بررسي فصول طبيعي در استان كرمانشاه

The Review of Natural Seasons in Kermanshah Province

The maximum, minimum and mean temperature data for 4 stations from Kermanshah province namely Kermanshah, Sarepole Zahab, Eslamabade gharb and Kangavar in a period of 15 years from 1986- 2000 were obtained and used. After reviewing and comparing the results, finally agglomerative hierarchical clustering analysis techniques were selected for the determination of natural seasons in Kermanshah province on the basis of 7 days daily average temperature data.The results of the study show that in Kermanshah province,the hole year basically is divided into two main seasons. Summer and winter are more important than other two seasons namely spring and autumn in this region. The seasons of spring and autumn are very short. On the basis of combined temperature indices of absolute minimum, maximum and mean weekly temperatures in Kermanshah province, winter lasts 16 weeks, summer 19 weeks, spring 9 weeks and autumn only 8 weeks. Natural seasons in this province do not start at the beginning of calender seasons. On the basis of the used indices, winter begins from the 48 tʹ week , spring from the 12 `h week , summer from the 21 ʹh week and autumn from 40 ʹh week of the year. These dates are true for other stations too. In the warm section of the province namely Sarepole Zahab station, spring begins when the temperature reaches 24.3 degrees centigrade, summer with 36.6 ,autumn with 34.5 and winter begins with 21.3 degrees centigrade. In the cold section of the province i.e. Kangavar station, spring begins when the temperature reaches 10.7 degrees centigrade, summer begins with 19.3, autumn with 15.8 and winter begins with 7.7 degrees centigrade. There is a general belief that says in cold regions of Kermanshah province the winter season is longer than the other 3 seasons and in warm section of this province the summer season is longer than the other 3 seasons too,but the results of this study did not confirm this belief.