A watershed water cycle simulation method considering water balance of lake area

Abstract

The application provides a watershed water cycle simulation method considering lake water balance, which comprises five steps of sub-basin unit division and coding, data processing and model construction, water cycle process simulation, simulation result verification and result statistical analysis. The river network is extracted based on DEM and is divided into general river network and lake river network, the same lake large water body range is divided into independent lake units, and the dry branch topological code is uniformly coded; the basic data is processed, and the lake unit is supplemented with special information; the differentiated simulation logic is designed for the river channel and the lake unit, and the key hydrological parameters are calculated respectively; and the model is verified by the measured data and is used for long series simulation of multiple scenes. The application solves the simulation distortion problem caused by generalizing the lake into the river channel in the prior art, improves the simulation accuracy, is suitable for small watershed and lake special research, and has strong operability.

Description

Technical Field

[0001] This invention belongs to the field of watershed water cycle simulation technology, and specifically relates to a watershed water cycle simulation method that considers the water balance of lake areas. Background Technology

[0002] Distributed hydrological process simulation is an important technical means in the field of watershed water cycle simulation. Among them, distributed hydrological models are important research tools. The core idea is to divide the study watershed into several computational units, use hydrological models to simulate the runoff generation process in each unit, and combine the upstream and downstream relationships to simulate the confluence process between units, so as to realize the overall characterization of the water cycle of the entire watershed. It is widely used in water resource assessment, water conservancy project planning, ecological protection and other scenarios.

[0003] In existing distributed hydrological models, computational units are mostly divided into sub-basins or grids, and the simulation of river water bodies is usually based on one-dimensional linear processes. However, for large bodies of water such as lakes within a basin, existing technologies generally do not consider their unique hydrological characteristics, but rather treat them as equivalent to rivers: by drawing virtual river networks within the lake area, simplifying the hydraulic connection between the lake and the rivers flowing into it through multiple river intersections, and dividing the lake into different computational units for simulation, the lake is essentially generalized to an ordinary river, completely ignoring the core role of lakes in water volume regulation and water level regulation.

[0004] The aforementioned processing methods result in the discretization of lake areas in hydrological simulations, making it impossible to maintain the integrity and consistency of lake units in the water cycle process. In scenarios with large watershed scales and lower requirements for lake water level and volume accuracy, this deficiency has a limited impact. However, in applications requiring precise characterization of lake water levels, inflow and outflow volumes, and regulation processes—such as small watershed simulations, specialized lake water volume studies, and assessments of the impact of water conservancy projects on lakes—existing technologies struggle to meet practical needs. The accuracy and reliability of simulation results decrease significantly, failing to truly reflect the regulatory impact of lakes on the watershed's water cycle process. This limits the depth and breadth of application of distributed hydrological models in relevant sub-fields.

[0005] Therefore, there is an urgent need for a watershed water cycle simulation technology that can highlight the hydrological characteristics of lakes and maintain the integrity of lake units, in order to solve the problem of insufficient simulation accuracy caused by unreasonable lake treatment methods in existing technologies. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a watershed water cycle simulation method that considers the water balance of lake areas, so as to realize the overall division of lake units and the accurate characterization of lake water level, inflow and outflow of water and regulation process, and provide reliable technical support for scenarios such as lake water resource assessment and water conservancy project impact assessment.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] This invention provides a watershed water cycle simulation method considering lake water balance, comprising the following steps:

[0009] Step 1: Sub-basin unit division and coding

[0010] The calculation units for sub-basins are divided based on the DEM, specifically including:

[0011] S11. The D8 method is used to extract the simulated river network. Based on whether it is located in a large lake body, the simulated river network is divided into general river network and lake river network.

[0012] S12, divide the simulated river network into sub-basin calculation units. In the general river network area, sub-basins are divided according to the confluence range of the river segments, and each sub-basin has only one unbranched river segment. In the lake river network area, the river network in the same large lake body is divided into the same unit. There are multiple intersecting river segments in the lake unit. The main stream river segment is used as the generalized river segment of the lake unit, and the river unit and lake unit are marked respectively.

[0013] S13 adopts the trunk-branch topology code encoding method, and uniformly encodes river units and lake units according to the upstream and downstream relationship of the river network. The sub-basins adopt a many-to-one confluence relationship, that is, a sub-basin has multiple upstream and one downstream.

[0014] Step 2, Data Processing and Model Building

[0015] Based on the sub-basin computing units obtained in step 1, the basic data are processed and a model is constructed;

[0016] The basic data includes meteorological, land use, vegetation parameters, soil, soil and water conservation measures, water intake and output, flow rate, and water level data; the data processing includes the basic information of the statistical sub-basin calculation unit and the relevant parameters of various basic data; additional information is added to the lake unit, including water level-storage capacity relationship, initial water level, and discharge rules.

[0017] Step 3, Simulation of the water circulation process

[0018] Water cycle processes were simulated for both river and lake units, including:

[0019] The simulation of the water cycle process in the river unit includes evaporation, infiltration, runoff generation, and confluence. The evaporation process is calculated using the Penman formula or the Penman Montes formula depending on whether there is vegetation. The infiltration and runoff generation are calculated using the formula for full storage or over-infiltration runoff generation. The confluence process is calculated using the kinematic wave method.

[0020] The simulation of the water cycle process of the lake unit includes evaporation, lake water balance, lake outflow, and lake water level. The evaporation process is calculated using the Penman formula. The water balance process uses the lake as the basic unit to count the upstream inflow, outflow, and storage. The outflow is determined based on the lake water level and dam scheduling factors. The water level is calculated based on the lake water level-reservoir capacity curve and the water storage at the end of the time period.

[0021] Step 4, Verification of simulation results

[0022] The simulation results of the model were verified using measured data. The flow process of the river unit was verified, and the lake water level process was verified in the lake unit. The verification scale included year, month and day.

[0023] Step 5, Statistical Analysis of Results

[0024] Establish application scenarios, conduct long-term simulations using the validated model, and perform statistical analysis on the simulation results.

[0025] Furthermore, in step 2, the meteorological data includes five elements: precipitation, temperature, sunshine, wind speed, and humidity; the soil and water conservation measures include terraced fields and silt-retaining dams.

[0026] Furthermore, in step 3, the infiltration process of the river channel unit is calculated based on the relationship between soil infiltration capacity and rainfall intensity, wherein the soil infiltration capacity is calculated according to the following formula:

[0027]

[0028] In the formula, Indicates infiltration capacity; This represents the total water capacity of the upper m-1 soil layer; This indicates the error caused by the different soil moisture contents in each of the m-1 soil layers above; Indicates the cumulative infiltration amount; This represents the hydraulic conductivity of the m-th soil layer.

[0029] Furthermore, in step 3, the runoff generation process of the channel unit includes the calculation of surface runoff, interflow runoff, and groundwater channel exchange, with the specific formulas as follows:

[0030] (1) Surface runoff:

[0031]

[0032]

[0033] In the formula, This indicates the initial depth of the depression during a given period; P represents the depth of the depression at the end of the period; E represents the amount of precipitation; F represents the amount of evaporation; and F represents the cumulative infiltration. Indicates the depth of surface runoff; Indicates the maximum depth of the depression;

[0034] (2) Interstitial runoff:

[0035]

[0036] In the formula, Indicates the depth of abortion in the soil within the calculation unit; θ represents the soil hydraulic conductivity along the slope direction corresponding to the soil layer with a volumetric water content of θ; slope represents the ground slope; L represents the river channel length within the calculation unit; d represents the thickness of the unsaturated soil layer; A u Indicates the area of ​​the calculation unit;

[0037] (3) Groundwater exchange volume in river channels:

[0038]

[0039] In the formula, RG represents the groundwater exchange volume in the river channel; Indicates the hydraulic conductivity of the riverbed soil; This represents the infiltration area of ​​the riverbed within the calculation unit; Indicates the thickness of the riverbed soil; Indicates the elevation of groundwater level; This indicates the elevation of the river channel water level.

[0040] Furthermore, in step 3, the confluence process of the river unit is calculated using the kinematic wave method, specifically through the following formula:

[0041] Continuity equation:

[0042] Equations of motion:

[0043] Manning formula:

[0044] In the formula, Q represents the flow rate of the cross-section; A represents the cross-sectional area of ​​the flow; t represents the time coordinate; and x represents the spatial coordinate along the river channel. Indicates the inflow rate per unit width; Indicates the friction gradient; R represents the average ground slope or river slope of the calculation unit; n represents the hydraulic radius of the flow section; and n represents the Manning roughness coefficient.

[0045] Furthermore, in step 3, the lake water balance is calculated using the following formula:

[0046]

[0047] In the formula, and These represent the lake's water storage at the beginning and end of the time period, respectively. This represents the amount of water flowing into the surface of the i-th upstream river unit; represents the amount of water flowing into the i-th upstream channel unit; m represents the number of channel units flowing into the lake unit; P represents precipitation; E represents evaporation. This means mm to 100 million. coefficient, This indicates the amount of water taken from the lake. Indicates the outflow of the lake. express / s transfers 100 million coefficient.

[0048] Furthermore, in step 3, the lake outflow is calculated using the following formula:

[0049]

[0050] In the formula, f represents the lake outflow pattern; h represents the water level; This refers to human factors, including dam and gate scheduling.

[0051] Furthermore, in step 3, the lake water level is calculated using the following formula:

[0052]

[0053] In the formula, h represents the water level; g represents the lake water level-reservoir capacity relationship curve; This indicates the lake's water storage at the end of the time period.

[0054] Furthermore, in step 4, the model calibration performance criteria include:

[0055] (1) Minimize the relative error of simulated flow rate / water level;

[0056] (2) Maximize the Nash-Sutcliffe efficiency coefficient for simulated runoff / water level;

[0057] The formulas for calculating the relative error (RE) and the efficiency coefficient (NSE) are as follows:

[0058]

[0059]

[0060] In the formula, RE represents the relative error of simulated runoff / water level; NSE represents the Nash-Sutcliffe efficiency coefficient; Indicates simulated flow rate / water level; Indicates the measured flow rate / water level; N represents the length of the simulation series; This represents the average value of the actual flow rate / water level in the simulated series.

[0061] The advantages of this invention compared to the prior art are as follows:

[0062] 1. This invention divides the large water body of the same lake into independent lake units and combines a many-to-one confluence coding scheme to fully preserve the hydrological characteristics of the lake and realistically simulate the inflow and outflow of water and the regulation process of the lake. It solves the simulation distortion problem caused by the generalization of lakes into rivers in the existing technology, and is especially suitable for small watershed or lake-specific research scenarios.

[0063] 2. This invention addresses the hydrological differences between rivers and lakes by designing differentiated simulation logic—the river unit focuses on the complete chain calculation of evaporation, infiltration, runoff generation, and confluence, while the lake unit focuses on water balance, outflow, and water level calculations. At the same time, it supplements lake-specific parameters to adapt to the simulation needs of different watershed scales and lake types.

[0064] 3. The watershed water cycle simulation method described in this invention enhances its operability and reliability: the model is constructed with a complete process of "unit division - data processing - process simulation - result verification - statistical analysis", which clarifies various data processing dimensions, calculation methods and verification standards (relative error + Nash-Sutcliffe efficiency coefficient). The technical details are clear and can be directly implemented by those skilled in the art, which is convenient for engineering promotion.

[0065] 4. In the watershed water cycle simulation method described in this invention, the river unit adopts mature and well-known calculation methods to ensure universality and efficiency, while the lake unit innovatively designs a dedicated simulation module to achieve refined simulation without increasing computational complexity, taking into account both long-series, large-scale watershed simulation and lake-specific calculation needs. Attached Figure Description

[0066] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0067] Figure 1 This is a schematic flowchart of the watershed water cycle simulation method considering lake water balance described in the embodiment.

[0068] Figure 2 A schematic diagram showing the division of calculation units for rivers and lakes in the Fuxian Lake basin;

[0069] Figure 3 Verification curves for runoff processes in river units within the Fuxian Lake basin;

[0070] Figure 4 Verification curves for the water level process of the lake unit;

[0071] Figure 5 A graph showing the changes in the inflow of water into Fuxian Lake and Xingyun Lake;

[0072] Figure 6 A cumulative anomaly map of the inflow of water into Fuxian Lake and Xingyun Lake. Detailed Implementation

[0073] The embodiments described are provided to better illustrate the present invention, but are not intended to limit the scope of the invention to the embodiments described. Therefore, non-essential improvements and adjustments made to the embodiments by those skilled in the art based on the above description are still within the scope of protection of the present invention.

[0074] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0075] The present invention will be described in detail below through embodiments. It should be understood that the following embodiments are only used to exemplify and further explain and illustrate the content of the present invention, and are not intended to limit the present invention.

[0076] Example 1

[0077] This embodiment provides a watershed water cycle simulation method that considers the water balance of a lake area, such as... Figure 1 As shown, it includes the following steps:

[0078] Step 1: Sub-basin unit division and coding

[0079] The calculation units for sub-basins are divided based on the DEM, specifically including:

[0080] S11 uses the D8 method to extract the simulated river network. Based on whether it is located in a large lake body, the simulated river network is divided into general river network and lake river network.

[0081] S12, divide the simulated river network into sub-basin calculation units. In the general river network area, sub-basins are divided according to the confluence range of the river segments, and each sub-basin has only one unbranched river segment. In the lake river network area, the river network in the same large lake body is divided into the same unit. There are multiple intersecting river segments in the lake unit. The main stream river segment is used as the generalized river segment of the lake unit, and the river unit and lake unit are marked respectively.

[0082] S13 adopts the trunk-branch topology code encoding method, and uniformly encodes the river channel unit and lake unit according to the upstream and downstream relationship of the river network, reflecting the upstream and downstream relationship between each sub-basin; the sub-basins adopt a many-to-one confluence relationship, that is, a sub-basin has multiple upstreams and one downstream; the river sub-basin generally has only 2-3 upstreams flowing into the river channel unit, while the lake unit may have dozens of upstreams flowing into the river channel unit depending on the situation.

[0083] Step 2, Data Processing and Model Building

[0084] Based on the sub-basin computing units obtained in step 1, the basic data are processed and a model is constructed;

[0085] The basic data includes meteorological, land use, vegetation parameters, soil, soil and water conservation measures, water intake, flow rate, and water level data; among which, meteorological data includes five elements: precipitation, temperature, sunshine, wind speed, and humidity; the soil and water conservation measures include terraces and silt-retaining dams.

[0086] The data processing procedure includes statistical analysis of basic information of sub-basin calculation units and relevant parameters of various basic data (meteorological data, land use percentage, vegetation parameters, soil type, area ratio of soil and water conservation measures, water consumption, etc.); river units and lake units are processed using a unified method. In addition, lake units are supplemented with additional information including water level-storage capacity relationship, initial water level, and discharge rules.

[0087] Step 3, Simulation of the water circulation process

[0088] Water cycle processes were simulated for both river and lake units, including:

[0089] The simulation of the water cycle process in the river unit includes evaporation, infiltration, runoff generation, and confluence. The evaporation process is calculated using the Penman formula (without vegetation) or the Penman Montes formula (with vegetation) depending on whether there is vegetation. Infiltration and runoff generation are calculated using the full-saturation or over-infiltration runoff generation formula. The confluence process is calculated using the kinematic wave method.

[0090] Penman formula:

[0091] Penman Montes formula:

[0092] In the formula: RN represents the net radiation (MJ / m²). 2 G represents the heat flux entering the water (); ); This represents the derivative of saturated water vapor pressure with respect to temperature (kPa / ℃). Indicates air density ( ); This represents the specific heat of air at constant pressure (J / kg / ℃). This represents the difference (kPa) between the actual water vapor pressure and the saturated water vapor pressure. This represents the impedance of the plant community (s / m). This represents the aerodynamic impedance of the evaporating surface (s / m). This represents the latent heat of vaporization of water (MJ / kg). The value represents the air humidity constant (kPa / ℃); P represents atmospheric pressure (kPa).

[0093] The infiltration process of the river channel unit is calculated based on the relationship between soil infiltration capacity and rainfall intensity, where soil infiltration capacity is calculated according to the following formula:

[0094]

[0095] In the formula, f represents the infiltration capacity (mm / h); This represents the total water capacity (mm) of the upper m-1 soil layer. This indicates the error (mm) caused by the different soil moisture content in each soil layer (m-1). Indicates cumulative infiltration volume (mm); This represents the hydraulic conductivity (mm / h) of the m-th soil layer.

[0096] The runoff generation process of a river unit includes the calculation of surface runoff, interflow runoff, and groundwater exchange volume. The specific formulas are as follows:

[0097] (1) Surface runoff:

[0098]

[0099]

[0100] In the formula, Indicates the initial depth of the depression (mm) at the beginning of the time period; P represents the depth of the depression at the end of the period (mm); E represents the precipitation (mm); F represents the evaporation (mm); and F represents the cumulative infiltration (mm). Indicates the depth of surface runoff during heavy rainfall (mm); Indicates the maximum depth of the depression (mm).

[0101] (2) Interstitial runoff:

[0102]

[0103] In the formula, Indicates the depth of abortion in the soil of the calculation unit (mm); The soil hydraulic conductivity (mm) along the slope direction corresponds to the soil layer with a volumetric water content of θ; slope represents the ground slope (radians); L represents the river length within the calculation unit (m); d represents the thickness of the unsaturated soil layer (m). Indicates the area of ​​the calculation unit ( ).

[0104] (3) Groundwater exchange volume in river channels:

[0105]

[0106] In the formula, RG represents the groundwater exchange volume in the river channel (mm). This represents the hydraulic conductivity of the riverbed soil (mm). Represents the infiltration area of ​​the riverbed within the calculation unit ( ); Indicates the thickness of the riverbed soil (m); Indicates the groundwater level elevation (m); Indicates the elevation of the river channel (m).

[0107] The confluence process of the river unit is calculated using the kinematic wave method, specifically through the following formula:

[0108] Continuity equation:

[0109] Equations of motion:

[0110] Manning formula:

[0111] In the formula, Q represents the flow rate of the cross-section ( A represents the cross-sectional area of ​​the flow path ( ); ); t represents the time coordinate; x represents the spatial coordinates along the river channel; Indicates the inflow rate per unit width (the ratio of the total inflow volume to the length of the river in a given unit). ); The friction gradient is represented by the proportionality coefficient tan(α), where α represents the angle between the slope and the horizontal plane. The average ground slope or river slope of the calculation unit (proportional series); R represents the hydraulic radius of the flow section (m); n represents the Manning roughness coefficient.

[0112] The simulation of the water cycle process of the lake unit includes evaporation, lake water balance, lake outflow, and lake water level. The evaporation process is calculated using the Penman formula. The water balance process uses the lake as the basic unit to count the upstream inflow, outflow, and storage. The outflow is determined based on the lake water level and dam scheduling factors. The water level is calculated based on the lake water level-reservoir capacity curve and the water storage at the end of the time period.

[0113] The evaporation process is calculated using the Penman formula (as shown above).

[0114] When calculating the water balance of a lake, the lake is used as a basic unit to statistically analyze the upstream inflow, lake outflow, and storage capacity. The calculation formula is as follows:

[0115]

[0116] In the formula, and These represent the lake's water storage at the beginning and end of the time period (in billions of 100 million units). ); This represents the amount of water (in billions) flowing into the surface of the i-th upstream river unit. ); This represents the amount of water (in billions) flowing into the i-th upstream channel unit underground. ); m represents the number of river units flowing into the lake unit; P represents precipitation (mm); E represents evaporation (mm). This means mm to 100 million. coefficient, This indicates the amount of water taken from the lake (in billions of yuan). ), Indicates the outflow of the lake ( ), express / s transfers 100 million coefficient.

[0117] Lake outflow is the volume of water flowing out of the lake into the downstream river channel, determined by factors such as lake level and dam / sluice gate operations, and is calculated using the following formula:

[0118]

[0119] In the formula, f represents the outflow rule of the lake (determined according to each lake); h represents the water level (m); and z represents human factors such as dam and gate scheduling.

[0120] The lake water level is calculated based on the lake water level-reservoir capacity curve and the water storage at the end of the time period, using the following formula:

[0121]

[0122] In the formula, h represents the water level (m); g represents the lake water level ~ reservoir capacity relationship curve; This represents the lake's water storage at the end of the period (in billions of 100 million). ).

[0123] Step 4, Verification of simulation results

[0124] The simulation results of the model were verified using measured data. The flow process of the river unit was verified, and the lake water level process was verified in the lake unit. The verification scale included year, month and day.

[0125] The criteria for model calibration include:

[0126] (1) Minimize the relative error of simulated flow rate / water level;

[0127] (2) Maximize the Nash-Sutcliffe efficiency coefficient for simulated runoff / water level;

[0128] The formulas for calculating the relative error (RE) and the efficiency coefficient (NSE) are as follows:

[0129]

[0130]

[0131] In the formula, RE represents the relative error (%) of simulated runoff / water level; NSE represents the Nash-Sutcliffe efficiency coefficient; Indicates simulated flow ( ) / water level (m); Indicates the measured flow rate ( ) / water level (m); N represents the length of the simulation series; Indicates the actual flow rate of the simulated series ( The average value of water level (m).

[0132] Step 5, Statistical Analysis of Results

[0133] Establish application scenarios (such as water cycle process simulation, lake water volume assessment, and the impact of water conservancy project construction), conduct long-term simulations using the validated model, and perform statistical analysis on the simulation results.

[0134] Application examples:

[0135] Taking the Fuxian Lake basin as an example, the water cycle simulation of the basin is carried out using the method described in the embodiment. This basin consists of two lakes, Fuxian Lake and Xingyun Lake. The basin is divided into computational units, such as... Figure 2 As shown, Fuxian Lake and Xingyun Lake are divided into independent units.

[0136] Based on the predefined sub-basin units, information on meteorology, land use, and water intake is processed to construct a model of the Fuxian Lake basin.

[0137] Verification of runoff processes in river units, such as Figure 3 As shown; verification of the lake unit water level process is as follows. Figure 4 As shown.

[0138] Analysis based on the Fuxian Lake model: Figure showing the variation of inflow into the lake in different regions. Figure 5 As shown in the figure, the cumulative anomaly of inflow into Fuxian Lake and Xingyun Lake is as follows: Figure 6 As shown in Table 1, the trend of water inflow into the lake is examined, and the contribution rate of different factors to the reduction of water volume in Fuxian Lake is shown in Table 2.

[0139] Table 1. Trend Verification Table of Inflow Water to the Lake

[0140]

[0141] Table 2. Statistical table of the contribution rate of different factors to the reduction of water volume in Fuxian Lake.

[0142]

[0143] Finally, it should be noted that the above is only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention (such as the application of various formulas, the order of steps, etc.) without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A watershed water cycle simulation method considering lake area water balance, characterized in that, The method includes the following steps: Step 1: Sub-basin unit division and coding The calculation units for sub-basins are divided based on the DEM, specifically including: S11. The D8 method is used to extract the simulated river network. Based on whether it is located in a large lake body, the simulated river network is divided into general river network and lake river network. S12, divide the simulated river network into sub-basin calculation units. In the general river network area, sub-basins are divided according to the confluence range of the river segments, and each sub-basin has only one unbranched river segment. In the lake river network area, the river network in the same large lake body is divided into the same unit. There are multiple intersecting river segments in the lake unit. The main stream river segment is used as the generalized river segment of the lake unit, and the river unit and lake unit are marked respectively. S13 adopts the trunk-branch topology code encoding method, and uniformly encodes river units and lake units according to the upstream and downstream relationship of the river network. The sub-basins adopt a many-to-one confluence relationship, that is, a sub-basin has multiple upstream and one downstream. Step 2, Data Processing and Model Building Based on the sub-basin computing units obtained in step 1, the basic data are processed and a model is constructed; The basic data includes meteorological, land use, vegetation parameters, soil, soil and water conservation measures, water intake and output, flow rate, and water level data; the data processing includes the basic information of the statistical sub-basin calculation unit and the relevant parameters of various basic data; additional information is added to the lake unit, including water level-storage capacity relationship, initial water level, and discharge rules. Step 3, Simulation of the water circulation process Water cycle processes were simulated for both river and lake units, including: The simulation of the water cycle process in the river unit includes evaporation, infiltration, runoff generation, and confluence. The evaporation process is calculated using the Penman formula or the Penman Montes formula depending on whether there is vegetation. The infiltration and runoff generation are calculated using the formula for full storage or over-infiltration runoff generation. The confluence process is calculated using the kinematic wave method. The simulation of the water cycle process of the lake unit includes evaporation, lake water balance, lake outflow, and lake water level. The evaporation process is calculated using the Penman formula. The water balance process uses the lake as the basic unit to count the upstream inflow, outflow, and storage. The outflow is determined based on the lake water level and dam scheduling factors. The water level is calculated based on the lake water level-reservoir capacity curve and the water storage at the end of the time period. Step 4, Verification of simulation results The simulation results of the model were verified using measured data. The flow process of the river unit was verified, and the lake water level process was verified in the lake unit. The verification scale included year, month and day. Step 5, Statistical Analysis of Results Establish application scenarios, conduct long-term simulations using the validated model, and perform statistical analysis on the simulation results.

2. The watershed water cycle simulation method according to claim 1, characterized in that, In step 2, the meteorological data includes five elements: precipitation, temperature, sunshine, wind speed, and humidity; the soil and water conservation measures include terraced fields and silt-retaining dams.

3. The watershed water cycle simulation method according to claim 1, characterized in that, In step 3, the infiltration process of the river channel unit is calculated based on the relationship between soil infiltration capacity and rainfall intensity, wherein the soil infiltration capacity is calculated according to the following formula: In the formula, Indicates infiltration capacity; This represents the total water capacity of the upper m-1 soil layer; This indicates the error caused by the different soil moisture contents in each of the m-1 soil layers above; Indicates the cumulative infiltration amount; This represents the hydraulic conductivity of the m-th soil layer.

4. The watershed water cycle simulation method according to claim 1, characterized in that, In step 3, the runoff generation process of the channel unit includes the calculation of surface runoff, interflow runoff, and groundwater channel exchange, and the specific formulas are as follows: (1) Surface runoff: In the formula, This indicates the depth of the reservoir at the beginning of the period; P represents the depth of water retention in the depression at the end of the period; E represents the amount of precipitation; F represents the amount of evaporation; and F represents the cumulative infiltration. Indicates the depth of surface runoff; Indicates the maximum depth of the depression; (2) Interstitial runoff: In the formula, Indicates the depth of abortion in the soil within the calculation unit; θ represents the soil hydraulic conductivity along the slope direction corresponding to the soil layer with a volumetric water content of θ; slope represents the ground slope; L represents the river length within the calculation unit; d represents the thickness of the unsaturated soil layer. Indicates the area of ​​the calculation unit; (3) Groundwater exchange volume in river channels: In the formula, RG represents the groundwater exchange volume in the river channel; Indicates the hydraulic conductivity of the riverbed soil; This represents the infiltration area of ​​the riverbed within the calculation unit; Indicates the thickness of the riverbed soil; Indicates the elevation of groundwater level; This indicates the elevation of the river channel water level.

5. The watershed water cycle simulation method according to claim 1, characterized in that, In step 3, the confluence process of the river unit is calculated using the kinematic wave method, specifically through the following formula: Continuity equation: Equations of motion: Manning Official: In the formula, Q represents the flow rate of the cross-section; A represents the cross-sectional area of ​​the flow; t represents the time coordinate; and x represents the spatial coordinate along the river channel. Indicates the inflow rate per unit width; Indicates the friction gradient; R represents the average ground slope or river slope of the calculation unit; n represents the hydraulic radius of the flow section; and n represents the Manning roughness coefficient.

6. The watershed water cycle simulation method according to claim 1, characterized in that, In step 3, the lake water balance is calculated using the following formula: In the formula, and These represent the lake's water storage at the beginning and end of the time period, respectively. This represents the amount of water flowing into the surface of the i-th upstream river unit; represents the amount of water flowing into the i-th upstream channel unit; m represents the number of channel units flowing into the lake unit; P represents precipitation; E represents evaporation. This means mm to 100 million. coefficient, This indicates the amount of water taken from the lake. Indicates the outflow of the lake. express / s transfers 100 million coefficient.

7. The watershed water cycle simulation method according to claim 1, characterized in that, In step 3, the lake outflow is calculated using the following formula: In the formula, f represents the lake outflow pattern; h represents the water level; and z represents human factors, including dam and gate scheduling.

8. The watershed water cycle simulation method according to claim 1, characterized in that, In step 3, the lake water level is calculated using the following formula: In the formula, h represents the water level; g represents the lake water level-reservoir capacity relationship curve; This indicates the lake's water storage at the end of the time period.

9. The watershed water cycle simulation method according to claim 1, characterized in that, In step 4, the criteria for model calibration include: (1) Minimize the relative error of simulated flow rate / water level; (2) Maximize the Nash-Sutcliffe efficiency coefficient for simulated runoff / water level; The formulas for calculating the relative error (RE) and the efficiency coefficient (NSE) are as follows: In the formula, RE represents the relative error of simulated runoff / water level; NSE represents the Nash-Sutcliffe efficiency coefficient; Indicates simulated flow rate / water level; Indicates the measured flow rate / water level; N represents the length of the simulation series; This represents the average value of the actual flow rate / water level in the simulated series.

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