A method for calculating evapotranspiration and component separation based on dynamic canopy extinction coefficient

Abstract

The application discloses a kind of based on dynamic canopy extinction coefficient evapotranspiration calculation and component splitting method, applied to farmland crop irrigation field, the method includes: discerning the main control factor of canopy extinction coefficient change;Based on main control factor, construct canopy extinction coefficient dynamic change law quantitative representation function;It is nested into single-source Penman-Monteith model or double-source Shuttleworth-Wallace model to replace conventional extinction coefficient fixed value scheme, and then estimate farmland evapotranspiration and its components (soil evaporation and crop transpiration).The application realizes the accurate quantitative representation of the dynamic change law of extinction coefficient.Compared with the traditional fixed value scheme, although the simulation effect of total evapotranspiration is slightly improved, the accuracy of component splitting of evapotranspiration can be effectively improved, i.e.the accuracy of the proportion of evaporation and transpiration.Compared with the proportion of evaporation and transpiration, the effect is stable and reliable after being verified in many places.

Description

Technical Field

[0001] This invention relates to the field of farmland crop irrigation, specifically to a method for calculating evapotranspiration and separating components based on dynamic canopy extinction coefficient. Background Technology

[0002] Evapotranspiration (ET) is a core component of the water and carbon processes in the soil-plant-atmosphere continuum, consisting of soil evaporation (E) and vegetation transpiration (T). e The former is often considered as ineffective water consumption in farmland, while the latter, due to its close relationship with yield formation, is often considered as productive water loss. Both are important aspects of agricultural water resource management. E and T vary across different farmland systems. e The proportion of ET varies greatly. Accurately estimating ET and dividing the components E and T e Accurate breakdown of these parameters plays a crucial role in assessing the effectiveness of farmland water consumption, developing irrigation systems, and estimating yields.

[0003] Current research indicates that commonly used ET simulation and component separation models, such as the dual-source Shuttleworth-Wallace model, perform well in ET estimation, but are less effective in separating ET components. In many classic ET models, water consumption calculations largely depend on available energy. For example, when calculating canopy transpiration T... e At this time, the available energy is the net radiation intercepted by the canopy, while the remaining portion of the total available energy is used to drive soil evaporation (E). The extinction coefficient C characterizes the degree to which the canopy intercepts radiation; the smaller the value, the more radiation penetrates the canopy to reach the soil, resulting in higher evaporation, and vice versa. Therefore, accurately assessing the value of C is a prerequisite for ensuring a reasonable energy distribution between the canopy and the soil.

[0004] However, due to the current lack of measured data on evapotranspiration (C), scholars' understanding of C remains relatively limited. In most evapotranspiration models, C is usually assumed to be a fixed constant. However, studies have confirmed that the C value not only varies with the seasons but also changes intraday, influenced by a combination of factors such as growth status and environmental conditions. The C value typically ranges between 0.3 and 1.5. This is because environmental conditions can alter canopy structure characteristics by changing leaf tilt angle and leaf distribution, thereby causing changes in radiation interception. Under many conditions, the output of ET models is highly sensitive to the C value; ignoring the dynamic changes in C is detrimental to the accurate estimation of ET and its components.

[0005] While existing studies on evapotranspiration estimation provide methods for quantitatively characterizing the dynamic changes in the extinction coefficient, and incorporate consideration of the impact of environmental factors on evapotranspiration, this method first constructs a comprehensive factor by identifying the main controlling factor of the extinction coefficient, and then calculates the dynamic extinction coefficient using the power function relationship between the comprehensive factor and the extinction coefficient. This method has proven effective in calculating daily water consumption, but its accuracy is insufficient when used for hourly water consumption calculations. Summary of the Invention

[0006] The purpose of this invention is to provide a method for calculating evapotranspiration and separating components based on dynamic canopy extinction coefficient, aiming to solve or improve at least one of the above-mentioned technical problems.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] A method for calculating evapotranspiration and separating components based on dynamic canopy extinction coefficient, comprising:

[0009] Step A: As the reproductive period progresses, the intensity of incident radiation above the canopy and the intensity of penetrating radiation below the canopy are measured regularly and multiple times during the day using a radiation sensor. The extinction coefficient of the canopy at each stage is calculated according to Beer's Law.

[0010]

[0011] In the formula, C is the extinction coefficient, and PAR is the extinction coefficient. in and PAR tr These represent the incident radiation intensity above the canopy and the penetrating radiation intensity below the canopy, respectively, both in MJ / m². -2 d -1 LAI stands for Leaf Area Index, and its unit is m². 2 m -2 .

[0012] Step B: Use mathematical methods to analyze the relationship between leaf area index (LAI) and major environmental factors and C, and determine whether the main controlling factors of C and the correlation between C and each main controlling factor are positive or negative;

[0013] Step C: Construct a dynamic extinction coefficient function using the main control factor. Based on the positive and negative values ​​of the relevant factors obtained in Step B, factors positively correlated with C are represented by the factor itself, while factors negatively correlated with C are represented by their reciprocals. Then, the extinction coefficient C is calculated using the following formula. d Dynamic change pattern:

[0014]

[0015] In the formula, C d f is the extinction coefficient. nis the nth principal control factor of the extinction coefficient, and a, b, c and d are parameters to be determined, where b, c and d represent the sensitivity coefficients of the factors corresponding to their bases;

[0016] For example, for crops with large variations in leaf area index (LAI), when soil moisture content (SWC) and net radiation (R) are relatively stable... n When the extinction coefficient is also the controlling factor, the expression for the dynamic extinction coefficient C is as follows:

[0017]

[0018] Note: Generally, the higher the SWC, the larger the C (positive correlation), and vice versa for LAI or R. n The larger the value, the smaller the value of C (negative correlation).

[0019] Step D1: Apply formula C d The Penman-Monteith model is used to replace the extinction coefficient constant parameter C to calculate the evapotranspiration water consumption T. e :

[0020]

[0021] In the formula: T e It is canopy transpiration, and its unit is MJ / m³. -2 d -1 △ represents the slope of the saturated vapor pressure versus temperature curve, with units of kPa℃. -1 ;R nc The net radiation intercepted by the canopy is expressed in MJ / m². -2 d -1 G represents soil heat flux, measured in MJ / m³. -2 d -1 ρ is the density of air, and its unit is g / mm³. -3 c p It is the specific heat at constant pressure, and its unit is MJ / kg. -1 ℃ -1 γ is the hygrometer constant, and its unit is kPa℃. -1 VPD is the saturated vapor pressure difference, and its unit is kPa; r c It is the canopy resistance, and its unit is sm. -1 ;r a It is aerodynamic drag, and its unit is sm. -1 Net radiation R intercepted by the canopy nc Calculate according to the following formula:

[0022] R nc =R n ×(1-exp(-C d ×LAI));

[0023] In the formula: R n It is the net radiation at the top of the canopy, and its unit is MJm. -2 d -1 C d The dynamic extinction coefficient is dimensionless; LAI is the canopy leaf area index, with units of m². 2 m -2 .

[0024] Step D2: Apply formula C d The Shuttleworth-Wallace model is introduced to replace the extinction coefficient constant parameter C, and the evapotranspiration ET and its component evapotranspiration water consumption T are calculated. e and soil evaporation E;

[0025] ET=C c PM c +C s PM s

[0026]

[0027] In the formula, ET is the evapotranspiration (MJ / m³). -2 d -1 ), where transpiration and evaporation are E and T, respectively. e (MJ m -2 d -1 PM c and PM s Evapotranspiration (MJ m³) under closed canopy and bare soil conditions, respectively. -2 d -1 ), C c and C s It is the corresponding proportionality coefficient; R s R c R a The variable is an intermediate variable with no definite meaning; D0 is the saturated vapor pressure difference (kPa) at the canopy height; r s c It is the canopy boundary layer drag (ms) -1 );r a c It is the aerodynamic drag from the canopy to the interior of the canopy (m / s). -1 );r a a Aerodynamic drag (m / s) from reference height to average canopy flux height -1 );r a s The aerodynamic drag (m / s) from the average height of canopy flux to the ground surface -1 );r s s It is surface resistance (ms)-1 );A and A s Available energy reaching the underlying surface and soil surface (MJ m) -2 d -1 ), calculate according to the following formula:

[0028] A = R n -G

[0029] A s =R ns -G

[0030] In the formula, G is the soil heat flux (MJm). -2 d -1 ), R ns The net radiation reaching the Earth's surface (MJ m -2 d -1 ), calculated according to the following formula:

[0031] R ns =R n ×exp(-C d ×LAI)

[0032] In the formula: R n It is the net radiation at the top of the canopy, and its unit is MJ / m². -2 d -1 C d The dynamic extinction coefficient is dimensionless; LAI is the canopy leaf area index, with units of m². 2 m -2 .

[0033] Optionally, the mathematical analysis method for identifying the main controlling factor of the extinction coefficient in step B can be selected from one or more of the following: regression analysis, principal component analysis, path analysis, redundancy analysis, structural equation modeling, and enhanced regression tree modeling.

[0034] Optionally, the calculation methods for each resistance in steps D1 and D2 adopt the commonly used methods recommended in relevant studies of the Penman-Monteith model and the Shuttleworth-Wallace model, respectively, and various suitable correction formulas are used according to actual conditions without special treatment.

[0035] Optionally, the Penman-Monteith model in step D1 is suitable for simulating only canopy transpiration T. e In this case, although the Penman-Monteith model is also often used to simulate farmland evapotranspiration (ET), its formula does not require an extinction coefficient to distinguish between canopy interception energy and soil interception energy. Therefore, when the Penman-Monteith model is used for ET simulation, the dynamic extinction coefficient cannot be used.

[0036] Optionally, the Shuttleworth-Wallace model in step D2 is suitable for simultaneously simulating evapotranspiration ET and decomposing ET into transpiration T. e And the situation regarding evaporation rate E.

[0037] Optionally, only one of steps D1 and D2 needs to be selected, when only the canopy transpiration T is simulated. e Under the given conditions, select step D1; when ET needs to be simulated and component separation is required, select step D2.

[0038] In summary, the beneficial effects of this application are as follows: It identifies the main controlling factors of canopy extinction coefficient changes; it constructs a quantitative characterization function for the dynamic change law of canopy extinction coefficient based on the main controlling factors; and it nests this function into a single-source Penman-Monteith model or a dual-source Shuttleworth-Wallace model to replace the conventional fixed-value scheme for extinction coefficient, thereby estimating farmland evapotranspiration and its components (soil evaporation and crop transpiration). This invention achieves accurate quantitative characterization of the dynamic change law of extinction coefficient. Compared with the traditional fixed-value scheme, although it has a small improvement in the simulation effect of total evapotranspiration, it can effectively improve the accuracy of evapotranspiration component breakdown, that is, improve the accuracy of the ratio of evaporation to transpiration. The effect has been verified to be stable and reliable in multiple locations. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of the calculation process of the present invention. Detailed Implementation

[0041] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0042] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0043] See Figure 1 This invention provides a method for calculating evapotranspiration and separating components based on the dynamic canopy extinction coefficient, comprising the following steps:

[0044] Step 1: Obtain the dynamic variation law of the extinction coefficient.

[0045] In this step, a radiation sensor can be used to periodically and repeatedly measure the intensity of incident radiation above the canopy and the intensity of penetrating radiation below the canopy during the day, and the extinction coefficient of the canopy at each stage can be calculated according to Beer's Law.

[0046]

[0047] In the formula, C is the extinction coefficient, and PAR is the extinction coefficient. in and PAR tr These represent the incident radiation intensity above the canopy and the penetrating radiation intensity below the canopy, respectively, both in MJ / m². -2 d -1 LAI stands for Leaf Area Index, and its unit is m². 2 m -2 .

[0048] Step 2: Identify the main control factor of the extinction coefficient.

[0049] In this step, the methods for identifying the controlling factors include, but are not limited to, regression analysis, principal component analysis, path analysis, redundancy analysis, and structural equation modeling. The weighting coefficients in the mathematical analysis are used to determine whether the controlling factors and their correlation with the extinction coefficient are positive or negative. Potential factors include, but are not limited to, leaf area index (LAI) and net radiation (R). n Temperature T a (Relative humidity RH, soil moisture content SW, saturated vapor pressure difference VPD, etc.)

[0050] Step 3, construct the dynamic function C of the extinction coefficient. d .

[0051] In this step, the extinction coefficient dynamic function C d Calculate according to the following formula:

[0052]

[0053] In the formula, C d f is the extinction coefficient; n The nth controlling factor of the extinction coefficient is used. Factors positively correlated with the extinction coefficient are the factor itself (such as f1 and f2), and factors negatively correlated with the extinction coefficient are the reciprocal of the factor (such as f3). a, b, c and d are parameters to be determined, where b, c and d represent the sensitivity coefficients of the factors corresponding to their bases.

[0054] Step 4: Water consumption simulation.

[0055] In this step, the dynamic extinction coefficient formula C dThe Penman-Monteith model is introduced to replace the extinction coefficient constant parameter C, and the evapotranspiration water consumption T is calculated. e , or C d The Shuttleworth-Wallace model is introduced to replace the extinction coefficient constant parameter C, and the evapotranspiration ET and its component evapotranspiration water consumption T are calculated. e And soil evaporation E. T is calculated based on the Penman-Monteith model. e as follows:

[0056]

[0057] In the formula: T e It is the transpiration rate (MJ / m³) -2 d -1 ); △ represents the slope of the saturated vapor pressure versus temperature curve (kPa℃). -1 ); R nc Net radiation intercepted by the canopy (MJ m -2 d -1 G represents soil heat flux (MJ / m³). -2 d -1 ); ρ is the air density (g / mm²). -3 );c p It is the specific heat at constant pressure (MJ kg) -1 ℃ -1 ); γ is the hygrometer constant (kPa℃) -1 VPD is the saturated vapor pressure difference (kPa); r c It is the canopy impedance (Sm -1 );r a It is aerodynamic impedance (Sm -1 Net radiation R intercepted by the canopy nc Calculate according to the following formula:

[0058] R nc =R n ×(1-exp(-C d ×LAI))

[0059] In the formula: R n Net radiation at the top of the canopy (MJ m) -2 d -1 );C d The extinction coefficient (dimensionless) is calculated using the dynamic function of the extinction coefficient as described above; LAI is the canopy leaf area index (m²). 2 m -2 ).

[0060] Aerodynamic impedance r a The field conditions are calculated using the following formula:

[0061]

[0062] Where: h c z is the canopy height (m); z is the reference height (m); u is the wind speed at the reference height (m / s). -1 ); k is the Karman constant (value 0.40); z0 is the momentum transport roughness length (m); d is the zero-plane displacement (m). Greenhouse conditions or other special conditions r a Appropriate calculation methods or targeted corrections are required.

[0063] Canopy impedance r c Using Jarvis class methods, calculate according to the following formula:

[0064]

[0065] In the formula: rst min The minimum stomatal resistance (sm) that may occur in the leaves within the canopy under ideal conditions. -1 ); LAI e X represents the effective leaf area index; i This represents the environmental factors that affect canopy impedance; F i (Xi) represents environmental factor X. i The constraint function for canopy impedance, with respect to photosynthetically active radiation (PAR), air temperature (Ta), saturated vapor pressure difference (VPD), and soil moisture content (SWC), is expressed as follows:

[0066]

[0067] In the formula: B is the asymptotic value of porosity at infinite radiation (Wm) -2 );T opt The optimal temperature for evapotranspiration (°C); VPD opt The optimal VPD (kPa) for transpiration is given; k1 and k2 are empirical coefficients; s is the soil moisture deficit corresponding to the start of decreased stomatal conductance; f0 is the degree of stomatal opening corresponding to a soil moisture deficit of 1; SMD is the soil moisture deficit calculated as (SW) max -SW) / (SW max -SW min ), where SW max and SW min These represent the maximum and minimum water content in the root zone, respectively.

[0068] Evapotranspiration ET and its component transpiration water consumption T were calculated based on the Shuttleworth-Wallace model. e Soil evaporation E is calculated using the following formula:

[0069] ET=Cc PM c +C s PM s

[0070]

[0071] In the formula, ET is the evapotranspiration (MJ / m³). -2 d -1 ), where transpiration and evaporation are E and T, respectively. e (MJ m -2 d -1 PM c and PM s Evapotranspiration (MJ m³) under closed canopy and bare soil conditions, respectively. -2 d -1 ), C c and C s It is the corresponding proportionality coefficient; R s R c R a The variable is an intermediate variable with no definite meaning; D0 is the saturated vapor pressure difference (kPa) at the canopy height; r s c It is the canopy boundary layer drag (ms) -1 );r a c It is the aerodynamic drag from the canopy to the interior of the canopy (m / s). -1 );r a a Aerodynamic drag (m / s) from reference height to average canopy flux height -1 );r a s The aerodynamic drag (m / s) from the average height of canopy flux to the ground surface -1 );r s s It is surface resistance (ms) -1 );A and A s Available energy reaching the underlying surface and soil surface (MJ m) -2 d -1 ), calculate according to the following formula:

[0072] A = R n -G

[0073] A s =R ns -G

[0074] In the formula, G is the soil heat flux (MJ / m³). -2 d -1 ), R nsThe net radiation reaching the Earth's surface (MJ m -2 d -1 ), calculated according to the following formula:

[0075] R ns =R n ×exp(-C d ×LAI)

[0076] In the formula: R n It is the net radiation at the top of the canopy, and its unit is MJ / m². -2 d -1 C d The dynamic extinction coefficient is dimensionless; LAI is the canopy leaf area index, with units of m². 2 m -2 .

[0077] Canopy resistance r s c Using Jarvis class methods, calculate according to the following formula:

[0078]

[0079] In the formula: rst min The minimum stomatal resistance (sm) that may occur in the leaves within the canopy under ideal conditions. -1 ); LAI e X represents the effective leaf area index; i This represents the environmental factors that affect canopy impedance; F i (Xi) represents environmental factor X. i The constraint function for canopy impedance, with respect to photosynthetically active radiation (PAR), air temperature (Ta), saturated vapor pressure difference (VPD), and soil moisture content (SWC), is expressed as follows:

[0080]

[0081] In the formula: B is the asymptotic value of porosity at infinite radiation (Wm) -2 );T opt The optimal temperature for evapotranspiration (°C); VPD opt The optimal VPD (kPa) for transpiration is given; k1 and k2 are empirical coefficients; s is the soil moisture deficit corresponding to the beginning of a decrease in stomatal conductance; f0 is the degree of stomatal opening corresponding to a soil moisture deficit of 1; SMD is the soil moisture deficit calculated using the formula (SWC). max -SWC) / (SWC max -SWC min ), of which SWC max and SWC min These represent the maximum and minimum water content in the root zone, respectively.

[0082] Surface resistance r s s Calculate using the following formula:

[0083]

[0084] In the formula, rss min Minimum surface resistance (ms) -1 );θ F 1 is field water holding capacity (%); swb is surface soil moisture content.

[0085] Aerodynamic drag r a c r a s and r a a Calculate using the following formulas respectively:

[0086]

[0087] In the formula: u h Wind speed at canopy height (ms) -1 ); w is the typical blade width (m); n is the eddy current diffusion attenuation constant; h c It is the average canopy height (m).

[0088]

[0089] k h =ku * (h c -d0)

[0090]

[0091] z0=min{0.3(h c -d0),Z 0g +0.3h c (c d LAI) 0.5}

[0092]

[0093] In the formula: z a It is the reference height; u h The wind speed at the reference altitude (m / s) -1 );C d K is the drag coefficient per unit blade. h It is the eddy diffusion coefficient (m 2 s -1 );Z 0g It is the surface roughness (m); u *Friction speed (ms) -1 ).

[0094] Example 1:

[0095] The experiment was conducted from May 2020 to May 2021 in Xinping County, Yuxi City, Yunnan Province (24°03′N-101°35′E), located in the Yuanjiang dry-hot valley, with a subtropical dry-hot climate and arid red soil. A typical economic orange orchard (2×3m spacing) was used as the research object, with the sweet orange variety as the study object. Intermittent supplementary drip irrigation was only applied during the dry season (January-March), with rain-fed trees during the remaining time. The orange trees are evergreen and do not shed their leaves throughout the year, exhibiting vigorous growth and relatively small fluctuations in leaf area index.

[0096] Example 2:

[0097] The experiment was conducted from April to October 2022 in Luochuan County, Yan'an City, Shaanxi Province (35°26′N, 109°13′E), located on the Loess Plateau with a temperate continental climate and medium loam soil. A typical rain-fed apple orchard (2×4m spacing) in this region was used as the research subject, with the variety being Yanchang Red Fuji. Apple trees are deciduous trees, and their leaf area index fluctuates significantly during the growth period, being low and growing rapidly in the early stages, then stabilizing in the middle and later stages.

[0098] Example 3:

[0099] The experiment was conducted from April to October 2022 in Yangling District, Shaanxi Province (34°27′N-108°20′E), located in the Guanzhong Plain, with a warm temperate semi-humid climate and silty loam soil. A typical vineyard in this area (planted from south to north, with a spacing of 0.8 × 3 m) was used as the research subject, with the variety being Black Sugar. The trellis system was a single-frame trellis, 1.5 m high, with cement posts spaced 3.5 m apart in each row, and three steel wires running through the top, middle, and bottom. The vineyard employed drip irrigation for thorough irrigation management, maintaining soil moisture content above 75% field capacity. Regular pruning maintained a relatively uniform height and crown size. The plants are deciduous fruit trees, and the leaf area index fluctuated significantly during the growth period, exhibiting a unimodal pattern of low leaf area in the early and late stages and high leaf area in the middle stage.

[0100] In the three examples above, Examples 1 and 2 used the Penman-Monteith model to estimate hourly evapotranspiration (evapotranspiration of apple and orange trees was determined using the heat ratio and heat diffusion methods, respectively). Example 3 used the Shuttleworth-Wallace model to estimate daily evapotranspiration (ET) and soil evaporation (E). All three examples used the extinction coefficient fixed-value model and the existing ZL 2023 1 1323337.1 extinction coefficient dynamic model as benchmarks for comparison. Parameter calibration and optimization were performed using Bayesian analysis, and posterior distribution sampling employed the Markov Chain Monte Carlo (MCMC) method based on Gibbs sampling. The model comparison process was conducted based on accuracy, using the coefficient of determination (R²). 2 The metrics used are relative error (MRE).

[0101] As shown in Table 1, the hourly evapotranspiration water consumption estimated by this invention is more accurate than that of the Penman-Monteith model under the extinction coefficient constant value model and the ZL2023 1 1323337.1 extinction coefficient dynamic model. For orange orchards and apple orchards, R 2 The extinction coefficients were increased from 0.54 and 0.52 in the fixed extinction coefficient scheme to 0.64 and 0.65 in the dynamic extinction coefficient scheme of ZL 2023 1 1323337.1, and further increased to 0.70 in the dynamic extinction coefficient scheme of this invention. Meanwhile, the relative error (MRE) decreased from 33.35% and 32.10% in the fixed extinction coefficient scheme to 21.58% and 17.15% in the dynamic extinction coefficient scheme of ZL 2023 1 1323337.1, and further decreased to 16.83% and 13.51% in the dynamic extinction coefficient scheme of this invention.

[0102] Furthermore, the accuracy of the estimated daily evapotranspiration ET in this invention is not significantly different from that of the Shuttleworth-Wallace model under the extinction coefficient constant value model and the extinction coefficient dynamic model of ZL 2023 11323337.1. However, the accuracy of the estimated daily evaporation E is significantly better than that of the extinction coefficient constant value model and the extinction coefficient dynamic model of ZL 2023 1 1323337.1. For the estimation of vineyard evaporation, R 2 The extinction coefficient was increased from 0.54 in the fixed extinction coefficient scheme to 0.80 in the dynamic extinction coefficient scheme of ZL 2023 1 1323337.1, and further increased to 0.83 in the dynamic extinction coefficient scheme of this invention. Meanwhile, the relative error (MRE) decreased from 32.49% in the fixed extinction coefficient scheme to 16.67% in the dynamic extinction coefficient scheme of ZL 2023 1 1323337.1, and further decreased to 14.23% in the dynamic extinction coefficient scheme of this invention.

[0103] The three examples above cover different climate types (hot and dry, semi-arid, semi-humid), crop types (oranges, apples, grapes), terrains (mountains, dry plateaus, plains), and time scales (daily and hourly), which can fully demonstrate the effects of the present invention. Comparatively, the present invention performs better in hourly-scale evapotranspiration simulation, significantly better than the method described in ZL202311323337.1, and better than the scheme with a fixed extinction coefficient. At the daily scale, the present invention still performs best, but the difference compared to the method described in ZL 202311323337.1 is not as significant as at the hourly scale. However, it demonstrates high stability and reliability in effectively ensuring the separation of ET components.

[0104] Table 1. Comparison of the estimation effects of the present invention, the extinction coefficient setting scheme, and the existing dynamic extinction coefficient setting scheme for transpiration or evaporation.

[0105]

[0106] Therefore, the present invention has the following beneficial effects:

[0107] I. This invention establishes a dynamic function of the extinction coefficient based on the principal controlling factors of the extinction coefficient identified by mathematical analysis methods. This function is then introduced into the Penman-Monteith equation or the Shuttleworth-Wallace equation. By correcting the canopy energy interception term and the soil energy interception term, the method achieves accurate estimation of evapotranspiration and soil evaporation. While this method does not significantly improve the simulation effect on the total evapotranspiration (ET), it can significantly improve the separation effect of ET components, specifically the canopy evapotranspiration (T) in ET. e The calculation accuracy of soil evaporation E has been significantly improved.

[0108] Second, the proposed method effectively considers the objective influence of environmental factors and vegetation growth status on the extinction coefficient. The proposed dynamic characterization function of the extinction coefficient breaks through the defect of setting the extinction coefficient as a fixed value in the traditional evapotranspiration model. The theoretical basis is more sufficient, and the estimation accuracy of transpiration and evaporation is significantly improved. This is conducive to improving agricultural irrigation efficiency and providing a more reliable basis for efficient water resource management.

[0109] Third, compared with existing methods for dynamically representing the extinction coefficient that only consider leaf area index in water consumption calculations, the method described above simultaneously considers the influence of leaf area index and environmental factors on the extinction coefficient, thus providing a more comprehensive representation of the dynamic changes in the extinction coefficient. Compared with the existing dynamic extinction coefficient representation method ZL202311323337.1, which simultaneously considers leaf area index and environmental factors, this method, by employing independent adjustment coefficients for different influencing factors, can take into account the differences in sensitivity of different factors to the extinction coefficient. It performs better when applied to conditions where the influence of various factors on the extinction coefficient varies significantly (e.g., on an hourly scale). In fact, the existing dynamic extinction coefficient representation method ZL 202311323337.1 uses a common adjustment coefficient for the main control factors, which is a special case of the method described in this invention. That is, when the influence of each main control factor on the extinction coefficient is relatively similar, the independent adjustment coefficients of each factor are approximately equal. In this case, the calculation results of the method described in this invention are almost identical to those of the method described in ZL202311323337.1. The existing method for dynamically characterizing the extinction coefficient described in ZL 202311323337.1 performs significantly better than the fixed-value scheme for extinction coefficient in daily-scale water consumption simulation. However, the method described in this invention is superior in hourly-scale farmland water consumption and component decomposition. Furthermore, the method described in this invention can also be used for daily-scale correlation calculations, with performance at least on par with the method described in ZL 202311323337.1. In summary, the method described in this invention has greater versatility and wider applicability.

[0110] The above description is merely a preferred embodiment of this application and an explanation of the technical principles and other solutions employed. Furthermore, the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A method for calculating evapotranspiration and separating components based on dynamic canopy extinction coefficient, characterized in that, The method includes the following steps: Step A: As the reproductive period progresses, the intensity of incident radiation above the canopy and the intensity of penetrating radiation below the canopy are measured regularly and multiple times during the day using a radiation sensor. The extinction coefficient of the canopy at each stage is calculated according to Beer's Law. In the formula, C is the extinction coefficient, and PAR is the extinction coefficient. in and PAR tr These represent the incident radiation intensity above the canopy and the penetrating radiation intensity below the canopy, respectively, both in MJ / m². -2 d -1 LAI stands for Leaf Area Index, and its unit is m². 2 m -2 ; Step B: Use mathematical methods to analyze the relationship between leaf area index (LAI) and major environmental factors and C, and determine whether the main controlling factors of C and the correlation between C and each main controlling factor are positive or negative; Step C: Construct a dynamic extinction coefficient function using the master control factor. Based on the positive and negative values ​​of the relevant factors obtained in Step B, factors positively correlated with C are represented by the factor itself, while factors negatively correlated with C are represented by their reciprocals. Then, the extinction coefficient C is calculated using the following formula. d Dynamic change pattern: In the formula, C d f is the extinction coefficient. n is the nth principal control factor of the extinction coefficient, and a, b, c and d are parameters to be determined, where b, c and d represent the sensitivity coefficients of the factors corresponding to their bases; For crops with large variations in leaf area index (LAI), when soil moisture content (SWC) and net radiation (R) are high... n When the extinction coefficient is also the controlling factor, the expression for the dynamic extinction coefficient C is as follows: Step D1: Apply formula C d The Penman-Monteith model is used to replace the extinction coefficient constant parameter C to calculate the evapotranspiration water consumption T. e : In the formula: T e This is canopy transpiration, measured in MJ / m³. -2 d -1 △ represents the slope of the saturated vapor pressure versus temperature curve, in kPa℃. -1 ;R nc Net radiation intercepted by the canopy, in MJ / m². -2 d -1 G represents soil heat flux, measured in MJ / m³. -2 d -1 ρ is the density of air, with units of g / mm³. -3 c p It is the specific heat at constant pressure, and the unit is MJ / kg. -1 ℃ -1 γ is the hygrometer constant, with units of kPa℃. -1 VPD is the saturated vapor pressure difference, measured in kPa; r c This is canopy resistance, measured in sm. -1 ;r a It is aerodynamic drag, measured in sm. -1 Net radiation R intercepted by the canopy nc Calculate according to the following formula: R nc =R n ×(1-exp(-C d ×LAI)); In the formula: R n It is the net radiation at the top of the canopy, and its unit is MJ / m². -2 d -1 C d The dynamic extinction coefficient is dimensionless; LAI is the canopy leaf area index, with units of m². 2 m -2 ; Step D2: Apply formula C d The Shuttleworth-Wallace model is introduced to replace the extinction coefficient constant parameter C, and the evapotranspiration ET and its component evapotranspiration water consumption T are calculated. e And soil evaporation E: ET=C c PM c +C s PM s In the formula, ET is the evapotranspiration rate, MJ / m -2 d -1 The transpiration and evaporation rates are E and T, respectively. e MJ m -2 d -1 PM c and PM s Evapotranspiration under closed canopy and bare soil conditions, respectively, in MJ / m³. -2 d -1 C c and C s It is the corresponding proportionality coefficient; R s R c R a The variable is an intermediate variable with no definite meaning; D0 is the saturated vapor pressure difference at the canopy height, in kPa; r s c It is the canopy boundary layer resistance, ms -1 ;r a c It is the aerodynamic drag from the canopy to the interior of the canopy, in milliseconds (ms). -1 ;r a a The aerodynamic drag from the reference height to the average height of the canopy flux, in milliseconds (ms) -1 ;r a s It is the aerodynamic drag from the average height of canopy flux to the ground surface, in milliseconds. -1 ;r s s It is surface resistance, ms -1 ;A and A s Available energy reaching the underlying surface and soil surface, respectively, in MJ m -2 d -1 Calculate according to the following formula: A=R n -G A s =R ns -G In the formula, G is the soil heat flux, MJ / m³. -2 d -1 ;R ns It is the net radiation reaching the Earth's surface, MJ m -2 d -1 Calculate according to the following formula: R ns =R n ×exp(-C d ×LAI) In the formula: R n It is the net radiation at the top of the canopy, and its unit is MJ / m². -2 d -1 C d The dynamic extinction coefficient is dimensionless; LAI is the canopy leaf area index, with units of m². 2 m -2 .

2. The method for calculating evapotranspiration and separating components based on dynamic canopy extinction coefficient as described in claim 1, characterized in that, Canopy transpiration T based on the Penman-Monteith model e The simulation method, or based on the Shuttleworth-Wallace model, farmland evapotranspiration ET and its components T e The simulation method for E, in step B, involves selecting one or more mathematical analysis methods to identify the controlling factor of the extinction coefficient from regression analysis, principal component analysis, path analysis, redundancy analysis, structural equation modeling, and enhanced regression tree model.

3. The method for calculating evapotranspiration and separating components based on dynamic canopy extinction coefficient as described in claim 1, characterized in that, Canopy transpiration T based on the Penman-Monteith model e The simulation method, or based on the Shuttleworth-Wallace model, farmland evapotranspiration ET and its components T e The simulation method for E, the calculation methods for each resistance in steps D1 and D2 respectively adopt the commonly used methods recommended in relevant studies of the Penman-Monteith model and the Shuttleworth-Wallace model, and various correction formulas are adopted according to actual conditions.

4. The method for calculating evapotranspiration and separating components based on dynamic canopy extinction coefficient as described in claim 1, characterized in that, Based on canopy transpiration water consumption T e The simulation method, in step D1, the Penman-Monteith model is suitable for simulating only canopy evapotranspiration. Although the Penman-Monteith model is also often used to simulate farmland evapotranspiration (ET), the formula does not require an extinction coefficient to distinguish between canopy intercepted energy and soil intercepted energy. Therefore, when the Penman-Monteith model is used for ET simulation, the dynamic extinction coefficient cannot be used.

5. The method for calculating evapotranspiration and separating components based on dynamic canopy extinction coefficient as described in claim 1, characterized in that, Based on farmland evapotranspiration ET and its component T e The simulation method for E, wherein the Shuttleworth-Wallace model in step D2 is suitable for simultaneously simulating evapotranspiration ET and decomposing ET into transpiration T e And the situation regarding evaporation rate E.

6. The method for calculating evapotranspiration and separating components based on dynamic canopy extinction coefficient as described in claim 1, characterized in that, Evapotranspiration T based on the Penman-Monteith model e The simulation method, or the evapotranspiration ET and its components T based on the Shuttleworth-Wallace model. e The simulation method for E involves selecting only one of steps D1 and D2. Step D1 is selected when only canopy transpiration is simulated, while step D2 is selected when ET needs to be simulated and its components are separated.

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