Evaluation of FAO WaPOR product and PYSEBAL algorithm in estimating The amount of water consumed

Evapotranspiration is an essential component of the hydrological cycle and a key element of water resources management, especially in arid and semi-arid regions. Today, remote sensing technology has made it possible to estimate evapotranspiration on a large scale, so using this technology can be considered as a promising method to reduce the spatial variation of evapotranspiration. In this study, the daily, monthly and seasonal changes of actual evapotranspiration were investigated using the global model of WaPOR product and PYSEBAL algorithm in Qazvin plain during the period from 2015 to 2021. The results obtained in this study were compared with Hargreaves and Samani evapotranspiration data, which is an accurate empirical method in the region. The mean deviation of the estimated and observed data in the daily scale in both models shows that the PYSEBAL algorithm has a more negligible difference and, in most cases, is close to the data obtained from the empirical method. While in WaPOR product, it was associated with underestimation compared to the empirical method during the almost entire period. WaPOR product was able to show the amount of seasonal evapotranspiration changes to a good extent, but it did not have good accuracy. This product had acceptable accuracy in spring and summer, but in autumn and winter, its accuracy decreases. The results showed that the WaPOR product can provide water needs for each time period, so it can play an important role in managing water resources, determining the required water consumption. PYSEBAL algorithm presented more accurate results than WaPOR product, so that the correlation coefficient values in PYSEBAL algorithm and WaPOR model are equal to 1.51 and 2.86 mm / day and the correlation coefficient values were 0.87 and 0.64, respectively. Therefore, if the studies on estimation of the amount of evapotranspiration for large areas (such as basins) and long periods are considered, the use of WaPOR products due to the lack of missing data can play a suitable role in managing water resources and water needs for the region or basin.