Mostafa Javadian and Ali Behrangi
Evapotranspiration is one of the main components of water and energy balance. In this study, we compare two ET products, suitable for regional analysis at high spatial resolution: WaPOR product developed by FAO and METRIC algorithm. WaPOR is based on ET-Look, which is a two-source model and relies on microwave images. WaPOR is unique as it has no limitation under cloudy days, but METRIC is limited by clouds. METRIC and WaPOR are more sensitive to land surface temperature and soil moisture, respectively. The results show that in most areas ET from METRIC is higher than WaPOR and the difference has an ascending trend with the elevation. The ET of lysimeter station is pretty close to METRIC based on a single observation. However, the fraction of ET to precipitation in rainfed agriculture areas shows that WaPOR is more accurate than METRIC, partly because annual ET cannot exceed annual precipitation in rainfed agriculture areas due to its limited water resources. This suggests that the spatial distribution of WaPOR might be better than METRIC, but not necessarily its amount. Furthermore, this study suggests that WaPOR might be a better scheme than METRIC in high-elevation areas.