Estimation Of Groundwater Evapotranspiration Based On White Method

In arid and semi-arid inland areas of northwestern China,the climate is dry,rainfall is scarce,evaporation is strong,and surface water is in short supply.Groundwater is an important source of water for maintaining human life,economic development and vegetation survival in dry areas.Evapotranspiration is one of the most important methods of excretion of groundwater in the region,accounting for more than 70%of the total discharge.Therefore,accurate calculation of evapotranspiration is not only an important contribution to the land surface hydrological cycle,quantitative assessment of groundwater resources,and planning and utilization of water and soil resources,but also rational development and utilization of groundwater resources in the concept of sustainable development,for surface vegetation in arid and semi-arid regions.The conservation and protection of water resources are of great significance.Analytical evapotranspiration has important scientific and practical effects on the accurate assessment of water resources in arid areas,the measurement of water resources carrying capacity,the reconstruction and protection of vegetation ecosystems,and energy development and construction.Therefore,there is an urgent need to further understand the groundwater evapotranspiration in the region.The factors affecting evapotranspiration are numerous and complex,and accurate calculation of evapotranspiration is very difficult.The White method estimates the evapotranspiration intensity with the advantages of direct simplicity,low cost,and wide application range.In this paper,the sand-sand-sand-shoal area in the southern margin of the Mu Us Desert is selected as the research area.Based on the basic theories of soil physics,groundwater dynamics,porous media fluid dynamics and hydrogeology,the research method combining in situ experiment and numerical simulation is adopted.Theoretical study on the soil-groundwater evaporation mechanism of Salix psammophila based on White method.Through research,the following results and understanding are obtained:(1)Among the influencing factors of evapotranspiration,the main controlling factors are net radiation and temperature,followed by wind speed and humidity.(2)The net replenishment rate term in the White method is improved and compared with the original White method.The results show that the average net replenishment rate of the original White method is 3.5 mm/h through the water balance calculation.The average net recharge rate of the method was 2.1 mm/h,and the improved White method was significantly closer to reality.(3)The results of saturated-unsaturated numerical simulation show that the total evapotranspiration calculated by the numerical model is 330.9 mm,and the total evapotranspiration estimated by the modified White method is 332.5 mm,which further verifies the reliability of the improved method.