Canopy conductivity simulation method and system based on saturation vapor pressure difference segmentation effect

Abstract

The invention provides a canopy conductivity simulation method and system based on a saturated vapor pressure difference segmentation effect. The method comprises the following steps: firstly, collecting meteorological data and basic information such as tree trunk liquid flow and sapwood area in a research area; the canopy conductance is calculated on the basis of the trunk liquid flow data and a simplified Penman-Monteith equation; secondly, analyzing a hysteretic response form and a segmented response equation of canopy conductance and meteorological factors through methods of drawing a scatter diagram, an outsourcing line and the like; then, establishing a canopy conductance model based on the response equation of the canopy conductance and the meteorological factors and the multiplication model; and finally, basic meteorological data are substituted into the model to simulate the canopy conductance of the area. According to the method, the response relation between the canopy conductance and the meteorological factors is considered, the relation between plant physiology and the environmental process can be more accurately understood, the method is crucial to accurate estimation of drainage basin transpiration, and the method has great significance in planning and research of water resources.

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 core 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. As an important channel for evapotranspiration, the opening and closing degree of vegetation stomata is an important variable controlling the exchange of water vapor and carbon dioxide between vegetation and the atmosphere, that is, 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 the sun's downward shortwave radiation and the air saturated water vapor pressure difference. Therefore, in model research, these variables are usually used as driving factors.

[0003] The study showed that there is an obvious segmented response characteristic between canopy conductance and air saturated vapor pressure difference, and different response relationships are shown between saturated vapor pressure difference and canopy conductance in different ranges. Considering the segmented response relationship of saturated vapor pressure difference and building a segmented simulation model of canopy conductance based on it can more accurately understand the relationship between plant physiology and environmental processes, which is crucial for accurately estimating basin transpiration. However, there are currently few studies on the above aspects, and a new scheme for studying and 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, so as to solve the defect that the driving variable research of canopy conductance in the prior art lacks systematic and effective means.

[0005] In a first aspect, the present invention provides a canopy conductance simulation method based on the segmented effect of saturated water vapor pressure difference, comprising: 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 value of the trunk sap flow density based on the sapwood area and the trunk sap flow density data; The tree canopy conductance is calculated based on the ground observation meteorological data and the weighted average value of the tree trunk sap flow density; 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 canopy conductance, downward shortwave radiation and saturated water vapor pressure difference by fitting the representative points; A canopy conductance simulation equation is constructed based on the single factor response equation.

[0006] According to a canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect provided by the present invention, ground observation meteorological data is obtained, 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 calculating in sections based on the air temperature and the relative humidity.

[0007] According to a canopy conductance simulation method based on the segmented effect of saturated water vapor pressure difference provided by the present invention, the sapwood area and trunk sap flow density data of each sample tree in the experimental area are collected, and the weighted average value of the trunk sap flow density is calculated based on the sapwood area and the trunk sap flow density data, including: The trunk sap flow density data of each sample tree was collected based on the thermal diffusion probe method; The diameter at breast height of different types of trees 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 a weighted average value of the trunk sap flow density.

[0008] According to a canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect provided by the present invention, the tree canopy conductance is calculated according to 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 observation meteorological data into the simplified Penman-Monteith equation, the following is obtained: ; ; Where Gc is the canopy conductance in mm s -1 , γ is the dry-wet coefficient, unit is kPa ℃ -1 , λ is the latent heat of vaporization of water, in 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, in 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.

[0009] According to a canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect provided by the present invention, after calculating the tree canopy conductance according to the ground observed meteorological data and the weighted average value of the trunk sap flow density, the method further includes: The optimized tree canopy conductance is obtained by performing data quality control on the tree canopy conductance by screening stable data in the middle of the growing season, eliminating data corresponding to rainy days, and selecting data corresponding to a saturated water vapor pressure difference greater than a preset value.

[0010] According to a canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect 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: 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 order from small to large according to the meteorological factors, and divide them into several data segments evenly; In the segmented interval corresponding to each data segment, all tree canopy conductances are arranged in ascending order, and then the maximum value of the tree canopy conductance with the preset percentage left and right quantiles as the segmented interval is extracted. 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 the data representative points is used as the horizontal coordinate of the representative point of the data segment.

[0011] 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: The extracted representative points are optimized using the least square method to obtain the optimized representative points; An exponential function constructed by using 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 the preset numerical range before and after the reference point as a candidate area, and determining the potential saturated water vapor pressure difference segmentation points with a preset step length and uniform distribution within the candidate area; The potential saturated water vapor pressure difference segmentation points are used for cyclic iteration to divide the data set into a left half data set and a right half data set, wherein a linear function is used to fit the left half data set, and a logarithmic function curve is used to fit the right half data set 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 the maximum, any segmentation point corresponding to the segmentation point is determined as the segmentation point of the segmentation 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.

[0012] According to a canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect provided by the present invention, a 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 canopy conductance maximum value, 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.

[0013] In a second aspect, the present invention further provides a canopy conductance simulation system based on the segmented effect of saturated water vapor pressure difference, comprising: An acquisition module is used to obtain ground observation meteorological data; A collection module 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; A calculation module, used for calculating the tree canopy conductance according to the ground observation meteorological data and the weighted average value of the tree trunk sap flow density; A fitting module 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 the downward shortwave radiation and the saturated water 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.

[0014] 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, a canopy conductance simulation method based on the segmented effect of saturated water vapor pressure difference as described above is implemented.

[0015] The canopy conductivity simulation method and system based on the segmented effect of saturated water vapor pressure difference provided by the present invention constructs a simulation model of tree canopy conductivity based on the segmented response relationship of canopy conductivity to meteorological factors by analyzing the influence of segmented simulated environmental variables on canopy conductivity. The relationship between plant physiology and environmental processes is fully considered, and the generated simulation results provide an important reference basis for accurate assessment of watershed hydrological simulation and water resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0017] Figure 1 It is one of the flow diagrams of the canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect provided by the present invention; 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; Figure 3 is a response relationship diagram of tree canopy conductance and meteorological factors Rsi and VPD provided by the present invention, wherein 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; Figure 4 It is a fitting process diagram 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) are the fitting process of the canopy conductance and Rsi and VPD response equations of pine trees; Figure 5 is a canopy conductance model fitting effect diagram provided by the present invention, wherein Figure 5 (a) and (b) are the simulation results of 1:1 canopy conductance of oak trees in 2021 and 2023. Figure 5 (c) and (d) are the simulation results of 1:1 canopy conductance of pine trees in 2021 and 2023; Figure 6 It is a structural schematic diagram of a canopy conductance simulation system based on the saturated water vapor pressure difference segmented effect provided by the present invention; Figure 7 It is a structural schematic diagram of the electronic device provided by the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] In view of the shortcomings of the prior art, the present invention proposes a canopy conductance simulation method based on the segmented effect of saturated vapor pressure difference, focusing on considering the hysteresis response characteristics between canopy conductance and downward shortwave radiation (Rsi) and saturated vapor pressure difference (VPD). Figure 1 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 As shown, including: Step 100: Acquire ground observation meteorological data; Step 200: 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; Step 300: Calculating the tree canopy conductance based on the ground-observed meteorological data and the weighted average value of the tree trunk sap flow density; Step 400: 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 canopy conductance, downward shortwave radiation and saturated water vapor pressure difference by fitting the representative points; Step 500: constructing a canopy conductance simulation equation based on the single factor response equation.

[0020] Specifically, Figure 2 As shown in the figure, firstly, the meteorological data and basic information such as trunk sap flow and sapwood area of ​​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 the downward shortwave radiation (Rsi) and the 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 the canopy conductance and Rsi and VPD; finally, the basic meteorological data are substituted into the model to simulate the canopy conductance of the area.

[0021] The present invention 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 for watershed hydrological simulation and accurate assessment of water resources.

[0022] Based on the above embodiment, step 100 includes: 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 calculating in sections based on the air temperature and the relative humidity.

[0023] 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 by segmentation of air temperature (Ta) and relative humidity (RH).

[0024] Based on the above embodiment, step 200 includes: The trunk sap flow density data of each sample tree was collected based on the thermal diffusion probe method; The diameter at breast height of different types of trees 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 a weighted average value of the trunk sap flow density.

[0025] The method used in the embodiment of the present invention to measure the trunk sap flow density is the widely used thermal diffusion probe method (TOP). 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.

[0026] Specifically, a pair of probes with a diameter of 2 mm and a spacing of 4 cm were inserted into the upper and lower trunks of trees at 1.2 m in height, and the upper probe was heated by a constant thermocouple to form a temperature difference with the lower probe. The temperature difference (∆T, ℃) between the two probes is controlled by the sap flow rate in the trunk. The greater the sap flow rate in 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. From this, the tree's trunk sap flow density (SFD, in g cm -2 d -1 ): ; 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 value of the 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.

[0027] The sapwood area (As) of trees is not easy to measure directly. Usually, the corresponding sapwood area is calculated by measuring the diameter at breast height (DBH) of the tree and combining the empirical formula of sapwood area-DBH of the corresponding tree. In this embodiment, the fitting formula of sapwood area (As)-DBH of oak and pine is as follows: Oak: ; pine: ; Next, the measured trunk sap flow density of each sample was calculated based on the sapwood area weighted average (ASFD, unit: g cm -2 d -1 ) to reflect the average characteristics of tree trunk sap flow in the forest stand: ; 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 observations of sample trees. In this embodiment, the n value of oak is 8, and the n value of pine is 3.

[0028] Based on the above embodiment, step 300 includes: Substituting the weighted average value of the trunk sap flow density and the saturated vapor pressure difference in the ground observation meteorological data into the simplified Penman-Monteith equation, the following is obtained: ; ; Where Gc is the canopy conductance in mm s -1 , γ is the dry-wet coefficient, unit is kPa ℃ -1 , λ is the latent heat of vaporization of water, in 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, in 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.

[0029] Based on the above embodiment, after step 300, the following steps are further included: The optimized tree canopy conductance is obtained by performing data quality control on the tree canopy conductance by screening stable data in the middle of the growing season, eliminating data corresponding to rainy days, and selecting data corresponding to a saturated water vapor pressure difference greater than a preset value.

[0030] 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 oak tree selects data from late April to mid-September, and the pine tree selects data throughout the year; (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 data with VPD ≥ 0.2 kPa are selected for analysis.

[0031] Based on the above embodiment, the 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: 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 order from small to large according to the meteorological factors, and divide them into several data segments evenly; In the segmented interval corresponding to each data segment, all tree canopy conductances are arranged in ascending order, and then the maximum value of the tree canopy conductance with the preset percentage left and right quantiles as the segmented interval is extracted. 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 the data representative points is used as the horizontal coordinate of the representative point of the data segment.

[0032] It should be noted that, in the present 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 the tree, 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 the canopy conductance to Rsi when there are no other factors limiting it, and the curve form of these points fitting is the single factor response form of the canopy conductance to Rsi. Then, scatter plots of Gc-Rsi and Gc-VPD are drawn by dividing different time periods with the meteorological factors Rsi and VPD as the horizontal coordinates and the canopy conductance Gc as the vertical coordinate. In the present embodiment, it can be clearly found that there is a hysteresis response relationship between the canopy conductance and Rsi and VPD, such as Figure 3 As shown, (a), (b), (c) are the hysteresis responses of oak canopy conductance to meteorological factors Rsi, VPD and Ta, respectively, and (d), (e), (f) are the hysteresis responses of pine canopy conductance to meteorological factors Rsi, VPD and Ta, respectively. Rsi or VPD in different ranges corresponds to different response function relationships.

[0033] Due to too much sample data, representative points are extracted by segmentation. A scatter plot is drawn with each meteorological factor as the horizontal coordinate and the canopy conductance as the vertical coordinate. All data samples are arranged in order from small to large according to the meteorological factors (Rsi or VPD), and are evenly divided into several segments (the number of segments can be appropriately selected without affecting the analysis results, and 100 is used as an example here). Next, representative points are extracted based on the outer envelope method, that is, in each segment interval, all Gc data are arranged in ascending order and the quantile of about 90% is taken as the maximum value of Gc in this segment, and used as the vertical coordinate of the representative point of this segment (in order to reduce the uncertainty of the sample, the maximum value is not taken directly). At the same time, the average value of all meteorological factor (Rsi or VPD) data in this segment is taken as the horizontal coordinate of the representative point of this segment.

[0034] Based on the above embodiment, the single factor response equations of canopy conductance, downward shortwave radiation and saturated water vapor pressure difference are determined by fitting the representative points in step 400, including: The extracted representative points are optimized using the least square method to obtain the optimized representative points; An exponential function constructed by using 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 the preset numerical range before and after the reference point as a candidate area, and determining the potential saturated water vapor pressure difference segmentation points with a preset step length and uniform distribution within the candidate area; The potential saturated water vapor pressure difference segmentation points are used for cyclic iteration to divide the data set into a left half data set and a right half data set, wherein a linear function is used to fit the left half data set, and a logarithmic function curve is used to fit the right half data set 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 the maximum, any segmentation point corresponding to the segmentation point is determined as the segmentation point of the segmentation 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.

[0035] Specifically, the embodiment of the present invention fits the extracted representative points to find the most suitable single-factor response curve form of canopy conductance (Gc) to downward shortwave radiation (Rsi) and saturated 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 canopy conductance, Rsi and VPD response equations of oak, and (c) and (d) are the fitting processes of the canopy conductance, Rsi and VPD response equations of pine.

[0036] The response equation of canopy conductance (Gc) to downward shortwave radiation (Rsi) is expressed by an exponential function: ; The response equation of canopy conductance (Gc) to saturated vapor pressure deficit (VPD) is expressed by a piecewise function, with a linear function on the left side of the segmentation point and a logarithmic function on the right side. In the process of constructing the response equation of canopy conductance to saturated vapor pressure deficit (VPD), the following processing was performed to determine the segmentation point: the segmentation point of the function of canopy conductance to saturated vapor pressure deficit was located near the VPD value range corresponding to the maximum value of Gc. Based on this, the VPD corresponding to the maximum value of Gc was taken as the reference point, and the numerical range of 0.4 kPa before and after the reference point was set as the candidate area. Potential VPD segmentation points were evenly set in this area with a step size of 0.02 kPa. The response equation was fitted by cyclic iteration using the potential VPD segmentation points. In each iteration, the data set was divided into two parts by the potential segmentation points. The left half of the data set was fitted using the linear function curve, and the right half of the data set was fitted using the logarithmic function curve. Specific boundary conditions are set at the segmentation points, that is, the function value of the linear function on the left at the segmentation point is required to be equal to the function value of the logarithmic function on the right at the segmentation point to ensure the continuity of the function. Subsequently, the coefficient of determination (R²) of the entire segmentation response equation obtained by fitting each potential segmentation point is calculated, and finally the VPD data point that makes the R² value of the fitting equation reach the maximum is selected, and this point is used as the segmentation point of the segmentation function. Combined with the above method, by comparing the R² values ​​of the potential segmentation points of oak trees, it can be determined that the segmentation point size of the oak segmentation function is 0.29 kPa, and the R² value of the overall fitting of the segmentation function is 0.78. Similarly, the segmentation point size of pine trees is 0.78 kPa, and the R² value of the overall fitting of the segmentation function is 0.94.

[0037]

[0038] Where VPD0 is the segmentation point of the piecewise function, which is related to the region, tree species, etc.

[0039] Based on the above embodiment, step 500 includes: Determine the maximum canopy conductance; The canopy conductance simulation equation is obtained by multiplying the canopy conductance maximum value, 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] Specifically, after the embodiment of the present invention determines the response equation form of canopy conductance to Rsi and VPD, it is assumed that the effects of downward shortwave radiation and saturated vapor pressure difference on canopy conductance are independent of each other. Referring to the Jarvis-Stewart model, the canopy conductance is simulated by a multiplication method, and the simulation equation form is as follows:

[0041] in, is the maximum value among the Gc measurements; is the response equation of Gc to Rsi, is the response equation of Gc to VPD.

[0042] 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.

[0043] The canopy conductivity simulation system based on the segmented effect of saturated water vapor pressure difference provided by the present invention is described below. The canopy conductivity simulation system based on the segmented effect of saturated water vapor pressure difference described below and the canopy conductivity simulation method based on the segmented effect of saturated water vapor pressure difference described above can be referenced to each other.

[0044] Figure 6 is a schematic diagram of the structure of a canopy conductance simulation system based on the saturated water 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: The acquisition module 61 is used to acquire ground-observed meteorological data; the collection 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 conductivity 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 conductivity 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 conductivity and the downward shortwave radiation and the saturated water vapor pressure difference by fitting the representative points; the construction module 65 is used to construct a canopy conductivity simulation equation based on the single factor response equation.

[0045] Figure 7 An example of a physical structure diagram of an electronic device is shown in FIG. 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, 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 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 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 with 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.

[0046] In addition, the logic instructions in the above-mentioned memory 730 can be implemented in the form of a software functional unit and can be stored in a computer-readable storage medium when it is sold or used as an independent product. Based on this understanding, the technical solution of the present invention can be essentially or partly embodied in the form of a software product that contributes to the prior art. The computer software product is stored in a storage medium, including several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

[0047] 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 according to 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.

[0048] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0049] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0050] 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 embodiments of the present invention.

Claims

1. A canopy conductance simulation method based on the segmented effect of saturated water 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 value of the trunk sap flow density based on the sapwood area and the trunk sap flow density data; The tree canopy conductance is calculated based on the ground observation meteorological data and the weighted average value of the tree trunk sap flow density; 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 canopy conductance, downward shortwave radiation and saturated water vapor pressure difference by fitting the representative points; A canopy conductance simulation equation is constructed based on the single factor response equation.

2. The canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect according to claim 1, characterized in that: Obtain ground observation 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 calculating in sections based on the air temperature and the relative humidity.

3. The canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect according to claim 1, characterized in that: The sapwood area and trunk sap flow density data of each sample tree in the experimental area are collected, and the weighted average value of the trunk sap flow density is calculated based on the sapwood area and the trunk sap flow density data, including: The trunk sap flow density data of each sample tree was collected based on the thermal diffusion probe method; The diameter at breast height of different types of trees 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 a weighted average value of the trunk sap flow density.

4. The canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect according to claim 1, characterized in that: The tree canopy conductance is calculated based on the ground observation meteorological data and the weighted average value of the tree 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 observation meteorological data into the simplified Penman-Monteith equation, the following is obtained: ； ； Where Gc is the canopy conductance in mm s -1 , γ is the dry-wet coefficient, unit is kPa ℃ -1 , λ is the latent heat of vaporization of water, in 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, in 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 saturated water vapor pressure difference segmented effect according to claim 1, characterized in that: After calculating the tree canopy conductance according to the ground observation meteorological data and the weighted average value of the tree trunk sap flow density, the method further includes: The optimized tree canopy conductance is obtained by performing data quality control on the tree canopy conductance by screening stable data in the middle of the growing season, eliminating data corresponding to rainy days, and selecting data corresponding to a saturated water vapor pressure difference greater than a preset value.

6. The canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect 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 order from small to large according to the meteorological factors, and divide them into several data segments evenly; In the segmented interval corresponding to each data segment, all tree canopy conductances are arranged in ascending order, and then the maximum value of the tree canopy conductance with the preset percentage left and right quantiles as the segmented interval is extracted. 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 the 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 saturated water vapor pressure difference segmented effect according to claim 6, characterized in that: 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: The extracted representative points are optimized using the least square method to obtain the optimized representative points; An exponential function constructed by using 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 the preset numerical range before and after the reference point as a candidate area, and determining the potential saturated water vapor pressure difference segmentation points with a preset step length and uniform distribution within the candidate area; The potential saturated water vapor pressure difference segmentation points are used for cyclic iteration to divide the data set into a left half data set and a right half data set, wherein a linear function is used to fit the left half data set, and a logarithmic function curve is used to fit the right half data set 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 the maximum, any segmentation point corresponding to the segmentation point is determined as the segmentation point of the segmentation 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.

8. The canopy conductance simulation method based on the saturated water vapor pressure difference segmented effect according to claim 7, 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 canopy conductance maximum value, 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.

9. A canopy conductance simulation system based on the segmented effect of saturated water vapor pressure difference, characterized in that: include: An acquisition module is used to obtain ground observation meteorological data; A collection module 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; A calculation module, used for calculating the tree canopy conductance according to the ground observation meteorological data and the weighted average value of the tree trunk sap flow density; A fitting module 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 the downward shortwave radiation and the saturated water 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.

10. 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 in any one of claims 1 to 8 is implemented.

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