Mapping of actual evapotranspiration over regional scale using NOAA/AVHRR satellite data
The main purpose of the study is to determine the volume of non-beneficial evaporation of water from the irrigation system and particularly from the fallow land. In this study, Surface Energy Balance Algorithm for Land (SEBAL) was applied to time series of NOAA/AVHRR data (April 1990-March 1991) for estimation of seasonal actual ET on a pixel-by-pixel basis over the Liyuankou Irrigation System (LIS) located along the Lower Yellow River basin of China. Three Landsat 5 TM images were also acquired at different stages during the crop growing seasons for land use classification.
Results showed that satellite observations along with meteorological information could yield fairly good estimates of spatially distributed seasonal actual ET for different land uses. The results were further compared with the crop potential evapotranspiration (ETc) calculations at meteorological stations in the LIS system, which showed a deviation of -8% between actual ET and ETc over the growing season of 1990-91, which is within an acceptable range. However, the accuracy of this comparison of modelled actual ET against measured data of ETc needs to be considered with respect to scale. The possible reason for the large deviation in actual ET estimation using the NOAA/AVHRR sensor is the course resolution. The seasonal actual ET results were used to close the water balance study of LIS. Finally, the mapping of spatial ET provided options to reduce the volume (31%) of non beneficial ET from fallow lands that would ultimately lead to improve water use efficiency of LIS.