Dynamic canopy extinction coefficient-based evapotranspiration calculation and component splitting method

Abstract

The invention discloses an evapotranspiration calculation and component splitting method based on a dynamic canopy extinction coefficient, which is applied to the field of farmland crop irrigation and comprises the following steps: judging a main control factor of canopy extinction coefficient change; constructing a canopy extinction coefficient dynamic change rule quantitative characterization function based on the main control factor; the method comprises the following steps of: nesting a single-source Penman-Monteith model or a double-source Shuttleworth-Wallace model to replace a conventional extinction coefficient fixed value scheme, and further estimating the evapotranspiration of the farmland and components (soil evaporation and crop evaporation) of the evapotranspiration of the farmland, wherein the evapotranspiration of the farmland and the components of the evapotranspiration of the farmland are the soil evaporation and the crop evaporation. According to the method, accurate quantitative characterization of the dynamic change rule of the extinction coefficient is achieved, compared with a traditional constant value taking scheme, although the total evapotranspiration simulation effect is slightly improved, the component splitting accuracy of the evapotranspiration can be effectively improved, that is, the accuracy of the evaporation capacity and the ratio of the evapotranspiration is improved, and the effect is stable and reliable through verification in many places.

Description

Technical Field

[0001] The present invention relates to the field of farmland crop irrigation, and in particular to a method for calculating evapotranspiration and separating components based on a dynamic canopy extinction coefficient. Background Art

[0002] Evapotranspiration (ET) is the core link in the water-carbon process of the soil-plant-atmosphere continuum, which consists of soil evaporation (E) and vegetation transpiration (T e The former is often considered to be ineffective water consumption in farmland, while the latter is often considered to be productive water loss because it is closely related to yield formation. Both are important aspects of agricultural water resources management. e The proportion of ET varies greatly. It is necessary to accurately estimate ET and divide the sub-items E and T e Accurate separation plays an important role in evaluating the effectiveness of farmland water consumption, formulating irrigation systems and estimating yields.

[0003] Current research shows that commonly used ET simulation and component separation models, such as the two-source Shuttleworth-Wallace model, work well in ET estimation, but are of course less effective in separating ET components. In many classic ET models, the water consumption calculation results rely heavily on available energy. For example, when calculating canopy transpiration T e When the available energy is the net radiation intercepted by the canopy, the remaining available energy drives soil evaporation E. The extinction coefficient (C) characterizes the degree of radiation interception by the canopy. A smaller value indicates more radiation penetrates the canopy and reaches the soil, leading to higher evaporation. Conversely, a higher value indicates more radiation is intercepted by the canopy, leading to higher transpiration. Therefore, accurately assessing C is crucial for ensuring a balanced energy distribution between the canopy and the soil.

[0004] However, due to the lack of actual measured data on C, scholars' understanding of C is still 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 changes with the season, but also changes within the day. Affected by many factors such as growth status and environmental conditions, the C value usually varies between 0.3 and 1.5. The reason is that environmental conditions will change the canopy structure characteristics by changing the leaf inclination angle, leaf distribution, etc., thereby causing changes in radiation interception. Under many conditions, the output results of the ET model are highly sensitive to the C value. Ignoring the dynamic changes in the C value is not conducive to the accurate estimation of ET and its components.

[0005] While existing evapotranspiration estimation research provides a quantitative method for characterizing the dynamic changes in the extinction coefficient, by increasing the consideration of the impact of environmental factors on transpiration water consumption, this method first constructs a comprehensive factor based on 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 been found to be effective in calculating water consumption on a daily scale, but it lacks accuracy when used for hourly water consumption calculations. Summary of the Invention

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

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] A method for calculating evapotranspiration and separating its components based on the dynamic canopy extinction coefficient includes:

[0009] Step A: As the growth period progresses, use a radiation sensor to regularly measure the incident radiation intensity above the canopy and the penetrating radiation intensity below the canopy multiple times a day, and calculate the canopy extinction coefficient at each stage according to Beer's law.

[0010]

[0011] Where C is the extinction coefficient, PAR in and PAR tr are the incident radiation intensity above the canopy and the penetrating radiation intensity below the canopy, both in MJ m -2 d -1 , LAI is the leaf area index, its unit is m 2 m -2 .

[0012] Step B: Use mathematical methods to analyze the relationship between leaf area index (LAI), 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: Use the master control factor to construct a dynamic extinction coefficient function. According to the positive and negative correlation factors obtained in step B, the factor that is positively correlated with C uses the factor itself, and the factor that is negatively correlated with C uses the inverse form of the factor. Then, the extinction coefficient C is calculated using the following formula: d Dynamic change rules:

[0014]

[0015] Where C d is the extinction coefficient, f nis the nth main controlling factor of the extinction coefficient, a, b, c and d are unknown parameters, where b, c and d represent the sensitivity coefficients of the factors corresponding to their bases respectively;

[0016] For example, for crops with large leaf area index (LAI), when soil water content (SWC) and net radiation (R) n When is also the main controlling factor of the extinction coefficient, the expression of the dynamic extinction coefficient C is as follows:

[0017]

[0018] Note: In general, the higher the SWC, the greater the C (positive correlation), on the contrary, LAI or R n The larger , the smaller C (negative correlation).

[0019] Step D1: Replace Formula C d The following Penman-Monteith model is introduced to replace the extinction coefficient constant parameter C to obtain the transpiration water consumption T e :

[0020]

[0021] Where: T e is the canopy transpiration, and its unit is MJm -2 d -1 ; △ is the slope of the saturated water vapor pressure and temperature curve, its unit is kPa℃ -1 ; R nc is the net radiation intercepted by the canopy, with the unit being MJm -2 d -1 ; G is the soil heat flux, its unit is MJm -2 d -1 ; ρ is the air density, its unit is gmm -3 ;c p is the specific heat at constant pressure, and its unit is MJkg -1 ℃ -1 ;γ is the hygrometer constant, its unit is kPa℃ -1 ; VPD is the saturated vapor pressure difference, its unit is kPa; r c is the canopy resistance, its unit is sm -1 ; r a is the aerodynamic drag, its unit is sm -1 ; Net radiation intercepted by the canopy R nc Calculate according to the following formula:

[0022] R nc =R n ×(1-exp(-C d ×LAI));

[0023] Where: R n is the net radiation at the top of the canopy, with the unit being MJm -2 d -1 ; C d is the dynamic extinction coefficient, dimensionless; LAI is the canopy leaf area index, its unit is m 2 m -2 .

[0024] Step D2: Replace Formula C d The following Shuttleworth-Wallace model is introduced to replace the extinction coefficient constant parameter C to obtain the evapotranspiration ET and its component transpiration water consumption T e and soil evaporation E;

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

[0026]

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

[0028] A=R n -G

[0029] A s =R ns -G

[0030] Where G is the soil heat flux (MJm -2 d -1 ), R ns is the net radiation reaching the surface (MJ m -2 d -1 ), calculated as follows:

[0031] R ns =R n ×exp(-C d ×LAI)

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

[0033] Optionally, the mathematical analysis method for identifying the main controlling factors of the extinction coefficient in step B can be selected from one or more of regression analysis, principal component analysis, path analysis, redundancy analysis, structural equation model, boosted regression tree model, etc.

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

[0035] Optionally, the Penman-Monteith model in step D1 is suitable for simulating only the canopy transpiration T e In this case, although the Penman-Monteith model is also commonly used to simulate farmland evapotranspiration (ET), its 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.

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

[0037] Optionally, only one of the steps D1 and D2 can be selected. When only simulating the canopy transpiration T e Select step D1 if necessary, and select D2 if ET simulation and component separation are required.

[0038] In summary, the beneficial effects of the present application are: identifying the main controlling factors of the canopy extinction coefficient change; constructing a quantitative characterization function of the dynamic change law of the canopy extinction coefficient based on the main controlling factors; embedding it into a single-source Penman-Monteith model or a dual-source Shuttleworth-Wallace model to replace the conventional fixed value scheme of the extinction coefficient, and then estimating the farmland evaporation and its components (soil evaporation and crop transpiration). The present invention realizes the accurate quantitative characterization of the dynamic change law of the extinction coefficient. Compared with the traditional fixed value scheme, although the improvement in the simulation effect of the total evaporation is small, it can effectively improve the accuracy of the component separation of the evaporation, that is, improve the accuracy of the ratio of evaporation to transpiration. The effect has been verified to be stable and reliable in many places. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 Schematic diagram of the calculation process of the present invention. DETAILED DESCRIPTION

[0041] The present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the relevant invention and are not intended to limit the invention. It should also be noted that, for ease of description, only portions relevant to the invention are shown in the accompanying drawings.

[0042] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0043] See also Figure 1 The embodiment of the present invention provides a method for calculating evapotranspiration and separating components based on a 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 regularly measure the incident radiation intensity above the canopy and the penetrating radiation intensity below the canopy multiple times during the day, and the canopy extinction coefficient at each stage can be calculated according to the following Beer's law:

[0046]

[0047] Where C is the extinction coefficient, PAR in and PAR tr are the incident radiation intensity above the canopy and the penetrating radiation intensity below the canopy, both in MJ m -2 d -1 , LAI is the leaf area index, its unit is m 2 m -2 .

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

[0049] In this step, the main control factor identification method includes but is not limited to regression analysis, principal component analysis, path analysis, redundancy analysis, structural equation model, etc., and the main control factor and the correlation between each main control factor and the extinction coefficient are determined by the weight coefficient in the mathematical analysis. Potential factors include but are not limited to leaf area index LAI, net radiation R n , temperature T a , relative humidity RH, soil moisture content SW, saturated water vapor pressure difference VPD, etc.).

[0050] Step 3: Construct the extinction coefficient dynamic function C d .

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

[0052]

[0053] Where C d is the extinction coefficient; f n is the nth main controlling factor of the extinction coefficient. Factors positively correlated with the extinction coefficient are the factors themselves (e.g., f1 and f2), while factors negatively correlated with the extinction coefficient are the reciprocals of these factors (e.g., f3). a, b, c, and d are undetermined parameters, where b, c, and d represent the sensitivity coefficients of the factors corresponding to their bases, respectively.

[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 to obtain the transpiration water consumption T e , or C d The Shuttleworth-Wallace model is introduced to replace the extinction coefficient constant parameter C to obtain the evapotranspiration ET and its component transpiration water consumption T. e and soil evaporation E. Among them, T is calculated based on the Penman-Monteith model e as follows:

[0056]

[0057] Where: T e is the transpiration rate (MJ m -2 d -1 ); △ is the slope of the saturated water vapor pressure and temperature curve (kPa℃ -1 );R nc is the net radiation intercepted by the canopy (MJ m -2 d -1 ); G is soil heat flux (MJ m -2 d -1 ); ρ is the air density (g mm -3 );c p 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 is the canopy impedance (sm -1 );r a is the aerodynamic impedance (sm -1 ). Net radiation intercepted by the canopy R nc Calculate according to the following formula:

[0058] R nc =R n ×(1-exp(-C d ×LAI))

[0059] Where: R n is the net radiation at the top of the canopy (MJ m -2 d -1 );C d is the extinction coefficient (dimensionless), which is calculated using the above formula of the extinction coefficient dynamic function; LAI is the canopy leaf area index (m 2 m -2 ).

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

[0061]

[0062] Where: h c is the canopy height (m); z is the reference height (m); u is the wind speed at the reference height (ms -1 ); k is the Karman constant (valued at 0.40); z0 is the momentum transfer roughness length (m); d is the zero plane displacement (m). Greenhouse conditions or other special conditions r a Appropriate calculation methods or targeted corrections need to be adopted.

[0063] Canopy impedance r c The Jarvis method is used and calculated according to the following formula:

[0064]

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

[0066]

[0067] Where: B is the asymptotic value of stomatal conductance when the radiation is infinite (Wm -2 );T opt is the optimum temperature for transpiration (℃); VPD opt is the optimum VPD for transpiration (kPa); k1 and k2 are empirical coefficients; s is the soil water deficit corresponding to the start of stomatal conductance decrease; f0 is the stomatal opening degree corresponding to the soil water deficit reaching 1; SMD is the soil water deficit calculated as (SW max -SW) / (SW max -SW min ), where SW max and SW min are the maximum and minimum water contents in the root zone, respectively.

[0068] Based on the Shuttleworth-Wallace model, evapotranspiration ET and its component transpiration water consumption T were calculated. e And soil evaporation E is calculated according to the following formula:

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

[0070]

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

[0072] A=R n -G

[0073] A s =R ns -G

[0074] Where G is the soil heat flux (MJ m -2 d -1 ), R nsis the net radiation reaching the surface (MJ m -2 d -1 ), calculated as follows:

[0075] R ns =R n ×exp(-C d ×LAI)

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

[0077] Canopy resistance r s c The Jarvis method is used and calculated according to the following formula:

[0078]

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

[0080]

[0081] Where: B is the asymptotic value of stomatal conductance when the radiation is infinite (Wm -2 );T opt is the optimum temperature for transpiration (℃); VPD opt is the optimum VPD for transpiration (kPa); k1 and k2 are empirical coefficients; s is the soil water deficit corresponding to the start of stomatal conductance decrease; f0 is the stomatal opening degree corresponding to the soil water deficit reaching 1; SMD is the soil water deficit calculated as (SWC max -SWC) / (SWC max -SWC min ), where SWC max and SWC min are the maximum and minimum water contents in the root zone, respectively.

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

[0083]

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

[0085] Aerodynamic drag r a c , r a s and r a a The following formulas are used for calculation:

[0086]

[0087] Where: u h is the wind speed at canopy height (ms -1 ); w is the typical blade width (m); n is the eddy diffusion attenuation constant; h c is the mean 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] Where: z a is the reference height; u h is the wind speed at the reference height (ms -1 );C d is the drag coefficient per unit blade; K h is the eddy diffusion coefficient (m 2 s -1 );Z 0g is the surface roughness (m); u *is the 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 dry-hot Yuanjiang River Valley, the area has a subtropical dry-hot climate and dry red soil. The study focused on a typical economic orange orchard (with a row spacing of 2 × 3 m) in the region. Sweet oranges were irrigated intermittently during the dry season (January to March) and rainfed the rest of the year. Orange trees are evergreen and maintain vigorous growth year-round, with relatively small fluctuations in their 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, the area has a temperate continental climate and medium loam soils. The study was conducted in a typical rain-fed apple orchard (with a row spacing of 2 × 4 m) in the region, using the Yanchang Red Fuji apple variety. Apple trees are deciduous trees, and their leaf area index fluctuates significantly during their growth period, with a low and rapid increase in the early stages and a stable trend in the middle and late stages.

[0098] Example 3:

[0099] The experiment was conducted from April to October 2018 to 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 silt loam soil. A typical vineyard in the region (with rows arranged from south to north and a spacing of 0.8 × 3 m) was selected as the research object, and the black sugar beet variety was selected. The vineyard trellis was a single trellis, 1.5 m high, with cement columns installed 3.5 m apart in each row, and three steel wires stretched at the top, middle, and bottom. The vineyard was fully irrigated using drip irrigation, and the soil moisture content was maintained at above 75% of field capacity. Regular pruning was performed to maintain a relatively uniform height and crown size. The plant is a deciduous fruit tree, and the leaf area index fluctuated greatly during growth, showing a single peak with low values ​​in the early and late stages and high values ​​in the middle stages.

[0100] In the above three examples, Examples 1 and 2 use the Penman-Monteith model to estimate hourly transpiration water consumption (the transpiration water consumption of apple trees and orange trees is measured by heat ratio and heat diffusion method respectively). Example 3 uses the Shuttleworth-Wallace model to estimate daily evapotranspiration ET and soil evaporation E. The three examples are all based on the extinction coefficient constant mode and the existing ZL 2023 1 1323337.1 extinction coefficient dynamic mode as comparison benchmarks. Bayesian analysis is used for parameter calibration and optimization, and the posterior distribution sampling adopts the Markov Chain Monte Carlo (MCMC) method based on Gibbs sampling. The model comparison process is carried out based on accuracy, and the determination coefficient (R 2 ) and relative error (MRE) are used as measurement indicators.

[0101] As shown in Table 1, the hourly transpiration water consumption estimated by the present invention is more accurate than the Penman-Monteith model under the extinction coefficient constant mode and the ZL2023 1 1323337.1 extinction coefficient dynamic mode. For orange and apple orchards, R 2 The relative error (MRE) improved from 0.54 and 0.52 in the fixed extinction coefficient scheme to 0.64 and 0.65 in the dynamic extinction coefficient scheme (ZL 2023 1 1323337.1), and further to 0.70 in the dynamic extinction coefficient scheme of the present invention. 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 (ZL 2023 1 1323337.1), and further to 16.83% and 13.51% in the dynamic extinction coefficient scheme of the present invention.

[0102] In addition, the accuracy of the daily evapotranspiration ET estimated by the present invention is not significantly different from that of the Shuttleworth-Wallace model under the extinction coefficient fixed value model and the ZL 2023 11323337.1 extinction coefficient dynamic model, but the accuracy of the daily evaporation E estimated by the present invention is significantly better than that of the extinction coefficient fixed value model and the ZL 2023 1 1323337.1 extinction coefficient dynamic model. 2 The MRE improved from 0.54 in the fixed extinction coefficient scheme to 0.80 in the dynamic extinction coefficient scheme (ZL 2023 1 1323337.1), and further to 0.83 in the dynamic extinction coefficient scheme of the present invention. The MRE decreased from 32.49% in the fixed extinction coefficient scheme to 16.67% in the dynamic extinction coefficient scheme (ZL 2023 1 1323337.1), and further to 14.23% in the dynamic extinction coefficient scheme of the present invention.

[0103] The above three examples cover different climate types (dry heat, semi-arid, semi-humid), crop types (oranges, apples, grapes), terrains (mountainous areas, dry plateaus, plains) and time scales (daily scale, hourly scale), which can more fully demonstrate the effects of the present invention. In comparison, the application effect of the present invention in the simulation of transpiration water consumption on the hourly scale is better, significantly better than the method described in ZL202311323337.1, and better than the fixed value scheme of the extinction coefficient. On the daily scale, the effect of the present invention is still the best, but the difference compared to the method described in ZL 202311323337.1 is not as obvious as on the hourly scale, but it is stable and reliable in effectively ensuring the separation of ET components.

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

[0105]

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

[0107] First, the present invention establishes a dynamic function of the extinction coefficient based on the main controlling factor of the extinction coefficient identified by the mathematical analysis method; introduces it into the Penman-Monteith equation or the Shuttleworth-Wallace equation, and achieves the purpose of accurately estimating transpiration water consumption and soil evaporation by correcting the canopy energy interception term and the soil energy interception term. The method has little effect on the simulation of the total water consumption of evapotranspiration (ET), but can significantly improve the effect of ET component separation, that is, the canopy transpiration (T) in ET is 0. e The calculation accuracy of soil evaporation E is significantly improved.

[0108] 2. The 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 constant value in the traditional evapotranspiration model. It has a more sufficient theoretical basis and significantly improves the estimation accuracy of transpiration and evaporation, which is conducive to improving agricultural irrigation efficiency and providing a more reliable basis for efficient water resources management.

[0109] 3. Compared with the existing dynamic characterization method of the extinction coefficient that only considers the leaf area index in the water consumption calculation, the method simultaneously considers the influence of the leaf area index and environmental factors on the extinction coefficient, and thus the characterization of the dynamic change law of the extinction coefficient is more complete. Compared with the existing dynamic characterization method of the extinction coefficient ZL202311323337.1 that considers both the leaf area index and environmental factors, by adopting independent adjustment coefficients for different influencing factors, the sensitivity differences of different factors to the extinction coefficient can be taken into account. When used under conditions where the influence of each factor on the extinction coefficient is relatively different (for example, on an hourly scale), the effect is better. In fact, the existing dynamic characterization method of the extinction coefficient ZL 202311323337.1 adopts a common adjustment coefficient for the main controlling factor, which is a special case of the method described in the present invention. That is, when the degree of influence of each main controlling factor on the extinction coefficient is relatively close, the independent adjustment coefficients of each factor are approximately equal. In this case, the calculation results of the method described in the present invention are almost identical to the results of the method recorded in ZL202311323337.1. The existing dynamic extinction coefficient characterization method described in ZL 202311323337.1 is significantly more effective than the fixed extinction coefficient method in simulating daily water consumption. However, the method described in the present invention is more effective in hourly farmland water consumption and component separation. The method described in the present invention can also be used for daily-scale related calculations, with results at least comparable to those described in ZL 202311323337.1. In summary, the method described in the present invention is more versatile and has higher applicability.

[0110] The above description is merely an illustration of the preferred embodiments of the present application and the technical principles employed. The scope of the invention herein is not limited to the technical solutions formed by the specific combination of the aforementioned technical features, but also encompasses other technical solutions formed by any combination of the aforementioned technical features or their equivalents without departing from the inventive concept. For example, a technical solution formed by replacing the aforementioned features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A method for calculating evapotranspiration and separating its components based on the dynamic canopy extinction coefficient, characterized in that: The method comprises the following steps: Step A: As the growth period progresses, use a radiation sensor to regularly measure the incident radiation intensity above the canopy and the penetrating radiation intensity below the canopy multiple times a day, and calculate the canopy extinction coefficient at each stage according to Beer's law. Where C is the extinction coefficient, PAR in and PAR tr are the incident radiation intensity above the canopy and the penetrating radiation intensity below the canopy, both in MJ m -2 d -1 , LAI is the leaf area index, its unit is m 2 m -2 ; Step B: Use mathematical methods to analyze the relationship between leaf area index (LAI), 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: Use the master control factor to construct a dynamic extinction coefficient function. According to the positive and negative correlation factors obtained in step B, the factor that is positively correlated with C uses the factor itself, and the factor that is negatively correlated with C uses the inverse form of the factor. Then, the extinction coefficient C is calculated using the following formula: d Dynamic change rules: Where C d is the extinction coefficient, f n is the nth main controlling factor of the extinction coefficient, a, b, c and d are unknown parameters, where b, c and d represent the sensitivity coefficients of the factors corresponding to their bases respectively; For crops with large leaf area index (LAI), when soil water content (SWC) and net radiation (R) n When is also the main controlling factor of the extinction coefficient, the expression of the dynamic extinction coefficient C is as follows: Step D1: Replace Formula C d The following Penman-Monteith model is introduced to replace the extinction coefficient constant parameter C to obtain the transpiration water consumption T e : Where: T e is the canopy transpiration, in MJm -2 d -1 ; △ is the slope of the saturated water vapor pressure and temperature curve, the unit is kPa℃ -1 ; R nc is the net radiation intercepted by the canopy, in MJm -2 d -1 ; G is soil heat flux, unit is MJm -2 d -1 ; ρ is the air density, unit is gmm -3 ;c p is the specific heat at constant pressure, in MJkg -1 ℃ -1 ;γ is the hygrometer constant, unit is kPa℃ -1 ; VPD is the saturated vapor pressure difference, unit is kPa; r c is the canopy resistance, in sm -1 ; r a is the aerodynamic drag, in sm -1 ; Net radiation intercepted by the canopy R nc Calculate according to the following formula: R nc =R n ×(1-exp(-C d ×LAI)); Where: R n is the net radiation at the top of the canopy, with units of MJ m -2 d -1 ; C d is the dynamic extinction coefficient, dimensionless; LAI is the canopy leaf area index, its unit is m 2 m -2 ; Step D2: Replace Formula C d The following Shuttleworth-Wallace model is introduced to replace the extinction coefficient constant parameter C to obtain evapotranspiration ET and its component transpiration water consumption T e And soil evaporation E: ET=C c PM c +C s PM s Where ET is evapotranspiration, MJ m -2 d -1 ; where transpiration and evaporation are E and T respectively e ,MJ m -2 d -1 ;PM c and PM s are the evapotranspiration under closed canopy and bare soil conditions, MJ m -2 d -1 ; C c and C s is the corresponding proportionality coefficient; R s 、R c 、R a It is an intermediate variable with no exact meaning; D0 is the saturated water vapor pressure difference at the canopy height, kPa; r s c is the canopy boundary layer resistance, ms -1 ; r a c is the aerodynamic drag from canopy to canopy interior, ms -1 ; r a a is the aerodynamic drag from the reference altitude to the canopy flux mean altitude, ms -1 ; r a s is the aerodynamic drag from the mean height of the canopy flux to the ground surface, ms -1 ; r s s is the surface resistance, ms -1 ;A and A s are the available energy reaching the underlying surface and the soil surface, MJ m -2 d -1 , calculated according to the following formula: A=R n -G A s =R ns -G Where G is the soil heat flux, MJ m -2 d -1 ; R ns is the net radiation reaching the surface, MJ m -2 d -1 , calculated as follows: R ns =R n ×exp(-C d ×LAI) Where: R n is the net radiation at the top of the canopy, with units of MJ m -2 d -1 ; C d is the dynamic extinction coefficient, dimensionless; LAI is the canopy leaf area index, its unit is m 2 m -2 .

2. The method for calculating evapotranspiration and separating components based on the dynamic canopy extinction coefficient according to claim 1, wherein: Canopy transpiration water consumption T based on the Penman-Monteith model e The simulation method of farmland evapotranspiration ET and its components T based on the Shuttleworth-Wallace model e and the simulation method of E, wherein the mathematical analysis method for identifying the main controlling factors of the extinction coefficient in step B is selected from one or more of regression analysis, principal component analysis, path analysis, redundancy analysis, structural equation model, and enhanced regression tree model.

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

4. The method for calculating evapotranspiration and separating components based on the dynamic canopy extinction coefficient according to claim 1, wherein: Based on canopy transpiration water consumption T e The simulation method is as follows: the Penman-Monteith model in step D1 is applicable to the case where only canopy transpiration is simulated. Although the Penman-Monteith model is also commonly 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 is not applicable.

5. The method for calculating evapotranspiration and separating components based on the dynamic canopy extinction coefficient according to claim 1, wherein: Based on farmland evapotranspiration ET and its components T e and E simulation method, the Shuttleworth-Wallace model in step D2 is suitable for simulating evapotranspiration ET and splitting ET into transpiration T e and evaporation rate E.

6. The method for calculating evapotranspiration and separating components based on the dynamic canopy extinction coefficient according to claim 1, wherein: Transpiration water consumption T based on the Penman-Monteith model e The simulation method of evapotranspiration ET and its components T based on the Shuttleworth-Wallace model e and E simulation method, only one of the steps D1 and D2 is selected, when only the canopy transpiration is simulated, step D1 is selected, when ET needs to be simulated and component separation is performed, step D2 is selected.

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