Estimating Reference Evapotranspiration with Incomplete Data (Case study: North Khorasan province, Iran)
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2. Material and Methods
2.1. Study Area
Study area is North Khorasan province, northern Iran comprising Bojnourd, Esfaraien, Jajarm and Mehmanak synoptic stations (Fig.1).
Fig. 1 ABOUT HERE.
Due to lack in the amounts of synoptic stations in the North Khorasan province (4 stations) and small numbers of data year in 3 out of 4 stations (Esfaraien, Jajarm and Mehmanak that just have between 4 to 5 years data), some auxiliary synoptic stations were needed in order to make calculations more exact. North Khorasan province is on the border of Iran and Turkmenistan. Therefore, selecting auxiliary stations was limited to three provinces including Semnan (southwest), Khorasan Razavi (east and south) and Golestan (west). Synoptic stations in Golestan province are located near Caspian Sea and have humid climate (according to De Martonne climate index), which are not in agreement with semi-arid climate of study area. Considering the fact that Semnan province has just two synoptic stations that are not located in Central Desert of Iran, Biarjmand and Shahroud were selected. Climate of other synoptic stations of this province are affected by hot Central Desert and would not be similar to study area. Thus, selected stations are located within 110 kilometers ring around North Khorasan province borders in Semnan and Khorasan Razavi provinces. Used weather stations and annual mean values of applied meteorological parameters for all stations are given in table 1.
Table 1 ABOUT HERE.
Since some stations were in non-reference conditions, temperature data have been corrected using Allen et al (1998) method. Moreover, Rs data quality was evaluated by Allen et al (1998) method and U2 and RH data were examined to be normal. After successful validatio...
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