آشكارسازي و تحليل روند دماي ايران در تراز 1000 هكتوپاسكال

Detection and analysis of temperature trend at the 1000 hPa level in Iran

دما از عناصر اساسي شكل‌گيري اقليم است و تغييرات آن مي‌تواند ساختار آب و هوايي هر منطقه‌اي را دگرگون سازد و موجب تغيير در وقوع پديده‌هاي حدي نظير خشكسالي، بارش‌هاي سنگين و توفان ‌شود. لذا بررسي روند دما در مقياس‌هاي مختلف زماني و مكاني بخش بزرگي از تحقيقات اقليم‌شناسي را به خود اختصاص داده است. اين تحقيق به‌منظور آشكارسازي تغييرات دماي تراز 1000 هكتوپاسكال در فصول مختلف از سال 1950 تا 2020 ميلادي در ايران صورت گرفته است. تحليل‌ها بر روي متغير ميانگين ماهانه دما در طول دوره 70 ساله با استفاده از پايگاه داده NCEP/NCAR انجام گرفته است. نمودارهاي سري زماني متغير مورد مطالعه با استفاده از آزمون من كندال در مقياس سالانه ترسيم شدند. براي آشكارسازي و تحليل روند دماي ايران در تراز 1000 هكتوپاسكال نقشه‌هاي ميانگين 10 ساله و نمودارهاي سري زماني سالانه ترسيم شد، نتايج نشان داد ميانگين سالانه دما در پهنه كشور ايران با آهنگ 1.34 درجه سانتي‌گراد (بالاتر از ميانگين جهاني با مقدار0.74 درجه سانتي‌گراد ) در هر سده داراي روند افزايشي است. مقادير متغير ميانگين سالانه دما در فصل‌هاي تابستان، پاييز و بهار داراي روند معني‌دار بوده و ميانگين دما در تراز 1000 هكتوپاسكال داراي روند صعودي است. بالاترين افزايش ميانگين دماي تراز 1000 هكتوپاسكال متعلق به فصل تابستان بوده و با مقدار 0.2 درجه سانتي‌گراد به ازاي هر 10 سال افزايش يافته است. نقشه‌هاي ده ساله ميانگين دما در فصول مختلف نشان دادند نيمه جنوبي ايران در طول دوره مطالعاتي داراي روند افزايشي دما بوده است.

Introduction Temperature is considered to be an important element of climate whose changes have important consequences for human life. The present study seeks to detect trends and significant changes in the temperature at the 1000 hPa level in Iran. Due to its geographical location, Iran climate is affected by various patterns of sea level pressure such as subtropical high-pressure, Siberian high-pressure, Monsoon low-pressure, the Mediterranean low pressure, Black Sea low pressure and Sudan low pressure during warm and cold seasons. These patterns have changed in different time series leaving adverse effects such as decreased precipitation and increased temperature, while probably changing Iran climate from semi-arid to arid and causing climate hazards. Having enough information on the temperature characteristics and its future trends, it is possible to decide on macro politics and a comprehensive method for the management of an area. Therefore, the present study aims to detect trends and significant changes in air temperature at the 1000 hPa level.   Materials & Methods 45 ° to 64 ° Eastern longitude and 45 ° to 64 ° latitude were selected to study temperature changes at the 1000 hPa level in Iran. In this study, temperature data of 1000 hPa level recorded in a 70-year statistical period (1950 to 2020) and data retrieved from NCEP/NCAR with a spatial resolution of 2.5 by 2.5 degrees have been used to prepare time series and necessary maps. The Kendall Man test was used to analyze the trend of time series. The 70-year statistical period (1950 - 2020) was divided into 10 decades and average seasonal temperature was used.   Results & Discussion The average temperature of Iran at the 1000 hPa level is rising by 1.34° C per century and its standard deviation has reached its maximum value in recent decades. In the last two decades of the statistical period, 30 ° C contour line has approached Iran from southwest. Temperature trend at the 1000 hPa level is investigated in 4 different seasons of Iran. Summer: according to the Mann-Kendall test, average temperature in summer shows a significant trend and has increased by 0.2 ° C every decade. Autumn: time series of temperature data in autumn shows a significant trend and the slope of the regression line (temperature) has increased with a rate of 0.0451 ° C every decade. Winter: average temperature has decreased at the beginning of the study series and increased at the end of the series. 15.26 ° C and 8.18 ° C (in 1966 and 1972) were the highest and the lowest average temperature recorded in winter, respectively. Spring:The average temperature in Iran has increased by 0.197 ° C every decade. In this 70-year statistical period, average temperature of Iran in this season was 24.37 ° C with the highest annual average temperature recorded as 27.18 ° C in 2008 and the lowest annual average temperature recorded as 21.83 ° C in 1972 and 1992.   Conclusion Average temperature in Iran is raising with a rate much higher than the global average (0.74 ° C per hundred years), due to wide fluctuations in the general circulation patterns of the atmosphere and changes in sea level pressure pattern. Thus, it can be predicted that the temperature in southern Iran may reach over 60 ° C by the end of the century threatening southern riparian provinces with dangerously rising water level and the risk of drowning. Wildfires will still be common in Iranian forests, the number and intensity of floods will increase sharply, and water resources will reach a critically low status.