Estimation of ETo with Hargreaves–Samani and FAO-PM temperature methods for a wide range of climates in Iran

Abstract

Monthly data records of 40 Iranian stations distributed over the country, for the period 1971-2005, were utilized for estimation of reference evapotranspiration (ET o ) using Penman-Monteith (PM-ET o ), Hargreaves-Samani (HS) and FAO-PM temperature (PMT) methods. To estimate ET o with HS and PMT methods, appropriate k Rs , an empirical radiation adjustment coefficient, were considered for each station, whereas T min was adjusted for estimation of T dew and used only for PMT computation. It was found that the appropriate k Rs for both HS and PMT methods are identical for a given station and it is generally smaller in sub-humid and humid than in semi-arid to hyper-arid climates. The performance of the PMT was further improved in both arid and humid climates when T min was adjusted. The result suggested that the HS and PMT methods appropriately predict ET o for all climatic regions of Iran if the appropriate k Rs was utilized. However, the considered methods showed weak performances for some stations in arid and hyper-arid climates of eastern and southern Iran owing to the effect of extreme and variable wind speed inherent in the PM-ET o . Thus, the role played by wind speed in ET o estimation was examined; the result indicated that the existence of extreme winds, and also the time variability of wind speed, is responsible for the observed discrepancies between PMT and PM-ET o estimates. The spatial patterns of ET o computed with HS and PMT methods found to be identical and resemble to that of PM-ET o , all showing a gradual increasing from north to south, with the lowest ET o values observed over northern humid and sub-humid climates of Iran and larger ET o for arid and hyper-arid climates in the southern and eastern country. Results indicated that the HS and PMT methods are appropriate alternatives for estimation of ET o for all climatic regions of Iran.

Estimativa da evapotranspiração de referência a partir de dados meteorológicos limitados

“…Portanto, ela é um parâmetro chave para estudos de avaliação ambiental e de manejo de bacias hidrográficas (Raziei & Pereira, 2013), para a estimativa da necessidade hídrica das culturas e para projetos e manejo de sistemas de irrigação (Kumar et al, 2008). As condições meteorológicas têm marcada influência sobre a ET; assim, pequenos erros em sua estimativa têm elevado impacto sobre o cálculo do balanço hidrológico de uma região (Allen et al, 2011b).…”

Métodos Empíricos Para Estimativa Da Evapotranspiração De Referência No Estado Do Rio De Janeiro

“…A evapotranspiração é um dos principais processos componentes do ciclo hidrológico e a principal componente no balanço hídrico do solo, no qual o seu conhecimento é essencial para um planejamento econômico no uso dos recursos hídricos (FANAYA JUNIOR et al, 2012); e serve de parâmetro para estudos de avaliação ambiental e de manejo de bacias hidrográficas (RAZIEI;PEREIRA, 2013).…”

Reference evapotranspiration estimates based on minimum meteorological variable requirements of historical weather data

“…It is especially applied to estimate crop water requirements and support irrigation scheduling and drought management (Raziei and Pereira, 2013). Evapotranspiration has also often been used to identify regions prone to drought, and it is an important field of research related to climate changes (Croitoru et al, 2013).…”