بررسی فصلی تبخیر تعرق مرجع و تحلیل حساسیت آن به عناصر هواشناسی در ایران

تبخیر تعرق ترکیب دو فرایند مجزّا، تبخیر از سطح خاک و تعرّق از گیاه است که میزان آن بستگی به عناصر مختلف هواشناسی دارد. از این رو شناخت عوامل موثر و میزان تاثیر هر عنصر بر تبخیر تعرق مرجع (et0) حائز اهمیت فراوان است. در پژوهش حاضر، برآورد et0 فصلی بر اساس آمار 45 ساله 2020-1976 سازمان هواشناسی 40 ایستگاه همدید به روش فائوپنمن مانتیث 56 محاسبه و بصورت نقشه های پهنه بندی ارائه شد. روند تغییرات et0 با آزمون های مَن-کندال و روند نوآورانه (ita) بررسی شد. به منظور بررسی میزان تاثیر هر عنصر بر et0، ضریب حساسیت فصلی با استفاده از روش sobol محاسبه شد. بدین صورت که توزیع آماری عناصر هواشناسی شامل رطوبت نسبی، ساعت آفتابی، متوسط، بیشینه و کمینۀ دما و سرعت باد؛ با محاسبۀ میانگین و واریانس هر پارامتر در دامنه 40%± برآورد شد و سپس با ثابت نگه داشتن هر متغییر، تغییر تمامی متغییرها ضریب حساسیت در مقیاس فصلی ارائه شد. براساس نتایج؛ میزان تاثیرگذاری عناصر هواشناسی در et0 در فصول مختلف سال متفاوت است. ضریب حساسیت برای میزان تاثیرگذاری هر عنصر شامل کمینۀ دما با 18.1%، سرعت باد 22.5%، سرعت باد 31.9% و بیشینۀ دما 20.4% به‌ترتیب در فصول بهار، تابستان، پاییز و زمستان رتبۀ نخست را در میزان تاثیرگذاری به خود اختصاص دادند. براساس یافته های پژوهش حاضر میزان تاثیرگذاری عناصر مختلف هواشناسی بر et0 در فصول مختلف تفاوت داشت که این مهم باید در برنامه ریزی و مدیریت بهینۀ منابع آب کشور مورد توجّه قرار بگیرد.

seasonal analysis of reference evapotranspiration and its sensitivity to meteorological elements in iran

introductionevapotranspiration is the combination of two separate processes, soil moisture evaporation, and plant transpiration, which amount depends on various meteorological elements. therefore, identifying the effective factors and the amount of their impact on reference evapotranspiration (et0) is important. this component plays an important role in various agricultural studies, including the design of irrigation and drainage systems, reservoir design, and irrigation planning (ahmadyan et al., 2023). accurate estimates of evaporation and transpiration play an important role in studies such as global climate change, and environmental evolution, and in various scientific fields such as hydrology, agriculture, forest and pasture management, and water resources management (kazemi, 2020). materials and methodsthe research was conducted in iran, and the data analyzed encompass various meteorological parameters, including maximum, average, and minimum temperatures, average relative humidity, wind speed, and sunshine hours. these data were collected on a daily basis from 40 synoptic stations across the country. the dataset spans from 1976 to 2020 and was sourced from the meteorological organization of the country (imo, 2022).the research employed the fao penman-monteith method, specifically the 56th version, to estimate seasonal et0 (evapotranspiration) values.in this research, for statistical evaluations of et0 and revealing the trend of time series on a seasonal scale, the non-parametric mann-kendall (m-k) test; (kendall, 1948; mann, 1945) was used. to identify the changing trend of the et0 time series, the ita method was used on a seasonal scale. four meteorological stations and the 45-year time scale (1976-2020) used in the current research, it had a better performance than other interpolation methods, which was used as the superior method. to understand the possible changes of one or more meteorological variables in et0, the sensitivity of reference evapotranspiration to six meteorological variables (relative humidity, hours of sunshine, average temperature, maximum temperature, minimum temperature, and wind speed) was estimated. for this purpose, sobol’s method (sobol, 1993). sensitivity analysis was used. results and discussionaccording to the et0 survey results, the highest amount of et0 was observed in the spring season in the south and south-eastern parts, and the highest average value was 1050 mm/year in zabul station. the increase of et0 in these areas can be due to the sun’s radiation and more warming of the earth’s surface in the southern latitudes of the country. in summer due to the length of the day and higher temperature, we saw an increase in et0, especially in the southern and southeastern regions of the country. in autumn, due to the decrease in the length of the day and the decrease in temperature, the amount of et0 has also decreased significantly in the northern parts of the country. in winter, with a decrease in temperature and an increase in relative humidity, which is more noticeable in northern than southern regions.in the summer season, all stations generally showed an increasing trend in et0. in most of the stations, the significance level was 5% and it did not follow a specific pattern. in the autumn season, an increasing trend of et0 was observed at a significant level of 5% in khoy and saqez stations, and a significant decreasing trend was observed in qazvin and shiraz stations. in the winter season, in the western and northwestern regions, all study stations showed an increasing trend of et0. finally, the overall results indicate that there is a significant increasing trend of et0 during the summer in iran. the graphical results of the et0 trend by the four seasons on a scale of 44 showed that, in general, there was an increasing trend in et0 in both high and low areas in all seasons.