Hydrological Process Of Green Water In The Nanxiaohegou Basin And Its Coupling Relationship With Vegetation Types

Water resources can be divided into two kinds:blue water and green water in ecohydrology,Blue water resources are water stored in rivers,lakes and aquifers.Green water refers to water directly from precipitation for evapotranspiration.In arid and semi-arid areas,green water is an important source for supportting rain raising agriculture.It plays a very important role in maintaining the coordination and balance of landscape ecosystem,supporting rain raising agriculture,maintaining the production function and service function of the earth's terrestrial ecosystem.The gully region of the Loess Plateau is widely distributed in the middle and south of the Loess Plateau.It is an important grain production base and rain raising agricultural region.Influenced by the temperate continental monsoon climate,the rainfall is relatively low and the spatial and temporal distribution is very uneven,and the shortage of water resources has become the biggest restriction factor for the environment and development of the region.At present,the work of returning farmland to forest and grass is the main way to control soil erosion and water conservation,It has been widely used and popularized in the Loess Plateau area.However,because.of the physiological characteristics of tree species,grass species and their response to climate and geographical location.The hydrological and ecological benefits of the application of eturning farmland to forest and grass are different.In addition,improper selection and arrangement of vegetation resulted in low economic and ecological benefits,dry soil layer and poor plant growth on the Loess Plateau.Therefore,it is necessary to explore the hydrological process and distribution characteristics of green water under the influence of different vegetation measures,and explore the relationship of green water transformation under the different vegetation measures and the coupling relationship between the supporting function and the measures of the water requirement of the vegetation,based on which,the rational restoration and management model of Vegetation have to be explored.On the basis of field observation experiments,the vegetation interception and low efficiency green water characteristics of Robinia pseudoacacia,Platycladus orientalis,Pinus tabulaeformis,alfalfa,weeds and Jujun grass sites in Nanxiaohegou basin were simulated and analyzed.On the basis of which,the Hydrus-ID model was used to simulating the dynamic characteristics of green water under the conditions of each vegetation.In addition,The hydrological cycle process is reasonably reproduced.According to the dynamic analysis of the daily scale and monthly green water dynamics and the response of the green water to the climate characteristics under the various vegetation conditions,the coupling relationship between the actual high efficient green water and the potential hige efficient green water in the monthly and growing season scales is systematically analyzed,and the final results are obtained as below:(1)The rainfall in Robinia pseudoacacia,Platycladus orientalis and Pinus tabulaeformis had a very significant linear relationship between rainfall and rainfall(P<0.01),and the penetration rate was exponentially correlated with the rainfall,and there was a significant exponential function relationship between the rainfall and the interception(P<0.01),and the stable interception rate of the three species were 13%,20%and 18%respectively.The Gash model can be used to simulate the total interception amount of Robinia pseudoacacia,Platycladus orientalis and Pinus tabulaeformis,while the Wang Yanhui model is not suitable for simulating the total amount of interception of Pinus tabulaeformis woodland.In the process of rainfall interception,the absolute error of Wang Yanhui model on the simulation results of Robinia pseudoacacia and Platycladus orientalis was distributed in-1.07?1.19mm and-2.06?2.59mm respectively,and the simulation results were better,and the error range was better than that of Gash model.In Pinus tabulaeformis woodland,the error of Gash model is-1.7?3.4mm,and the simulation result is better than that of Wang Yanhui model.(2)The canopy resistance in a wide variety of fields showed a certain dynamics during the growing season.The absolute error of soil evaporation model based on its backstepping results in the process of simulation of soil evaporation in Robinia pseudoacacia,Platycladus orientalis and Pinus tabulaeformis soil was distributed in-1.6?2.4mm,-2.3?3.4mm and-3.5?2.2mm respectively,in alfalfa,weeds and Jujun grass,it was-1.1?1.1mm,-1.2?1.6mm and-1.2?1.6mm respectively.There was a significant(P<0.01)linear relationship between soil surface resistance and soil moisture content in all fields,The absolute error of soil evaporation model based on the fitting results is distributed between-0.6?0.5mm,-0.9?0.8mm and-0.4?2.1mm in Robinia pseudoacacia,Platycladus orientalis and Pinus tabulaeformis sites respectively,while in alfalfa,weeds and Jujun grass sites,it were distributed between-0.8?0.3mm,-0.1?0.9mm and-0.3?1.0mm respectively,and the fitting results of soil surface resistance were practical.(3)The daily scale green water of Robinia pseudoacacia,Platycladus orientalis,Pinus tabulaeformis,alfalfa,weeds and Jujun grass in the 3 periods were distributed in 0-5.9,0?5.2,0?5.7,0?5.2,0?5.2 and 0?7.6mm respectively.The low efficiency green water was distributed in 0?3.5.0?3.6.0?4.0mm,0?2.8.0?3.3 and 0?3.1mm respectively.While the green water storage was in 252.5?382.1,356.6?891.4mm,262.2?375.0mm,416.0?553.2mm and 520.1?591.3mm.In the early growing season of Robinia pseudoacacia and Platycladus orientalis,low efficiency green water is the main part of green water,which is a high efficient green water for Pinus tabulaeformis.At the same time,Pinus tabulaeformis has strong function of nourish water source in non growing season.Among the three grass species,the weeds land has a strong function of water conservation.(4)Under the 4 climate scenarios,the amount of high efficient green water in each area was characterized by the year of wet year>normal year>dry year.The response degree of high efficient green water to the future and different hydrological years is as follows:Robinia pseudoacacia>Platycladus orientalis>Pinus tabulaeformis,for grass land,it was alfalfa>weeds>Jujun Grass;For the low efficiency green water,the low efficiency green water of every site was also shown as wet year>normal year>dry year undern all climatic scenarios.The effect of climate change on the low efficiency green water in the arbor like land was greater,and the low efficiency of water was less in response to the climate characteristics in the grassland like land.(5)Under all climatic conditions,the high efficiency green water deficiency of Robinia pseudoacacia,Platycladus orientalis,Pinus tabulaeformis,alfalfa,weeds and Jujun grass sites were distributed in 320.2?430.7mm,226.9?424.0mm,113.9?258.6mm,370.6?538.6mm,298.8?425.7mm and 303.5?391.4mm respectively,all of which were characterized as the dry year>norman year>wet year?In the arbor land,the loss of high efficiency green tree showed the characteristics of Robinia pseudoacacia>Platycladus orientalis>Pinus tabulaeformis,While in the grassland,it was alfalfa>weeds>Jujun Grass.The high efficiency green water content of Pinus tabulaeformis is higher,its water conservation function and water use function are superior to Robinia pseudoacacia and Platycladus orientalis.Jujun grass has a higher degree of satisfaction in high efficiency green water content,but its high efficiency of green water dissipation is relatively large,which is likely to cause a significant reduction in green water storage.Therefore,it is not suitable for large-scale cultivation.The Platycladus orientalis in the arbor forest and the grass land in the grassland have great potential for the transformation of green water from low efficiency green water to high efficiency green water.(6)The change of climate characteristics has a certain effect on the inefficiency and low efficiency green water.The effect of rainfall on high and low efficiency green water in the same period is obviously stronger than that of the temperature.The linear relationship between the high efficient green water quantity and the low efficiency green water content are all very significant(P<0.01).while for the high efficiency green water deficit,it was mainly caused by the change of the potential high efficiency green water by temperature.The analysis shows that the high efficiency green tree deficiency in every growing season has a very significant linear relationship with the accumulated temperature(P<0.01),which is negatively related to the rainfall.