A method for estimating surface evapotranspiration considering land-atmosphere coupling

Abstract

The present invention provides a method for estimating surface evapotranspiration considering land-air coupling, which belongs to the field of surface evapotranspiration estimation. The method includes constructing a time continuity equation of temperature and specific humidity in the boundary layer of the land-air coupling system; combining the relationship between saturated water vapor deficit and temperature and specific humidity to determine the time continuity equation of saturated water vapor deficit in the boundary layer; constructing a first-order non-homogeneous ordinary differential equation of saturated water vapor deficit in the boundary layer, solving the relationship between saturated water vapor deficit in the boundary layer and saturated water vapor deficit in the entrainment layer, saturated water vapor deficit on the surface and land-air coupling factor; combining the surface energy balance equation and the water vapor transport equation to obtain the surface evapotranspiration characterization equation under land-air coupling. The present invention solves the problem that the existing methods cannot characterize the land-air coupling, especially the influence of the entrainment effect at the top of the atmospheric boundary layer on the surface evapotranspiration process.

Description

Technical Field

[0001] The invention belongs to the field of surface evapotranspiration estimation, and in particular relates to a surface evapotranspiration estimation method taking land-atmosphere coupling into consideration. Background Art

[0002] Evapotranspiration is a key process in the water and energy cycle of the land-atmosphere system, and is also a key indicator for meteorological and hydrological simulation and crop water demand prediction. Exploring the mechanism of surface evapotranspiration changes under land-atmosphere interaction is of great significance for improving the accuracy of surface evapotranspiration estimation, rationally optimizing crop irrigation schedules, and accurately guiding agricultural water management.

[0003] Surface evapotranspiration refers to the process in which water vapor from the surface of soil vegetation and free water surface escapes to the free atmosphere driven by solar radiation energy in the land surface-near-ground atmosphere system, including evaporation from the water (land) surface, transpiration from vegetation, and canopy interception. The most widely used evapotranspiration estimation model is mainly based on the Penman theory. This theory assumes that the water vapor in the atmospheric boundary layer is constant, and focuses on describing the response relationship between the surface water supply and the near-ground atmospheric state to the evapotranspiration process. By considering the heterogeneous characteristics of the underlying surface moisture-energy-vegetation, single-source, dual-source, multi-source, and sparse vegetation evapotranspiration models have been developed successively. However, the evapotranspiration model based on the land surface perspective does not fully consider the impact of atmospheric state changes on the evapotranspiration process. The actual evapotranspiration process is synergistically regulated by land-atmosphere coupling. Therefore, the quantification of the evapotranspiration process mechanism also needs to consider the impact of boundary layer water-heat coupling, especially the entrainment effect caused by boundary layer development.

[0004] Although a large number of studies have reported the impact of land-atmosphere coupling on regional evapotranspiration, few studies have proposed intuitive and concise evapotranspiration characterization functions that quantify the land-atmosphere effect with evapotranspiration as the core variable. Today, the in-depth development of boundary layer theory provides theoretical conditions for the reconstruction of the evaporation formula. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for estimating surface evapotranspiration taking into account the land-atmosphere coupling effect, which solves the problem that the prior methods are unable to characterize the influence of the land-atmosphere coupling effect, especially the entrainment effect at the top of the atmospheric boundary layer, on the surface evapotranspiration process. At the same time, a contribution rate expression is proposed to quantify the contributions of the radiation term, land surface term, atmospheric term and land-atmosphere coupling term to the evapotranspiration process.

[0006] In order to achieve the above objectives, the technical solution adopted by the present invention is: a method for estimating surface evapotranspiration considering land-air coupling, comprising the following steps:

[0007] S1. Based on the boundary layer water and heat transfer theory, the functional relationship between temperature and specific humidity and water and heat flux at the surface and top of the atmospheric boundary layer in the land-atmosphere coupled system is derived, and the time continuity equations of temperature and specific humidity are constructed;

[0008] S2. Based on the time continuity equation of temperature and specific humidity, combined with the relationship between saturated water vapor deficit D and temperature and specific humidity, the saturated water vapor deficit D in the boundary layer is derived. R The time continuity equation of

[0009] S3. Constructing the saturated water vapor deficit in the boundary layer D R The first-order nonhomogeneous ordinary differential equation is solved to obtain the saturated water vapor deficit D in the boundary layer. R Saturated water vapor deficit in the entrained layer D e , Surface saturated water vapor deficit D s and the relationship between the land-atmosphere coupling factor;

[0010] S4, based on saturated water vapor deficiency in the boundary layer D R The time continuity equation of derives the relationship between surface evapotranspiration and saturated water vapor deficit D in the boundary layer R The functional relationship of is obtained by combining the surface energy balance equation and the water vapor transport equation with the relationship obtained in step S3 to obtain the surface evapotranspiration characterization equation under the land-atmosphere coupling effect;

[0011] S5. Based on the equation for characterizing surface evapotranspiration under land-atmosphere coupling, the equations for the contribution of radiation term, surface term, atmospheric term and land-atmosphere coupling term to surface evapotranspiration are derived respectively to quantify the impact of land-atmosphere coupling on evapotranspiration.

[0012] Furthermore, the time continuity equations of temperature and specific humidity are as follows:

[0013]

[0014] Among them, θ R and q R represent the potential temperature and specific humidity inside the boundary layer, respectively, F H and F E They represent the surface sensible heat flux and surface latent heat energy respectively, ρ represents the air density inside the boundary layer, c p represents the specific heat at constant pressure, h represents the height of the atmospheric boundary layer, g e represents the average velocity at the top of the boundary layer, θ e and q e represent the potential temperature and specific humidity of the entrained layer respectively, t represents the time period, and λ represents the latent heat of vaporization.

[0015] Furthermore, the saturated water vapor deficit D in the boundary layer R The time continuity equation is as follows:

[0016]

[0017] Where t represents the time period, ε a Represents the slope of the saturated specific humidity-potential temperature curve, F H and F E They represent the surface sensible heat flux and surface latent heat energy respectively, ρ represents the air density inside the boundary layer, h represents the height of the atmospheric boundary layer, λ represents the latent heat of vaporization, and g e represents the average velocity at the top of the boundary layer, c p represents the specific heat at constant pressure, θ e represents the potential temperature of the entrainment layer, θ R represents the potential temperature inside the boundary layer, q e represents the specific humidity of the entrained layer, q R Represents the specific humidity inside the boundary layer.

[0018] Furthermore, the saturated water vapor deficit D in the boundary layer R Saturated water vapor deficit in the entrained layer D e , Surface saturated water vapor deficit D s The expression of the relationship between the land-atmosphere coupling factor is as follows:

[0019]

[0020] ω=g e / g a

[0021]

[0022] Where ω represents the land-atmosphere coupling strength, represents the number of land-atmosphere couplings within the study period t, D 0 represents the initial saturated water vapor deficit in the atmospheric boundary layer, g e Indicates the entrainment rate, g a is the surface transmission rate, t 0 represents the duration of land-atmosphere coupling, and t represents the time period.

[0023] Furthermore, the surface evapotranspiration characterization equation is as follows:

[0024]

[0025] Rn=F H +F E +G

[0026] Where λET represents the surface latent heat flux, Rn and G represent the surface net radiation and soil heat flux, respectively, and δ trepresents the time scaling factor, ρ represents the air density in the boundary layer, λ represents the latent heat of vaporization, γ represents the hygrometer constant in the boundary layer, and g a is the surface transmission rate, represents the number of land-atmosphere couplings within the study period t, m represents the comprehensive index of land-atmosphere coupling, ω represents the intensity of land-atmosphere coupling, and F H and F E They represent the surface sensible heat flux and surface latent heat energy respectively.

[0027] Furthermore, the equation for the contribution of radiation term to surface evapotranspiration is as follows:

[0028]

[0029] λET Rn =Δ(Rn-G) / (Δ+γ)

[0030] Among them, CR Rn represents the contribution rate of radiation term to surface evapotranspiration, λ represents the latent heat of vaporization, λET Rn represents the radiation term that affects evapotranspiration, ET represents surface evapotranspiration, Rn represents surface net radiation, G represents soil heat flux, δ t represents the time scaling factor, γ represents the hygrometer constant in the boundary layer, ρ represents the air density in the boundary layer, λ represents the latent heat of vaporization, and g a is the surface transmission rate, represents the number of land-atmosphere couplings within the study period t, m represents the comprehensive index of land-atmosphere coupling, and ω represents the intensity of land-atmosphere coupling.

[0031] Furthermore, the equation for the contribution of the surface term to surface evapotranspiration is as follows:

[0032]

[0033] λET LS =-δ t ργλg a D s / (Δ+γ)

[0034] Among them, CR LS Represents the contribution rate of the surface term to surface evapotranspiration, λET LS Represents the land surface term that affects evapotranspiration.

[0035] Furthermore, the equation for the atmospheric contribution to surface evapotranspiration is as follows:

[0036]

[0037]

[0038] Among them, CRAT represents the contribution of atmospheric terms to surface evapotranspiration, λET AT Represents the atmospheric terms that affect evapotranspiration.

[0039] Furthermore, the equation for the contribution of the land-atmosphere coupling term to surface evapotranspiration is as follows:

[0040]

[0041] Among them, CR LAC represents the contribution rate of land-atmosphere coupling to surface evapotranspiration, λET LAC Indicates land energy.

[0042] Beneficial effects of the present invention:

[0043] The present invention considers the quantitative influence of land-atmosphere coupling, especially the entrainment effect at the top of the atmospheric boundary layer, on the surface evapotranspiration process, which helps to deeply understand the response mechanism of surface evapotranspiration under the background of climate change and improve the scientificity and accuracy of evapotranspiration estimation. The radiation contribution rate, land surface contribution rate, atmospheric contribution rate and land-atmosphere coupling contribution rate expressions are proposed to quantitatively analyze the attribution of evapotranspiration changes, which helps to accurately identify its main controlling factors. It has important theoretical significance for scientifically understanding the mechanism of the surface evapotranspiration process under the background of intensified climate change, and also provides theoretical support for precise crop water management and fine simulation of hydrological cycle, solving the problem that existing methods cannot characterize the influence of land-atmosphere coupling, especially the entrainment effect at the top of the atmospheric boundary layer, on the surface evapotranspiration process. At the same time, the contribution rate expression is proposed to quantify the contribution of radiation term, land surface term, atmospheric term and land-atmosphere coupling term to the evapotranspiration process.

[0044] (1) The existing surface evapotranspiration estimation method fails to consider the impact of land-atmosphere coupling on the evapotranspiration process. The present invention introduces the boundary layer water and heat transfer theory and proposes a surface evapotranspiration estimation method under land-atmosphere coupling, which improves the understanding of the mechanism of the entire evapotranspiration process.

[0045] (2) The existing surface evapotranspiration attribution analysis method does not take into account the land-atmosphere coupling factor, which may lead to uncertainty in the attribution of evapotranspiration changes, thereby affecting the accuracy of identifying the main controlling factors. Based on the established surface evapotranspiration estimation method under the effect of land-atmosphere coupling, this paper proposes an expression for the land-atmosphere coupling contribution rate, quantitatively characterizes the land-atmosphere coupling effect that affects evapotranspiration changes, and improves the comprehensiveness of the attribution analysis of evapotranspiration changes;

[0046] (3) The present invention can reveal the response mechanism of the entire process of surface evapotranspiration, identify the land-atmosphere coupling effect that affects the change of surface evapotranspiration, and help improve the scientific understanding of the surface evapotranspiration process. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1The present invention is a flow chart of the method.

[0048] Figure 2 Schematic diagram of water and heat transfer in the boundary layer of the land-atmosphere coupled system in this embodiment.

[0049] Figure 3 This is a schematic diagram of the method for estimating surface evapotranspiration under land-atmosphere coupling in this embodiment. DETAILED DESCRIPTION

[0050] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0051] Example

[0052] like Figure 1-Figure 3 As shown, Figure 2 In, S I and S S represent the upper boundary surface (top of the atmospheric boundary layer) and the surface boundary surface respectively, R represents the air column; θ, q and D represent the potential temperature, specific humidity and saturated water vapor deficit in the boundary layer respectively, h represents the boundary layer height, Figure 3 In the formula, ET represents surface evapotranspiration. The present invention provides a method for estimating surface evapotranspiration taking into account the land-atmosphere coupling effect, and the implementation method is as follows:

[0053] S1. Based on the boundary layer water and heat transfer theory, the functional relationship between temperature and specific humidity and the water and heat flux at the surface and top of the atmospheric boundary layer in the land-atmosphere coupled system is derived, and the time continuity equations of temperature and specific humidity are constructed.

[0054] In this embodiment, the water and heat factors of the surface layer, the atmospheric boundary layer and the atmospheric entrainment layer under the land-air coupling affect each other and constrain each other. It is assumed that the atmospheric elements (potential temperature and specific humidity) inside the boundary layer are approximately in a steady state within the time period (dt), and the change of the state of the atmospheric elements is affected by both the land surface process (surface layer) and the atmospheric process (entrainment layer). The research object is generalized as a volume R and a boundary surface S = S s +S I +S o To determine the mass of air entering R, assume that the top of the boundary layer (above R) passes through S I The average flow rate is g e , then the air mass flow into R is ρg e S I[kg / s], where ρ represents the air density. For a fully mixed R, the internal potential temperature and specific humidity conservation equations are:

[0055]

[0056] Where R is the volume of the air column (m 3 ), ρ represents the air density inside the boundary layer (kg / m 3 ), c p It represents the specific heat at constant pressure (MJ / (kg·℃)), and are the rate of change of potential temperature (℃ / s) and specific humidity (g / kg / s) in the boundary layer, respectively. s and S I are the areas of the water and heat exchange interface between the surface layer and the top of the atmosphere and the boundary layer (m 2 ), F H and F E are the surface sensible heat flux and surface latent heat flux (MJ·m 2 ·s -1 ), λ represents the latent heat of vaporization (kJ / kg), θ R and q R represent the potential temperature (℃) and specific humidity (g / kg) inside the boundary layer, θ e and q e represent the potential temperature (℃) and specific humidity (g / kg) of the entrainment layer, g e It represents the average velocity at the top of the boundary layer or the entrainment rate (m / s).

[0057] Assuming that the three-dimensional unit air column R is regular, we can approximately have: S s ≈S I =S,R=S×h, where h represents the height of the atmospheric boundary layer, m. Substituting into equations (1) and (2), the potential temperature and specific humidity conservation equations in the system can be written as:

[0058]

[0059] Among them, θ R and q R represent the potential temperature and specific humidity inside the boundary layer, respectively, F H and F E They represent the surface sensible heat flux and surface latent heat energy respectively, ρ represents the air density inside the boundary layer, c p represents the specific heat at constant pressure, h represents the height of the atmospheric boundary layer, g e represents the average velocity at the top of the boundary layer, θ e and q e represent the potential temperature and specific humidity of the entrained layer respectively, t represents the time period, and λ represents the latent heat of vaporization.

[0060] S2. Based on the time continuity equation of temperature and specific humidity, combined with the relationship between saturated water vapor deficit D and temperature and specific humidity, the saturated water vapor deficit D in the boundary layer is derived. R The time continuity equation of .

[0061] In this embodiment, the surface energy flux F in the land-atmosphere coupled system E and F H Acting on the saturated water vapor deficit D through potential temperature θ and specific humidity q R , D R The relationship between potential temperature and specific humidity is:

[0062]

[0063] Among them, q s represents the saturated specific humidity, θ R represents the potential temperature inside the boundary layer, q R represents the actual specific humidity inside the boundary layer, and f() represents the corresponding functional relationship.

[0064] The partial derivatives of potential temperature and specific humidity are:

[0065]

[0066] in, represents the saturated specific humidity in the boundary layer, c p represents the specific heat at constant pressure, ε a represents the slope of the saturated specific humidity-potential temperature curve, and λ represents the latent heat of vaporization.

[0067] Then the continuity equation of saturated water vapor deficit time can be obtained:

[0068]

[0069] Here, t represents the time period.

[0070] Substituting equations (6) and (7) into (8), we can obtain:

[0071]

[0072] S3. Constructing the saturated water vapor deficit in the boundary layer D R The first-order nonhomogeneous ordinary differential equation is solved to obtain the saturated water vapor deficit D in the boundary layer. R Saturated water vapor deficit in the entrained layer D e , Surface saturated water vapor deficit D s and the relationship between the land-atmosphere coupling factor;

[0073] In this embodiment, the first term on the right side of equation (9) is the effect of changes in surface sensible heat flux and latent heat flux on changes in water vapor deficit in the boundary layer. The second term on the right side of the equation is transformed as follows:

[0074]

[0075] Among them, ε ae It represents the approximate slope of the saturated specific humidity-potential temperature curve. represents the saturated specific humidity of the entrained layer, q sat(θ) represents the saturated specific humidity in the boundary layer.

[0076] definition:

[0077]

[0078] E D =g e (D e -D R )(12)

[0079]

[0080] Among them, F D It represents the saturated water vapor pressure difference from the surface into the boundary layer R, E D represents the saturated water vapor deficit difference exchanged with R through the entrainment process, Δ D It represents the error caused by the linear assumption of the slope of saturated water vapor deficit-temperature (the slope value is replaced by tangent line instead of secant line), which is also an important assumption used in the derivation of Penman-Monteith equation. The calculation formula is:

[0081]

[0082] Where θ represents the potential temperature, The saturated specific humidity of the entrained layer is expressed as: represents the saturated specific humidity in the boundary layer.

[0083] Since (ε a -ε ae ) is very close to 0, so Δ D is a negligible nonlinear value, that is, Δ D ≈0.

[0084] Approximately:

[0085]

[0086] definition:

[0087] ω=g e / g a (16)

[0088] t 0 =h / (g e +g a )(17)

[0089]

[0090] The above formula (15) can be regarded as The first-order nonhomogeneous ordinary differential equation of , by solving the equation we can get:

[0091]

[0092] Where ω represents the land-atmosphere coupling strength, represents the number of land-atmosphere couplings within the study period t, D 0 represents the initial saturated water vapor deficit in the atmospheric boundary layer, g e Indicates the entrainment rate, g a represents the surface transmission rate, t represents the time period, and t 0 It represents the duration of land-atmosphere coupling, which characterizes the time (s) required for the boundary layer to reach a steady state under the action of land-atmosphere coupling.

[0093] The above formula (19) is the saturated water vapor deficit D in the boundary layer. R Saturated water vapor deficit in the entrained layer D e , Surface saturated water vapor deficit D s and the general relationship of land-atmosphere coupling factors.

[0094] S4, based on saturated water vapor deficiency in the boundary layer D R The time continuity equation of derives the relationship between surface evapotranspiration and saturated water vapor deficit D in the boundary layer R The functional relationship of , and combined with the surface energy balance equation and the water vapor transport equation and the relationship obtained in step S3, the surface evapotranspiration characterization equation under the land-atmosphere coupling is obtained.

[0095] In this embodiment, the surface energy balance equation is:

[0096] Rn=F H +F E +G(20)

[0097] Among them, F H and F E Rn and G represent the surface sensible heat flux and surface latent heat energy, respectively. Rn and G represent the surface net radiation and soil heat flux, respectively. The unit is (MJ·m 2 ·s -1 ).

[0098] Combining (20) and (19) and substituting them into (11), we can obtain:

[0099]

[0100] After transformation:

[0101]

[0102] Where λET represents the surface latent heat flux, Rn and G represent the surface net radiation and soil heat flux, respectively, and δ t represents the time scaling factor, ρ represents the air density in the boundary layer, λ represents the latent heat of vaporization, γ represents the hygrometer constant in the boundary layer, and g a is the surface transmission rate, represents the number of land-atmosphere couplings within the study period t, m represents the comprehensive index of land-atmosphere coupling, ω represents the intensity of land-atmosphere coupling, and F H and F E They represent the surface sensible heat flux and surface latent heat energy respectively.

[0103] The above equation (22) is the characterization equation of surface evapotranspiration under land-atmosphere coupling.

[0104] S5. Based on the characterization equation of surface evapotranspiration under land-atmosphere coupling, the equations for the contribution of radiation term, surface term, atmospheric term and land-atmosphere coupling term to surface evapotranspiration are derived respectively, the impact of land-atmosphere coupling on evapotranspiration is quantified, and the estimation of surface evapotranspiration is completed.

[0105] In this embodiment, in order to clarify the influence of each component of evapotranspiration on the evapotranspiration process, the present invention proposes the contribution rate expressions of four components:

[0106] The equation for the contribution of radiation term to surface evapotranspiration is as follows:

[0107]

[0108] λET Rn =Δ(Rn-G) / (Δ+γ)(24)

[0109] Among them, CR Rn represents the contribution rate of radiation term to surface evapotranspiration, λ represents the latent heat of vaporization, λET Rn represents the radiation term that affects evapotranspiration, ET represents surface evapotranspiration, Rn represents surface net radiation, G represents soil heat flux, δ t represents the time scaling factor, γ represents the hygrometer constant in the boundary layer, ρ represents the air density in the boundary layer, λ represents the latent heat of vaporization, and g a is the surface transmission rate, represents the number of land-atmosphere couplings within the study period t, m represents the comprehensive index of land-atmosphere coupling, and ω represents the intensity of land-atmosphere coupling.

[0110] The equation for the contribution of the surface term to surface evapotranspiration is as follows:

[0111]

[0112] λET LS =-δ t ργλg a D s / (Δ+γ)(26)

[0113] Among them, CR LS Represents the contribution rate of the surface term to surface evapotranspiration, λET LS Represents the land surface term that affects evapotranspiration.

[0114] The equation for the atmospheric contribution to surface evapotranspiration is as follows:

[0115]

[0116]

[0117] Among them, CR AT represents the contribution of atmospheric terms to surface evapotranspiration, λET AT Represents the atmospheric terms that affect evapotranspiration.

[0118] The equation for the contribution of land-atmosphere coupling to surface evapotranspiration is as follows:

[0119]

[0120] λET LAC =δ t ργλg a m(ωD e +D s ) / (Δ+γ)(30)

[0121] Among them, CR LAC represents the contribution rate of land-atmosphere coupling to surface evapotranspiration, λET LAC represents land-atmosphere coupling.

[0122] In this embodiment, while proposing a new method for estimating evapotranspiration, the present invention considers the influence of land-atmosphere coupling on the evapotranspiration process, especially the influence of the entrainment process at the top of the atmospheric boundary layer. Based on the boundary layer water and heat transfer theory and combined with the surface energy balance equation, an equation for estimating surface evapotranspiration under land-atmosphere coupling is constructed, and the influence of radiation terms, land surface terms, atmospheric terms and land-atmosphere coupling terms on the evapotranspiration process is analyzed. A contribution rate expression is proposed to quantitatively characterize the land-atmosphere coupling effect. Starting from the boundary layer water and heat transfer continuity equation, the present invention fully considers the influence of land surface processes and free atmospheric processes on the water and heat inside the boundary layer. Through mathematical derivation, a full-process characterization model of evapotranspiration under land-atmosphere coupling is constructed, in order to enhance the understanding of the mechanism of the surface evapotranspiration process.

Claims

1. A method for estimating surface evapotranspiration considering land-atmosphere coupling, characterized in that: The following steps are involved: S1. Based on the boundary layer water and heat transfer theory, the functional relationship between temperature and specific humidity and water and heat flux at the surface and top of the atmospheric boundary layer in the land-atmosphere coupled system is derived, and the time continuity equations of temperature and specific humidity are constructed; S2. Based on the time continuity equation of temperature and specific humidity, combined with the relationship between saturated water vapor deficit D and temperature and specific humidity, the saturated water vapor deficit D in the boundary layer is derived. R The time continuity equation of S3. Constructing the saturated water vapor deficit in the boundary layer D R The first-order nonhomogeneous ordinary differential equation is solved to obtain the saturated water vapor deficit D in the boundary layer. R Saturated water vapor deficit in the entrained layer D e , Surface saturated water vapor deficit D s and the relationship between the land-atmosphere coupling factor; S4, based on saturated water vapor deficiency in the boundary layer D R The time continuity equation of derives the relationship between surface evapotranspiration and saturated water vapor deficit D in the boundary layer R The functional relationship of is obtained by combining the surface energy balance equation and the water vapor transport equation with the relationship obtained in step S3 to obtain the surface evapotranspiration characterization equation under the land-atmosphere coupling effect; S5. Based on the equation for characterizing surface evapotranspiration under land-atmosphere coupling, the equations for the contribution of radiation term, surface term, atmospheric term and land-atmosphere coupling term to surface evapotranspiration are derived respectively to quantify the impact of land-atmosphere coupling on evapotranspiration.

2. The method for estimating surface evapotranspiration considering land-atmosphere coupling according to claim 1, characterized in that: The time continuity equations for temperature and specific humidity are as follows: Among them, θ R and q R represent the potential temperature and specific humidity inside the boundary layer, respectively, F H and F E They represent the surface sensible heat flux and surface latent heat energy respectively, ρ represents the air density inside the boundary layer, c p Indicates specific heat at constant pressure, h The atmospheric boundary layer height, g e represents the average velocity at the top of the boundary layer, θ e and q e represent the potential temperature and specific humidity of the entrained layer respectively, t represents the time period, and λ represents the latent heat of vaporization.

3. The method for estimating surface evapotranspiration considering land-atmosphere coupling according to claim 1, characterized in that: The saturated water vapor deficit in the boundary layer is D R The time continuity equation is as follows: Where t represents the time period, ε a Represents the slope of the saturated specific humidity-potential temperature curve, F H and F E They represent the surface sensible heat flux and surface latent heat energy respectively, ρ represents the air density inside the boundary layer, h represents the height of the atmospheric boundary layer, λ represents the latent heat of vaporization, and g e represents the average velocity at the top of the boundary layer, c p represents the specific heat at constant pressure, θ e represents the potential temperature of the entrainment layer, θ R represents the potential temperature inside the boundary layer, q e represents the specific humidity of the entrained layer, q R Represents the specific humidity inside the boundary layer.

4. The method for estimating surface evapotranspiration considering land-atmosphere coupling according to claim 1, characterized in that: The saturated water vapor deficit in the boundary layer is D R Saturated water vapor deficit in the entrained layer D e , Surface saturated water vapor deficit D s The expression of the relationship between the land-atmosphere coupling factor is as follows: ω=g e / g a Where ω represents the land-atmosphere coupling strength, represents the number of land-atmosphere couplings within the study period t, D0 represents the initial saturated water vapor deficit in the atmospheric boundary layer, g e Indicates the entrainment rate, g a represents the surface transmission rate, t0 represents the duration of land-air coupling, and t represents the time period.

5. The method for estimating surface evapotranspiration considering land-atmosphere coupling according to claim 1, characterized in that: The surface evapotranspiration characterization equation is as follows: Rn=F H +F E +G Where λET represents the surface latent heat flux, Rn and G represent the surface net radiation and soil heat flux, respectively, and δ t represents the time scaling factor, ρ represents the air density in the boundary layer, λ represents the latent heat of vaporization, γ represents the hygrometer constant in the boundary layer, and g a is the surface transmission rate, represents the number of land-atmosphere couplings within the study period t, m represents the comprehensive index of land-atmosphere coupling, ω represents the intensity of land-atmosphere coupling, and F H and F E They represent the surface sensible heat flux and surface latent heat energy respectively, and D0 represents the initial saturated water vapor deficit in the atmospheric boundary layer.

6. The method for estimating surface evapotranspiration considering land-atmosphere coupling according to claim 1, characterized in that: The equation for the contribution of radiation term to surface evapotranspiration is as follows: λET Rn =Δ(Rn-G) / (Δ+γ) Among them, CR Rn represents the contribution rate of radiation term to surface evapotranspiration, λ represents the latent heat of vaporization, λET Rn represents the radiation term that affects evapotranspiration, ET represents surface evapotranspiration, Rn represents surface net radiation, G represents soil heat flux, δ t represents the time scaling factor, γ represents the hygrometer constant in the boundary layer, ρ represents the air density in the boundary layer, λ represents the latent heat of vaporization, and g a is the surface transmission rate, represents the number of land-atmosphere couplings within the study period t, m represents the comprehensive index of land-atmosphere coupling, ω represents the intensity of land-atmosphere coupling, and D0 represents the initial saturated water vapor deficit in the atmospheric boundary layer.

7. The method for estimating surface evapotranspiration considering land-atmosphere coupling according to claim 6, characterized in that: The equation for the contribution of the surface term to surface evapotranspiration is as follows: Among them, CR LS Represents the contribution rate of the surface term to surface evapotranspiration, λET LS Represents the land surface term that affects evapotranspiration.

8. The method for estimating surface evapotranspiration considering land-atmosphere coupling according to claim 6, characterized in that: The equation for the atmospheric contribution to surface evapotranspiration is as follows: Among them, CR AT represents the contribution of atmospheric terms to surface evapotranspiration, λET AT Represents the atmospheric terms that affect evapotranspiration.

9. The method for estimating surface evapotranspiration considering land-atmosphere coupling according to claim 6, characterized in that: The equation for the contribution of land-atmosphere coupling to surface evapotranspiration is as follows: Among them, CR LAC represents the contribution rate of land-atmosphere coupling to surface evapotranspiration, λET LAC represents land-atmosphere coupling.

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