Study On The Evapotranspiration Loss In Lower Reaches Of The Yellow River

Water resource is not very much abundant in China, thus optimized allocation and rational utilization for water resources should be carried out. And the natural loss, one of the key factors, must be paid more attention to. Evapotranspiration is an important part of natural loss in river basins, the study on which will give support to water regulation and evaluation, and will do great significance especially under the trend of climate change. The lower Yellow River is taken as an example in this paper. Study on evapotranspiration mode is done by distinguishing different kinds of land use in the basin. The aim is to set up a complete model for the study basin, and to calculate the water consumption and analyze the changing tendency as well.The underlying surface is complex in the lower Yellow River with water surface as well as a mass of bare bottomland and crops. The theoretical calculation and physical model experiment are combined: Penman-Monteith equation recommended by FAO is used to calculate the evaporation capacity, indicating evaporation from water surface. As Penman-Monteith equation needs much meteorological data, it is simplified in the paper, and its rationality is also validated;the crop coefficient is introduced to calculate the evapotrnspiration of crop;the physical model is set up because of the complexity of bottomland evapotranspiratin. When the measured data and necessary parameters are gained, the one-dimensional equation of unsaturated soil water flow movement is applied in theoretical calculation to describe the soil water movement under natural evaporation condition and the change of soil evapotranspiration with phreatic groundwater table. The result shows great accuracy and rational change tendency. Study on evapotranspiration in the basin has been accomplished by combining different types of evapotranspiration results with the underlying surface distribution and area data offered by Remote Sense information. Meanwhile, the effect of temperature increase on evapotranspiration under the trend of climate warming is discussed.The weather and soil parameters are simplified in the model set up in this paper. So it needs less data and parameters with better applicability and can be used for other basins' evapotranspiration simulation and calculation after further improvements.