Canopy conductance simulation method and system based on the segmented effect of saturated vapor pressure difference

Abstract

The present invention provides a canopy conductance simulation method and system based on the segmented effect of saturated vapor pressure difference, including: first, collecting meteorological data and basic information such as tree trunk sap flow and sapwood area in the study area; then calculating canopy conductance based on trunk sap flow data and a simplified Penman-Monteith equation; then, analyzing the hysteresis response form and segmented response equation of canopy conductance and meteorological factors by drawing scatter plots and outer lines; then, establishing a canopy conductance model based on the response equation and continuous multiplication model of canopy conductance and meteorological factors; finally, substituting basic meteorological data into the model to simulate the canopy conductance of the area. The present invention considers the response relationship between canopy conductance and meteorological factors, and can more accurately understand the relationship between plant physiology and environmental processes. It is crucial for accurately estimating basin transpiration and is of great significance to water resources planning research.

Description

Technical Field

[0001] The present invention relates to the field of hydrological environment technology, and in particular to a canopy conductance simulation method and system based on the saturated water vapor pressure difference segmentation effect. Background Art

[0002] Terrestrial evapotranspiration plays a central role in the coupling of the global water cycle and energy cycle, and has an important regulatory effect on energy balance, hydrological response and climate at the basin and even global scales. Vegetation stomata are important channels for evapotranspiration, and their opening and closing degree is an important variable controlling the exchange of water vapor and carbon dioxide between vegetation and the atmosphere. In other words, the opening of the stomata plays a key role in controlling water loss and carbon acquisition in terrestrial ecosystems. Among them, canopy conductance, as a representation of stomatal opening in the canopy or ecosystem, is the focus of model research in research fields such as hydrology, ecology, and climate change. Canopy conductance is usually controlled by downward shortwave solar radiation and the difference in saturated water vapor pressure of the air. Therefore, these variables are usually used as driving factors in model research.

[0003] Research has shown that canopy conductance exhibits distinct segmented responses to air saturation vapor pressure difference, with different response relationships between saturation vapor pressure difference and canopy conductance exhibiting distinct responses within different ranges. Considering this segmented response relationship and constructing a segmented canopy conductance simulation model based on it can provide a more accurate understanding of the relationship between plant physiology and environmental processes, which is crucial for accurately estimating watershed transpiration. However, current research in this area is limited, and a new approach to analyzing the segmented characteristics of canopy conductance is needed. Summary of the Invention

[0004] The present invention provides a canopy conductance simulation method and system based on the segmented effect of saturated water vapor pressure difference, which is used to solve the defect of the existing technology that there is a lack of systematic and effective means for studying the driving variables of canopy conductance.

[0005] In a first aspect, the present invention provides a canopy conductance simulation method based on the segmented effect of saturated vapor pressure difference, comprising:

[0006] Obtain ground observation meteorological data;

[0007] Collecting sapwood area and trunk sap flow density data of each sample tree in the experimental area, and calculating a weighted average of the trunk sap flow density based on the sapwood area and the trunk sap flow density data;

[0008] Calculating the tree canopy conductance based on the ground-observed meteorological data and the weighted average value of the tree trunk sap flow density;

[0009] Drawing a scatter plot of the tree canopy conductance and meteorological factors, extracting representative points of the scatter plot based on the outer envelope method, and determining the single-factor response equations of canopy conductance, downward shortwave radiation, and saturation vapor pressure difference by fitting the representative points;

[0010] A canopy conductance simulation equation is constructed based on the single factor response equation.

[0011] According to the present invention, a canopy conductance simulation method based on the segmented effect of saturated water vapor pressure difference is provided to obtain ground observation meteorological data, including:

[0012] Based on the preset measurement time resolution, an automatic weather station is used to collect air temperature, relative humidity and downward shortwave radiation;

[0013] The saturated water vapor pressure difference is obtained by segmented calculation based on the air temperature and the relative humidity.

[0014] According to a canopy conductance simulation method based on the segmented effect of saturated vapor pressure difference provided by the present invention, sapwood area and trunk sap flow density data of each sample tree in an experimental area are collected, and a weighted average value of trunk sap flow density is calculated based on the sapwood area and trunk sap flow density data, including:

[0015] The trunk sap flow density data of each sample tree was collected based on the heat diffusion probe method;

[0016] The diameter at breast height of different tree species is measured, and the sapwood area is calculated using the empirical formula of sapwood area-diameter at breast height of the tree;

[0017] A weighted calculation is performed based on the trunk sap flow density data, the sapwood area and the number of sample tree observations to obtain the weighted average value of the trunk sap flow density.

[0018] According to a canopy conductance simulation method based on the segmented effect of saturated vapor pressure difference provided by the present invention, tree canopy conductance is calculated based on the ground-observed meteorological data and the weighted average value of the trunk sap flow density, including:

[0019] Substituting the weighted average value of the trunk sap flow density and the saturated vapor pressure difference in the ground-observed meteorological data into the simplified Penman-Monteith equation yields:

[0020] ;

[0021] ;

[0022] Where Gc is the canopy conductance, in mm s -1 , γ is the wet / dry coefficient, unit is kPa ℃ -1, λ is the latent heat of vaporization of water, unit is J kg -1 Tr is the canopy transpiration rate calculated from the weighted average of the trunk sap flow density, in mm s -1 , As / Ag is the ratio of the total area of ​​stand sapwood to the area of ​​the plot, and ASFD is the weighted average of the trunk sap flow density (gcm -2 d -1 , c p is the specific heat capacity of moist air, in J kg -1 ℃ -1 , ρ is the density of moist air, in kg m -3 , VPD is the saturated water vapor pressure difference, the unit is kPa.

[0023] According to the present invention, a canopy conductance simulation method based on the segmented effect of saturated vapor pressure difference, after calculating the tree canopy conductance based on the ground-observed meteorological data and the weighted average value of the trunk sap flow density, further includes:

[0024] The optimized tree canopy conductance was obtained by performing data quality control on the tree canopy conductance by screening stable data in the middle of the growing season, excluding data corresponding to rainy days, and selecting data corresponding to data greater than a preset saturated water vapor pressure difference.

[0025] According to a canopy conductance simulation method based on the segmented effect of saturated vapor pressure difference provided by the present invention, a scatter plot of the tree canopy conductance and meteorological factors is drawn, and representative points of the scatter plot are extracted based on the outer envelope method, including:

[0026] determining the downward shortwave radiation or the saturated water vapor pressure difference as the meteorological factor;

[0027] Draw a scatter plot with each meteorological factor as the horizontal axis and the tree canopy conductance as the vertical axis;

[0028] Arrange all data samples in ascending order according to the meteorological factors and divide them into several data segments on average;

[0029] In the segmented interval corresponding to each data segment, all tree canopy conductances are arranged in ascending order, and then the preset percentage left and right quantiles are extracted as the maximum value of the tree canopy conductance in the segmented interval. The maximum value of the tree canopy conductance is used as the vertical coordinate of the representative point of the data segment, and the average value of all data representative points is used as the horizontal coordinate of the representative point of the data segment.

[0030] According to a canopy conductance simulation method based on the segmented effect of saturated water vapor pressure difference provided by the present invention, the single-factor response equations of canopy conductance, downward shortwave radiation and saturated water vapor pressure difference are determined by fitting the representative points, including:

[0031] The extracted representative points are optimized using the least squares method to obtain the optimized representative points;

[0032] An exponential function constructed by the first coefficient, the second coefficient, the third coefficient, the fourth coefficient and the downward shortwave radiation is used as a single-factor response equation of canopy conductance to downward shortwave radiation;

[0033] Taking the maximum value of the tree canopy conductance as a reference point, taking a preset numerical range before and after the reference point as a candidate area, and determining evenly distributed potential saturated water vapor pressure difference segmentation points with a preset step size within the candidate area;

[0034] Using the potential saturated vapor pressure difference segmentation points to perform cyclic iteration, the data set is divided into a left half data set and a right half data set, wherein the left half data set is fitted with a linear function, and the right half data set is fitted with a logarithmic function curve, to determine the segmentation points of the piecewise function;

[0035] When the function value of the linear function at any segmentation point is equal to the function value of the logarithmic function curve at any segmentation point, and the determination coefficient of the entire segmentation response equation obtained by fitting each potential saturated vapor pressure difference segmentation point reaches a maximum, the any segmentation point is determined to be the segmentation point of the piecewise function;

[0036] A piecewise function constructed with the fifth coefficient, the sixth coefficient, the seventh coefficient, the eighth coefficient, the saturated water vapor pressure difference and the piecewise function segmentation points is used as a single factor response equation of canopy conductance to saturated water vapor pressure difference.

[0037] According to a canopy conductance simulation method based on the segmented effect of saturated vapor pressure difference provided by the present invention, a canopy conductance simulation equation is constructed based on the single factor response equation, including:

[0038] Determine the maximum canopy conductance;

[0039] The canopy conductance simulation equation is obtained by multiplying the maximum canopy conductance, the single factor response equation of the canopy conductance to downward shortwave radiation, and the single factor response equation of the canopy conductance to saturated water vapor pressure difference.

[0040] In a second aspect, the present invention further provides a canopy conductance simulation system based on the segmented effect of saturated vapor pressure difference, comprising:

[0041] Acquisition module, used to obtain ground observation meteorological data;

[0042] a collection module, configured to collect sapwood area and trunk sap flow density data of each sample tree in the experimental area, and calculate a weighted average value of the trunk sap flow density based on the sapwood area and the trunk sap flow density data;

[0043] a calculation module, configured to calculate the tree canopy conductance based on the ground-observed meteorological data and the weighted average value of the tree trunk sap flow density;

[0044] a fitting module for drawing a scatter plot of the tree canopy conductance and meteorological factors, extracting representative points of the scatter plot based on an envelope method, and determining single-factor response equations of canopy conductance, downward shortwave radiation, and saturation vapor pressure difference by fitting the representative points;

[0045] A construction module is used to construct a canopy conductance simulation equation based on the single factor response equation.

[0046] In a third aspect, the present invention also provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the canopy conductance simulation method based on the segmented effect of saturated water vapor pressure difference as described above is implemented.

[0047] The present invention provides a canopy conductance simulation method and system based on the segmented effect of saturated vapor pressure difference. By analyzing the impact of segmented simulated environmental variables on canopy conductance, a simulation model of tree canopy conductance is constructed based on the segmented response relationship of canopy conductance to meteorological factors. The method fully considers the relationship between plant physiology and environmental processes. The generated simulation results provide an important reference basis for watershed hydrological simulation and accurate assessment of water resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0049] Figure 1 This is one of the flow charts of the canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect provided by the present invention;

[0050] Figure 2 This is the second flow chart of the canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect provided by the present invention;

[0051] Figure 3 The diagram of the relationship between the tree canopy conductance and the meteorological factors Rsi and VPD provided by the present invention is shown in FIG. Figure 3 (a), (b), and (c) are the hysteresis responses of oak canopy conductance to meteorological factors Rsi, VPD, and Ta, respectively. Figure 3(d), (e), and (f) are the hysteresis responses of pine canopy conductance to meteorological factors Rsi, VPD, and Ta, respectively;

[0052] Figure 4 This is a diagram of the fitting process of the response equation of tree canopy conductance and meteorological factors Rsi and VPD provided by the present invention, wherein Figure 4 (a) and (b) are the fitting process of the oak canopy conductance and Rsi, VPD response equation. Figure 4 (c) and (d) show the fitting process of the canopy conductance, Rsi and VPD response equations of pine trees;

[0053] Figure 5 This is a canopy conductance model fitting effect diagram provided by the present invention, wherein Figure 5 (a) and (b) are the 1:1 simulation results of oak canopy conductance in 2021 and 2023. Figure 5 (c) and (d) are the 1:1 simulation results of canopy conductance of pine trees in 2021 and 2023;

[0054] Figure 6 Schematic diagram of the structure of the canopy conductance simulation system based on the saturated water vapor pressure difference segmented effect provided by the present invention;

[0055] Figure 7 It is a structural schematic diagram of the electronic device provided by the present invention. DETAILED DESCRIPTION

[0056] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0057] In view of the shortcomings of the existing technology, this paper proposes a canopy conductance simulation method based on the segmented effect of saturated water vapor pressure difference, focusing on considering the hysteresis response characteristics between canopy conductance and downward shortwave radiation (Rsi) and saturated water vapor pressure difference (VPD). Figure 1 This is one of the flow charts of the canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect provided by the embodiment of the present invention, such as Figure 1 Shown, including:

[0058] Step 100: Acquire ground observation meteorological data;

[0059] Step 200: collecting sapwood area and trunk sap flow density data of each sample tree in the experimental area, and calculating a weighted average of the trunk sap flow density based on the sapwood area and the trunk sap flow density data;

[0060] Step 300: Calculating tree canopy conductance based on the ground-observed meteorological data and the weighted average of the tree trunk sap flow density;

[0061] Step 400: drawing a scatter plot of the tree canopy conductance and meteorological factors, extracting representative points of the scatter plot based on the outer envelope method, and determining single-factor response equations of canopy conductance, downward shortwave radiation, and saturation vapor pressure difference by fitting the representative points;

[0062] Step 500: Construct a canopy conductance simulation equation based on the single factor response equation.

[0063] Specifically, if Figure 2 As shown in the figure, firstly, the meteorological data and basic information such as trunk sap flow and sapwood area of ​​the sample trees in the study area are measured and collected; then, the canopy conductance is calculated based on the trunk sap flow data and the saturated water vapor pressure difference data; then, the response equation form of the canopy conductance and downward shortwave radiation (Rsi) and saturated water vapor pressure difference (VPD) is determined by drawing scatter plots and envelope lines; next, a canopy conductance model is established based on the response equation of canopy conductance and Rsi and VPD; finally, the basic meteorological data are substituted into the model to simulate the canopy conductance of the area.

[0064] This paper analyzes the impact of segmented simulated environmental variables on canopy conductance, constructs a simulation model of tree canopy conductance based on the segmented response relationship of canopy conductance to meteorological factors, and fully considers the relationship between plant physiology and environmental processes. The generated simulation results provide an important reference basis for watershed hydrological simulation and accurate assessment of water resources.

[0065] Based on the above embodiment, step 100 includes:

[0066] Based on the preset measurement time resolution, an automatic weather station is used to collect air temperature, relative humidity and downward shortwave radiation;

[0067] The saturated water vapor pressure difference is obtained by segmented calculation based on the air temperature and the relative humidity.

[0068] Specifically, the embodiment of the present invention uses an automatic weather station to monitor ground meteorological data, including air temperature (Ta), relative humidity (RH), downward shortwave radiation (Rsi), saturated water vapor pressure difference (VPD), etc. The measurement time resolution is 10 minutes, where the saturated water vapor pressure difference is calculated segmentally by air temperature (Ta) and relative humidity (RH).

[0069] Based on the above embodiment, step 200 includes:

[0070] The trunk sap flow density data of each sample tree was collected based on the heat diffusion probe method;

[0071] The diameter at breast height of different tree species is measured, and the sapwood area is calculated using the empirical formula of sapwood area-diameter at breast height of the tree;

[0072] A weighted calculation is performed based on the trunk sap flow density data, the sapwood area and the number of sample tree observations to obtain the weighted average value of the trunk sap flow density.

[0073] The embodiment of the present invention adopts the widely used thermal diffusion probe method (TOP) to measure the trunk sap flow density. The thermal probe method mainly uses the temperature difference between probes to calculate the trunk sap flow rate. The monitored trees are oak and pine.

[0074] Specifically, a pair of probes, each 2 mm in diameter and 4 cm apart, were inserted into the upper and lower trunks of trees at 1.2 m breast height. The upper probe was heated using a constant temperature couple, creating a temperature difference with the lower probe. The temperature difference (∆T, °C) between the two probes is controlled by the trunk sap flow rate. The greater the sap flow rate within the trunk, the greater the temperature drop of the upper probe per unit time, and the smaller the temperature difference between the upper and lower probes. This allows the calculation of the tree's trunk sap flux density (SFD, in g cm) -2 d -1 ) :

[0075] ;

[0076] Where ∆T = T 上 - T 下 , is the temperature difference between the upper and lower probes (°C); ∆T M =max(T 上 - T 下 ), is the maximum temperature difference between the upper and lower probes (°C); T 上 and T 下 are the temperatures of the upper and lower probes (°C), respectively.

[0077] The sapwood area (As) of trees is difficult to measure directly. It is usually calculated by measuring the tree's diameter at breast height (DBH) and using the empirical formula of sapwood area - DBH for the corresponding tree. In this example, the sapwood area (As) - DBH fitting formula for oak and pine trees is as follows:

[0078] Oak:

[0079] ;

[0080] pine:

[0081] ;

[0082] Next, the measured trunk sap flow density of each sample was calculated based on the weighted average of the sapwood area (ASFD, unit is g cm -2 d -1 ) to reflect the average characteristics of stand stem sap flow:

[0083] ;

[0084] Among them, SFD i (g cm -2 d -1 ) represents the trunk sap flow density of each sample tree, As i (cm²) represents the sapwood area of ​​each sample tree, and n represents the number of sample trees observed. In this example, n is 8 for oak trees and 3 for pine trees.

[0085] Based on the above embodiment, step 300 includes:

[0086] Substituting the weighted average value of the trunk sap flow density and the saturated vapor pressure difference in the ground-observed meteorological data into the simplified Penman-Monteith equation yields:

[0087] ;

[0088] ;

[0089] Where Gc is the canopy conductance, in mm s -1 , γ is the wet / dry coefficient, unit is kPa ℃ -1 , λ is the latent heat of vaporization of water, unit is J kg -1 Tr is the canopy transpiration rate calculated from the weighted average of the trunk sap flow density, in mm s -1 , As / Ag is the ratio of the total area of ​​stand sapwood to the area of ​​the plot, and ASFD is the weighted average of the trunk sap flow density (gcm -2 d -1 , c p is the specific heat capacity of moist air, in J kg -1 ℃ -1 , ρ is the density of moist air, in kg m -3 , VPD is the saturated water vapor pressure difference, the unit is kPa.

[0090] Based on the above embodiment, after step 300, the following steps are further included:

[0091] The optimized tree canopy conductance was obtained by performing data quality control on the tree canopy conductance by screening stable data in the middle of the growing season, excluding data corresponding to rainy days, and selecting data corresponding to data greater than a preset saturated water vapor pressure difference.

[0092] Specifically, in order to control the quality of the data and facilitate subsequent analysis, the embodiment of the present invention performs quality control on the calculated canopy conductance data. The quality control process includes the following three steps: (1) Select stable data in the middle of the growing season for analysis. In this embodiment, the data from late April to mid-September are selected for oak trees, and the data for the whole year are selected for pine trees; (2) Since the trunk sap flow data on rainy days is unstable, the data on rainy days are eliminated; (3) When VPD < 0.2 kPa, the canopy conductance calculation error is large, and the data with VPD ≥ 0.2 kPa are selected for analysis.

[0093] Based on the above embodiment, step 400 of drawing a scatter plot of the tree canopy conductance and meteorological factors and extracting representative points of the scatter plot based on the outer envelope method includes:

[0094] determining the downward shortwave radiation or the saturated water vapor pressure difference as the meteorological factor;

[0095] Draw a scatter plot with each meteorological factor as the horizontal axis and the tree canopy conductance as the vertical axis;

[0096] Arrange all data samples in ascending order according to the meteorological factors and divide them into several data segments on average;

[0097] In the segmented interval corresponding to each data segment, all tree canopy conductances are arranged in ascending order, and then the preset percentage left and right quantiles are extracted as the maximum value of the tree canopy conductance in the segmented interval. The maximum value of the tree canopy conductance is used as the vertical coordinate of the representative point of the data segment, and the average value of all data representative points is used as the horizontal coordinate of the representative point of the data segment.

[0098] It should be noted that, in this embodiment, the canopy conductance simulation model is mainly constructed based on the meteorological factors Rsi and VPD. First, the response equation form of the canopy conductance to Rsi and VPD is determined based on the partial regression method. Taking the partial correlation response between canopy conductance (Gc) and downward shortwave radiation (Rsi) as an example, when the saturated water vapor pressure difference (VPD) does not affect the canopy conductance of trees, the response function of Gc to Rsi can be determined, that is, at a given Rsi level, the highest Gc is the true response of canopy conductance to Rsi when there are no other factors restricting it, and the curve form of these points fitting is the single factor response form of canopy conductance to Rsi. Then, scatter plots of Gc-Rsi and Gc-VPD are drawn for different time periods with the meteorological factors Rsi and VPD as the horizontal coordinates and the canopy conductance Gc as the vertical coordinate. In this embodiment, it can be clearly found that there is a hysteresis response relationship between canopy conductance and Rsi and VPD, as shown in Figure 2. Figure 3 Figures (a), (b), and (c) show the hysteretic responses of oak canopy conductance to the meteorological factors Rsi, VPD, and Ta, respectively. Figures (d), (e), and (f) show the hysteretic responses of pine canopy conductance to the meteorological factors Rsi, VPD, and Ta, respectively. Different ranges of Rsi or VPD correspond to different response function relationships.

[0099] Due to the excessive number of sample data, representative points were extracted by segmentation. A scatter plot was drawn with each meteorological factor as the horizontal axis and canopy conductance as the vertical axis. All data samples were arranged in ascending order of meteorological factor (Rsi or VPD) and evenly divided into a number of segments (the number of segments can be selected appropriately without affecting the analysis results; 100 is used as an example here). Next, representative points were extracted using the envelope method. Within each segment, all Gc data were sorted in ascending order and the 90th percentile was taken as the maximum Gc value for that segment. This was used as the vertical axis for the representative point for that segment (to reduce sample uncertainty, the maximum value was not directly taken). The average value of all meteorological factor (Rsi or VPD) data for that segment was also taken as the horizontal axis for the representative point for that segment.

[0100] Based on the above embodiment, the single-factor response equations of canopy conductance, downward shortwave radiation, and saturation vapor pressure difference determined by fitting the representative points in step 400 include:

[0101] The extracted representative points are optimized using the least squares method to obtain the optimized representative points;

[0102] An exponential function constructed by the first coefficient, the second coefficient, the third coefficient, the fourth coefficient and the downward shortwave radiation is used as a single-factor response equation of canopy conductance to downward shortwave radiation;

[0103] Taking the maximum value of the tree canopy conductance as a reference point, taking a preset numerical range before and after the reference point as a candidate area, and determining evenly distributed potential saturated water vapor pressure difference segmentation points with a preset step size within the candidate area;

[0104] Using the potential saturated vapor pressure difference segmentation points to perform cyclic iteration, the data set is divided into a left half data set and a right half data set, wherein the left half data set is fitted with a linear function, and the right half data set is fitted with a logarithmic function curve, to determine the segmentation points of the piecewise function;

[0105] When the function value of the linear function at any segmentation point is equal to the function value of the logarithmic function curve at any segmentation point, and the determination coefficient of the entire segmentation response equation obtained by fitting each potential saturated vapor pressure difference segmentation point reaches a maximum, the any segmentation point is determined to be the segmentation point of the piecewise function;

[0106] A piecewise function constructed with the fifth coefficient, the sixth coefficient, the seventh coefficient, the eighth coefficient, the saturated water vapor pressure difference and the piecewise function segmentation points is used as a single factor response equation of canopy conductance to saturated water vapor pressure difference.

[0107] Specifically, the embodiment of the present invention fits the extracted representative points to find the most suitable single-factor response curve of canopy conductance (Gc) to downward shortwave radiation (Rsi) and saturation vapor pressure difference (VPD). All parameters in the fitting process are optimized using the least squares method. The fitting process is as follows: Figure 4 As shown, (a) and (b) are the fitting processes of the oak canopy conductance, Rsi, and VPD response equations, and (c) and (d) are the fitting processes of the pine canopy conductance, Rsi, and VPD response equations.

[0108] The response equation of canopy conductance (Gc) to downward shortwave radiation (Rsi) is expressed as an exponential function:

[0109] ;

[0110] The response equation of canopy conductance (Gc) to vapor pressure deficit (VPD) is expressed as a piecewise function, with a linear function on the left and a logarithmic function on the right. To determine the segmentation points, the following process was used to construct the response equation for canopy conductance to vapor pressure deficit (VPD): the segmentation points of the canopy conductance to vapor pressure deficit function were located near the VPD range corresponding to the maximum Gc value. Based on this, the VPD corresponding to the maximum Gc value was used as the reference point, and the range of 0.4 kPa before and after the reference point was defined as the candidate region. Potential VPD segmentation points were evenly assigned within this region with a step size of 0.02 kPa. The response equation was fitted using the potential VPD segmentation points through an iterative process. In each iteration, the dataset was divided into two parts using the potential segmentation points. The left half of the dataset was fitted using the linear curve, while the right half was fitted using the logarithmic curve. Specific boundary conditions were set at the segmentation points, requiring that the value of the linear function on the left be equal to the value of the logarithmic function on the right at the segmentation point to ensure function continuity. Subsequently, the coefficient of determination (R²) of the entire piecewise response equation obtained by fitting each potential segmentation point was calculated. Finally, the VPD data point that maximized the R² value of the fitted equation was selected as the segmentation point of the piecewise function. By combining the above methods and comparing the R² values ​​of the potential segmentation points of oak trees, it was determined that the segmentation point size of the oak piecewise function was 0.29 kPa, and the R² value of the overall piecewise function fit was 0.78. Similarly, the segmentation point size of pine trees was 0.78 kPa, and the R² value of the overall piecewise function fit was 0.94.

[0111]

[0112] Where VPD0 is the segmentation point of the piecewise function, which is related to the region, tree species, etc.

[0113] Based on the above embodiment, step 500 includes:

[0114] Determine the maximum canopy conductance;

[0115] The canopy conductance simulation equation is obtained by multiplying the maximum canopy conductance, the single factor response equation of the canopy conductance to downward shortwave radiation, and the single factor response equation of the canopy conductance to saturated water vapor pressure difference.

[0116] Specifically, after determining the response equation form of canopy conductance to Rsi and VPD, the embodiment of the present invention assumes that the effects of downward shortwave radiation and saturation vapor pressure difference on canopy conductance are independent of each other. Referring to the Jarvis-Stewart model, a continuous multiplication method is used to simulate canopy conductance. The simulation equation form is as follows:

[0117]

[0118] in, is the maximum value of Gc measurement; is the response equation of Gc to Rsi, is the response equation of Gc to VPD.

[0119] Based on the canopy conductance simulation equation constructed above, the canopy conductance in different years in the study area involved in the embodiment is simulated, and the simulation effect is as follows: Figure 5 As shown, (a) and (b) are the simulation results of the canopy conductance of oak in 2021 and 2023 with a ratio of 1:1, and (c) and (d) are the simulation results of the canopy conductance of pine in 2021 and 2023 with a ratio of 1:1. It can be seen that the simulation results R 2 Both are greater than 0.65.

[0120] The canopy conductance simulation system based on the segmented effect of saturated water vapor pressure difference provided by the present invention is described below. The canopy conductance simulation system based on the segmented effect of saturated water vapor pressure difference described below and the canopy conductance simulation method based on the segmented effect of saturated water vapor pressure difference described above can be referenced to each other.

[0121] Figure 6 is a structural diagram of a canopy conductance simulation system based on the saturated vapor pressure difference segmented effect provided by an embodiment of the present invention, such as Figure 6 As shown, it includes: an acquisition module 61, a collection module 62, a calculation module 63, a fitting module 64 and a construction module 65, wherein:

[0122] The acquisition module 61 is used to obtain ground-observed meteorological data; the acquisition module 62 is used to collect the sapwood area and trunk sap flow density data of each sample tree in the experimental area, and calculate the weighted average value of the trunk sap flow density based on the sapwood area and the trunk sap flow density data; the calculation module 63 is used to calculate the tree canopy conductance based on the ground-observed meteorological data and the weighted average value of the trunk sap flow density; the fitting module 64 is used to draw a scatter plot of the tree canopy conductance and meteorological factors, extract representative points of the scatter plot based on the outer envelope method, and determine the single-factor response equations of the canopy conductance and downward shortwave radiation and saturated water vapor pressure difference by fitting the representative points; the construction module 65 is used to construct a canopy conductance simulation equation based on the single-factor response equation.

[0123] Figure 7 An example of a physical structure diagram of an electronic device is shown below. Figure 7As shown, the electronic device may include: a processor (processor) 710, a communication interface (Communications Interface) 720, a memory (memory) 730 and a communication bus 740, wherein the processor 710, the communication interface 720, and the memory 730 communicate with each other through the communication bus 740. The processor 710 can call the logic instructions in the memory 730 to execute a canopy conductance simulation method based on the segmented effect of saturated water vapor pressure difference, which method includes: obtaining ground observation meteorological data; collecting sapwood area and trunk sap flow density data of each sample tree in the experimental area, and calculating the weighted average value of trunk sap flow density based on the sapwood area and the trunk sap flow density data; calculating the tree canopy conductance according to the ground observation meteorological data and the weighted average value of the trunk sap flow density; drawing a scatter plot of the tree canopy conductance and meteorological factors, extracting representative points of the scatter plot based on the outer envelope method, and determining the single-factor response equations of the canopy conductance to downward shortwave radiation and saturated water vapor pressure difference by fitting the representative points; and constructing a canopy conductance simulation equation based on the single-factor response equation.

[0124] Furthermore, the logic instructions in the aforementioned memory 730 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product, stored in a storage medium, includes instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0125] On the other hand, the present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, is implemented to execute the canopy conductance simulation method based on the segmented effect of saturated water vapor pressure difference provided by the above-mentioned methods, the method comprising: obtaining ground-observed meteorological data; collecting sapwood area and trunk sap flow density data of each sample tree in the experimental area, and calculating a weighted average value of trunk sap flow density based on the sapwood area and the trunk sap flow density data; calculating the tree canopy conductance based on the ground-observed meteorological data and the weighted average value of the trunk sap flow density; drawing a scatter plot of the tree canopy conductance and meteorological factors, extracting representative points of the scatter plot based on the outer envelope method, and determining the single-factor response equations of the canopy conductance to downward shortwave radiation and saturated water vapor pressure difference by fitting the representative points; and constructing a canopy conductance simulation equation based on the single-factor response equation.

[0126] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one location or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of the present embodiment. Persons of ordinary skill in the art will be able to understand and implement the present invention without inventive effort.

[0127] Through the above description of the embodiments, those skilled in the art will clearly understand that each embodiment can be implemented using software plus a necessary general-purpose hardware platform, or of course, hardware. Based on this understanding, the essence of the above technical solution, or the portion that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a magnetic disk, or an optical disk, and includes a number of instructions for causing a computer device (such as a personal computer, server, or network device) to execute the methods described in each embodiment or certain portions of the embodiments.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A canopy conductance simulation method based on the segmented effect of saturated vapor pressure difference, characterized in that: include: Obtain ground observation meteorological data; Collecting sapwood area and trunk sap flow density data of each sample tree in the experimental area, and calculating a weighted average of the trunk sap flow density based on the sapwood area and the trunk sap flow density data; Calculating the tree canopy conductance based on the ground-observed meteorological data and the weighted average value of the tree trunk sap flow density; Drawing a scatter plot of the tree canopy conductance and meteorological factors, extracting representative points of the scatter plot based on the outer envelope method, and determining the single-factor response equations of canopy conductance, downward shortwave radiation, and saturation vapor pressure difference by fitting the representative points; Constructing a canopy conductance simulation equation based on the single factor response equation; The single-factor response equations of canopy conductance, downward shortwave radiation, and saturation vapor pressure difference are determined by fitting the representative points, including: The extracted representative points are optimized using the least squares method to obtain the optimized representative points; An exponential function constructed by the first coefficient, the second coefficient, the third coefficient, the fourth coefficient and the downward shortwave radiation is used as a single-factor response equation of canopy conductance to downward shortwave radiation; Taking the maximum value of the tree canopy conductance as a reference point, taking a preset numerical range before and after the reference point as a candidate area, and determining evenly distributed potential saturated water vapor pressure difference segmentation points with a preset step size within the candidate area; Using the potential saturated vapor pressure difference segmentation points to perform cyclic iteration, the data set is divided into a left half data set and a right half data set, wherein the left half data set is fitted with a linear function, and the right half data set is fitted with a logarithmic function curve, to determine the segmentation points of the piecewise function; When the function value of the linear function at any segmentation point is equal to the function value of the logarithmic function curve at any segmentation point, and the determination coefficient of the entire segmentation response equation obtained by fitting each potential saturated vapor pressure difference segmentation point reaches a maximum, the any segmentation point is determined to be the segmentation point of the piecewise function; A piecewise function constructed with the fifth coefficient, the sixth coefficient, the seventh coefficient, the eighth coefficient, the saturated water vapor pressure difference and the piecewise function segmentation points is used as a single factor response equation of canopy conductance to saturated water vapor pressure difference.

2. The canopy conductance simulation method based on the saturation vapor pressure difference segmented effect according to claim 1, characterized in that: Obtain ground-based meteorological data, including: Based on the preset measurement time resolution, an automatic weather station is used to collect air temperature, relative humidity and downward shortwave radiation; The saturated water vapor pressure difference is obtained by segmented calculation based on the air temperature and the relative humidity.

3. The canopy conductance simulation method based on the saturation vapor pressure difference segmented effect according to claim 1, characterized in that: Collecting sapwood area and trunk sap flow density data for each sample tree in the experimental area, and calculating a weighted average trunk sap flow density based on the sapwood area and trunk sap flow density data, including: The trunk sap flow density data of each sample tree was collected based on the heat diffusion probe method; The diameter at breast height of different tree species is measured, and the sapwood area is calculated using the empirical formula of sapwood area-diameter at breast height of the tree; A weighted calculation is performed based on the trunk sap flow density data, the sapwood area and the number of sample tree observations to obtain the weighted average value of the trunk sap flow density.

4. The canopy conductance simulation method based on the segmented effect of saturated vapor pressure difference according to claim 1, characterized in that: The tree canopy conductance is calculated based on the ground-observed meteorological data and the weighted average value of the trunk sap flow density, including: Substituting the weighted average value of the trunk sap flow density and the saturated vapor pressure difference in the ground-observed meteorological data into the simplified Penman-Monteith equation yields: ； ； Where Gc is the canopy conductance, in mm s -1 , γ is the wet / dry coefficient, unit is kPa ℃ -1 , λ is the latent heat of vaporization of water, unit is J kg -1 Tr is the canopy transpiration rate calculated from the weighted average of the trunk sap flow density, in mm s -1 , As / Ag is the ratio of the total area of ​​stand sapwood to the area of ​​the plot, and ASFD is the weighted average stem sap flow density (g cm -2 d -1 , c p is the specific heat capacity of moist air, in J kg -1 ℃ -1 , ρ is the density of moist air, in kg m -3 , VPD is the saturated water vapor pressure difference, the unit is kPa.

5. The canopy conductance simulation method based on the saturation vapor pressure difference segmented effect according to claim 1, characterized in that: After calculating the tree canopy conductance based on the ground-observed meteorological data and the weighted average value of the tree trunk sap flow density, the method further includes: The optimized tree canopy conductance was obtained by performing data quality control on the tree canopy conductance by screening stable data in the middle of the growing season, excluding data corresponding to rainy days, and selecting data corresponding to data greater than a preset saturated water vapor pressure difference.

6. The canopy conductance simulation method based on the segmented effect of saturated vapor pressure difference according to claim 1, characterized in that: Drawing a scatter plot of the tree canopy conductance and meteorological factors, and extracting representative points of the scatter plot based on the outer envelope method, including: determining the downward shortwave radiation or the saturated water vapor pressure difference as the meteorological factor; Draw a scatter plot with each meteorological factor as the horizontal axis and the tree canopy conductance as the vertical axis; Arrange all data samples in ascending order according to the meteorological factors and divide them into several data segments on average; In the segmented interval corresponding to each data segment, all tree canopy conductances are arranged in ascending order, and then the preset percentage left and right quantiles are extracted as the maximum value of the tree canopy conductance in the segmented interval. The maximum value of the tree canopy conductance is used as the vertical coordinate of the representative point of the data segment, and the average value of all data representative points is used as the horizontal coordinate of the representative point of the data segment.

7. The canopy conductance simulation method based on the segmented effect of saturated vapor pressure difference according to claim 6, characterized in that: The canopy conductance simulation equation is constructed based on the single factor response equation, including: Determine the maximum canopy conductance; The canopy conductance simulation equation is obtained by multiplying the maximum canopy conductance, the single factor response equation of the canopy conductance to downward shortwave radiation, and the single factor response equation of the canopy conductance to saturated water vapor pressure difference.

8. A canopy conductance simulation system based on the segmented effect of saturated water vapor pressure difference, based on the canopy conductance simulation method based on the segmented effect of saturated water vapor pressure difference according to any one of claims 1 to 7, characterized in that: include: Acquisition module, used to obtain ground observation meteorological data; a collection module, configured to collect sapwood area and trunk sap flow density data of each sample tree in the experimental area, and calculate a weighted average value of the trunk sap flow density based on the sapwood area and the trunk sap flow density data; a calculation module, configured to calculate the tree canopy conductance based on the ground-observed meteorological data and the weighted average value of the tree trunk sap flow density; a fitting module for drawing a scatter plot of the tree canopy conductance and meteorological factors, extracting representative points of the scatter plot based on an envelope method, and determining single-factor response equations of canopy conductance, downward shortwave radiation, and saturation vapor pressure difference by fitting the representative points; A construction module is used to construct a canopy conductance simulation equation based on the single factor response equation.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect as described in any one of claims 1 to 7 is implemented.

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