واکاوی تغییرات مقدار، فراوانی، و شدت بارش‏ سالانۀ ناحیۀ خزری طی دورۀ آماری 1966-2016

بارش یکی از عناصر و فرایندهای اصلی اقلیم هر منطقه است که در برنامه‏ریزی‏های شهری و روستایی، مکان‏یابی صنعتی، معماری، کشاورزی، صنایع، و ... نقش تعیین‏کننده دارد. ازاین‏رو، در تحقیق حاضر تلاش شده است تا مقدار، فراوانی، و شدت بارش‏های سالانه ناحیه خزری ارزیابی شود. بدین‏منظور، از داده‏های روزانه 385 ایستگاه ‏همدید، اقلیم‏شناسی، و باران‏سنجی سازمان هواشناسی کشور و ایستگاه‏های باران‏سنجی وزارت نیرو طی بازه زمانی 1996-2016 استفاده ‏شده ‏است. با برازش مدل رگرسیون خطی به روش پارامتری، روند مقدار، فراوانی، و شدت بارش سالانه بررسی شد. نتایج حاصل از این پژوهش که در دیگر مطالعات مشهود نبوده ‏است بیانگر این است که میانگین بارش سالانه و فراوانی آن به‏ترتیب در 61.4درصد و 47.1درصد از پهنه دارای روند افزایشی است. شدت بارش سالانه در همه پهنه دارای رفتار ایستاست. روند ضریب تغییرات میانگین بارش سالانه نشان داد که گستره تحت حاکمیت روند ایستا بیشتر است؛ به‏‏طوری‏که در همه خط ساحلی و بخش‏هایی از ارتفاعات البرز توزیع بارش در گذر زمان در طی فصل‏های مختلف سال تغییری نکرده‏ است. بخش‏های شرقی ناحیه، ارتفاعات البرز (جنوب دریای خزر)، بخش‏هایی از ارتفاعات البرز غربی، و بخش بسیار کوچکی از غرب ناحیه روند کاهشی در ضریب تغییرات میانگین بارش سالانه دیده می‏شود.

Analysis of the Amount, Frequency and Intensity of Annual Precipitation in Caspian Region during 19662016

IntroductionPrecipitation is one of the most important climatic elements in every given region that plays a decisive role in urban and rural planning, architecture, agriculture, industry, and so on. Accordingly, the present study attempts to evaluate the amount, frequency and intensity of annual precipitation in the Caspian coastal region in which the economic planning is fundamentally based on precipitation. The spatial temporal variations of the parameter in this region affects many climatic and environmental phenomena (such as runoff, flood, air temperature, humidity), as well as many human activities (such as agriculture and housing). On the other hand, the growing need for recognizing its climatic features is one of the essential requirements of human life today. In addition, previous studies in this part of the country have mainly examined one of the characteristics of precipitation, but the present study attempts to analyze three characteristics (amount, frequency and intensity) of the element.  Materials and methodsTo this end, the daily data of 385 stations of Meteorological Organization and the Ministry of Energy’s have been used for the period of 20161966 (51 years). Then, the amount, frequency and intensity of annual precipitation were investigated and finally, the trend was verified by fitting the linear regression model using parametric method.Results and discussionThe results showed that the annual precipitation in 61.4% and the frequency of precipitation in 47.1% of the study area has an increasing trend. The annual precipitation is also stationary in entire study area. The trend of the variation coefficient in the month to month precipitation indicated that the stationary trend is overcome in the majority of the area. Consequently, precipitation throughout the coastline and parts of Alborz mountain chain has not changed during the year. Some parts of the area including the eastern parts, the Alborz mountain (south of the Caspian Sea), parts of the western Alborz, and a very small part of the west have experienced declining trend in the coefficient of variation in the annual rainfall. The results indicate that the precipitation in the Caspian region has a strong inverse correlation with the longitude, a inverse correlation with altitude, and a poor direct correlation with latitude. The relationship between precipitation and the number of rainy days is higher than other events with a direct and high correlation. In other words, with increasing rainfall, the number of rainy days also increases. With increase in the longitude of the mountains, the number of rainy days is reduced. The least inverse relationship is between the number of precipitation days and latitude and longitude.ConclusionThe average annual rainfall in the Caspian region showed that the average annual precipitation in the coastline is higher, especially in the southwestern part of the Caspian Sea.  The precipitation decreases as it passes from the coast.The results of this study are consistent with the findings of some researchers. The maximum number of rainy days is on the part of the western and southern Caspian Sea (Bandar Anzali). The maximum average annual precipitation is in the coasts of the Caspian Sea and its minimum in the eastern part and Alborz Highlands. Thus, the precipitation varies considerably in different parts of the Caspian region; these conditions can have an influence on the increase of greenhouse gases at the local level as well as the distance from the huge Caspian Sea. Frequency of crossing or formation of synoptic systems has led to precipitation changes in different parts. Therefore, understanding this issue and its causes can be important in the study of water resources, soil and ecosystems in the region, as well as the urban and environmental management of this valuable area of ​​the country. Therefore, it is suggested that the changes in the synoptic systems and the changes and seasonal shifting of precipitation in this region should be considered.