Impact of Alternative Data on the Penman-Monteith Method Considering Windy Conditions in the Semi-Arid Area

Homayoon Ganji^1, and Takamitsu Kajisa¹

¹Graduate School of Bioresources, Mie University, 514-8507 Kurimamachiya-Cho 1577, Tsu, Japan

Cite this paper

Homayoon Ganji and Takamitsu Kajisa. Impact of Alternative Data on the Penman-Monteith Method Considering Windy Conditions in the Semi-Arid Area. American Journal of Water Resources. 2018; 6(6):217-223. doi: 10.12691/AJWR-6-6-2

Abstract

When real data are unavailable, the standard Penman-Monteith method for estimating reference evapotranspiration can be calculated using alternative input data: wind speed from a nearby station, the default global average wind speed, solar radiation based on temperature and vapour pressure based on the minimum temperature. These alternative data are recommended in FAO paper 56. In this study, we assessed the accuracy achieved when using these alternative data for reference evapotranspiration estimation in a semi-arid region characterised by a strong persistent wind speed. Western Afghanistan was selected as the study site, as it is exposed to strong winds over the 120-day period from June to September. Significant differences were found in the estimates produced using full data and those obtained using wind speed data from a nearby station, the default global average wind speed, and vapour pressure based on the minimum temperature. Root Mean Square Error (RMSE) was found 1.51 mm d^-1, 1.27 mm d^-1 and 1.07 mm d^-1, respectively. Errors were especially significant on days with strong wind. The smallest RMSE of 0.36 mm d^-1 was found when basing solar radiation on temperature. The assumption that the dew point temperature will be close to the minimum temperature was shown to be unreliable on days of strong wind.

Keywords

reference evapotranspiration, Penman-Monteith, alternative data, strong wind, semi-arid

Copyright

This work is licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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