Abstract: [Objective] Continuous monitoring of evapotranspiration (ET) in regional scale is critical for water resource management and understanding of the processes of water and energy cycles. In order to provide support for improving algorithm of ET estimation and to preliminarily clarify the spatial and temporal patterns of ET in northern China, different ET retrieving methods were compared to select suitable method for application in complex surface areas.[Method] In this study, three ET retrieving methods based on feature space were validated and compared by employing remote sensing images acquired from moderate resolution Imaging Spectro radiometer (MODIS) data set, meteorological data and surface ET flux measured by eddy covariance under a coordinated enhanced observation project in arid and semi-arid regions. Based on the suitable method selected from the comparison, spatial distribution and seasonal variation of ET over northern China were simulated and analyzed.[Result] The results showed that:Wang's method resulted a better correlation and less errors than the other methods (R²=0.65,RMSE=0.17) in evaporative fraction (EF) modeling over Northern China. Suffering from decreasing surface temperature along with the increasing elevation, Jiang's and Roerink's methods had overestimated EF in high altitude regions over the west part of Northern China. EF of northern China was calculated from Wang's method and then ET was retrieved. The regression analysis showed a good correlation between modeled and measured (R²=0.57,RMSE=0.78 mm·d^-1). In general, spatial pattern of ET in northern China showed the characteristics as high east and low west. ET reached peak in summer and reduced to minimum in winter. ET in spring is slightly higher than that is in autumn. In winter, ET in most parts of northern China is lower than 0.5 mm·d^-1. In spring, ET increased obviously except for desert region such as Junggar, Qaidam and Tarim in the northwest part of China. ET in most region reached to 0.8 mm·d^-1 or more. In summer, ET in the entire region reached peak and greater than 1.5 mm·d^-1 in most areas. In Autumn, ET dropped to 1 mm·d^-1 or less significantly except in North part of China and the Qinling Mountains which were kept at 1-2.5 mm·d^-1.[Conclusion] Wang's method is thought to be suitable for ET retrieving over northern China, which is not heavily relied on the ground meteorological data. This method can reduce the errors caused by uncertainties from meteorological parameters, indicating an application potential in regions which have great drops in elevation and complex underlying surfaces.

Key words: northern China, evaporative fraction, evapotranspiration, remote sensing, feature space