Using constant wind speed for estimating reference evapotranspiration in arid and semi-arid regions

Abstract

Despite the global abundance of water, some regions suffer from water scarcity due to climatic and their impact. Evapotranspiration ET plays a crucial role in calculating the amount of water required for crops, and any deficiency leads to decreased productivity. Wind speed in arid and semi-arid regions is a critical factor in exacerbating water deficits. Reliance on default values, such as the global constant (2 m/s), can have an impact. Libya exemplifies this problem. Agriculture there faces a dual challenge: a water deficit resulting from agricultural expansion and a severe lack of meteorological data. This deficiency leads to use alternatives such as the wind constant, highlighting the need to evaluate its accuracy compared to local data. The problem addressed by this study is the lack of clarity regarding the accuracy of this constant when estimating ET in Libya. This study aims to bridge the research gap by quantitatively assessing the impact of this assumption. The study utilized data from the research stations of the Faculty of Agriculture at the University of Tripoli. The results showed an average ET of 5.46 mm/day, totaling 2311.16 mm. When comparing the calculated Eto with station data and the calculated Eto with the default constant, the coefficient of determination (R²) was 0.984, indicating a strong positive correlation, with an RMSE error of 0.036. The stability of the results is attributed to the presence of windbreaks surrounding the station, as wind showed a very weak correlation (r² = 0.03). The study concludes that the Penman-Monteith equation performed well in managing variables such as wind speed and recommends its use within site limitations, while emphasizing the need for testing in open areas to assess the impact of the absence of windbreaks.