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The purpose of this study is predicting climate changes and investigating the effect of probable climate change on the growing degree-days in the northwest of Iran. For this purpose the climatic data of seven synoptic stations during a 25 years period (1985-2009) was collected including Oroomieh, Tabriz, Zanjan, Sanandaj, Ghazvin, Kermanshah, and Hamedan were used as the base period and thus temperature variations periods (2030-2011 and 2065-2046) through HadCM3 model was simulated. For the little power of temporal and spatial distinction of this model, its outputs were downscaled using LARS-WG software and presented under Emission Scenarios including A1B (moderate scenario), A2 (maximum or pessimistic scenario), and B1 (minimum or optimistic scenario). Calibration, verification and Performance Model with the rate of the adaption of observed data and the simulated measures through statistics , RMSE and MAE were analyzed. Finally, using the simulated temperature growing degree-day was calculated and compared under 4 Base temperature including 0°,5°,10°, and 15° centigrade in the basic span (1985-2009) and future span (2011-2030 and 2046-2065). The results of simulation show that temperature change in north-west areas under all three A1B, A2, and B1 scenario are increasing in the future, but the differences among these three scenarios in each period is inconsiderable. In total the most temperature increasing was detected as 0/7 centigrade in A2 scenario for 2011-2030 period and 2/3 centigrade under A1B scenario for 2046-2065 period. Generally with the temperature increasing, the amounts of growing degree-day without exception increases in review periods and under the four Base temperature. Under studied scenarios, the Bases temperature of 0° centigrade had the most and 15° centigrade had the least impressibility from climate changes, so that the most increasing in calculated degree-day measures under 0° and 15° centigrade bases in the first period to the basic scenario (1985-2009) respectively was simulated as 207/4 and 120/6 degree-day under A2 scenario and for the second period to the 752/5 and 463/5 degree-day under A1B scenario.
 

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plants needs a certain amount of heat at the time of planting and during its growth period, The temperature requirements of the 704 single-cross cultivar of maize in Moghan weather conditions have been found in this study to determine its temperature requirements in its different growing stages in order to investigate the feasibility of its planting in the north west regions of Iran. Daily weather statistics presenting the minimum, maximum and average temperature of 51 Synoptic stations from Meteorological Organization of Iran have been used in this study, their statistical periods range from 1 to 30 years (1365-1395), the statistics and information about 5 main phenology stages of 704 single-cross variety maize which are recorded continually in Agricultural Weather Service of Moghan station in Pars Abad from 1390 to 1391 are provided. Then the 15-day averages from April 21st to July 22nd is obtained. The relationship between the temperature and the height in the linear regression is calculated .Map of heat supply date for seed sowing in all stations from the first half of May was drawn in the GIS. The plant collective growth degree days and the number of days in every phenology phase are calculated for all of the stations and the related maps are plotted.Then,the final map plotted by combining the layers thermal, height, slope and land use in the study area. The results of this study only 27.6% of the study area is able of maize cultivating.