Reference evapotranspiration estimate with limited weather data across a range of Mediterranean climates

Abstract

The standard FAO Penman-Monteith (PM-ET o) method for computing the reference evapotranspiration (ET o), in addition to air temperature, needs data on solar radiation or sunshine duration, relative humidity and wind speed which are often lacking and/or do not respect appropriate quality requirements. Hence, in many cases, ET o has to be estimated with limited weather data using maximum and minimum temperature only. Essentially, two procedures are used when no more than temperature data are available: (i) the well-known Hargreaves-Samani equation (HS), or (ii) the PM-ET o method with weather parameters estimated from the limited available data, called PM temperature (PMT) method. The application of these temperature-based approaches often led to contradictory results for various climates and world regions. The data used in the analysis refer to 577 weather stations available through the CLIMWAT database. The results, confirmed by various statistical indicators, emphasized that: (a) in hyper-arid and arid zones, the performance of HS and PMT methods are similar, with root mean square errors (RMSEs) around 0.60-0.65 mm d À1 ; (b) in semi-arid to humid climates, the PMT method produced better results than HS, with RMSE smaller than 0.52 mm d À1 ; (c) the performance of PMT method could be improved when adopting the corrections for aridity/humidity in the estimation of the dew point temperature from minimum temperature data. The spatial elaboration of results indicated high variability of ET o estimates by different methods. Thus, a site-specific analysis using daily datasets of sufficient quality is needed for the validation and calibration of temperature methods for ET o estimate. Maps presenting indicative results on under/over estimation of ET o by both temperature methods may be useful for their more accurate application over different Mediterranean climates.

Estimativa da evapotranspiração de referência a partir de dados meteorológicos limitados

“…Martí et al (2010) (Figura 2 B). Todorovic et al (2013) realizaram estimativas em 577 estações meteorológicas, distribuídas em 16 países do Mediterrâneo, e obtiveram desempenho semelhante para os modelos HS e PM u2 , em regiões hiperáridas, com valores de RMSE em torno de 0,60-0,65 mm por dia. Segundo os autores, em regiões semiáridas ou úmidas, o método PM u2 apresentou melhores resultados, com o menor valor de RMSE, de 0,52 mm por dia.…”

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

“…Table 5 was generated with data from Table 4 and shows the ranking of the methods based on four different performance evaluation criteria. The indices considered as criteria in Table 5 include precision and accuracy and are widely used in model performance studies (Willmott, 1982;Camargo and Sentelhas, 1997;Willmott and Matsuura, 2005;Borges Júnior et al, 2012;Melo and Fernandes, 2012;Cristea et al, 2013;Todorovic et al, 2013;Kisi, 2014). The criteria used to compare the methods greatly affect the rank.…”

“…Bachour et al (2013) commented that the HargreavesSamani method often tends to systematically overestimate or underestimate ET 0 unless regional calibration is performed. Todorovic et al (2013) highly recommend testing and calibrating the Hargreaves-Samani against the FAO Penman-Monteith method under different Mediterranean climates and geographic-orographic conditions when good quality data sets are available. Borges Júnior et al (2012) obtained reductions of 69% to 25% and 52% to 15% in the systematic portion of MSE for dry and rainy periods, respectively, after calibrating the coefficients and exponents of Equation [3] when estimating ET 0 from meteorological data of a district of the Agrest region of Pernambuco State (Brazil).…”

“…The R a values were calculated following the procedures described by Allen et al (1998); the latitude of the region under study was taken into account, as well as the daily estimate of N. The a s and b s values were assumed to be equal to 0.25 and 0.50, respectively, as suggested by Allen et al (1998). (Allen et al, 1998;Todorovic et al, 2013). Equation [6] is Equation [5] with an additional linear coefficient (k 3 ).…”

Assessment of reference evapotranspiration and global solar radiation in Yucatán Peninsula Mexico

“…Many studies have evaluated for the estimation of the FAO ET0 using only minimum and maximum temperature data (PMT). Annandale et al (2002) in South Africa, Trajkovic (2005) in Serbia, Popova et al (2006) in south Bulgaria, Jabloun and Sahli (2008) in Tunisian, Cai et al (2009) in the North of China, López-Moreno et al (2009) in Spanish Pyrinee, Martinez and Thepadia (2010) in Florida (USA), Gocic and Trajkovic (2010) in Davis (California, USA), Kra (2010) in four countries of west Africa, Raziei and Pereira (2003) in Iran, Todorovic et al (2013) in 16 mediterranean countries, Vangelis et al (2013) in Greece, Pandey and Pandey (2016) in India and Ren et al (2016) in inner Mongolia (China), among others. In this study, we used Hargreaves and Samani formulation HS Hargreaves and Samani 1985;Hargreaves and Allen 2003) and the PMT formulation to estimate ET0 because they require only air temperature data.…”