Author(s)

Zafar Gafurov¹, Sarvarbek Eltazarov², Bekzod Akramov¹, Tulkun Yuldashev¹, Kakhramon Djumaboev¹, Oyture Anarbekov¹

¹International Water Management Institute (Central Asia Office), Tashkent, Uzbekistan.
²Leibniz Institute of Agricultural Development in Transition Economies, Halle, Germany.

Reference evapotranspiration (ETo) is a key factor in determining the amount of water needed for crops, which is crucial to correct irrigation planning. FAO Penman-Monteith (EToPM) is among the most popular method to estimate ETo. Apparently sometimes it is difficult to compute ETo using Penman-Monteith due to challenges on data availability. FAO Penman-Monteith method requires many parameters (solar radiation, air temperature, wind speed and humidity), while Hargreaves-Samani method calculates ETo based on air temperature. Because Central Asia is a data limited region with weather stations unable to provide all required parameters for the PM method, this study aimed to estimate ETo using the Hargreaves and Samani (HS) method in Karshi Steppe, in Kashkadarya province, in southern Uzbekistan, based on data from 2011 to 2017. Reference evapotranspiration calculated by non-modified HS method is underestimated during the summer months. The reason for this underestimation might be higher air temperature and wind speed during these months. Therefore, the HS method in its original form cannot be used in our study area to estimate ETo. Modification of the EToHS, through application of a bias correction factor, had better performance and allowed improving the accuracy of the ETo calculation for this region. The calculated ETo values can inform decision making and management practices regarding water allocation, irrigation scheduling and crop selection in dry land regions of Amudarya river basin and the greater Central Asia area.

Reference Evapotranspiration, Hargreaves-Samani, Penman-Monteith, Amudarya River Basin

Gafurov, Z. , Eltazarov, S. , Akramov, B. , Yuldashev, T. , Djumaboev, K. and Anarbekov, O. (2018) Modifying Hargreaves-Samani Equation for Estimating Reference Evapotranspiration in Dryland Regions of Amudarya River Basin. Agricultural Sciences, 9, 1354-1368. doi: 10.4236/as.2018.910094.