تحلیل پهنه‌ای روند تغییرات و آشکارسازی نقطه‌ی شکستِ سری زمانی تبخیر-تعرق ماهانه در مازندران

نوع مقاله : مقاله پژوهشی

نویسندگان

1 استادیار هواشناسی کشاورزی، گروه مهندسی آب، دانشگاه علوم کشاورزی و منابع طبیعی ساری

2 دانشجوی دکتری هواشناسی کشاورزی، گروه مهندسی آب، دانشکده مهندسی زراعی، دانشگاه علوم کشاورزی و منابع طبیعی ساری، ساری، ایران.

چکیده

تبخیر-تعرق مرجع به‌عنوان شاخص مهمی از تقاضای تبخیر نیوار، یک عامل مهم برای مطالعات اقلیمی و هیدرولوژیکی است. با توجه به وقوع تغییر اقلیم و ایجاد نوسانات زیاد در میزان بارش و وقوع خشک‌سالی‌های ضعیف تا شدید، مطالعه در زمینه‌ی بررسی تغییرات تبخیر-تعرق حائز اهمیت است. در این پژوهش، به‌منظور بررسی تغییرات زمانی-مکانی روند و نقطه‌ی شکست در سری زمانی تبخیر-تعرق مرجع برای فصل‌های مختلف سال در استان مازندران در یک دوره‌ی 40 ساله (2020-1981) از داده‌های شبکه‌ای ماهواره‌ای (با وضوح حدود 5 کیلومتر) استفاده شد. جهت بررسی تغییرات روند و ارائه پهنه‌ی تغییرات نقطه‌ی شکست در تبخیر-تعرق از آزمون‌های ناپارامتری من-کندال، شیب سن، پتیت و رگرسیون چندک استفاده شد. ضریب همبستگی بین داده‌های تبخیر-تعرق شبکه‌ای با داده‌های زمینی ایستگاهی در اغلب ایستگاه­ها بیش از 9/0 و میانگین مقدار اریب 24/0 برآورد شد. نتایج آزمون پتیت، بیشترین زمان وقوع تغییرات ناگهانی در تبخیر-تعرق مرجع در فصل‌های بهار، پاییز و زمستان را به ترتیب در سال­های 2013، 2010-2007 و 1999 نشان داد. مقادیر بالای تبخیر-تعرق برای فصل‌های بهار در نیمه‌ی شرقی، برای تابستان در نیمه‌ی شمالی و برای زمستان در نوار جنوبی و غربی افزایش (به ترتیب با درصد شیب فصلی 45، 75 و 120 درصد) اما برای فصل پاییز در شمال استان کاهش (با شیب 45- درصد) یافته است. به‌طورکلی نرخ شیب‌های معنی‌دار افزایشی برای مقادیر بالای تبخیر-تعرق بیشتر از میانگین بوده است. افزایش قابل‌توجه مقادیر بالای تبخیر-تعرق به‌ویژه در فصل خشک سال، موجب کاهش منابع آب و اختلال در بخش کشاورزی خواهد شد. بنابراین باید روش‌های علمی و عملی برای مدیریت تبخیر-تعرق مرجع در سطح استان لحاظ شود.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Spatial Analysis of Changes and Detection of Jump of Monthly Evapotranspiration Time Series in Mazandaran

نویسندگان [English]

  • Reza Norooz Valashedi 1
  • Sedigheh Bararkhanpour-Ahmadi 2
1 Assistant Professor, Water Engineering Department, Sari Agricultural Sciences and Natural Resources University, Sari, Iran.
2 PhD student of Agricultural Meteorology, Water Engineering Department, Sari Agricultural Sciences and Natural Resources University, Sari, Iran
چکیده [English]

Reference evapotranspiration as an important indicator of demand for air evaporation is an important factor for climatic and hydrological studies. Due to the occurrence of climate change and the occurrence of large fluctuations in precipitation and the occurrence of mild to severe droughts, it is important to study the evapotranspiration changes. In this study, to investigate the temporal-spatial changes of trend and change point in the reference evapotranspiration time series for different seasons in Mazandaran province, 40 years data (1981-2020) from satellite networks (with a resolution of about 5 km) were used. Non-parametric Mann-Kendall, Sen's slope, Pettitt's test (Non-Parametric Rank Test) and quantile regression were used to investigate the changes in the trend and to present the range of fracture point changes in the evapotranspiration. The correlation coefficient between network evaporation-transpiration data and ground station data was estimated to be more than 0.9 in most of the stations and the average value of BIAS was 0.24. The results of Pettitt's test showed the time of sudden changes in reference evapotranspiration in spring, autumn and winter seasons in 2013, 2007-2010 and 1999, respectively, in most cases. Very high values of evapotranspiration increased in spring in the eastern half, in summer in the northern half and in winter in the southern and western strips (with a seasonal slope percentage of 45, 75 and 120 percent, respectively), but they decreased in autumn in the north of the province (with a slope of -45 percent). In general, significantly increasing slope rates for high values of evapotranspiration were higher than average. A significant increase in high amounts of evapotranspiration, especially in the dry season, will reduce water resources and disrupt the agricultural sector. Therefore, scientific and practical methods for managing reference evapotranspiration in the province should be considered.

کلیدواژه‌ها [English]

  • Evapotranspiration
  • Temporal - Spatial Trend
  • Change Point
  • Extreme Values

EXTENDED ABSTRACT

 

Introduction

Reference evapotranspiration (ET0) as an important indicator of demand for air evaporation is an important factor for climatic and hydrological studies. Due to the occurrence of climate change and the occurrence of large fluctuations in precipitation and the occurrence of mild to severe droughts, it is important to study the evapotranspiration changes. Extreme events such as floods, storms and droughts are often caused by extreme weather. Therefore, in addition to studying the average data in investigating changes in meteorological and hydrological parameters, it is necessary to examine very low or very high values of evapotranspiration and other meteorological parameters. Therefore, in this research, regression methods and statistical tests were used in order to investigate the temporal-spatial changes of ET0 in Mazandaran province. In order to investigate the trend and change point in the ET0 time series, the Mann-Kendall, Sen's slope and Pettit non-parametric tests were used, and to investigate the trend in extreme values of ET0, the quantile regression method was used.

 

Material and Methods

In this research, the monthly ET0 grid data (monthly sum in mm) was used, which was extracted from the TerraClimate database (with a resolution of about 5 km) and was calculated using the FAO Penman Monteith method. In the first step, checking the accuracy of grid data with the ET0 data from the nearest synoptic station to the grid position (calculated by Torrent-White method) was performed using Root Mean Square Error, BIAS and Spearman correlation test statistical evaluation indicators. Then, a seasonal time series of grid ET0 data was prepared for the entire Mazandaran province in a period of 40 years (1981-2020). In the next step, the trend of changes and the change point in the monthly ET0 time series in different seasons were performed using Mann-Kendall, Pettitt statistical tests and the quantile regression method, and the results (slope and significance of the trend and the year of the change point ) was zoned for the whole province in the GIS environment. Then the results were analyzed and compared.

 

Results and discussion

The correlation coefficient between network evaporation-transpiration data and ground station data was estimated to be more than 0.9 in most of the stations and the average value of BIAS was 0.24. The results of Pettitt's test showed the time of sudden changes in reference evapotranspiration in spring, autumn and winter seasons in 2013, 2007-2010 and 1999, respectively, in most cases. Very high values of evapotranspiration increased in spring in the eastern half, in summer in the northern half and in winter in the southern and western strips (with a seasonal slope percentage of 45, 75 and 120 percent, respectively), but they decreased in autumn in the north of the province (with a slope of -45 percent). In general, significantly increasing slope rates for high values of evapotranspiration were higher than average.

 

Conclusion

The significant increase in high amounts of evapotranspiration, especially in the dry season, will reduce water resources and disrupt the agricultural sector. , which, if not managed on time, will cause irreparable damages in the agricultural sector, especially in the dry season. Therefore, scientific and practical methods for managing reference evapotranspiration in the province should be considered.

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