Abstract:Evapotranspiration (ET) from the wetland of the Yellow River Delta (YRD) is one of the important components in the water cycle, which represents the water consumption by vegetation and evaporation from land surfaces such as the water and bare soil. Water shortage reduces photosynthesis and, therefore, the growth rate of vegetation. Healthy and abundant vegetation is necessary to protect the wetland ecosystem. Reliable estimates of the total amount of water required and of actual water consumption by the wetland are necessary to protect the YRD wetlands. In this study, the SEBS (Surface Energy Balance System) model based on the Energy Balance method was used to calculate daily ET using conventional meteorological data and instantaneous observations of land surface reflectance and temperature from MODIS when the data were available on clouds-free days. A detailed vegetation classification map was used to identify different vegetation types to parameterize surface roughness. An algorithm based on the Fourier transform was then applied to generate a time series of daily ET over a year period by filling the gaps in the calculated daily ET time series due to clouds. Annual ET between 2001 and 2005 was calculated after filling the gaps in the daily ET for each yearly data set. The estimated daily ET was validated by comparing the ET over open water bodies with the pan evaporation observations at meteorological stations. The error of estimate of the monthly ET was 16.4mm or 11.9%, which is comparable with the accuracy of ground measurements. The ecological water demand by Phragmites australis including Phragmites australis-swamp and Phragmites australis-meadow which is the dominant wetland vegetation and the amount of water supply to maintain Phragmites australis in a good growth condition, were evaluated for the period between 2001 and 2005. The ET in the areas around water bodies, by the sea shores and the Yellow River former channel and in the swamps near the banks of Yellow River shows higher values, while the ET in residential areas is rather low. The yearly ET over different wetland vegetation types shows varying values ranging between 671 mm and 1017 mm. The interannual variation of the total ET is not very significant. The highest monthly ET is observed in May, June and July, ranging between 110mm and 120mm. Most of Phragmites australis wetland was affected by water shortages, with evident impacts on growth, from 2001 to 2005. The situation in 2002 was the worst due to less precipitation while it was improved after 2004 since higher precipitation was observed in 2004. The amount of the required water supply in 2002 was the highest between 0.099 billion m3 to 0.319 billion m3, while it was the lowest in 2004 between 0.03 billion m3 to 0.239 billion m3.