A method and device for calculating soil water-groundwater based on a water potential gradient in a land surface hydrology model

Abstract

This invention discloses a method and apparatus for calculating soil water-groundwater in a land surface hydrological model based on water potential gradient, relating to the field of coupled soil water-groundwater modeling technology. The method includes constructing a vertically layered land surface hydrological model; constructing soil water control equations to calculate the soil free water content and matrix potential of the soil layers; determining the distribution relationship between the deep unsaturated soil and groundwater level based on the groundwater level at the current step; calculating the total water volume of the deep unsaturated soil layer and the groundwater layer; calculating the water potential gradient between the matrix potential and the groundwater level at the current calculation step, and solving for the vertical water flux at the lower boundary of the soil layer; calculating the horizontal lateral water flux of the groundwater layer based on the groundwater level difference between adjacent grids; updating the total water volume of the deep unsaturated soil layer and the groundwater layer based on the vertical and horizontal lateral water fluxes and the unconfined groundwater movement equation, and inverting and updating to obtain the groundwater level at the next step.

Description

Technical Field

[0001] This invention relates to a method and apparatus for calculating soil water-groundwater in a land surface hydrological model based on water potential gradient, belonging to the field of soil-water-groundwater coupled modeling technology. Background Technology

[0002] The land surface hydrosphere is a major habitat for life on Earth. It is not only a primary area affected by global environmental change but also the lower boundary of Earth system simulators. However, land surface models and hydrological models are developed by different disciplines, focusing on different scientific questions and application areas, with varying emphases, research scales, and technical methods. Land surface models primarily consider vertical water movement and have a simplified understanding of groundwater processes, while hydrological models provide a weaker physical description of soil moisture and heat than land surface models. Establishing a model for water exchange between soil layers and unconfined groundwater layers is a key issue in achieving two-way coupling between land surface and hydrological models.

[0003] There are some shortcomings in the existing technology:

[0004] 1. Existing technologies typically set the lower boundary of the soil layer as a fixed impermeable or free-drainage boundary, resulting in water that can only move downwards or cannot be exchanged;

[0005] 2. Existing technologies use models that simplify the exchange process due to interlayer discontinuities, neglecting the continuous distribution and dynamic storage mechanism of water in the transition zone, causing simulation results to deviate from actual hydrological processes;

[0006] 3. In terms of model coupling implementation, existing technologies often lack a coherent feedback mechanism: the infiltration amount calculated by the soil water module may be used as a simple source term input to the groundwater module, but the updated groundwater level is not fed back in real time to affect the calculation of the soil water potential gradient in the next time step. Summary of the Invention

[0007] The purpose of this invention is to provide a method and apparatus for calculating soil water and groundwater in a land surface hydrological model based on water potential gradient. By establishing a method for calculating the vertical water flux of the bottom layer of soil based on water potential gradient and using it as the source and sink term in the groundwater movement equation, the complex hydraulic connection between soil water and groundwater in nature is effectively reflected, realizing the two-way coupling of soil water and groundwater in the model and improving the simulation accuracy of water cycle process components.

[0008] To achieve the above objectives, the present invention is implemented using the following technical solution.

[0009] On one hand, this invention provides a method for calculating soil water-groundwater ratio in a land surface hydrological model based on water potential gradient, comprising:

[0010] Construct a vertically layered land surface hydrological model; wherein, from top to bottom, the model includes a soil layer, a deep unsaturated soil layer, and a groundwater layer, and the lower boundary of the soil layer is set as a permeable boundary;

[0011] Construct soil water control equations to describe soil water movement;

[0012] Within each calculation step:

[0013] Based on the soil water control equation, the soil free water content and matrix potential of the soil layer are calculated;

[0014] Obtain the groundwater level at the current calculation step, and determine the distribution relationship between the deep unsaturated soil and the groundwater level based on the groundwater level;

[0015] Based on the distribution relationship, the total water volume of the deep unsaturated soil layer and the groundwater layer is calculated.

[0016] Based on the matrix potential and the groundwater level at the current calculation step, calculate the water potential gradient between the two, and solve the vertical water flux at the lower boundary of the soil layer based on the water potential gradient.

[0017] The horizontal lateral water flux of the groundwater layer is calculated based on the groundwater level difference between adjacent grids.

[0018] Based on the total water volume, vertical water flux, and horizontal lateral water flux, and using the unconfined groundwater movement equation, update the total water volume of the deep unsaturated soil layer and groundwater layer.

[0019] Based on the updated total water volume, the groundwater level for the next calculation step is obtained by inversion update;

[0020] The updated groundwater level will be used in the next calculation time step to redetermine the distribution relationship between the deep unsaturated soil layer and the groundwater level.

[0021] Furthermore, the soil water control equation is the Richard equation modified with lower boundary conditions, and the expression of the Richard equation is as follows:

[0022] (1),

[0023] In the formula, θ represents the soil free water content, t represents time, and z represents the elevation of a certain point in the aquifer;

[0024] K(θ) represents the soil hydraulic conductivity as a function of soil free water θ.

[0025] ψ(θ) represents the soil matrix potential as a function of soil free water θ;

[0026] K s ψ represents the saturated hydraulic conductivity of soil. s denoted by saturated matrix potential, and B represents a constant related to soil texture.

[0027] Furthermore, the distribution relationship between the deep unsaturated soil and the groundwater level is expressed as follows:

[0028] d dsl =h b -h(2)

[0029] In the formula, d dsl h represents the thickness of deep unsaturated soil. b The elevation of the lower boundary of the soil layer is represented by h, and the elevation of the groundwater level is represented by h.

[0030] Furthermore, based on the thickness of the deep unsaturated soil, and assuming that the moisture profile of the deep unsaturated soil layer at the current thickness is in equilibrium within a calculation step, the expression for the free water content θ(z) at a certain elevation of the deep unsaturated soil layer, based on the equilibrium state, is as follows:

[0031] (3),

[0032] In the formula, z represents the elevation of a certain point in the deep unsaturated soil layer. h b It indicates the elevation of the lower boundary of the soil layer.

[0033] Furthermore, the expression for the total water volume of the deep unsaturated soil layer and the groundwater layer is as follows:

[0034] (4),

[0035] In the formula, V represents the total water volume of the deep unsaturated soil layer and the groundwater layer; h0 represents the elevation of the lower impermeable boundary of the groundwater aquifer; C represents a constant, C = (B – 1) / B; θ fc This represents the soil wilting moisture content; define x(h) b )=1+(h b – h) / ψ s .

[0036] Furthermore, assuming that the water potential changes linearly from the center of the bottom soil layer through the deep unsaturated soil layer to the groundwater level, the expression for the water potential gradient between the center of the bottom soil layer and the deep unsaturated soil layer is as follows:

[0037] (5),

[0038] In the formula, Ф represents the total water potential; The soil matrix potential at the center of the soil strata (b1) varies with the soil free water content (θ); h represents the groundwater level. b1 It indicates the elevation of the center of the bottom layer of the soil.

[0039] Based on the water potential gradient, the expression for the vertical water flux D at the lower boundary, calculated using the unsaturated soil flow formula, is as follows:

[0040] (6),

[0041] In the formula, K(θ) represents the soil hydraulic conductivity as a function of soil free water θ.

[0042] Furthermore, the horizontal lateral water flux of the groundwater layer is calculated based on the groundwater level difference between adjacent grids:

[0043] (7),

[0044] In the formula, Q y (h) represents the horizontal lateral water exchange flux of the groundwater layer in the y-direction, which varies with the groundwater level h. x (h) represents the horizontal lateral water exchange flux of the groundwater layer in the x-direction as a function of the groundwater level h; K s It represents the saturated hydraulic conductivity of the groundwater layer.

[0045] Furthermore, the specific expression for the formula governing the total water volume change based on the unconfined groundwater movement equation is as follows:

[0046] (8),

[0047] In the formula, V(h) represents the total water volume of the deep unsaturated soil layer and groundwater layer as the groundwater level h changes; L represents the side length of the grid cell in the model calculation; A represents the area of ​​the grid cell, A=L×L; ξ represents the water flux between surface rivers and lakes and the deep unsaturated soil layer and groundwater layer.

[0048] Furthermore, based on the unconfined groundwater movement equation, a total water volume change formula is constructed to obtain the updated total water volume V of the deep unsaturated soil layer and groundwater layer. The groundwater level is then updated by inversion based on the updated total water volume V.

[0049] (9),

[0050] In the formula, ψ s h represents the saturated matrix potential. new This indicates the updated groundwater level.

[0051] On the other hand, the present invention also provides a calculation device for soil water-groundwater in a land surface hydrological model based on water potential gradient, comprising:

[0052] The model building module is configured to construct a vertically layered land surface hydrological model, wherein the model includes a soil layer, a deep unsaturated soil layer and a groundwater layer from top to bottom, and the lower boundary of the soil layer is set as a permeable boundary.

[0053] The governing equation construction module is configured to: construct the soil water governing equations to describe soil water movement;

[0054] The governing equation solving module is configured to calculate the soil free water content and matrix potential of the soil layer.

[0055] The distribution relationship determination module is configured to: obtain the groundwater level at the current calculation step, and determine the distribution relationship between the deep unsaturated soil and the groundwater level based on the groundwater level;

[0056] The total water volume calculation module is configured to calculate the total water volume of the deep unsaturated soil layer and the groundwater layer based on the distribution relationship.

[0057] The vertical flux calculation module is configured to: calculate the water potential gradient between the matrix potential and the groundwater level at the current calculation step, and solve the vertical water flux at the lower boundary of the soil layer based on the water potential gradient.

[0058] The horizontal lateral flux calculation module is configured to calculate the horizontal lateral water flux of the groundwater layer based on the groundwater level difference between adjacent grids.

[0059] The total water volume update module is configured to update the total water volume of the deep unsaturated soil layer and groundwater layer based on the vertical water flux and the horizontal lateral water flux, and the unconfined groundwater movement equation.

[0060] The groundwater level update module is configured to: invert and update the groundwater level based on the updated total water volume; wherein the updated groundwater level will be used to redetermine the distribution relationship between the deep unsaturated soil layer and the groundwater level in the next calculation time step.

[0061] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0062] This invention sets the lower boundary of the soil layer as a permeable boundary, and the vertical water flux D at the lower boundary is determined by the water potential gradient between the soil subsurface and the groundwater level. This allows the vertical water flux D to be either positive or negative—infiltration occurs when the soil water potential is higher than the groundwater level (i.e., D is positive), and capillary upwelling occurs when D is negative, thus achieving bidirectional water flow and avoiding the situation in traditional methods where water can only move downwards or cannot be exchanged. This invention adds a deep unsaturated soil layer between the soil layer and the groundwater layer, allowing the soil water potential and groundwater potential to transition continuously through this layer, avoiding the simplification of the exchange process caused by discontinuities between layers in traditional models. This invention directly calculates the vertical and horizontal water fluxes as source and sink terms based on the unconfined groundwater movement equation, thereby quantifying the influence of the soil module and transferring it to the groundwater module. Subsequently, by updating the total groundwater volume and inverting to obtain a new groundwater level, this new water level is fed back into the next long calculation. This closed-loop mechanism ensures that the soil water and groundwater conditions can interact and adjust in real time and dynamically, simulating a real feedback process. Attached Figure Description

[0063] Figure 1 The diagram shows a flowchart of a method for calculating soil water-groundwater based on a land surface hydrological model provided by the present invention. Detailed Implementation

[0064] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations thereof. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0065] The term "and / or" simply describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. Additionally, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0066] Example 1

[0067] See Figure 1 This embodiment introduces a method for calculating soil water-groundwater in a land surface hydrological model based on water potential gradient.

[0068] Land surface hydrological models simulate the movement of water from the surface to aquifers several meters or even hundreds of meters deep, including the soil layer above the surface, the saturated groundwater layer at the bottom, and the deep unsaturated zone between the two.

[0069] First, this embodiment collects spatial data such as the Digital Elevation Model (DEM), soil type distribution map, and groundwater aquifer elevation model of the target watershed, as well as time-series meteorological driving data such as precipitation, temperature, and radiation. Based on the spatial scale of the simulated target, the region is discretized into a regular grid with a resolution of 3 to 20 km. In this embodiment, the region is discretized into a 10 km × 10 km regular network, and within each network, multiple soil layers are set in the vertical direction, and the soil moisture content and groundwater level of each layer are initialized.

[0070] Next, this embodiment performs the calculation steps in one-hour increments:

[0071] Step S1: Construct a vertically layered land surface hydrological model; wherein, the model includes a soil layer, a deep unsaturated soil layer and a groundwater layer from top to bottom, and the lower boundary of the soil layer is set as a permeable boundary;

[0072] Land surface hydrological models simulate the movement of water from the surface to aquifers several meters or even hundreds of meters deep, including the soil layer above the surface, the saturated groundwater layer at the bottom, and the deep unsaturated zone between the two.

[0073] Step S2: Construct the soil water control equation to describe soil water movement;

[0074] The soil layer is a soil layer of a certain thickness on the surface of the earth. It is usually divided into several vertical layers. The vertical water flux in the soil layer between each layer is solved by the soil water Richard equation. The water flux at the upper boundary is the surface infiltration I, and the lower boundary must be set as a permeable boundary. The vertical water flux D at the lower boundary is determined by the water potential gradient between the bottom layer of the soil layer and the groundwater level.

[0075] For each rule network, the soil free water content θ of the soil layer of the previous step length is calculated. old Using the initial values ​​and meteorological data at the current step size, the soil free water content θ and corresponding matrix potential ψ of each soil layer are obtained at the current time t using the Richard equation for soil water. The specific expression of the Richard equation for soil water is as follows:

[0076] (1),

[0077] In the formula, θ represents the soil free water content, t represents time, and z represents the elevation of a certain point in the aquifer;

[0078] This represents the rate of change of soil free water content θ with time t, and By using the soil free water content θ at the previous moment old As an initial value, the rate of change is obtained from expression (1). Based on the step time Δt, the soil free water content θ at the current moment is obtained. new .

[0079] K(θ) represents the soil hydraulic conductivity as a function of soil free water θ.

[0080] ψ(θ) represents the soil matrix potential as a function of soil free water θ;

[0081] K s ψ represents the saturated hydraulic conductivity of soil. s denoted by saturated matrix potential, and B represents a constant related to soil texture.

[0082] In this embodiment, K s ψ represents the maximum water conductivity when the soil pores are completely filled with water; s The value of B represents the suction required for the largest pore in the soil to begin draining water; B represents the pore size distribution index, which is used to control the soil water holding curve. A high B value means that the soil pore size is relatively uniform and can release a large amount of water with a small change in suction; while a high B value means that the soil pore size is uneven.

[0083] Expression (10) can be derived from this:

[0084] (10)

[0085] Expression (10) is a functional formula for θ, where {B, K} s , ψ s , z} are constants. For expression (10), a fast implicit difference solution is performed to calculate the soil free water content θ and the corresponding matrix potential ψ.

[0086] The vertical water flux D at the lower boundary of the Richard equation for soil water is determined by the aforementioned water potential gradient between the subsurface soil and the groundwater level. That is, the lower boundary satisfies the condition: D = f(ψ, h), where D represents the vertical water flux at the lower boundary. This achieves bidirectional coupling between the soil water and groundwater modules. When D > 0, it indicates that soil water recharges groundwater through infiltration; when D < 0, it indicates that groundwater recharges soil water through capillary upwelling. Simultaneously, the conventional method for calculating the water flux at the lower boundary of the soil layer is retained, i.e., the zero-flux boundary (D = 0) or the free permeability boundary (D = K(θ)). The specific expression is as follows: (The equation is missing from the provided text.)

[0087] (11),

[0088] In the formula, Ф represents the total water potential, which is usually composed of gravitational potential μ and matrix potential ψ; z represents the elevation of a certain point in the deep unsaturated soil layer. h b It indicates the elevation of the lower boundary of the soil layer.

[0089] Step S3: Obtain the groundwater level at the current calculation step, and determine the distribution relationship between the deep unsaturated soil and the groundwater level based on the groundwater level;

[0090] In nature, the area between soil water and groundwater is a continuous, dynamically varying unsaturated transition zone. To establish a continuous aquifer from the soil layer to the lower boundary of the groundwater, this embodiment adds a deep unsaturated soil layer between the soil layer and the groundwater layer, with the thickness d of the deep unsaturated soil layer. dsl Equal to the lower boundary elevation h of the soil layer b The difference between the groundwater level and the elevation h, i.e., d dsl =h b -h, the thickness of the deep unsaturated soil layer d dsl It varies with the rise or fall of the groundwater level.

[0091] To facilitate numerical solution of the model, the deep unsaturated soil layer and the groundwater layer are assumed to be homogeneous in all aspects and have the same hydraulic characteristic parameters. The water profile of the deep unsaturated soil layer is in equilibrium within one calculation step, that is, the vertical water flux q at all points inside the deep unsaturated soil layer is 0. Substituting into expression (11), we get the following expression:

[0092] (12),

[0093] In the formula, Ф=μ(z)+ψ(z), and to simplify the calculation, the potential energy unit of a unit weight of water is normalized to obtain ψ(z)=z; at the same time, in this embodiment, the vertical axis is denoted as downward as positive.

[0094] Will and Substituting into expression (12), we get:

[0095] (13)

[0096] Between the groundwater level h and the elevation z of a certain point in the deep unsaturated soil layer, the integral and derivative of both sides of expression (13) are as follows:

[0097] (14)

[0098] At groundwater level h, the soil free water content θ(h) = 1. After derivation and calculation, the expression (14) can be used to obtain the expression for the soil free water content θ(z) at a certain elevation z in the deep unsaturated soil layer as follows:

[0099] (3),

[0100] From expression (3), we can see that θ(z) is a function of (z,h), and ψ s B and B represent constants related to the granular medium of the soil layer. Therefore, the soil free water content θ(z) at a certain elevation z in the deep unsaturated soil layer is only related to the groundwater level elevation h.

[0101] Step S4: Calculate the total water volume of the deep unsaturated soil layer and the groundwater layer based on the distribution relationship;

[0102] Transform θ(z) in expression (3) into θ(z) = x(z) –1 / B Where, x(z) = 1 + (z – h) / ψ s Furthermore, due to the difference between the free soil water content θ and the actual soil water content θ a The relationship expression is as follows:

[0103] (15)

[0104] In the formula, θ fc This represents the soil wilting moisture content. When the soil moisture content is less than the soil wilting moisture content θ, fc Although soil-bound water is difficult for plants to move and utilize, it is still part of the soil water content; therefore, the actual soil water content θ includes soil hygroscopic water and film water. a The expression is as follows:

[0105] (16)

[0106] Elevation of the lower boundary of the soil layer h b It is a constant. After obtaining the groundwater level elevation h at each calculation step, the water content of the deep unsaturated soil layer is calculated from the groundwater level elevation h to the lower boundary elevation h of the soil layer. b Integrate to obtain the water volume V of that layer. u Therefore, the upper and lower boundaries are respectively the elevation h of the lower boundary of the soil layer. b For a deep, unsaturated soil layer at a groundwater level of h, the water volume V of this layer is... u The expression is as follows:

[0107] (17)

[0108] Integrating expression (18) yields the water volume V of the deep unsaturated soil layer. u The expression is as follows:

[0109] (18)

[0110] In the formula, the constant C = (B – 1) / B.

[0111] Assuming that both the deep unsaturated soil layer and the groundwater layer are homogeneous media, meaning that the hydrophysical properties of the two layers are uniformly distributed and isotropic within the layers; based on this, at the current calculation step size, the total water volume V of the deep unsaturated soil layer and the groundwater layer can be calculated from the groundwater level h to the lower boundary h of the soil layer in the deep unsaturated soil layer. b The water content V obtained by integrating the water content of this layer u The result is obtained by superimposing the water volume of the groundwater layer, and the expression is as follows:

[0112] (4),

[0113] In the formula, h0 represents the elevation of the lower impermeable boundary of the groundwater aquifer; the total water volume V multiplied by the soil porosity is equal to the equivalent water depth of the corresponding aquifer.

[0114] Step S5: Calculate the water potential gradient between the matrix potential and the groundwater level at the current calculation step, and solve the vertical water flux at the lower boundary of the soil layer based on the water potential gradient.

[0115] Under natural conditions, the potential energy affecting the movement of free water in soil mainly consists of two parts: gravitational potential (μ) and matrix potential (ψ). Gravitational potential (μ) arises from the gravitational force acting on soil moisture, while matrix potential (ψ) arises from the adsorption and capillary forces of soil particles. The expression for total water potential is as follows:

[0116] Ф=μ(z)+ψ(θ)(19).

[0117] Since the heterogeneity of deep soil texture is relatively small, it is assumed that the water potential changes linearly from the center of the bottom soil layer through the deep unsaturated soil layer to the groundwater level. The expression for its water potential gradient is as follows:

[0118] (5),

[0119] In the formula, The soil matrix potential at the center of the soil strata (b1) varies with the soil free water content (θ); the saturated matrix potential (ψ) of the groundwater layer. sat Record it as 0.

[0120] Substituting expression (5) into expression (11), we obtain the following expression for the vertical water flux D at the lower boundary calculated using the unsaturated soil flow formula:

[0121] (6),

[0122] In the formula, hydraulic conductivity K and soil subsurface matrix potential ψ b1 The groundwater level h is a calculation variable. The water flux D at the lower boundary of the soil layer is jointly determined by the potential of the soil matrix and the groundwater level. As the potential of the soil matrix and the groundwater level change at each time step, water is replenished upward or transported downward, realizing the bidirectional coupling of the soil water and groundwater modules.

[0123] Step S6: Calculate the horizontal lateral water flux of the groundwater layer based on the groundwater level difference between adjacent grids;

[0124] The pores of the groundwater layer are filled with water, and the entire layer is in a saturated state, so its matrix potential can be considered zero. The lateral movement of water in the groundwater layer is mainly driven by the groundwater level difference between adjacent grids. The vertical water flux D at the lower boundary of the soil layer is set as the vertical source and sink term of the total water volume V of the deep unsaturated soil layer and the groundwater layer. Using Darcy's law of groundwater, the horizontal lateral water flux between adjacent grids is calculated, and the expression is as follows:

[0125] (7),

[0126] In the formula, Q y (h) represents the horizontal lateral water exchange flux of the groundwater layer in the y-direction, which varies with the groundwater level h. x (h) represents the horizontal lateral water exchange flux of the groundwater layer in the x-direction as a function of the groundwater level h; the two correspond to two mutually perpendicular directions on the horizontal plane; K s This represents the saturated hydraulic conductivity of the groundwater layer, a key parameter of the aquifer medium that characterizes the ability to transport water when the pores are completely filled with water. Its value can be obtained through site pumping tests, empirical formulas, or by consulting regional hydrogeological atlases.

[0127] Step S7: Based on the vertical water flux and the horizontal lateral water flux, update the total water volume of the deep unsaturated soil layer and the groundwater layer according to the unconfined groundwater movement equation;

[0128] The total water volume V of deep unsaturated soil layers and groundwater layers is affected by the vertical water flux D and the horizontal lateral water flux Q. x and Q y However, this changes, and based on the principle of water balance, the equation for the movement of unconfined groundwater is established, as follows:

[0129] (8),

[0130] In the formula, V(h) represents the total water volume of the deep unsaturated soil layer and groundwater layer as the groundwater level h changes; L represents the side length of the grid cell in the model calculation; A represents the area of ​​the grid cell, A=L×L; ξ represents the water flux between surface rivers and lakes and the deep unsaturated soil layer and groundwater layer; A×D represents the total water exchange rate from the soil layer to the groundwater layer.

[0131] Furthermore, by substituting expression (6) into expression (8), a two-way coupling between the soil layer and the groundwater layer is established; at the same time, by substituting expression (7) into expression (8), the total water volume change of the deep unsaturated soil layer and the groundwater layer caused by vertical water exchange and lateral horizontal movement is updated.

[0132] This step summarizes the water exchange from the upper soil layer, the horizontal groundwater exchange between adjacent grids, and the exchange with surface rivers and lakes, including all water exchanges entering and leaving the groundwater system. This summary ensures that the total water volume delivered to the next step is not lacking in any component.

[0133] In step S4, the expression (4) for the total water volume V of the deep unsaturated soil layer and the groundwater layer is given, where x(h b )=1+(h b – h) / ψ s Substituting into expression (18), we get the following expression:

[0134] (9),

[0135] In the formula, ψ s h represents the saturated matrix potential. new This indicates the updated groundwater level.

[0136] Step S8: Based on the updated total water volume, invert and update the groundwater level; wherein, the updated groundwater level will be used to redetermine the distribution relationship between the deep unsaturated soil layer and the groundwater level in the next calculation time step.

[0137] In step S7, the updated total water volume V of the deep unsaturated soil layer and groundwater layer is obtained. This step uses the updated total water volume V as input, and solves the expression (9) between the total water volume and the groundwater level. The new groundwater level elevation h is then derived by using the bisection search method. new Updated groundwater level elevation h newThis will serve as the input for the next long step, used to redetermine the distribution relationship between the deep unsaturated soil layer and the groundwater level. It will also directly serve as the key boundary condition for the next long step soil water calculation, thereby dynamically adjusting the vertical water exchange flux D at the bottom of the soil layer to complete the calculation process of one long step cycle.

[0138] Through steps S1 to S8, a two-way coupling calculation method for soil water and groundwater based on water potential gradient in a land surface hydrological model was established, ultimately realizing two-way, dynamic physical coupling between the soil water module and the groundwater module.

[0139] Using the soil water-groundwater calculation method based on the land surface hydrological model provided in this embodiment, the Nash efficiency coefficient was improved from 0.78 to 0.83 in the daily flow simulation results of the Lutai hydrological station on the main stream of a certain watershed, achieving a good improvement effect.

[0140] Example 2

[0141] Based on the same inventive concept as Embodiment 1, this embodiment introduces a calculation device for soil water-groundwater based on a land surface hydrological model using water potential gradient, comprising:

[0142] The model building module is configured to construct a vertically layered land surface hydrological model, wherein the model includes a soil layer, a deep unsaturated soil layer and a groundwater layer from top to bottom, and the lower boundary of the soil layer is set as a permeable boundary.

[0143] The governing equation construction module is configured to: construct the soil water governing equations to describe soil water movement;

[0144] The governing equation solving module is configured to calculate the soil free water content and matrix potential of the soil layer.

[0145] The distribution relationship determination module is configured to: obtain the groundwater level at the current calculation step, and determine the distribution relationship between the deep unsaturated soil and the groundwater level based on the groundwater level;

[0146] The total water volume calculation module is configured to calculate the total water volume of the deep unsaturated soil layer and the groundwater layer based on the distribution relationship.

[0147] The vertical flux calculation module is configured to: calculate the water potential gradient between the matrix potential and the groundwater level at the current calculation step, and solve the vertical water flux at the lower boundary of the soil layer based on the water potential gradient.

[0148] The horizontal lateral flux calculation module is configured to calculate the horizontal lateral water flux of the groundwater layer based on the groundwater level difference between adjacent grids.

[0149] The total water volume update module is configured to update the total water volume of the deep unsaturated soil layer and groundwater layer based on the vertical water flux and the horizontal lateral water flux, and the unconfined groundwater movement equation.

[0150] The groundwater level update module is configured to: invert and update the groundwater level based on the updated total water volume; wherein the updated groundwater level will be used to redetermine the distribution relationship between the deep unsaturated soil layer and the groundwater level in the next calculation time step.

[0151] The specific functions of each module described above are explained in the relevant content of the method in Embodiment 1, and will not be repeated here.

[0152] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0153] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0154] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0155] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0156] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for calculating soil water-groundwater ratio in a land surface hydrological model based on water potential gradient, characterized in that, include: Construct a vertically layered land surface hydrological model; wherein, from top to bottom, the model includes a soil layer, a deep unsaturated soil layer, and a groundwater layer, and the lower boundary of the soil layer is set as a permeable boundary; Construct soil water control equations to describe soil water movement; Within each calculation step: Based on the soil water control equation, the soil free water content and matrix potential of the soil layer are calculated; Obtain the groundwater level at the current calculation step, and determine the distribution relationship between the deep unsaturated soil and the groundwater level based on the groundwater level; Based on the distribution relationship, the total water volume of the deep unsaturated soil layer and the groundwater layer is calculated. Based on the matrix potential and the groundwater level at the current calculation step, calculate the water potential gradient between the two, and solve the vertical water flux at the lower boundary of the soil layer based on the water potential gradient. The horizontal lateral water flux of the groundwater layer is calculated based on the groundwater level difference between adjacent grids. Based on the total water volume, vertical water flux, and horizontal lateral water flux, and using the unconfined groundwater movement equation, update the total water volume of the deep unsaturated soil layer and groundwater layer. Based on the updated total water volume, the groundwater level for the next calculation step is obtained by inversion update; The updated groundwater level will be used in the next calculation time step to redetermine the distribution relationship between the deep unsaturated soil layer and the groundwater level.

2. The method for calculating soil water-groundwater in a land surface hydrological model based on water potential gradient according to claim 1, characterized in that, The soil water control equation is the Richard equation modified with lower boundary conditions, and the expression of the Richard equation is as follows: （1）， In the formula, θ represents the soil free water content, t represents time, and z represents the elevation of a certain point in the aquifer; K(θ) represents the soil hydraulic conductivity as a function of soil free water θ. ψ(θ) represents the soil matrix potential as a function of soil free water θ; K s ψ represents the saturated hydraulic conductivity of soil. s denoted by saturated matrix potential, and B represents a constant related to soil texture.

3. The method for calculating soil water-groundwater in a land surface hydrological model based on water potential gradient according to claim 2, characterized in that, The distribution relationship between the deep unsaturated soil and the groundwater level is expressed by the following expression: d dsl =h b -h(2) In the formula, d dsl h represents the thickness of deep unsaturated soil. b The elevation of the lower boundary of the soil layer is represented by h, and the elevation of the groundwater level is represented by h.

4. The method for calculating soil water-groundwater in a land surface hydrological model based on water potential gradient according to claim 3, characterized in that, Based on the thickness of the deep unsaturated soil layer, assuming the moisture profile of the deep unsaturated soil layer at the current thickness is in equilibrium within a calculation step, the expression for the free water content θ(z) at a certain elevation of the deep unsaturated soil layer, based on this equilibrium state, is as follows: （3）， In the formula, z represents the elevation of a certain point in the deep unsaturated soil layer. h b It indicates the elevation of the lower boundary of the soil layer.

5. The method for calculating soil water-groundwater in a land surface hydrological model based on water potential gradient according to claim 4, characterized in that, The expression for the total water volume of the deep unsaturated soil layer and the groundwater layer is as follows: （4）， In the formula, V represents the total water volume of the deep unsaturated soil layer and the groundwater layer; h0 represents the elevation of the lower impermeable boundary of the groundwater aquifer; C represents a constant, C = (B – 1) / B; θ fc This represents the soil wilting moisture content; define x(h) b )=1+(h b –h) / ψ s .

6. The method for calculating soil water-groundwater in a land surface hydrological model based on water potential gradient according to claim 1, characterized in that, Assuming the water potential changes linearly from the center of the bottom soil layer through the deep unsaturated soil layer to the groundwater level, the expression for the water potential gradient between the center of the bottom soil layer and the deep unsaturated soil layer is as follows: （5）， In the formula, Ф represents the total water potential; The soil matrix potential at the center of the soil strata (b1) varies with the soil free water content (θ); h represents the groundwater level. b1 Indicates the elevation of the center of the bottom layer of the soil; Based on the water potential gradient, the expression for the vertical water flux D at the lower boundary, calculated using the unsaturated soil flow formula, is as follows: （6）， In the formula, K(θ) represents the soil hydraulic conductivity as a function of soil free water θ.

7. The method for calculating soil water-groundwater in a land surface hydrological model based on water potential gradient according to claim 1, characterized in that, The horizontal lateral water flux of the groundwater layer is calculated based on the groundwater level difference between adjacent grids. （7）， In the formula, Q y (h) represents the horizontal lateral water exchange flux of the groundwater layer in the y-direction, which varies with the groundwater level h. x (h) represents the horizontal lateral water exchange flux of the groundwater layer in the x-direction as a function of the groundwater level h; the two correspond to two mutually perpendicular directions on the horizontal plane; K s It represents the saturated hydraulic conductivity of the groundwater layer.

8. The method for calculating soil water-groundwater in a land surface hydrological model based on water potential gradient according to claim 7, characterized in that, The specific expression for the formula of total water volume change based on the equation of motion of unconfined groundwater is as follows: （8）， In the formula, V(h) represents the total water volume of the deep unsaturated soil layer and groundwater layer as the groundwater level h changes; L represents the side length of the grid cell in the model calculation; A represents the area of ​​the grid cell, A=L×L; ξ represents the water flux between surface rivers and lakes and the deep unsaturated soil layer and groundwater layer.

9. The method for calculating soil water-groundwater in a land surface hydrological model based on water potential gradient according to claim 8, characterized in that, The total water volume change formula is constructed based on the unconfined groundwater movement equation to obtain the updated total water volume V of the deep unsaturated soil layer and groundwater layer. The groundwater level is then updated by inversion based on the updated total water volume V. （9）， In the formula, ψ s h represents the saturated matrix potential. new This indicates the updated groundwater level.

10. A calculation device for soil water-groundwater in a land surface hydrological model based on water potential gradient, characterized in that, include: The model building module is configured to construct a vertically layered land surface hydrological model, wherein the model includes a soil layer, a deep unsaturated soil layer and a groundwater layer from top to bottom, and the lower boundary of the soil layer is set as a permeable boundary. The governing equation construction module is configured to: construct the soil water governing equations to describe soil water movement; The governing equation solving module is configured to calculate the soil free water content and matrix potential of the soil layer. The distribution relationship determination module is configured to: obtain the groundwater level at the current calculation step, and determine the distribution relationship between the deep unsaturated soil and the groundwater level based on the groundwater level; The total water volume calculation module is configured to calculate the total water volume of the deep unsaturated soil layer and the groundwater layer based on the distribution relationship. The vertical flux calculation module is configured to: calculate the water potential gradient between the matrix potential and the groundwater level at the current calculation step, and solve the vertical water flux at the lower boundary of the soil layer based on the water potential gradient. The horizontal lateral flux calculation module is configured to calculate the horizontal lateral water flux of the groundwater layer based on the groundwater level difference between adjacent grids. The total water volume update module is configured to update the total water volume of the deep unsaturated soil layer and groundwater layer based on the vertical water flux and the horizontal lateral water flux, and the unconfined groundwater movement equation. The groundwater level update module is configured to: invert and update the groundwater level based on the updated total water volume; wherein the updated groundwater level will be used to redetermine the distribution relationship between the deep unsaturated soil layer and the groundwater level in the next calculation time step.

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