-west of the province and north of Badrud – Natanz station. During December, the only region with trend in province is decreasing trend region and it is only observable at Natanz station. With consideration of the befitted line gradient December has had -0.001 Centigrade Degrees per year. 

The inferred results from studies for the procedure of average of maximum temperature at Isfahan Province make clear in this research that during the cold months of the year no tangible trend is observed in most of the areas at Isfahan Province and increasing or decreasing trends also have dedicated limited levels to themselves in a manner, so that in January there is no trend in the said parameter at the province and the whole of its area includes the region without trend. These findings are in agreement with the obtained results from the research of Movahedi & Colleagues, (19:1384) for Marun basin. With warming weather, increasing and decreasing trends are also divulged in a manner so that only increasing trends are observed during the Spring, but with the beginning of Summer, the decreasing trends are also divulged in the province. With consideration of the performed studies, the highest percent of the area for increasing trend region in April with 52.2 % of the province area consists of 2225 pixels, and the highest percent of negative trend region is considerable with 13.1 % of the province area and 559 pixels in June. It shall be mentioned that April with 2.2 Centigrade Degrees has the highest increase rate and June with -.25 Centigrade Degrees has the highest decrease rate during the recent half century. In general, no trend exists in most of the months.