A watershed hydrological simulation method and system embedding canopy interception mechanism

Abstract

This invention discloses a watershed hydrological simulation method and system incorporating a canopy interception mechanism, belonging to the field of hydrological model optimization and watershed hydrological simulation. By embedding a revised Gash canopy interception model module into the SWAT model, a single rainfall event is divided into wetting, saturated, and arid stages, and the interception and evaporation amounts at each stage are dynamically calculated. Simultaneously, trunk interception is considered, setting a maximum trunk interception capacity, with any excess considered as effective rainfall. The original SWAT canopy interception calculation is replaced with the Gash canopy interception model module, and the interception capacity parameter is dynamically updated based on the leaf area index. The Canmx parameter is set to zero to achieve water volume closure. The intercepted evaporation is included in the evapotranspiration term, and the effective rainfall is used for runoff and runoff simulation. This invention solves the problem of low accuracy in hydrological simulation of forest-covered areas and achieves accurate simulation of watershed hydrological processes.

Description

Technical Field

[0001] This invention relates to the field of hydrological model optimization and watershed hydrological simulation, and in particular to a watershed hydrological simulation method and system that incorporates a canopy interception mechanism. Background Technology

[0002] The SWAT (Soil and Water Assessment Tool) model is a widely used distributed hydrological model with good spatial resolution and process mechanism description capabilities. It can simulate various hydrological and ecological processes, including rainfall, evapotranspiration, soil moisture movement, runoff formation, and non-point source pollution transport. This model has significant application value in watershed water resource management, ecosystem service assessment, and climate change impact analysis. In the SWAT model, rainfall is a key variable driving the hydrological cycle, and it is typically intercepted by the vegetation canopy before entering the soil and surface runoff. Currently, the calculation of canopy interception in the SWAT model mainly relies on the empirical parameter Canmx, which is set as the maximum interception capacity of the vegetation canopy. This parameter is used to directly deduct a fixed amount of rainfall as interception loss in each rainfall event, thus obtaining the effective rainfall amount used for subsequent hydrological calculations.

[0003] However, the traditional Canmx method has certain limitations. It treats canopy interception as a fixed upper limit, ignoring the dynamic evolution of canopy wetting, saturation, and drying stages during rainfall, and failing to consider the impact of key variables such as rainfall intensity, leaf area index (LAI), rainfall duration, and evaporation on the interception process. In areas with frequent changes in rainfall intensity or significant seasonal fluctuations in vegetation structure, this static setting may lead to systematic biases in the estimation of effective rainfall, thus affecting the accuracy of runoff simulation and soil moisture dynamics. Furthermore, Canmx parameters typically require regional calibration, and their values ​​vary considerably across different forest types and climatic conditions, lacking clear physical justification and limiting the model's generalization and application in various regions.

[0004] In the field of forestry hydrology, the Gash model, as a classic analytical model for canopy interception, has been widely used to simulate rainfall redistribution on forest surfaces. This model divides a single rainfall event into wetting, saturation, and drying phases, simulating the dynamic changes in canopy water storage, evaporation, and throughfall, respectively, and considering actual processes such as trunk interception and evaporation during rainfall, thus improving the physical description of canopy interception behavior. The revised Gash canopy interception model module is structurally simpler, has strong parameter measurability, is applicable to various forest types, and its simulation effects at both event-scale and daily-scale have been fully validated. However, existing SWAT models have not yet systematically integrated the dynamic computational logic of the Gash model; they mainly operate as independent models and have not achieved effective coupling with mainstream hydrological simulation platforms, limiting their application potential in distributed watershed simulation.

[0005] Therefore, in order to more accurately reflect the dynamic impact of forest vegetation on rainfall redistribution, it is necessary to systematically integrate the revised Gash canopy interception model module with the SWAT model to construct a canopy interception simulation framework with physical mechanisms, so as to replace the existing empirical interception methods and improve the accuracy and reliability of watershed hydrological simulation. Summary of the Invention

[0006] The present invention aims to at least partially solve one of the technical problems in the related art.

[0007] This invention proposes a watershed hydrological simulation method that embeds a canopy interception mechanism. This method can dynamically simulate the interception loss of each rainfall event, incorporate it into the water balance as an evaporation process, and update the effective rainfall in real time for runoff calculation. This significantly improves the realism and accuracy of rainfall-runoff simulation in forest vegetation cover areas.

[0008] Another objective of this invention is to propose a watershed hydrological simulation system with an embedded canopy interception mechanism.

[0009] To achieve the above objectives, this invention proposes a watershed hydrological simulation method incorporating a canopy interception mechanism, comprising:

[0010] The revised Gash canopy interception model module is embedded in the SWAT model. The Gash model takes rainfall, leaf area index (LAI), average tree height and meteorological parameters as input, divides a single rainfall event into wet phase, saturated phase and dry phase, and dynamically calculates the canopy interception and intercepted evaporation in each phase.

[0011] The amount of evaporation cut off from the output of the Gash model module is included in the evaporation term of the SWAT model.

[0012] The effective rainfall output from the Gash model module is used to replace the original rainfall input in the SWAT model for subsequent runoff, infiltration, and runoff simulations, thereby improving the accuracy of the SWAT model in hydrological simulations in forest-covered areas.

[0013] The watershed hydrological simulation method with embedded canopy interception mechanism in this embodiment of the invention may also have the following additional technical features:

[0014] In one embodiment of the present invention, the revised Gash canopy retention model module divides a single rainfall event into a wet phase, a saturated phase, and a dry phase, and calculates the retention loss sequentially; wherein...

[0015] During the wet phase, all rainwater is retained when the accumulated rainfall does not reach the maximum retention capacity of the canopy.

[0016] During the saturation stage, once the canopy water storage reaches its capacity, the evaporation loss that is continuously retained is calculated based on the ratio of rainfall intensity to canopy evaporation rate.

[0017] After the rainfall stops during the dry phase, all the trapped water remaining on the canopy and trunk surface evaporates;

[0018] Simultaneously considering the trunk interception process, a maximum trunk interception capacity is set. When the canopy is saturated, rainwater flows to the trunk in a predetermined proportion and prioritizes filling the trunk interception capacity. Any portion exceeding the capacity is directly included in the effective rainfall as trunk runoff.

[0019] In one embodiment of the present invention, the coupling between the revised Gash canopy interception model module and the SWAT model is achieved by embedding a canopy interception calculation module between the rainfall input and the hydrological calculation unit of the SWAT model;

[0020] The canopy interception calculation module receives rainfall input from SWAT and outputs the calculated effective rainfall to the runoff and runoff collection unit of SWAT, structurally replacing the original canopy interception calculation of the SWAT model; and dynamically updates the canopy interception capacity parameter according to the vegetation leaf area index, so that the maximum canopy interception capacity is adjusted with seasonal changes to improve the model's adaptability to different stand densities and growth stages.

[0021] In one embodiment of the present invention, the interception loss I is added to the evapotranspiration item and included in the water balance to complete the simulation of the hydrological process of the day.

[0022] In one embodiment of the present invention, the Canmx in the SWAT model is set to approximately zero, and only the dynamic simulation of canopy interception by the Gash module is retained to achieve water volume closure of the coupled structure.

[0023] To achieve the above objectives, another aspect of the present invention proposes a watershed hydrological simulation system embedding a canopy interception mechanism, comprising:

[0024] The interception calculation module is used to receive rainfall data and vegetation parameters, and simulate the canopy interception and evaporation process in stages according to rainfall intensity, LAI, tree height and evaporation rate, and output the effective rainfall and intercepted evaporation.

[0025] The hydrological simulation module is used to simulate hydrological processes such as runoff generation, infiltration, and evapotranspiration. It receives effective rainfall data through a data interaction interface and replaces the original rainfall input, while also including the intercepted evaporation in its evapotranspiration item.

[0026] The data interaction interface is used to connect the Gash model module and the SWAT hydrological simulation module to realize data input, output and feedback, thereby constructing a Gash-SWAT coupled system with dynamic canopy interception response.

[0027] The watershed hydrological simulation method and system with embedded canopy interception mechanism of the present invention replaces the original SWAT interception processing by embedding Gash calculation logic through a modular structure, so that the interception loss of each rainfall event is dynamically estimated and included in the evaporation term, and the effective rainfall is updated in real time and then transmitted to the runoff generation module.

[0028] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0029] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0030] Figure 1 This is a flowchart of a watershed hydrological simulation method with an embedded canopy interception mechanism according to an embodiment of the present invention;

[0031] Figure 2 This is a flowchart illustrating the coupling of the Gash canopy cutoff model and the SWAT model according to an embodiment of the present invention.

[0032] Figure 3 This is a schematic diagram illustrating the principle of precipitation redistribution simulation using the revised Gash canopy interception model module according to an embodiment of the present invention.

[0033] Figure 4 This is a schematic diagram of the SWAT model simulation according to an embodiment of the present invention;

[0034] Figure 5 This is a structural diagram of a watershed hydrological simulation system with an embedded canopy interception mechanism according to an embodiment of the present invention. Detailed Implementation

[0035] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0036] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0037] The following describes, with reference to the accompanying drawings, a watershed hydrological simulation method and system based on an embedded canopy interception mechanism proposed according to embodiments of the present invention.

[0038] Figure 1 This is a flowchart of a watershed hydrological simulation method incorporating an embedded canopy interception mechanism according to an embodiment of the present invention, as shown below. Figure 1 As shown, it includes:

[0039] A revised Gash canopy interception model module is embedded into the SWAT model. This module receives rainfall, leaf area index (LAI), average tree height, and meteorological parameters as input. It divides a single rainfall event into wet, saturated, and dry phases, dynamically calculating canopy interception and intercepted evaporation in each phase.

[0040] During the wet phase, all rainwater is trapped when the accumulated rainfall does not reach the canopy's maximum retention capacity.

[0041] During the saturation stage, once the canopy water storage reaches its capacity, the evaporation loss that is continuously retained is calculated based on the ratio of rainfall intensity to canopy evaporation rate.

[0042] During the drying phase, all the trapped water remaining on the canopy and trunk surface evaporates after the rainfall stops;

[0043] Simultaneously considering the trunk interception process, a maximum trunk interception capacity is set. When the canopy is saturated, rainwater flows to the trunk in a predetermined proportion and prioritizes filling the maximum trunk interception capacity. The portion exceeding the capacity is directly included in the effective rainfall as trunk runoff.

[0044] The revised Gash canopy interception model module is coupled with the SWAT model by embedding a canopy interception calculation module between the rainfall input and hydrological calculation unit of the SWAT model. The canopy interception calculation module receives the rainfall input from the SWAT model and outputs the calculated effective rainfall to the runoff and runoff collection unit of the SWAT model, structurally replacing the original canopy interception calculation of the SWAT model. Furthermore, the canopy interception capacity parameter is dynamically updated according to the vegetation leaf area index, so that the maximum canopy interception capacity is adjusted with seasonal changes.

[0045] By setting the Canmx parameter in the SWAT model to approximately zero and retaining only the revised Gash canopy interception model module for dynamic simulation of canopy interception, water volume closure of the coupled structure is achieved.

[0046] The evaporation rate is included in the evaporation term of the SWAT model based on the evaporation rate output by the revised Gash canopy trapping model module.

[0047] The effective rainfall output from the revised Gash canopy interception model module is used to replace the original rainfall input in the SWAT model for subsequent runoff generation, infiltration, and runoff simulations, thereby improving the accuracy of the SWAT model in hydrological simulations in forest-covered areas.

[0048] Specifically, the revised Gash canopy interception model module of this invention divides a single rainfall process into a wet phase, a saturation phase, and a dry phase, and calculates the interception loss sequentially. In the wet phase, when the cumulative rainfall does not reach the maximum interception capacity of the canopy, all rainwater is intercepted. In the saturation phase, when the canopy water storage reaches its capacity, the evaporation loss of continuous interception is calculated according to the ratio of rainfall intensity to canopy evaporation rate. In the dry phase, after the rainfall stops, all intercepted water remaining on the canopy and trunk surfaces evaporates. The algorithm also considers the trunk interception process, sets a maximum trunk interception capacity, and when the canopy is saturated, rainwater flows to the trunk in a predetermined proportion and prioritizes filling the trunk interception capacity. The portion exceeding the capacity is directly included in the effective rainfall as trunk runoff. A revised Gash canopy interception model module is coupled with the SWAT model by embedding a canopy interception calculation module between the rainfall input and hydrological calculation unit of the SWAT model. The interception calculation module receives the rainfall input from SWAT and outputs the calculated effective rainfall to the runoff and runoff collection units of SWAT, structurally replacing the original canopy interception calculation of the SWAT model. Furthermore, the method dynamically updates the canopy interception capacity parameter based on the vegetation leaf area index, adjusting the maximum canopy interception capacity according to seasonal changes to improve the model's adaptability to different stand densities and growth stages. The interception loss I is added to the evapotranspiration term and included in the water balance to complete the daily hydrological process simulation. The Canmx in the SWAT model is set to approximately zero, retaining only the dynamic simulation of canopy interception by the Gash module, thus achieving water volume closure in the coupled structure.

[0049] Furthermore, it can be seen that the SWAT model divides the watershed into multiple sub-watersheds, and further subdivides them into hydrological response units (HRUs) based on factors such as land use, soil type, topography, and slope. As the smallest computational unit in the SWAT model simulation, the HRU's delineation criteria require that each unit maintain consistency in land use, soil type, and slope characteristics, and that hydrological processes be simulated using lumped parameters. The accuracy of the HRU delineation directly affects the accuracy of the simulation results. During the simulation, SWAT considers the spatiotemporal heterogeneity of various hydrological units within the watershed, enabling the simulation of hydrological processes such as rainfall, surface runoff formation, dynamic changes in soil moisture, groundwater recharge processes, vegetation transpiration, and soil evaporation (evapotranspiration). The rainfall event-driven calculation mechanism automatically identifies continuous events in hourly or daily rainfall data, independently executing the Gash process for each rainfall event, dividing it into three stages: wetting, saturation, and drying, and calculating canopy interception and evaporation loss respectively. It also integrates with the evapotranspiration module: intercepted evaporation is recorded in real-time in the SWAT water... The invention addresses several key aspects of the SWAT model: 1) Decomposing the evaporation term in the equilibrium phase to achieve process-level decomposition of total evapotranspiration; 2) Dynamically updating effective rainfall: By updating canopy interception loss hourly, the net rainfall available for runoff and infiltration calculations is dynamically corrected, improving the model's accuracy in watershed water input calculations; 3) Simple parameter integration: Only a few observable parameters such as leaf area index (LAI), average tree height, and initial rainfall intensity need to be input, lowering the barrier to model application; 4) Wide adaptability: Applicable to various forest types, including coniferous, broadleaf, and sparse forests, and possesses good adaptability in areas with significant seasonal leaf area changes. The purpose of this invention is to overcome the shortcomings of existing SWAT model canopy interception methods. The original interception module of the SWAT model simply estimates the interception amount using static parameters and leaf area index, ignoring the dynamic process of canopy wetting-saturation-drying during rainfall events and key physical parameters. This invention provides a technical solution to couple a revised Gash canopy interception model to the SWAT model.

[0050] like Figure 2 , 3 As shown in Figures 4 and 5, the watershed hydrological simulation method of the present invention will be further described in conjunction with the accompanying drawings.

[0051] Initialization and Parameter Setting. Based on the forest vegetation type, elevation data, and meteorological data of the study area, the parameters required for the Gash model are set. The canopy water storage capacity (S) is determined by analyzing the linear relationship between rainfall, throughflow, and stem flow in a single consecutive rainfall event sufficient to saturate the canopy. The S value corresponds to the negative intercept of this regression line with the axes of throughflow and stem flow. The free throughflow coefficient (ρ), representing the amount of rainfall falling directly to the ground without reaching the canopy, is usually assumed to be 1 - c, where c is derived from LAI, using the following equation:

[0052]

[0053] The trunk storage capacity (St) and the proportion of precipitation flowing into the trunk stem flow (pt) are estimated using the negative intercept and slope obtained from linear regression analysis between precipitation and stem flow. The rainfall required to fully saturate the canopy (P′G) and trunk (P′t) is then determined according to the following formula:

[0054]

[0055]

[0056] in, Meaning average rainfall intensity (mm h) -1 ), The average evaporation rate of a saturated tree canopy during rain (mm h) -1 ), defined as = / c;S c The canopy storage capacity (in millimeters) per unit area is defined as S. c =S / c. The evaporation rate E of the forest canopy in rain is calculated using the Penman-Monteith equation, which applies to saturated canopies and assumes zero canopy drag.

[0057]

[0058] Where Δ represents the slope of the curve relating saturated vapor pressure and temperature (kPa). C 1 Rn represents the net radiation (wm) at the canopy surface. 2 ), Density of dry air (kg m³) 3 ), C p The specific heat capacity of air (J kg) C 1D represents the vapor pressure difference (kPa), g a The aerodynamic flux between the blade surface and the reference point (ms) 1 ), The latent heat of water evaporation (kPa) C 1 ), γ is the wet / dry constant (J kg) 1 ).

[0059] Canopy interception calculation: Each rainfall event can be divided into three stages, (1) wetting stage, at which time the rainfall (P) G (1) mm) is below the threshold required to saturate the canopy. The stage from the start of rainfall until the canopy reaches saturated water storage capacity is the first stage in which rainfall is intercepted by the plant canopy to moisten the leaves and branches. Before saturation, rainfall is mainly used to fill the gap in canopy water storage. At the same time, direct penetrating rain is generated in a certain proportion. If a small amount of intercepted water begins to evaporate (such as when the rainfall intensity is lower than the evaporation capacity during light rain), the model will also consider the synchronous evaporation loss. However, the wet stage is mainly marked by the canopy reaching full storage capacity. (2) Saturation stage: When rainfall accumulates to saturate the canopy (i.e., the canopy interception reaches S), the saturation stage begins. At this time, the canopy is full of water. Every moment, new rainfall will generate instantaneous penetrating rainfall and trunk flow. The proportion of penetrating rainfall will increase in the saturated state compared to the wet stage because the canopy is full. However, at the same time, the water on the surface of the canopy will continue to evaporate, causing the canopy to continuously empty a portion of its capacity because the canopy can no longer store additional water. At this time, the average rainfall intensity exceeds the average evaporation rate of a completely wet canopy. (3) Dry stage: When the rainfall event ends, a certain amount of water often remains on the canopy. That is, after the rainfall stops, without new rainfall, all the water stored in the canopy will gradually evaporate into the atmosphere until the canopy becomes dry again. The canopy water is reduced at each time step, and the simulation continues until the canopy water retention drops to zero.

[0060]

[0061] The input data for the SWAT model, including soil, land use, and meteorological data, were prepared in the usual manner. Meanwhile, the Canmx parameter for the corresponding vegetation in the SWAT model was set to a very small value (close to 0) to avoid interference from internal rainfall interception calculations. This ensures that subsequent rainfall interception calculations are entirely handled by the Gash module.

[0062] Establish a coupled framework. Insert the call interface for the Gash interception calculation module into the source code or workflow script of the SWAT model. For example, before the daily rainfall enters the hydrological balance calculation, first call the Gash model to calculate the canopy interception, where P...G To calculate the daily rainfall, input the rainfall amount P1 into the SWAT system. G -I. During each rainfall event, the model updates the effective rainfall in real time based on the interception calculation, including various parameters set in step 1 and the current vegetation status (such as LAI value), to realize the interception calculation based on the revised Gash model, and returns the effective rainfall P and the intercepted evaporation I.

[0063] Update SWAT hydrological calculations. The acquired effective rainfall P is transferred back to the SWAT model's main workflow, replacing the original daily rainfall used in SWAT for infiltration and runoff calculations. SWAT then uses its built-in water balance model to calculate processes such as soil saturation runoff and interflow using the new effective rainfall P. Simultaneously, the interception loss I is added as canopy evaporation to SWAT's evapotranspiration term: in practice, this can be achieved by adding the total daily evaporation to SWAT (e.g., the sum of evaporation and transpiration) to ensure water balance closure.

[0064]

[0065] Where SWt represents the soil moisture content (mm) at the end of the simulation; SW0 represents the soil moisture content (mm) at the start of the simulation; t represents the simulation time (d), i.e., the total simulation time is td; P1 represents the total effective rainfall (mm) on day i; Q surf E represents the surface runoff (mm) on day i; a W represents the evapotranspiration loss (mm) on day i; seep Q represents the amount of water that infiltrates through the soil on day i (mm); gw This represents the amount of water (mm) flowing back to groundwater on day i. Surface runoff and precipitation runoff are calculated using the SCS curve number method, as follows:

[0066]

[0067] Q surf P1 represents cumulative runoff in millimeters; P2 represents effective rainfall on a given day in meters. a The initial loss amount is represented by millimeters, including soil recharge, vegetation retention, and pre-drainage infiltration; S represents the reserved parameter, in millimeters.

[0068] Soil moisture, after being lost through vegetation absorption or transpiration, seeps into the soil layer and may infiltrate downwards to replenish groundwater, potentially forming loamy streams on the surface. The following formula is used for calculating loamy streams in the SWAT model.

[0069]

[0070] Among them, Qlat SW indicates the flow rate in the soil, expressed in mm / h. ly This represents the excess water flow in the saturation zone, expressed in mm; K sat The soil's hydraulic conductivity under saturated conditions is expressed in mm / h; slp represents the slope; Φ represents the total porosity of the soil layer; L hill The length of the hillside is represented in meters (m). Groundwater is a significant component of the SWAT model's influence within the sub-basin area, primarily originating from submerged and pressurized deep aquifers. The specific equations used to calculate groundwater within the basin are as follows:

[0071]

[0072] in, This represents the amount of groundwater (mm) flowing into the stream on day i. This represents the amount of groundwater (mm) that flows into the stream on day (i-1); t is the time step, in days. This represents the recharge flow rate (mm) from the aquifer on day i. It is the base current decay coefficient.

[0073] Simulation and Calibration. After completing the above modifications, the coupled model is run to perform hydrological simulations of the target watershed. Due to the introduction of new interception parameters, it is necessary to calibrate the parameters using observational data to improve simulation accuracy. The coefficients of determination (R²) are used. 2 ), Nash-Sutcliffe efficiency coefficient (E) ns The model performance is evaluated using the coefficient of variation (PBIAS) and root mean square error (RMSD), and the calculation method is as follows:

[0074]

[0075]

[0076]

[0077]

[0078] in These are simulated values. For simulated average value, For the observed values, This represents the average observed value.

[0079] Table 1. Components of canopy interception loss in the revised Gash canopy interception model

[0080]

[0081] Through the above implementation steps, this invention successfully embeds the revised Gash interception model into the SWAT hydrological model, achieving an improvement in effective rainfall calculation. Compared to the uncoupled model, the SWAT-revies Gash coupled model can dynamically simulate the evolution of canopy interception for each rainfall event, significantly improving the accuracy and reliability of forest rainfall-runoff simulations. This improvement is particularly significant in areas with high forest cover and high rainfall variability, enhancing the simulation of rainfall redistribution and hydrological responses. The method of this invention provides a more reliable modeling tool for watershed management and ecohydrological research, which can be used to assess the impact of forest ecosystem-intercepted precipitation on water resources, and further extended to the simulation analysis of forest hydrological functions under climate change scenarios.

[0082] The following are the specific implementation steps of the embodiments of the present invention:

[0083] Meteorological data (rainfall, radiation, temperature, humidity, etc.), vegetation parameters (mainly leaf area index LAI and canopy structure information), and land use and soil type data are used for SWAT initialization.

[0084] Maximum canopy water storage capacity S (estimated based on LAI), free penetration coefficient p, trunk water storage capacity St, evaporation rate E (calculated using the Penman-Monteith equation).

[0085] Before SWAT enters the simulation for day i, the rainfall P1 for that day is passed to the Gash module.

[0086] According to P G LAI and meteorological parameters, the Gash module judges and calculates canopy interception in the following stages: wetting stage (P G <P ′ G ), saturation stage (P G ≥ P ′ G (Calculate evaporation during rain), drying stage (evaporation of residual trapped water after rainfall ends).

[0087] Gash module output: Effective rainfall P1 = P G – I, the amount of evaporation retained. Feedback to the SWAT main process, replacing the original rainfall input in the SWAT model with P1, and incorporating I into the evapotranspiration term.

[0088] Update soil moisture and groundwater status, store the simulation results for the day, start the simulation for day i+1, and repeat the steps until the simulation ends.

[0089] In summary, the beneficial effects of this invention are as follows:

[0090] (1) The original SWAT structure is kept stable, and the Gash module can be flexibly embedded and removed, improving the maintainability and extensibility of the model;

[0091] (2) The interception calculation process is more consistent with the physical process of rainfall, which significantly improves the accuracy of rainfall distribution simulation;

[0092] (3) It requires fewer parameters and has wide applicability. Because this invention provides a more accurate estimate of interception evaporation, the actual effective rainfall entering the soil and river channels is dynamically corrected, thus making the runoff calculation more reliable. Traditional SWAT often overestimates surface runoff and infiltration due to underestimating interception, leading to runoff simulation bias. This invention reduces the rainfall input reaching the surface by increasing interception losses, which can reduce the peak runoff and the total runoff, and more closely approximate the observed flow process.

[0093] (4) It is applicable to various forest types such as coniferous forest, broad-leaved forest, and sparse forest, and the interception capacity can be dynamically adjusted through the leaf area index. It is of great significance for flood forecasting, drought assessment and water conservation, especially in watersheds with high forest coverage.

[0094] (5) Adapting to simulation needs at different spatiotemporal scales, supporting daily and time-scale data input, and suitable for climate change impact simulation and ecological flow regulation research. In traditional interception models, Canxmx is an empirical parameter, whose value is not easy to measure directly, usually relying on calibration and exhibiting high variability in different regions and forest types. However, the parameters required by this invention, such as LAI, tree height, and rainfall intensity, have clear physical meanings and can be obtained from actual measurements or remote sensing. They can be set without repeated trial calculations and calibrations, greatly facilitating the promotion and application of the model in different regions. At the same time, the method of this invention is applicable to various forest types, including coniferous forests, broad-leaved forests, and sparse woodlands. The model reflects vegetation density through the LAI parameter, thus adapting well to seasonal leaf area changes in deciduous forests: when LAI decreases during the leaf-fall season, the model automatically reduces the interception capacity, reflecting the situation where branch interception is the main feature; when LAI increases during the growing season, the interception capacity is enhanced. In contrast, the fixed Canxmx method often requires parameter adjustment or fails to reflect the effects of leaf drop when seasonal changes are significant. Therefore, this invention has a wider range of applicability and can achieve reliable simulation results in watersheds with different climate zones and phenological characteristics.

[0095] The watershed hydrological simulation method with embedded canopy interception mechanism according to embodiments of the present invention can dynamically simulate the interception loss of each rainfall event, include it in the water balance as an evaporation process, and update the effective rainfall in real time for runoff calculation, thereby significantly improving the realism and accuracy of rainfall-runoff simulation in forest vegetation cover areas.

[0096] To achieve the above embodiments, such as Figure 5As shown, this embodiment also provides a watershed hydrological simulation system 10 with an embedded canopy interception mechanism, including:

[0097] The canopy interception calculation module 100 is used to receive rainfall data and vegetation parameters, and simulate the canopy interception and evaporation process in stages according to rainfall intensity, leaf area index (LAI), tree height and evaporation rate, and output the effective rainfall and intercepted evaporation.

[0098] The hydrological simulation module 200 is used to perform hydrological process simulations of runoff generation, infiltration, and evapotranspiration. It receives effective rainfall data through a data interaction interface and replaces the corresponding original rainfall input. At the same time, it includes the intercepted evaporation in the corresponding evapotranspiration item.

[0099] The data interaction interface 300 is used to connect the Gash canopy interception model module and the SWAT hydrological simulation module to realize data input, output and feedback, thereby constructing a Gash-SWAT coupled system with dynamic canopy interception response.

[0100] Furthermore, the revised Gash canopy retention model module divides a single rainfall event into a wet phase, a saturated phase, and a dry phase, and calculates the retention loss sequentially; among which,

[0101] During the wet phase, all rainwater is retained when the accumulated rainfall does not reach the maximum retention capacity of the canopy.

[0102] During the saturation stage, once the canopy water storage reaches its capacity, the evaporation loss that is continuously retained is calculated based on the ratio of rainfall intensity to canopy evaporation rate.

[0103] After the rainfall stops during the dry phase, all the trapped water remaining on the canopy and trunk surface evaporates;

[0104] Simultaneously considering the trunk interception process, a maximum trunk interception capacity is set. When the canopy is saturated, rainwater flows to the trunk in a predetermined proportion and prioritizes filling the trunk interception capacity. Any portion exceeding the capacity is directly included in the effective rainfall as trunk runoff.

[0105] Furthermore, the revised Gash canopy interception model module is coupled with the SWAT model by embedding a canopy interception calculation module between the rainfall input and hydrological calculation unit of the SWAT model;

[0106] The canopy interception calculation module receives rainfall input from SWAT and outputs the calculated effective rainfall to the runoff and runoff collection unit of SWAT, structurally replacing the original canopy interception calculation of the SWAT model; and dynamically updates the canopy interception capacity parameter according to the vegetation leaf area index, so that the maximum canopy interception capacity is adjusted with seasonal changes to improve the model's adaptability to different stand densities and growth stages.

[0107] Furthermore, the interception loss I is added to the evapotranspiration term and included in the water balance to complete the daily hydrological process simulation.

[0108] Furthermore, by setting Canmx in the SWAT model to approximately zero and retaining only the dynamic simulation of canopy interception by the Gash module, water flow closure of the coupled structure is achieved.

[0109] The watershed hydrological simulation system with embedded canopy interception mechanism according to embodiments of the present invention can dynamically simulate the interception loss of each rainfall event, include it in the water balance as an evaporation process, and update the effective rainfall in real time for runoff calculation, thereby significantly improving the realism and accuracy of rainfall-runoff simulation in forest vegetation cover areas.

[0110] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0111] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

Claims

1. A watershed hydrological simulation method embedding a canopy interception mechanism, characterized in that, include: A revised Gash canopy interception model module is embedded into the SWAT model. This module receives rainfall, leaf area index (LAI), average tree height, and meteorological parameters as input. It divides a single rainfall event into wet, saturated, and dry phases, dynamically calculating canopy interception and intercepted evaporation in each phase. During the wet phase, all rainwater is trapped when the accumulated rainfall does not reach the canopy's maximum retention capacity. During the saturation stage, once the canopy water storage reaches its capacity, the evaporation loss that is continuously retained is calculated based on the ratio of rainfall intensity to canopy evaporation rate. During the drying phase, all the trapped water remaining on the canopy and trunk surface evaporates after the rainfall stops; Simultaneously considering the trunk interception process, a maximum trunk interception capacity is set. When the canopy is saturated, rainwater flows to the trunk in a predetermined proportion and prioritizes filling the maximum trunk interception capacity. The portion exceeding the capacity is directly included in the effective rainfall as trunk runoff. The revised Gash canopy interception model module is coupled with the SWAT model by embedding a canopy interception calculation module between the rainfall input and hydrological calculation unit of the SWAT model. The canopy interception calculation module receives the rainfall input from the SWAT model and outputs the calculated effective rainfall to the runoff and runoff collection unit of the SWAT model, structurally replacing the original canopy interception calculation of the SWAT model. Furthermore, the canopy interception capacity parameter is dynamically updated according to the vegetation leaf area index, so that the maximum canopy interception capacity is adjusted with seasonal changes. By setting the Canmx parameter in the SWAT model to approximately zero and retaining only the revised Gash canopy interception model module for dynamic simulation of canopy interception, water volume closure of the coupled structure is achieved. The evaporation rate is included in the evaporation term of the SWAT model based on the evaporation rate output by the revised Gash canopy trapping model module. The effective rainfall output from the revised Gash canopy interception model module is used to replace the original rainfall input in the SWAT model for subsequent runoff generation, infiltration, and runoff simulations, thereby improving the accuracy of the SWAT model in hydrological simulations in forest-covered areas.

2. A watershed hydrological simulation system embedding a canopy interception mechanism, characterized in that, include: The canopy interception calculation module, embedding a revised Gash canopy interception model algorithm, receives rainfall, leaf area index (LAI), average tree height, and meteorological parameters as input. It divides a single rainfall event into wet, saturated, and dry phases, dynamically calculating the canopy interception and intercepted evaporation at each phase. During the wet phase, all rainwater is trapped when the accumulated rainfall does not reach the canopy's maximum retention capacity. During the saturation stage, once the canopy water storage reaches its capacity, the evaporation loss that is continuously retained is calculated based on the ratio of rainfall intensity to canopy evaporation rate. During the drying phase, all the trapped water remaining on the canopy and trunk surface evaporates after the rainfall stops; Meanwhile, the canopy interception calculation module takes into account the trunk interception process and sets the maximum trunk interception capacity. When the canopy is saturated, rainwater flows to the trunk in a predetermined proportion and fills the maximum trunk interception capacity first. The part exceeding the capacity is directly included in the effective rainfall as trunk water flow. The hydrological simulation module is used to simulate hydrological processes such as runoff generation, infiltration, and evapotranspiration. The data interaction interface is used to connect the canopy interception calculation module and the hydrological simulation module to realize data input, output and feedback, thereby constructing a Gash-SWAT coupled system with dynamic canopy interception response; in, By embedding a canopy interception calculation module between the rainfall input and hydrological calculation unit of the SWAT model, the revised Gash canopy interception model module and the SWAT model are coupled. The canopy interception calculation module receives the rainfall input from the SWAT model and outputs the calculated effective rainfall to the runoff and runoff collection unit of the hydrological simulation module, structurally replacing the original canopy interception calculation of the SWAT model. Furthermore, the canopy interception capacity parameter is dynamically updated according to the vegetation leaf area index, so that the maximum canopy interception capacity is adjusted with seasonal changes. By setting the Canmx parameter in the SWAT model to approximately zero and retaining only the dynamic simulation of canopy interception by the canopy interception calculation module, the water volume closure of the coupled structure is achieved. Based on the intercepted evaporation output by the canopy interception calculation module, the intercepted evaporation is included in the evapotranspiration item of the hydrological simulation module and then included in the water balance to complete the daily hydrological process simulation. The effective rainfall output from the canopy interception calculation module is used to replace the original rainfall input in the hydrological simulation module for subsequent runoff generation, infiltration, and runoff simulation.

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