مقايسه تبخير-تعرق مرجع پنمن-مانتيث ASCE و پنمن-مانتيث فائو-۵۶ در مقياس هاي زماني زيرروزانه مختلف: يك مطالعه عددي

آب و خاک  

دوره 29 - شماره 5

نوع مقاله: Original Article
چكيده: در پژوهش حاضر، برآوردهاي تبخير-تعرق مرجع (ETo) حاصل از مدل هاي پنمن-مانتيث ASCE و فائو-۵۶ (به‌ترتيب، ASCE-PM و FAO۵۶-PM) در مقياس هاي زماني زيرروزانه مختلف از طريق اجراي يك آزمايش محاسباتي مورد مقايسه قرار گرفت. داده هاي هواشناسي در مقياس هاي زماني روزانه و زيرروزانه مختلف (يك تا ۳۶۰ دقيقه) با استفاده از داده هاي روزانه بلندمدت ايستگاه سينوپتيك آبادان (۵۹ ساله) و يك چارچوب ريزمقياس سازي اطلاعات هواشناسي توليد گرديد. نتايج نشان داد در فصول گرم سال، مقادير مجموع ۲۴ ساعته مولفه هاي تشعشع و آيروديناميك و ETo اشتقاق يافته از هر دو مدل ASCE-PM و FAO۵۶-PM از انطباق بهتري با مقادير نظير روزانه برخوردار بودند. عملكرد هر دو مدل در بازسازي مقادير روزانه مولفه آيروديناميك بهتر از عملكرد آنها در بازسازي مقادير روزانه مولفه تشعشع بود. در مقايسه با مدل FAO۵۶-PM، عملكرد مدل ASCE-PM در بازسازي مقادير روزانه ETo نسبت به نحوه محاسبه تشعشع خالص طول موج بلند (Rnl) از حساسيت بيشتري برخوردار بود. نتايج نشان داد اتخاذ يك گام زماني كوچكتر، لزوما به بهبود انطباق مقادير مجموع ۲۴ ساعته و مقادير روزانه ETo نمي انجامد. به-منظور برآورد تبخير-تعرق مرجع زيرروزانه در شرايط اقليمي منطقه مطالعاتي، استفاده از مدل ASCE-PM بر اساس انتگرال مقادير Rnl اشتقاقي از برآوردهاي تشعشع خورشيدي در شرايط آسمان صاف (Rso) حاصل از يك مدل فيزيكي-بنيان برآورد تشعشع خورشيدي در بازه‌هاي زماني يك ثانيه اي با ميانگين ضريب كارآيي مدل برابر با 0.9970 نسبت به ساير گزينه هاي مورد بررسي ارجح مي باشد.
A Comparison of ASCE and FAO56 Reference Evapotranspiration at Different Subdaily Timescales: a Numerical Study
Article Type: Original Article
Abstract: Introduction: Subdaily estimates of reference evapotranspiration (ETo) are needed in many applications such as dynamic agro-hydrological modeling. The ASCE and FAO56 Penman–Monteith models (ASCE-PM and FAO56-PM, respectively) has received favorable acceptance and application over much of the world, including the United States, for establishing a reference evapotranspiration (ETo) index as a function of weather parameters. In the past several years various studies have evaluated ASCE-PM and FAO56-PM models for calculating the commonest hourly or 15-min ETo either by comparing them with lysimetric measurements or by comparison with one another (2, 3, 5, 9, 10, 11, 16, 17, 19). In this study, sub-daily ETo estimates made by the ASCE-PM and FAO56-PM models at different timescales (1-360 min) were compared through conduction of a computational experiment, using a daily to sub-daily disaggregation framework developed by Parchami-Araghi et al. (14).
Materials and Methods: Daily and sub-daily weather data at different timescales (1-360 min) were generated via a daily-to-sub-daily weather data disaggregation framework developed by Parchami-Araghi et al. (14), using long-term (59 years) daily weather data obtained from Abadan synoptic weather station. Daily/subdaily net long wave radiation (Rnl) was estimated through 6 different approaches, including using two different criteria for identifying the daytime/nighttime periods : 1) the standard criteria implemented in both ASCE-PM and FAO56-PM models and 2) criterion of actual time of sunset and sunrise in combination with 1) estimation of clear-sky radiation (Rso) based on the standard approach implemented in both ASCE-PM and FAO56-PM models (1st and 2nd Rnl estimation approaches, respectively), 2) integral of the Rso estimates derived via a physically based solar radiation model developed by Yang et al. (25), YNG model, for one-second time-steps (3rd and 4th Rnl estimation approaches, respectively), and 3) integral of the calculated Rnl based on Rso estimates derived via YNG model for one-second time-steps (5th and 6th Rnl estimation approaches, respectively). The capability of the two models for retrieving the daily ETo was evaluated, using root mean square error RMSE (mm), the mean error ME (mm), the mean absolute error ME (mm), Pearson correlation coefficient r (-), and Nash–Sutcliffe model efficiency coefficient EF (-). Different contributions to the overall error were decomposed using a regression-based method (7).
Results and Discussion: Results showed that during the summer days, 24h sum of sub-daily radiation and aerodynamic components of ETo and the estimated ETo derived from both models were in a better agreement with the respective daily values. The reason for this result can be attributed to the nighttime value of cloudiness function (f) and the longer nighttime during the cold seasons. Because the nighttime values for f are equal the f value at the end of the previous daylight period until the next daylight period. The difference between sub-daily ETo derived from the ASCE-PM and FAO56-PM models during the day and night was highly dependent on the wind speed. In case of both models, daily aerodynamic component of ETo (ETo d,aero) were reproduced more efficiently, compared to radiation component (ETo d,rad). Except in the case of 6th Rnl estimation approach, FAO56-PM model (with a mean model efficiency (MEF) of 0.9934 to 0.9972) had better performance in reproducing the daily values of ETo (ETo d ), compared to ASCE-PM model (with a MEF of 0.9910 to 0.9970). The agreement between 24h sum and daily values of aerodynamic component had a lower sensitivity to the adopted time-scale, compared to the radiation component. Compared to the FAO56-PM model the performance of the ASCE-PM model in reproducing the ETo d,rad, ETo d,aero and ETo d had higher sensitivity to the approach utilized for calculation of Rnl and hence, to the uncertainty of net radiation. Results showed that a smaller time step does not necessarily leads to an improvement in agreement between 24h sum of subdaily and daily values of ETo. Deficiency of the standard daytime/nighttime identification criteria resulted in a higher daily averaged daytime (1.3831 to 1.6753 h) used in cloudiness function calculations, compared to the respective value used in calculations of the radiation and aerodynamic components. In order to estimate the sub-daily ETo under climatic condition of the studied region, the use of ASCE-PM model based on the 6th Rnl estimation approach, (ASCEPM)6, with a MEF of 0.9970 is preferred, compared to other studied alternatives. Another advantage of the (ASCE-PM)6 and (FAO56-PM)6 models is their computational efficiency in case of their implementation in hydrological models.
قیمت : 20,000 ريال