جستجوی مقالات مرتبط با کلیدواژه « reference evapotranspiration » در نشریات گروه « اکولوژی »

The correct estimation of reference evapotranspiration (ET0) is considered in order to accurately monitor the water requirement of crops and water balance in large scale irrigation and drainage plans.The present study aim to evaluation of spatial and temporal of twenty-four different methods to predict ET0 based on air temperature, solar radiation and mass transfer models, in 11 stations of Khuzestan province in Iran (1996-2005). The results were compared with the result of the FAO Penman – Monteith method (PMF-56) with use of statistical indices: R2, RMSE and PBIAS. Also the best map of each category was provided in the ArcGIS software. The results showed that, the methods have different performance in different seasons, but the performance of the models at most in the methods is satisfactory, this can be due to the same climate type and geographic location. Also according to the annual results, among the methods based on air temperature, Blaney and Criddle methods with R2=0.92 and RMSE=2.9 and Hargreaves and Samani methods with R2=0.91 and RMSE=2.2, among the methods based on solar radiation, Doorenbos and Pruitt methods with R2=0.93 and RMSE=3.0 and among the methods based on mass transfer, WMO method with R2=0.97 and RMSE=5.0, had the best performance to predict reference evapotranspiration comparing with PMF-56 in Khuzestan province. Finally, according to the annual, results the based on air temperature methods were the most accurate in Khuzestan province. It is notably, temporarily, summer season was the least accuracy in all methods of temperature, radiation and mass transfer.

Evaluation of water requirement in designing irrigation systems and water supply in agriculture is important. The aim of this study was to estimate and determine the spatial pattern of water requirement of apple tree using weather stations statistics from 1985 to 2013 in apple tree cultivation areas in Iran. Initially, annual reference evapotranspiration was estimated based on the FAO, Penman-Monteith model, In the following, the stages of growth the summer apple Kohanz crab and autumn apple Red-Delicious were identified. Eto calculation annual results and water requirement of growth stages were identified using ArcGIS10.2 as a spatial pattern for each variety. The results showed that the annual ETo in the North-Eastern and Southern regions of the apple cultivation area cultivar reaches more than 2000 mm. The summer apple Kohanz crab has less water requirement than autumn apple Red-Delicious varieties and the middle stage of growth in apple trees have the highest water requirement. The spatial changes in evapotranspiration and water requirement apple trees are due to altitude factor. From the north to the south and from the West to the East, the apple cultivation areas in Iran increases the amount of water requirement.

Estimating and determining of rice water requirement, being the main cultivate of Rasht region, is crucial for devoting water to this region. Equations which are used to calculate the reference evapotranspiration (ET0) are not match to all climatic conditions, due to their empirical bases. So, it is necessary to clarify proper methods for each region. Crop coefficient (Kc) is also the main parameter for determining each plant’s potential evapotranspiration and subsequently plant water requirement. Hence in this study, evapotranspiration data for grass and rice i.e. Binam and Khazar cultivars were collected in Rice Research Institute of Rash, by using drainable lysimeter at ten-day periods during three consecutive crop seasons. The reference evapotranspiration were calculated and compared with 16 empirical equations results included in Ref-ET software. Significant differences of them have been evaluated using SPSS software. Also, the crop coefficient values were calculated for each variety of rice. In all three equations i.e. Hargreaves, Priestley-Taylor and Penman (FAO 24) have not shown any significant differences. Among three methods, Hargreaves equation is recommended for Rasht region because, this equation as compared with others is a temperature-based method and would consider global warming phenomenon. Also, the average of crop coefficient (Kc) for Khazar and Binam in three consecutive crop seasons were 1.10 and 1.09, respectively.

In this study, climatic parameters are used to evaluate the sensitivity of reference evapotranspiration in Isfahan and Rasht with two semi-arid and moderate climates using two intelligent methods during 1970-2010. In this research, multi-layer precpetron e (MLP) and gene expression programming (GEP) intelligent models are used in order to analyze the sensitivity of reference evapotranspiration to meteorological parameters. Results of correlation of the parameters showed, in Isfahan and Rasht, maximum and minimum temperatures have the highest correlation with correlation coefficients of 0.968 and 0.926 with other parameters, and in Isfahan wind speed and maximum temperature with a coefficient of 0.067 and in Rasht, minimum humidity and wind speed with a coefficient of 0.001 have lowest correlations. The results of the survey indicate that in Isfahan using MLP model and the maximum and minimum temperature, humidity, wind speed and number of sunshine hours as inputs, with the root mean square error (RMSE) equal to 0.418 mm/day was the best results for estimating reference evapotranspiration. The application of MLP model in Rasht, with the inputs of maximum and minimum temperature, the maximum humidity and the number of sunshine hours has less error and higher correlation coefficient and the values of reference evapotranspiration are much more similar to reality. Also, about the evapotranspiration of reference plant in relation to parameters that are used in this study the results showed that in two study places, the correlation coefficient between wind speed and reference evapotranspiration are 0.3 and 0.061 in Isfahan and Rasht, respectively which are the lowest coefficients.

Food and Agriculture Organization(FAO), has offered the Penman model (FAO-56PM) as a standard model to estimate reference evapotranspiration of crops. The lack of some climatological variables such as solar radiation, relative humidity and wind speed can be a major obstacle in estimating evapotranspiration by FAO-56PM. To overcome this problem, a series of relations and equations is used in the form of the Penman model. By considering these facts, assessmentthe accuracy and validity of this model in different regions, is important. In this studythe equations for estimating the parameters of wind speed , relative humidity and solar radiation were used, and finally the potential evapotranspiration was estimated in the Aydoghmush basin. For this purpose, data of 5 climatological stations in Aydoghmush river basinwas used. Comparing estimated and obtained evapotranspiration values, determined that there is a small difference between ETO values in both cases. In this study, the highest and lowest values of RMSE and MBE have been estimated from 0.227 to 0.971 and -0.271 to 0.724 respectively. According to the results it can be said that by using the computational data evapotranspiration values can be estimated with the greatest accuracy.

Iran is a part of the world's arid and semi-arid areas and encounters severe lack of water resources. Evapotranspiration is a major component of the hydrological cycle and its precise determination has a high importance in the studies of hydrological balance measurement, design and management of irrigation systems, product yield simulation and design and water resources management. At present, there are various methods for calculating the reference evapotranspiration. According to some researches, FAO-Penman-Monteith method is the most accurate method for the estimating of both dry and wet weather conditions after lysimeter weight method. In this study, the amount of reference evapotranspiration was calculated using FAO-Penman-Monteith method in 29 selected synoptic and climatology stations in Yazd. Then, they were classified in two ways: Firstly, through an establishment of a relationship between evapotranspiration parameters and height, and secondly, through Inverse Distance Weighting (IDW). Finally, variations of reference evapotranspiration in different land cover throughout the province were analyzed. Method Reference evapotranspiration maps show that the amount of evapotranspiration is higher in central, southern and some western areas of the province than in northern and eastern areas.