Abstract. The agricultural activities, hydrologic cycle, and ecological environment are seriously influenced by evapotranspiration (ET), especially in arid and semi-arid areas. A new method for estimating daily global solar radiation (GSR) over rugged terrains in the middle Heihe River Basin is developed on the basis of Iqbal model C. And with the land surface parameters retrieved from multisource remote sensing data, a daily surface ET on June 21–24, 2009, is simulated by using surface energy balance algorithm for land (SEBAL) model. The results show:

1. An improved daily GSR with a resolution of 100 m × 100 m is implemented. The mean absolute bias error (MABE) is 9 W/m², and the mean absolute relative bias error (MARBE) is 2.5 %. The MABE of the daily GSR using the SEBAL model is 122.2 W/m², and the MARBE is 33.9 %.

2. The spatial distribution of the daily GSR is more reasonable using the improved model than the original model. The GSR is larger on a sunny slope (an open place) than on a shady slope (a rugged place).

3. Bringing the new model into SEBAL significantly improves the accuracy of the ET. The MABE of ET decreases from 2.1 mm (original scheme) to 0.6 mm (improved scheme), and the MARBE declines from 44 % to 13 % accordingly. Moreover, the spatiotemporal resolution of the ET simulation is effectively improved by the combined moderate-resolution imaging spectroradiometer and thematic mapper surface parameters.

4. All highest ET value appeared in all types of water bodies, followed by farmland, forest, wetland, and residential areas, the lowest values appeared over bare rock land. The water consumption in these areas is dominated by agriculture. The new results provide better theoretical basis and scientific guidance for ecosystem protection and sustainable utilization of water resources.