survey and forecast of minimum temperature trends of iran

1. introduction climate is a large system which is produced due to the relation and action between other large systems. if a change occurs in one of these systems, other systems will coordinate themselves with the change fast or slowly. the consequences of this coordination will impress the system that is starter of this change and an endless continuum of the links connects these systems together. according to the nature of the climate elements used in the form of different time scales, the time variations of climate elements are very important. study of the time changes are performed via different models such as trend, seasonal, periodic and random models. 2. material and methods the statistical population in this study is monthly, seasonal and annual minimum temperature of 236 synoptic and climatology stations in iran, which samples with 78 synoptic and climatology stations were randomly selected due to their minimum temperature with high statistical period (higher than 30 years) and during 1958-2008. the lost minimum temperature of some stations was reconstructed using the least square method. the first step in a research for using tendency models is the measurement of series. joiner and smirnov tests were used for normal and abnormal measurement, tr parametric test was used for the measurement of trend models, proportionate with data nature for stations with minimum normal temperature and daniels nonparametric test was utilized for stations with minimum abnormal temperature. tr test: the above-mentioned test is considered as one of the important parametric tests. the value of tr test can be calculated using the following equation: (1) daniels, test one of the most important nonparametric tests is daniels test. for the calculation of this test with frequency more than 30, the following equation can be used: (2) the application of fitting, smoothing and prediction models: the series with trend and seasonal changes can be smoothed and predicted with holt method. the smoothing form: (3) the prediction form: (4) 3. results and discussion regarding to the joiner and smirnov tests used for the evaluation of data distribution, among 78 stations, minimum temperatures of 19 stations have abnormal distribution. the daniels nonparametric test was used for the evaluation of the series with abnormal distribution and the tr parametric test was used for the evaluation of minimum temperature of other stations with normal distribution. the obtained results of tr test show that the minimum temperature has tendency changes or trend for stations of chadegan, noushahr, hamedan, shargh esfahan, khoshkedaran, zabol, bandar torkman, talasar, kalaleh, jask, miandouab, iranshahr, hamandabsard, bajestan, sedeh brjand, mahmoodabad, semnan, chabahar, emamghais, tashkouyeh, rineh larijan, bandar lengeh, ahvaz, bam, torbat heydareh, abadan, boushehr, tabriz, kerman, khoramabad, banadr anzali, bandar abass, kermanshah, sabzevar, shiraz, ramsar, shahroud, tehran, shahrekord, zahedan and yazd. among these, the obtained value for the minimum temperature of khoramabad, bandar abass and shahrekord is negative. it shows that there are negative trends in minimum temperature for these stations and positive trends for other stations. using daniels test for the stations with abnormal distribution, minimum temperature has tendency changes for stations of bahookalat, lahijan, pilimbra, sarbaz, dargzin, zardgol, fassa, rasht, mashhad, babolsar and tabass. since this value is positive for all of stations except fassa, the minimum temperature of these stations has an increasing trend. compared to the obtained predictions using holt method and the minimum temperature average during the past years, we will have an increase in minimum temperature in different regions of iran during period of 30, 40 and 50 following years. the predicted values will show an increase of 0.16 degree for the minimum temperature in the northwest areas, 0.02-0.32 degree or an average of 0.17 degree in west, 0.12-0.27 degree or an average of 0.19 degree in southwest, 0.27-0.45 degree or an average of 0.36 degree in east, -0.27-0.28 degree in south, -0.35-.28 degree in north, 0.09-0.47 degree southeast in and 0.03-0.67 degree in central areas. 4. conclusion the results of this study show that among 78 stations, the minimum temperature for19 stations have abnormal distribution. the minimum temperature for these stations was measured with daniels nonparametric test and the annual minimum temperature for other stations with normal distribution was measured with tr parametric test. according to the two applied tests (tr and daniels) on the stations of iran, the results show that the minimum temperature for 26 stations are without any trend pattern. tendency changes for 48 stations are shown as positive and tendency of trend changes for minimum temperature of 4 stations of khoramabad, bandar abass, shahrekord and fassa are obtained as descending. also the series of annual minimum temperature for 52 stations in iran have been measured and predicted with different alpha coefficients. the forecasts show that minimum temperature will increase in the west areas between 0.02-0.32 degree, east areas between 0.27-0.45degree, south areas between -0.27-0.28 degree and north areas between -0.35-2.28 degrees.