تغییرات شدت بارش متاثر از تغییر اقلیم در ایستگاه سینوپتیک بابلسر (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
منحنی های شدت- مدت- فراوانی بارندگی یا روابط دیگری که بتواند شدت بارندگی را به ازای یک تداوم مشخص تعیین کند از ملزومات طراحی در هر پروژه هیدرولوژیکی است، چرا که سیل طراحی بر اساس رگبار طراحی بوده و رگبار نیز دارای تداوم معینی است که می بایست شدت آن مشخص شود. پدیده تغییر اقلیم ناشی از گرم شدن کره زمین بر مقدار و به تبع آن شدت بارش ها در مناطق مختلف جغرافیایی تاثیرگذار است. به منظور بررسی اثر گرم شدن کره زمین بر شدت بارندگی ها در ایستگاه سینوپتیک بابلسر، دوره مورد مطالعه به دو بازه زمانی 26 ساله (1968-1993) و (1994-2019) تقسیم شد. شدیدترین رگبار 10، 20، 30، 40، 50، 60، 90 دقیقه، 2، 4، 6، 9، 12، 18 و 24 ساعت هر سال از روی تمام رگبارهای رخ داده در آن سال استخراج شد. سپس با استفاده از نرم افزار EasyFit و با آزمون نکویی برازش کولموگروف- اسمیرنوف برای هر یک از 28 سری داده ها، مقادیر شدت بارندگی برای دوره بازگشت های 2، 5، 10، 25، 50 و 100 ساله به دست آمد. نتایج نشان داد که شدت بارش های 10 و 20 دقیقه ای و 18 و 24 ساعته بازه زمانی دوم نسبت به بازه زمانی اول به ترتیب 54، 17، 35 و 35 درصد افزایش یافته در حالی که شدت بارش های 50، 60، 90 دقیقه ای و 2، 4، 6 و 9 ساعته به ترتیب 10، 26، 31، 35، 34، 20 و 10 درصد کاهش یافته است. آزمون tجفتی انجام شده با نرم افزار SPSS روی پارامترهای دما نشان داد که در بازه زمانی دوم نسبت به زمانی اول افزایش دما رخ داده است که مقدار افزایش دمای میانگین26 ساله بازه زمانی دوم نسبت به بازه زمانی اول، 16/1 درجه سانتیگراد بوده است. همچنین بر اساس آزمون من کندال انجام شده روی داده های 52 ساله پارامترهای دما، روند صعودی مشاهده شد. به عنوان نتیجه کلی می توان عنوان نمود که تغییر اقلیم باعث افزایش شدت بارش های کوتاه مدت(5/%35) و بلند مدت(35%) و کاهش شدت رگبارهای میان مدت(24%) در ایستگاه سینوپتیک بابلسر شده است.Changes in rainfall intensity due to climate changes in Babolsar Synoptic Station
Extended Abstract Introduction Industrialization of communities and increased greenhouse gasses in the previous decades have resulted in increased global temperature and changes in climate parameters which are generally called climate change in scientific texts. Climate change has resulted in changes of temporal and local precipitation patterns all around the world. Consequently, hydrological cycle has changed affecting intensity, duration and frequency of rainfall events. Intensity- duration- frequency curves are used to provide an economic and safe design for drainage facilities, check dams, urban water management structures such as culverts, surface water and sewage systems. They are also used in landslides studies. The present study seeks to compare rainfall intensities in Babolsar Synoptic Station before and after 1993 to understand the effect of climate changes on rainfall intensities during the mentioned 52-year statistical period. Materials&Methods The first synoptic station of Mazandaran province was set up in Babolsar city in 1952. With an elevation of -21 m from sea level and 7 m from the Caspian Sea level, it is located at the east longitude of 52o, 39̍, 30̎ and the north latitude of 36o, 43. The station has a mean annual rainfall of 928 mm and an average of 99 rainy days. To understand the effect of climate changes on rainfall intensities in different durations and return periods in Babolsar Synoptic Station, statistical period was divided into two 26-year subperiods (before: from 1968 to 1993 and after: from 1994 to 2019). Rainfall intensities were calculated separately for each of the 14 duration series (10, 20, 30, 40, 50, 60, 90 minutes and 2, 4, 6, 9, 12, 18 and 24 hours) with return periods of 2, 5, 10, 25, 50 and 100 years and compared together. Then, a paired t-test was conducted to prove the difference between two series of rainfall intensity to be significant. Moreover, 5 annual air temperature parameters including minimum absolute temperature, maximum absolute temperature, average minimum temperature, average maximum temperature and average temperature were investigated in both subperiods and analyzed using a paired t-test in SPSS software. Results were used to investigate temperature and precipitation changes during the statistical period and prove the difference between before and after time series data to be significant. Mann-Kendall test was also carried out on 5 air temperature parameters collected during the 52-year time series data to find ascending or descending trends. Results&Discussion Compared to the first subperiod, the average rainfall intensities have increased in 10, 20, 30 minute and 12, 18 and 24-hour durations of the second statistical subperiod, while the opposite has occurred in 40, 50, 60, 90-minute, and 2, 4, 6 and 9-hour durations. However, statistical analysis has proved increased rainfall intensities in 10 and 20-minute, and 18 and 24-hour durations and decreased rainfall intensities in 50, 60, 90-minute, and 2, 4, 6 and 9-hour durations of the second statistical period to be significant. A paired t-test was conducted to compare rainfall intensity in the statistical subperiods and find out its effects on climate change. Results indicated that except for data collected in 30 and 40-minute and 12-hour durations, the difference between other paired series was significant at a less than 5% level. Moreover, except for maximum absolute air temperature, other air temperature parameters showed a significant difference at less than 0.5% level. Furthermore, all 5 parameters showed an increase in the second study period indicating a warmer climate in Babolsar. However, paired t-test results indicated that despite the reduction of mean annual rainfall in the second statistical period, difference between the two series was not significant at any acceptable level of significance. Moreover, results of the Mann-Kendall test indicated that average air temperature, average maximum air temperature, average minimum air temperature and minimum absolute air temperature have shown an ascending trend at a 1% significant level, while maximum absolute temperature lacked a specific trend and showed leap changes. Annual rainfall also showed random changes and lacked a specific trend during the 52 year statistical period. Conclusion Results of the Man-Kendall and paired t-test have shown that a significant increase have occurred in air temperature during the 52-year statistical period (1968-2019) resulting in climate changes. It can be concluded that climate change has increased the intensity of short-term (shorter than 40 minutes) and long-term (longer than 12 hours) precipitations and reduced the intensity of medium-term precipitations in Babolsar Synoptic Station. Moreover, climate change has increased the intensity of precipitations with short and long return periods while reducing the intensity of precipitations with medium-term return periods in the aforementioned Synoptic Station.
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