River basin hydrological simulation method and system embedded with canopy interception mechanism

Abstract

The invention discloses a basin hydrological simulation method and system embedded with a canopy interception mechanism, and the method comprises the steps: embedding a revised Gash canopy interception model module in an SWAT model, dividing a rainfall event into a wetting stage, a saturation stage and a drying stage according to the parameters of rainfall, a leaf area index and a tree height, dynamically calculating the canopy interception amount and the interception evaporation amount, and carrying out the calculation of the canopy interception amount and the interception evaporation amount. The effective rainfall capacity is used for replacing original rainfall input in the SWAT model, the adjusting effect of the forest canopy on the rainfall process is reflected more truly, and the basin hydrological simulation precision is improved. According to the method, the response and simulation capability of the SWAT model to the hydrological process of the underlying surface of the forest is effectively improved, the dynamic response to effective rainfall and evaporation terms is enhanced, the method is suitable for watershed hydrological process modeling of various forest types, and the reliability of flood forecasting and water conservation evaluation is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of hydrological model optimization and watershed hydrological simulation, and particularly relates to a watershed hydrological simulation method and system embedded with a canopy interception mechanism. BACKGROUND

[0002] The SWAT (Soil and Water Assessment Tool) model is a widely used distributed hydrological model with good spatial resolution and process mechanism description capability, which can simulate various hydrological and ecological processes including rainfall, evapotranspiration, soil moisture movement, runoff formation and non-point source pollution transport. The model has important application value in watershed water resources management, ecosystem service evaluation and climate change impact analysis. In the SWAT model, rainfall is the key variable driving the hydrological cycle, which is usually 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, used to directly deduct a fixed amount of rainfall as interception loss in each rainfall event, thereby obtaining the effective rainfall for subsequent hydrological calculation.

[0003] However, the traditional Canmx method has certain limitations. It regards canopy interception as a fixed upper limit, ignoring the evolution of canopy wetting, saturation and drying during rainfall process, and does not consider the influence of rainfall intensity, leaf area index (LAI), rainfall duration and rainfall evaporation on the interception process. In areas where rainfall intensity changes frequently or vegetation structure has significant seasonal fluctuations, this static setting may cause systematic bias in the estimation of effective rainfall, thereby affecting the accuracy of runoff simulation and soil moisture dynamics. In addition, the Canmx parameter usually needs to rely on regional calibration, and its value varies greatly in different forest types and climate conditions, lacking clear physical basis, which limits the promotion and application of the model in different regions.

[0004] In the field of forest hydrology, Gash model, as a classic canopy interception analytical model, has been widely used in the simulation of rainfall redistribution of forest underlying surface. The model divides a single rainfall event into wetting, saturation and drying stages, respectively simulates the dynamic changes of canopy storage, evaporation and throughfall, and considers the actual processes such as stemflow interception and rain evaporation, thereby improving the physical description ability of canopy interception behavior. The revised Gash model is more concise in structure, has strong parameter measurability, is suitable for various forest types, and its simulation effect on event scale and daily scale has been fully verified. However, the existing SWAT model has not systematically integrated the dynamic calculation logic of Gash model, and mainly runs as an independent model, which cannot be effectively coupled with the mainstream hydrological simulation platform, limiting its application potential in distributed watershed simulation.

[0005] Therefore, in order to more accurately reflect the dynamic influence of forest vegetation on rainfall redistribution, it is necessary to systematically integrate the revised Gash model with the SWAT model, and construct a canopy interception simulation framework with physical mechanism to replace the existing empirical interception method, and improve the accuracy and reliability of watershed hydrological simulation. SUMMARY

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

[0007] The present application proposes a watershed hydrological simulation method embedded with canopy interception mechanism, which can dynamically simulate the interception loss of each rainfall event, and take it into water balance as an evaporation process, and update the effective rainfall in real time for runoff calculation, thereby significantly improving the authenticity and accuracy of rainfall-runoff simulation in forest vegetation coverage area.

[0008] Another object of the present application is to propose a watershed hydrological simulation system embedded with canopy interception mechanism.

[0009] To achieve the above object, the present application proposes a watershed hydrological simulation method embedded with canopy interception mechanism, comprising:

[0010] In the SWAT model, the revised Gash canopy interception model module is embedded, the Gash model receives rainfall, leaf area index LAI, average tree height and meteorological parameters as input, divides a single rainfall event into wetting, saturation and drying stages, and dynamically calculates the canopy interception and interception evaporation of each stage;

[0011] According to the interception evaporation output by the Gash model module, it is taken into the evapotranspiration item of the SWAT model;

[0012] The effective rainfall output by the Gash model module replaces the original rainfall input in the SWAT model and is used for subsequent runoff generation, infiltration, and runoff simulations, thereby improving the hydrological simulation accuracy of the SWAT model in forest vegetation coverage areas.

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

[0014] In one embodiment of the present invention, the revised Gash model divides a single rainfall process into a wet stage, a saturated stage, and a dry stage and calculates the interception loss in sequence; wherein,

[0015] In the wet stage, when the accumulated rainfall does not reach the maximum interception capacity of the canopy, all the rainwater is intercepted;

[0016] In the saturation stage, when the canopy water storage reaches capacity, the evaporation loss of continued interception is calculated according to the ratio of rainfall intensity to canopy evaporation rate;

[0017] During the dry phase, all trapped water remaining in the canopy and trunk surfaces evaporates after rainfall stops;

[0018] At the same time, the trunk interception process is taken into consideration and the maximum trunk interception capacity is set. When the canopy is saturated, rainwater flows to the trunk according to a predetermined proportion and fills the trunk interception capacity first. The part exceeding the capacity is directly counted as trunk flow and included in the effective rainfall.

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

[0020] The canopy interception calculation module receives rainfall input from SWAT and outputs the calculated effective rainfall to SWAT's runoff and runoff aggregation unit, structurally replacing the original canopy interception calculation of the SWAT model; and dynamically updates the canopy interception capacity parameters based on the vegetation leaf area index, so that the maximum canopy interception capacity adjusts with seasonal changes, thereby improving the model's adaptability to different stand densities and growing periods.

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

[0022] In one embodiment of the present invention, 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 closure of the coupled structure.

[0023] To achieve the above objectives, the present invention further provides a watershed hydrological simulation system embedded with a canopy interception mechanism, comprising:

[0024] A interception calculation module is used for receiving rainfall data and vegetation parameters, simulating canopy interception and evaporation process in stages according to rainfall intensity, LAI, tree height and evaporation rate, and outputting effective rainfall and interception evaporation;

[0025] A hydrological simulation module is used for executing hydrological process simulation such as runoff generation, infiltration and evapotranspiration, receiving effective rainfall through a data interaction interface and replacing original rainfall input, and adding interception evaporation to evapotranspiration;

[0026] A data interaction interface is used for connecting the Gash model module and the SWAT hydrological simulation module, realizing data input, output and feedback, so as to build a Gash-SWAT coupling system with dynamic canopy interception response.

[0027] The watershed hydrological simulation method and system embedding canopy interception mechanism according to the embodiment of the application embed Gash calculation logic through a modular structure, replace original SWAT interception processing, so that interception loss of each rainfall event is dynamically estimated and added to the evaporation item, and effective rainfall is updated in real time and then transmitted to the runoff generation module.

[0028] Additional aspects and advantages of the application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0029] The above and / or additional aspects and advantages of the application will become apparent and be readily appreciated from the following description, taken in conjunction with the accompanying drawings, in which:

[0030] Figure 1 is a flowchart of the watershed hydrological simulation method embedding canopy interception mechanism according to the embodiment of the application;

[0031] Figure 2 is a flowchart of the coupling of the Gash canopy interception model and the SWAT model according to the embodiment of the application;

[0032] Figure 3 is a schematic diagram of the revised Gash model simulating rainfall redistribution according to the embodiment of the application;

[0033] Figure 4 is a schematic diagram of the SWAT model simulation according to the embodiment of the application;

[0034] Figure 5 is a structure diagram of the watershed hydrological simulation system embedding canopy interception mechanism according to the embodiment of the application. DETAILED DESCRIPTION

[0035] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other in the case of no conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0036] In order for those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the protection scope of the present application.

[0037] The method and system for simulating watershed hydrology embedded with canopy interception mechanism according to the embodiments of the present application will be described below with reference to the accompanying drawings.

[0038] Figure 1 is a flow chart of the method for simulating watershed hydrology embedded with canopy interception mechanism according to the embodiments of the present application, as shown in Figure 1 , which comprises:

[0039] S1, embedding the revised Gash canopy interception model module in the SWAT model, the Gash model receiving rainfall, leaf area index LAI, average tree height and meteorological parameters as inputs, dividing a single rainfall event into wet stage, saturation stage and dry stage, and dynamically calculating canopy interception and interception evaporation in each stage;

[0040] S2, according to the interception evaporation output by the Gash model module, adding it to the evapotranspiration item of the SWAT model; S3, according to the effective rainfall output by the Gash model module, replacing the original rainfall input in the SWAT model, which is used for subsequent runoff generation, infiltration and runoff simulation, and improving the hydrological simulation accuracy of the SWAT model in the forest vegetation coverage area.

[0041] Specifically, the revised Gash model algorithm of the present application divides a single rainfall process into a wet stage, a saturation stage and a dry stage to calculate interception loss in sequence, wherein in the wet stage, rainwater is all intercepted when the cumulative amount of rainfall does not reach the maximum interception capacity of the canopy, in the saturation stage, evaporation loss of the sustained interception is calculated according to the ratio of rainfall intensity to canopy evaporation rate when the canopy water storage reaches the capacity, and in the dry stage, the interception water remaining in the canopy and the surface of the tree trunk is all evaporated after the rainfall stops; the algorithm simultaneously considers the process of tree trunk interception, sets the maximum interception capacity of the tree trunk, and when the canopy is saturated, rainwater flows to the tree trunk in a predetermined proportion and fills the interception capacity of the tree trunk preferentially, and the part exceeding the capacity is directly counted as tree trunk runoff and enters the effective rainfall. The coupling of the revised Gash model and the SWAT model is realized by embedding a canopy interception calculation module between the rainfall input and the hydrological calculation module of the SWAT model, the interception calculation module receives the rainfall input of the SWAT and outputs the calculated effective rainfall to the runoff and flow calculation unit of the SWAT, and the interception calculation of the original canopy of the SWAT model is replaced in structure; and the method dynamically updates the canopy interception capacity parameter according to the vegetation leaf area index, so that the maximum interception capacity of the canopy is adjusted with the seasons to improve the adaptability of the model to different stand densities and growth periods. The interception loss I is added to the evapotranspiration item and included in the water balance to complete the simulation of the daily hydrological process. The Canmx in the SWAT model is set to approximately zero, and only the dynamic simulation of the canopy interception by the Gash module is retained, so as to realize the water quantity closure of the coupling structure.

[0042] Further, it is known that the SWAT model divides the basin into multiple sub-basins, and further divides hydrological response units (HRUs) according to land use, soil type and terrain, slope and other factors. The hydrological response unit is the smallest calculation unit of the SWAT model simulation, and the division standard requires that the land use, soil type and slope characteristics in each unit remain consistent, and the hydrological process is simulated by applying the lumped parameters. The division accuracy of the hydrological response unit directly affects the accuracy of the simulation results. In the simulation process, SWAT considers the spatial and temporal heterogeneity of each hydrological unit in the basin, realizes the simulation of rainfall, surface runoff formation, soil moisture dynamic change, groundwater recharge process, vegetation transpiration and soil evaporation (evapotranspiration) and other hydrological processes Rainfall event driven computer mechanism: the model automatically identifies the continuous event in the hourly or daily rainfall data, and independently executes the Gash process for each rainfall, which is divided into three stages of wet, saturated and dry, and the canopy interception and evaporation loss are calculated respectively; Linkage with evapotranspiration module: the interception evaporation is real-time counted into the evaporation item in the water balance of SWAT, realizing the process level splitting of total evapotranspiration; Dynamic update of effective rainfall: through the hourly update of canopy interception loss, the net rainfall available for runoff and infiltration calculation is dynamically corrected, which improves the authenticity of the model in the basin water input; Parameter integration is simple: only a small amount of observable parameters such as leaf area index (LAI), average tree height, initial rainfall intensity need to be input, which reduces the application threshold of the model; Wide adaptability: suitable for various forest types including coniferous forest, broad-leaved forest and sparse forest, and has good adaptability in areas with significant seasonal leaf area change. The purpose of the present application is to overcome the shortcomings of the existing SWAT model canopy interception method, and the original interception module of the SWAT model only estimates the interception amount by using static parameters and leaf area index, ignoring the dynamic process of canopy wet-saturated-dry in the rainfall event and key physical parameters. A technical scheme for coupling the revised Gash canopy interception model to the SWAT model is provided.

[0043] As Figure 2 , 3 and 4, the watershed hydrological simulation method of the embodiments of the present application is further described in combination with the drawings.

[0044] Initialization and parameterization. The parameters required for the Gash model were set according to the forest vegetation type in the study area, elevation data, and meteorological data. The canopy storage capacity (S) was determined by analyzing the linear relationship between the rainfall and throughfall, and the sum of stemflow for individual consecutive rainfall events sufficient to saturate the canopy. The S value corresponds to the negative intercept of this regression line with the throughfall and stemflow sum axis. The free throughfall coefficient (p) represents the amount of rainfall that falls directly on the ground without reaching the canopy and is usually assumed to be 1 - c, where c is derived from the LAI using the following equation:

[0045]

[0046] The stem storage capacity (St) and the proportion of precipitation that drains into the stemflow (pt) were estimated by the negative intercept and slope of the linear regression analysis between precipitation and stemflow, respectively. The amount of rainfall required to saturate the canopy (P') and the stem (P') was determined according to the following equations:

[0047]

[0048]

[0049] where, represents the average rainfall intensity (mm h -1 ), represents the average evaporation rate of the saturated canopy in the rain (mm h -1 ), defined as S c represents the canopy storage capacity per unit area of coverage (mm), defined as S c = S / c. The evaporation rate of the forest canopy in the rain E is calculated by the Penman-Monteith equation, which is applicable to a saturated canopy with a canopy resistance set to zero.

[0050]

[0051] where, Δ represents the slope of the saturated vapor pressure versus temperature curve (kPa °C -1 ), Rn represents the net radiation at the canopy surface (w m -2 ), p a represents the density of dry air (kg m -3 ), C p represents the specific heat capacity of air (J kg °C -1 ), D represents the vapor pressure difference (kPa), g a represents the aerodynamic conductance between the leaf surface and the reference point (m s -1 ), and λ represents the latent heat of water evaporation (kPa °C -1), γ is the Priestley-Taylor constant (J kg -1 ).

[0052] Canopy interception calculation: Each rainfall event can be divided into three stages, (1) wetting stage, when the rainfall (P G , mm) is below the threshold value required to saturate the canopy, from the beginning of the rainfall until the canopy reaches the saturated storage capacity, in this stage, the rainfall is first intercepted by the plant canopy to wet the leaves and branches, before reaching saturation, the rainfall is mainly used to fill the canopy storage gap, while a certain proportion of direct throughfall is produced, if a small amount of intercepted water begins to evaporate (such as light rain when the rainfall intensity is lower than the evaporation capacity), the model also considers the simultaneous evaporation loss, but the wetting stage is mainly marked by reaching the full capacity of the canopy storage; (2) saturation stage, when the cumulative rainfall makes the canopy reach saturation (i.e. the canopy interception reaches S), the saturation stage is entered. At this time, the canopy storage is full, and every moment of new rainfall will produce immediate throughfall and stem flow, among them, the proportion of throughfall will increase compared to the wetting stage, because the canopy is full and overflowing; but at the same time, the water on the surface of the canopy will continue to evaporate, making the canopy storage constantly empty a part of the capacity, because the canopy cannot store additional water at this time the average rainfall intensity exceeds the average evaporation rate of the fully wet canopy; (3) drying stage, when the rainfall event ends, there is often a certain amount of water left on the canopy, i.e. after the rainfall stops, without new rainfall replenishment, the water stored in the canopy gradually evaporates into the atmosphere until the canopy becomes dry again, reducing the canopy storage at each time step, and continuing to simulate until the canopy interception is reduced to zero.

[0053]

[0054] The soil, land use, meteorological and other input data required by the SWAT model itself are prepared in the conventional way. At the same time, the Canmx parameter corresponding to the vegetation in the SWAT model is set to a very small value (close to 0) to avoid the interference of its internal interception calculation on the results, which ensures that the subsequent rainfall interception is completely taken over by the Gash module for calculation.

[0055] Coupling framework building. In the source code or flow script of the SWAT model, the calling interface of the Gash interception calculation module is inserted. For example, before the daily rainfall enters the hydrological balance calculation, the Gash model is called to calculate the canopy interception, where P G is the daily rainfall, the rainfall P1 = P G -I input into the SWAT system. In each rainfall event, the model updates the effective rainfall in real time according to the interception calculation, including the parameters set in step 1 and the current vegetation state (such as LAI value), realizes the interception calculation based on the revised Gash model, and returns the effective rainfall P and the interception evaporation I.

[0056] Update SWAT hydrological calculations. The obtained effective rainfall P is passed back to the main process of the SWAT model, replacing the daily rainfall used in the original SWAT for infiltration and runoff calculations. SWAT then uses the new effective rainfall P to calculate processes such as soil storage, excess infiltration, and intersoil flow according to its built-in water balance model. At the same time, the interception loss I is added to the evapotranspiration term of SWAT as canopy evaporation: in specific implementation, the total evaporation of the day can be added to SWAT (for example, the sum of evaporation and transpiration) to ensure a closed water balance.

[0057]

[0058] Where SWt represents the soil moisture content at the end of the simulation (mm); SW0 represents the soil moisture content at the beginning of the simulation (mm); t represents the simulation time (d), that is, the total simulation time is td; P1 represents the total effective rainfall on the i-th day (mm); Q surf represents the surface runoff on day i (mm); E a represents the transpiration loss on day i (mm); W seep represents the amount of water that permeates through the soil on day i (mm); Q gw The amount of water flowing back to the groundwater on day i (mm). The surface runoff and precipitation runoff are calculated using the SCS curve number method as follows:

[0059]

[0060] where Q surf Indicates the cumulative runoff, in millimeters; P1 indicates the effective rainfall on a certain day, in m; I a It represents the initial loss, including soil recharge, plant retention and pre-drainage infiltration, in millimeters; S represents the reserve parameter, in mm.

[0061] After soil moisture is lost through processes such as vegetation absorption or transpiration, it infiltrates into the soil layer and may seep downward to replenish groundwater, potentially forming loamy streams on the surface. The following formula is used to calculate loamy streams in the SWAT model.

[0062]

[0063] Among them, Q lat Indicates the flow rate in loam, in mm / h; SW ly Indicates the excess water flow in the saturated zone, in mm; K sat It represents the hydraulic conductivity of soil in saturated state, in mm / h; slp represents the slope; Φ represents the total pore content of the soil layer; L hillLength of the hill slope in m. Groundwater is an important component of the SWAT model that is affected by the subbasin and is mainly derived from deep aquifers that are flooded and pressurized. The specific equation used to calculate groundwater within the basin is as follows:

[0064] Q gw,i = Q gw,i-1 × exp(-α gw × t) + W rchrg × [1 - exp(-α gw × Δt)]

[0065] where Q gw,i is the groundwater flow into the stream on day i (mm); Q gw,i-1 is the groundwater flow into the stream on day (i-1) (mm); t is the time step in days; W rchrg is the recharge from the aquifer on day i (mm); and α gw is the baseflow recession coefficient.

[0066] Modeling and calibration. After the above modifications, the coupled model was run to perform hydrologic simulations for the target basin. Due to the introduction of the new interception parameter, it was necessary to calibrate the parameters using observed data to improve the accuracy of the simulations. The model performance was evaluated using the coefficient of determination (R 2 ), the Nash-Sutcliffe efficiency coefficient (E ns ), the percent bias (PBIAS), and the root mean square error (RMSD), which were calculated as follows:

[0067]

[0068] where Q sim,i is the simulated value, is the simulated mean, Q obs,i is the observed value, is the observed mean.

[0069] Table 1. Components of tree canopy interception loss in the revised Gash model

[0070]

[0071] Through the above implementation steps, the revised Gash interception model is successfully embedded in the SWAT hydrological model, and the calculation of effective rainfall is improved. Compared with before coupling, the SWAT-revies Gash coupling model can dynamically simulate the evolution of canopy interception of each rainfall, greatly improving the accuracy and reliability of the simulation of rainfall-runoff of forest land. Especially in the area with high forest coverage and large rainfall variability, this improvement is particularly significant for the simulation of rainfall redistribution and hydrological response. The method of the application provides a more reliable model tool for watershed management and eco-hydrological research, which can be used to evaluate the influence of forest ecosystem interception of rainfall on water resources, and further expand to the simulation analysis of forest hydrological function under the scenario of climate change.

[0072] The following is the specific implementation steps of the embodiments of the application:

[0073] Meteorological data (rainfall, radiation, temperature, humidity, etc.), vegetation parameters (mainly leaf area index LAI, crown structure information), land use and soil type data, for SWAT initialization.

[0074] The maximum water storage capacity of the canopy S (estimated according to LAI), the free penetration coefficient p, the trunk water storage capacity St, and the evaporation rate E (calculated using the Penman-Monteith equation).

[0075] Before the SWAT enters the i-day simulation, the daily rainfall P1 is transmitted to the Gash module.

[0076] According to P G , LAI and meteorological parameters, the Gash module judges and calculates the canopy interception in the following stages in turn: wetting stage (P G < P ′ G ), saturation stage (P G ≥ P ′ G , calculate the evaporation in the rain), and dry stage (evaporate residual interception water after rainfall ends).

[0077] Gash module output: effective rainfall P1=P G -I, interception evaporation I. Feedback to the SWAT main process, replace the original rainfall input in the SWAT model with P1, and include I in the evapotranspiration term.

[0078] Update soil moisture and groundwater state, store daily simulation results, enter i+1 day simulation, repeat the steps until the simulation is completed.

[0079] In summary, the beneficial effects of the application are:

[0080] (1) The stability of the original SWAT structure is retained, and the Gash module can be flexibly embedded and removed, improving the maintainability and scalability of the model;

[0081] (2) The interception calculation process is more consistent with the physical process of rainfall, significantly improving the accuracy of rainfall distribution simulation;

[0082] (3) The parameter requirements are small and the method has wide applicability. Since the present invention provides a more accurate estimate of interception and evaporation, the effective rainfall actually entering the soil and river channels is dynamically corrected, making the runoff calculation more reliable. Traditional SWAT underestimates interception and often overestimates surface runoff and infiltration, resulting in runoff simulation deviations. The present invention reduces the rainfall input reaching the surface by increasing interception losses, which can reduce the runoff peak and the total runoff volume, making it closer to the observed flow process.

[0083] (4) It is applicable to various forest types such as coniferous forests, broad-leaved forests, and sparse forests, and the interception capacity can be dynamically adjusted through the leaf area index. It is especially important for flood forecasting, drought assessment, and water conservation in basins with high forest coverage.

[0084] (5) It adapts to the simulation needs of different spatiotemporal scales, supports daily and period scale data input, and is suitable for climate change impact simulation and ecological flow regulation research. The Canxmx in the traditional interception model is an empirical parameter, and its value is not easy to measure directly. It usually depends on calibration and has large variability between different regions and different forest types. The parameters required by the present invention, such as LAI, tree height, rainfall intensity, etc., all have clear physical meanings and can be obtained by field measurement or remote sensing. They can be set without repeated trial calculations and calibrations, which greatly facilitates the promotion and application of the model in different regions. At the same time, the method of the present invention is applicable to a variety of forest types, including coniferous forests, broad-leaved forests, sparse woodlands, etc. The model reflects vegetation density through the LAI parameter, so it can also adapt well to seasonal leaf area changes in deciduous forests: when the LAI decreases during the leaf-fall season, the model automatically reduces the interception capacity, reflecting the situation where branch interception is the main factor; when the LAI increases during the growing season, the interception capacity is enhanced. In comparison, the fixed Canxmx method often requires parameter adjustment or is difficult to reflect the impact of leaf drop when seasonal changes are significant. Therefore, the present invention has a wider applicability and can achieve reliable simulation results in watersheds with different climatic zones and phenological characteristics.

[0085] The watershed hydrological simulation method with an embedded canopy interception mechanism according to an embodiment 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 authenticity and accuracy of rainfall-runoff simulation in forest vegetation coverage areas.

[0086] In order to implement the above embodiment, Figure 5As shown, the embodiment also provides a watershed hydrological simulation system 10 embedded with a canopy interception mechanism, comprising:

[0087] An interception calculation module 100 receives rainfall data and vegetation parameters, simulates the canopy interception and evaporation process in stages according to rainfall intensity, LAI, tree height and evaporation rate, and outputs effective rainfall and interception evaporation;

[0088] A hydrological simulation module 200 simulates hydrological processes such as runoff, infiltration, and evaporation, receives effective rainfall through a data interaction interface and replaces the original rainfall input, and also accounts for interception evaporation in the evaporation term.

[0089] A data interaction interface 300 connects the Gash model module and the SWAT hydrological simulation module, realizes data input, output and feedback, and thus builds a Gash-SWAT coupling system with dynamic canopy interception response.

[0090] Further, the revised Gash model algorithm divides a single rainfall process into wet, saturated and dry stages to calculate interception loss in sequence; wherein,

[0091] In the wet stage, when the cumulative rainfall does not reach the maximum interception capacity of the canopy, all the rainwater is intercepted;

[0092] In the saturated stage, when the canopy water storage reaches the capacity, the evaporation loss of the continuous interception is calculated according to the ratio of rainfall intensity to canopy evaporation rate;

[0093] In the dry stage, after the rainfall stops, all the intercepted water remaining on the canopy and the trunk surface evaporates;

[0094] Meanwhile, the trunk interception process is considered, and the maximum trunk interception capacity is set. When the canopy is saturated, rainwater flows to the trunk in a predetermined proportion and fills the trunk interception capacity first. The part exceeding the capacity is directly counted as effective rainfall.

[0095] Further, the coupling of the revised Gash model and the SWAT model is realized by embedding the canopy interception calculation module between the rainfall input and the hydrological calculation module of the SWAT model.

[0096] The canopy interception calculation module receives the rainfall input of the SWAT and outputs the calculated effective rainfall to the runoff and runoff calculation unit of the SWAT, which structurally replaces the original canopy interception calculation of the SWAT model. And according to the vegetation leaf area index, the canopy interception capacity parameter is dynamically updated, so that the maximum interception capacity of the canopy adjusts with the seasons, to improve the adaptability of the model to different stand densities and growth periods.

[0097] Further, the interception loss amount I is added to the evaporation term to be included in the water balance, and the daily hydrological process simulation is completed.

[0098] Further, the Canmx in the SWAT model is set to be approximately zero, and only the dynamic simulation of the interception of the canopy layer by the Gash module is retained to realize the water balance closure of the coupling structure.

[0099] The watershed hydrological simulation system embedded with the canopy interception mechanism according to the embodiments of the present application can dynamically simulate the interception loss of each rainfall event, include it in the water balance as the evaporation process, and update the effective rainfall in real time for the runoff calculation, thereby significantly improving the authenticity and precision of the rainfall-runoff simulation in the forest vegetation coverage area.

[0100] In the description of the present specification, the description of the terms “one embodiment”, “some embodiments”, “an example”, “a specific example”, or “some examples” and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the different embodiments or examples described in the present specification and the features of the different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0101] In addition, the terms “first”, “second” are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with “first”, “second” can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of “a plurality of” is at least two, for example, two, three, etc., unless otherwise specifically limited.

Claims

1. A watershed hydrological simulation method embedded with canopy interception mechanism, characterized in that: include: The revised Gash canopy interception model module is embedded in the SWAT model. The Gash model receives rainfall, leaf area index (LAI), average tree height, and meteorological parameters as inputs, divides a single rainfall event into wet, saturated, and dry phases, and dynamically calculates canopy interception and intercepted evaporation in each phase. According to the intercepted evaporation output by the Gash model module, it is included in the evaporation term of the SWAT model; The effective rainfall output by the Gash model module replaces the original rainfall input in the SWAT model and is used for subsequent runoff generation, infiltration, and runoff simulations, thereby improving the hydrological simulation accuracy of the SWAT model in forest vegetation coverage areas.

2. The method according to claim 1, characterized in that The revised Gash model divides a single rainfall process into the wet stage, saturated stage and dry stage, and calculates the interception loss in sequence; In the wet stage, when the accumulated rainfall does not reach the maximum interception capacity of the canopy, all the rainwater is intercepted; In the saturation stage, when the canopy water storage reaches capacity, the evaporation loss of continued interception is calculated according to the ratio of rainfall intensity to canopy evaporation rate; During the dry phase, all trapped water remaining in the canopy and trunk surfaces evaporates after rainfall stops; At the same time, the trunk interception process is taken into consideration and the maximum trunk interception capacity is set. When the canopy is saturated, rainwater flows to the trunk according to a predetermined proportion and fills the trunk interception capacity first. The part exceeding the capacity is directly counted as trunk flow and included in the effective rainfall.

3. The method according to claim 2, characterized in that The revised Gash model is coupled with the SWAT model by embedding the canopy interception calculation module between the rainfall input and the hydrological calculation module of the SWAT model. The canopy interception calculation module receives rainfall input from SWAT and outputs the calculated effective rainfall to SWAT's runoff and runoff aggregation unit, structurally replacing the original canopy interception calculation of the SWAT model; and dynamically updates the canopy interception capacity parameters based on the vegetation leaf area index, so that the maximum canopy interception capacity adjusts with seasonal changes, thereby improving the model's adaptability to different stand densities and growing periods.

4. The method according to claim 3, characterized in that The interception loss I is added to the evapotranspiration term and included in the water balance to complete the hydrological process simulation for the day.

5. The method according to claim 4, characterized in that The Canmx in the SWAT model was set to approximately zero, and only the dynamic simulation of canopy interception by the Gash module was retained to achieve water closure of the coupled structure.

6. A watershed hydrological simulation system embedded with a canopy interception mechanism, characterized in that: include: The interception calculation module receives rainfall data and vegetation parameters, simulates the canopy interception and evaporation process in stages based on rainfall intensity, LAI, tree height, and evaporation rate, and outputs effective rainfall and interception evaporation; The hydrological simulation module is used to simulate hydrological processes such as runoff, infiltration, and evapotranspiration. It receives effective rainfall through the data interaction interface and replaces its original rainfall input, while also including the intercepted evaporation in its evapotranspiration item. 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 building a Gash-SWAT coupled system with dynamic canopy interception response.

7. The system according to claim 6, characterized in that The revised Gash model algorithm divides a single rainfall process into the wet stage, saturated stage and dry stage and calculates the interception loss in sequence; In the wet stage, when the accumulated rainfall does not reach the maximum interception capacity of the canopy, all the rainwater is intercepted; In the saturation stage, when the canopy water storage reaches capacity, the evaporation loss of continued interception is calculated according to the ratio of rainfall intensity to canopy evaporation rate; During the dry phase, all trapped water remaining in the canopy and trunk surfaces evaporates after rainfall stops; At the same time, the trunk interception process is taken into consideration and the maximum trunk interception capacity is set. When the canopy is saturated, rainwater flows to the trunk according to a predetermined proportion and fills the trunk interception capacity first. The part exceeding the capacity is directly counted as trunk flow and included in the effective rainfall.

8. The system according to claim 7, characterized in that The revised Gash model is coupled with the SWAT model by embedding the canopy interception calculation module between the rainfall input and the hydrological calculation module of the SWAT model. The canopy interception calculation module receives rainfall input from SWAT and outputs the calculated effective rainfall to SWAT's runoff and runoff aggregation unit, structurally replacing the original canopy interception calculation of the SWAT model; and dynamically updates the canopy interception capacity parameters based on the vegetation leaf area index, so that the maximum canopy interception capacity adjusts with seasonal changes, thereby improving the model's adaptability to different stand densities and growing periods.

9. The system according to claim 8, characterized in that The interception loss I is added to the evapotranspiration term and included in the water balance to complete the hydrological process simulation for the day.

10. The system according to claim 9, characterized in that The Canmx in the SWAT model was set to approximately zero, and only the dynamic simulation of canopy interception by the Gash module was retained to achieve water closure of the coupled structure.

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