Temporal-spatial scale effect on actual evapotranspiration in a semi-arid basin

This paper developed an approach of the accuracy assessment in multi temporal-spatial scales. The SEBAL model and Thornthwaite water balance model were employed to calculate the daily ETa on three spatial scales. Then, three time scales ETa were expanded. Of them, the units were delineated by hydrological response unit (HRU). The calculating results of two models were compared on different scales. The results were that with the increase of temporal scale, the slopes of regression curves between unit results from two methods were 0.555, 0.667 and 0.813, with related coefficients of 0.714, 0.809 and 0.762. The ET difference decreased with the increase of spatial scale. On a monthly scale, the average of relative errors was over 30% at point scale, 10.3% and 1.59% at unit and basin scale, with RMSE of 8.32%, 9.51% and 0.43%. The better accuracy could be achieved at the larger scales because of the uncertainty decreasing. Experimental results indicated that temporal uncertainty is a key issue which needs further study, and the remote sensing method at the unit scale is beneficial to the water resources assessment and ET management in a changing regional environment.