A method for estimating actual evapotranspiration in a watershed considering the water use mechanism of vegetation

Abstract

The present invention relates to a method for estimating actual evapotranspiration of a watershed considering the mechanism of water use by vegetation, and belongs to the technical field of methods for estimating actual evapotranspiration of a watershed. The method comprises the following steps: obtaining an input data set of a study period of a study watershed and performing preprocessing; using the input data set to calculate the multi-year average precipitation of the whole watershed representing the multi-year average actual evapotranspiration water supply of the study watershed and the multi-year average potential evapotranspiration of the whole watershed representing the multi-year average actual evapotranspiration energy supply of the study watershed; expressing the multi-year average net primary productivity of vegetation in the whole watershed through the photosynthetically active radiation and light energy utilization rate absorbed by vegetation; developing a Budyko formula considering the mechanism of water use by vegetation to calculate the multi-year average actual evapotranspiration of the whole watershed; thereby maximizing the degree of quantification of vegetation in the process of calculating the actual evapotranspiration of the watershed using the traditional Budyko formula, and also improving the estimation accuracy of the actual evapotranspiration of the watershed.

Description

Technical Field

[0001] The invention relates to a method for estimating actual evapotranspiration of a watershed, and in particular to a method for estimating evapotranspiration of a watershed taking into account a water use mechanism of vegetation. Background Art

[0002] Basin evapotranspiration is the liquid-gas phase transition process of water in the basin into water vapor. As the core link of the basin water cycle and the key to grasping the water and heat transfer law of the atmosphere-vegetation-soil continuum, it is of great significance for the study of climate evolution, water and heat balance, water energy cycle, eco-hydrology, vegetation ecosystem water consumption and drought monitoring. As a regulating variable of hydrological processes such as soil moisture, groundwater recharge and runoff, basin evapotranspiration has guiding significance for improving the scientific management of basin water resources, mastering the water demand of agricultural production at the basin scale, and gaining insight into the evolution of basin water resources under the dual influence of climate change and human activities.

[0003] The actual evapotranspiration in the water cycle of a river basin becomes difficult to accurately estimate due to the combined influence of complex underlying surface conditions and climate change. There are four main methods for estimating actual evapotranspiration: 1) Instrumental observation, which uses observation instruments to directly measure actual evapotranspiration. The advantage is that the relative true value of the observed surface evapotranspiration can be directly obtained with high accuracy, but the construction and operation of monitoring stations require a lot of manpower and financial resources, and the limited spatial coverage of observation points makes it difficult to obtain actual evapotranspiration data in the river basin; 2) Remote sensing evapotranspiration, which uses the surface temperature inverted by thermal infrared remote sensing, supplemented by meteorological data and other remote sensing parameters to estimate actual evapotranspiration. It is an important method for estimating actual evapotranspiration and a hot area of ​​thermal infrared remote sensing research. The advantage is that it can estimate the actual evapotranspiration of a river basin over a large area with high spatial resolution. The disadvantage is that instantaneous remote sensing data can only estimate the actual evapotranspiration for a very short period of time, and the extrapolation of actual evapotranspiration for other periods of time will cause large temporal and spatial differences. Error; 3) Meteorological method, which deduces actual evapotranspiration based on the ratio of water vapor flow to momentum, requires input of wind speed and water vapor pressure at different heights, and involves aerodynamics of the near-surface layer. Its advantage is that it has a good physical basis, but its disadvantage is that the mathematical equations describing actual evapotranspiration are relatively complex and not convenient for practical application; 4) Model simulation, which has the advantage of being able to rely on meteorological reanalysis data and underlying surface parameters such as soil and vegetation to continuously predict actual evapotranspiration in time and space according to its inherent water transfer simulation equation. Although it is convenient for estimating the actual evapotranspiration of the basin, the low spatial resolution of meteorological reanalysis data during model simulation makes the spatial resolution of simulating actual evapotranspiration relatively low. In addition, the spatial resolution and time span of the underlying soil and vegetation parameters during simulation need to be improved, which inevitably causes errors in the simulation of actual evapotranspiration.

[0004] In order to estimate the actual evapotranspiration of a watershed more conveniently and quickly, reduce the limitations brought by the temporal and spatial resolution of meteorological data, and reduce the reliance on the physical parameter data of the underlying soil vegetation, a method for estimating the actual evapotranspiration of a watershed was invented by using the Budyko formula that describes the water-heat coupling process and considering the vegetation water use mechanism to reflect the physiological process of vegetation absorbing soil moisture for evapotranspiration. Summary of the invention

[0005] In order to overcome the shortcomings of the existing basin actual evapotranspiration estimation method, the purpose of the present invention is to provide a basin actual evapotranspiration estimation method that requires as little input as possible, has efficient calculation, is easy to apply, and can reflect the vegetation water use process, so as to improve the efficiency of basin actual evapotranspiration estimation and effectively reduce the error caused by the Budyko formula due to inadequate consideration of vegetation water use.

[0006] In view of the above technical problems, the present invention provides a method for estimating actual evapotranspiration of a watershed taking into account the water use mechanism of vegetation, comprising:

[0007] Obtain the input data set for the study period of the study basin and perform preprocessing;

[0008] The input data set is used to calculate the multi-year average precipitation of the whole area, which represents the multi-year average actual evapotranspiration water supply of the study basin, and the multi-year average potential evapotranspiration of the whole area, which represents the multi-year average actual evapotranspiration energy supply of the study basin;

[0009] The average net primary productivity of vegetation in the basin over many years is studied by expressing the photosynthetically active radiation absorbed by vegetation and the utilization rate of light energy.

[0010] The Budyko formula considering the water use mechanism of vegetation was developed to calculate the actual evapotranspiration of the whole basin averaged over many years.

[0011] In one embodiment, an input data set of a study period of a study basin is obtained and preprocessed, wherein the input data set includes: digital elevation model, precipitation, air temperature, daily minimum temperature, daily maximum temperature, actual water vapor pressure, solar radiation at the top of the atmosphere, actual sunshine hours, maximum possible sunshine hours, surface albedo, surface air pressure, 2-meter wind speed above the ground, day sequence, latitude, vegetation index, and maximum light energy utilization rate;

[0012] The preprocessing includes: using a digital elevation model to extract the boundary of the watershed, performing spatial interpolation on the meteorological data, using the watershed boundary to spatially clip the interpolated meteorological data and the surface albedo and vegetation index, and performing spatial averaging on the clipped input data set to obtain the multi-year average value of the entire study watershed.

[0013] In one embodiment, the input data set is used to calculate the multi-year average precipitation of the whole area representing the multi-year average actual evapotranspiration water supply of the study basin and the multi-year average potential evapotranspiration of the whole area representing the multi-year average actual evapotranspiration energy supply of the study basin, including:

[0014] The input data set is used to calculate the multi-year average precipitation of the whole area, which represents the multi-year average actual evapotranspiration water supply of the study basin, specifically:

[0015]

[0016] In the formula, G represents the number of grid points of input data after spatial interpolation in the study basin, Y represents the number of years of study time, and D y represents the number of days in year y, P gyd represents the daily precipitation at the g-th grid point on the d-th day of the y-th year in the study basin (mm / d), and P represents the multi-year average precipitation of the entire study basin (mm / year);

[0017] The input data set is used to calculate the multi-year average potential evapotranspiration of the whole basin, which represents the multi-year average actual evapotranspiration energy supply of the study basin. Specifically, it is:

[0018]

[0019]

[0020] In the formula, E gydP , R n , G 0 ,γ,Δ,T,u 2 、e s 、e a They represent the daily potential evapotranspiration (mm / d) and the daily net radiation on the crop surface (MJ / (m 2 d)), daily soil heat flux (MJ / (m 2 d)), daily average value of hygrometer constant (kPa / ℃), daily average value of slope of saturated water vapor pressure and temperature relationship curve (kPa / ℃), daily average value of air temperature (℃), daily average value of wind speed at 2m above the ground (m / s), daily average value of air saturated water vapor pressure (kPa), daily average value of actual air water vapor pressure (kPa), daily scale G 0 Assuming it is 0, by day E gydP The value can be used to obtain the multi-year average potential evapotranspiration E of the whole basin. P value.

[0021] In one embodiment, the multi-year average net primary productivity of vegetation in the entire watershed is studied by expressing the photosynthetically active radiation absorbed by vegetation and the light energy utilization rate, including:

[0022] Calculates the photosynthetically active radiation absorbed by vegetation, including:

[0023] The solar shortwave radiation flux received by the ground is calculated through the solar constant, sunshine hours, solar declination, day sequence, and daily solar radiation at the upper boundary of the atmosphere at different latitudes. Specifically:

[0024]

[0025]

[0026] d r =1+0.033cos(0.0172J)

[0027] rad=0.0409sin(0.0172J-1.39)

[0028]

[0029] In the formula, R s is the solar shortwave radiation flux (MJ / (m 2 d)), that is, the solar radiation received by the ground, n is the actual sunshine hours, directly obtained from the meteorological station, N is the possible maximum sunshine hours, n / N is the sunshine percentage, J is the day sequence, lat is the latitude of the grid point, π is pi, and rad is the solar magnetic declination (rad);

[0030] Calculate the absorption ratio of the vegetation layer to the incident photosynthetically active radiation, specifically:

[0031]

[0032] Where, VI max To study the maximum value of the watershed vegetation index, VI min To study the minimum value of the vegetation index in the watershed, for a watershed covered by multiple vegetation, VI max and VI min In order to study the minimum and maximum values ​​of vegetation index of various vegetation types in the basin by area weight, FPAR max In order to study the maximum value of the incident photosynthetically active radiation absorption ratio of the vegetation in the basin, FPAR min In order to study the minimum value of the incident photosynthetically active radiation absorption ratio of watershed vegetation, for watersheds covered by multiple vegetation types, FPAR max and FPAR min To study the minimum and maximum area-weighted values ​​of the incident photosynthetically active radiation absorption ratio of various vegetation types in the basin;

[0033] Calculate the photosynthetically active radiation absorbed by vegetation, specifically:

[0034] APAR=0.5R sFPAR

[0035] In the formula, the constant 0.5 means that the effective solar radiation that can be used by vegetation accounts for half of the total solar radiation;

[0036] Calculate the light energy utilization rate of vegetation, specifically:

[0037] ε=T ε1 T ε2 W ε ε max

[0038]

[0039] T ε2 =1.184(1+exp(0.2(T opt -10-T)) / exp(0.3(T opt -10+T)))

[0040] W ε =0.5+0.5ET / E P

[0041] Where ε is the light energy conversion rate of vegetation (gC / MJ), T ε1 and T ε2 is the temperature stress coefficient, ε max is the maximum light energy conversion rate of vegetation under ideal conditions (gC / MJ). When studying a watershed with multiple vegetation coverage, it can be obtained by weighting the maximum light energy conversion rate of each vegetation by area. opt The average temperature of the month when the vegetation index reaches the highest in the basin is considered to be the most suitable temperature for vegetation growth. When the average temperature of a month is less than or equal to -10℃, T opt is 0, that is, photosynthetic production is 0, T ε1 represents the limitation of plant sublimation on photosynthesis under low and high temperature conditions, T ε2 Indicates that the temperature changes from the most suitable temperature T opt The effect of changing to high and low temperatures on the gradual decrease in light energy conversion efficiency is that when the average temperature of a month is 10℃ higher or 13℃ lower than the most suitable temperature, the T ε2 Equal to the average temperature of the month when it is the most suitable temperature T ε2 Half of the value, W ε It represents the water stress coefficient, reflecting the effect of water conditions on the conversion of vegetation light energy. Its value range is 0.5-1, where 0.5 corresponds to extremely dry conditions and 1 corresponds to very wet conditions. ET is the average actual evapotranspiration of the study basin over many years (mm / year). P To study the multi-year average potential evapotranspiration of the basin (mm / year);

[0042] The average net primary productivity of vegetation in the whole basin over many years was obtained, specifically:

[0043]

[0044]

[0045] Where, NPP gym represents the average monthly vegetation net primary productivity (gC / (m 2 month)), NPP represents the average net primary productivity of vegetation in the whole basin over many years (gC / (m 2 year);

[0046] In one embodiment, the Budyko formula considering the water use mechanism of vegetation is developed to calculate the actual evapotranspiration of the basin averaged over many years in the entire basin, including:

[0047] The Budyko formula considering the water use mechanism of vegetation is developed as follows:

[0048]

[0049] In the formula, ω represents the vegetation water use coefficient. Substituting ω = NPP / ET into the above formula, we can get:

[0050]

[0051]

[0052] Through mathematical derivation, the above formula can be converted into:

[0053]

[0054] The analytical solution of the above quadratic equation is:

[0055]

[0056] Where ET is the actual evapotranspiration of the whole basin averaged over many years (mm / year).

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] The invention provides a method for estimating actual evapotranspiration of a watershed considering the water use mechanism of vegetation. Compared with the method for estimating actual evapotranspiration of a watershed using the traditional Budyko formula, the invention considers the comprehensive water use efficiency of the vegetation system in the traditional Budyko formula, and expresses it as the ratio of the net primary productivity of vegetation to the water consumed by evapotranspiration, thereby expanding the value range [0.1, 2.0] of the vegetation water use coefficient in the traditional Budyko formula to an adaptive value for the growth and development of vegetation according to natural climatic conditions, and studying the multi-year average net primary productivity of vegetation in the whole watershed through the expression of photosynthetically active radiation absorbed by vegetation and light energy utilization rate, which is specifically embodied in that the photosynthetically active radiation absorbed by vegetation is segmented using the absorption ratio of the vegetation layer to the incident photosynthetically active radiation, and the light energy utilization rate of vegetation is quantified using the temperature stress coefficient and the water stress coefficient reflecting the influence of water conditions on the light energy conversion of vegetation, thereby improving the quantification degree of vegetation in the process of calculating actual evapotranspiration of the watershed using the traditional Budyko formula as much as possible, and also improving the estimation accuracy of actual evapotranspiration of the watershed. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to better explain the technical solutions in the embodiments of the present invention, the following is a summary of the drawings used in the embodiments of the present invention. It is obvious that the following drawings are only some embodiments of the present invention and should not be regarded as limiting the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative work.

[0060] Figure 1 A flow chart of a method in an embodiment of the present invention; DETAILED DESCRIPTION

[0061] The following will be combined with the drawings in the embodiments of the present invention to describe the purpose, technical solutions and features of the embodiments of the present invention in detail and completely. It is obvious that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. With reference to the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] The purpose of the present invention is to provide a method for estimating the actual evapotranspiration of a watershed taking into account the water use mechanism of vegetation, thereby improving the degree of quantification of vegetation in the process of calculating the actual evapotranspiration of a watershed using the traditional Budyko formula. In order to make the purpose, features and advantages of the present invention more obvious, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0063] Please refer to Figure 1 , Figure 1 The method flow chart of the embodiment provided by the present invention is as follows Figure 1 The method comprises the following steps:

[0064] S1 obtains the input data set of the study basin and the study period and performs preprocessing;

[0065] S2 uses the input data set to calculate the multi-year average precipitation of the whole area, which represents the multi-year average actual evapotranspiration water supply of the study basin, and the multi-year average potential evapotranspiration of the whole area, which represents the multi-year average actual evapotranspiration energy supply of the study basin;

[0066] S3 studies the multi-year average net primary productivity of vegetation in the basin through the expression of photosynthetically active radiation absorbed by vegetation and light energy utilization rate;

[0067] S4 developed the Budyko formula taking into account the water use mechanism of vegetation to calculate the actual evapotranspiration of the entire basin averaged over many years.

[0068] As a further preferred technical solution, in step S1, the input data set of the study basin study period is obtained and preprocessed, and the input data set includes: digital elevation model, precipitation, air temperature, daily minimum temperature, daily maximum temperature, actual water vapor pressure, solar radiation at the top of the atmosphere, actual sunshine hours, maximum possible sunshine hours, surface albedo, surface air pressure, 2-meter wind speed above the ground, day sequence, latitude, vegetation index, and maximum light energy utilization rate;

[0069] The preprocessing includes: using a digital elevation model to extract the boundary of the watershed, performing spatial interpolation on the meteorological data, using the watershed boundary to spatially clip the interpolated meteorological data and the surface albedo and vegetation index, and performing spatial averaging on the clipped input data set to obtain the multi-year average value of the entire study watershed.

[0070] As a further preferred technical solution, in step S2, the use of the input data set to calculate the global multi-year average precipitation representing the multi-year average actual evapotranspiration water supply of the study basin and the global multi-year average potential evapotranspiration representing the multi-year average actual evapotranspiration energy supply of the study basin includes:

[0071] The input data set is used to calculate the multi-year average precipitation of the whole area, which represents the multi-year average actual evapotranspiration water supply of the study basin, specifically:

[0072]

[0073] In the formula, G represents the number of grid points of input data after spatial interpolation in the study basin, Y represents the number of years of study time, and D y represents the number of days in year y, P gyd represents the daily precipitation at the g-th grid point on the d-th day of the y-th year in the study basin (mm / d), and P represents the multi-year average precipitation of the entire study basin (mm / year);

[0074] The input data set is used to calculate the multi-year average potential evapotranspiration of the whole basin, which represents the multi-year average actual evapotranspiration energy supply of the study basin. Specifically, it is:

[0075]

[0076]

[0077] In the formula, E gydP , R n , G 0 ,γ,Δ,T,u 2 、e s 、e a They represent the daily potential evapotranspiration (mm / d) and the daily net radiation on the crop surface (MJ / (m 2 d)), daily soil heat flux (MJ / (m 2 d)), daily average value of hygrometer constant (kPa / ℃), daily average value of slope of saturated water vapor pressure and temperature relationship curve (kPa / ℃), daily average value of air temperature (℃), daily average value of wind speed at 2m above the ground (m / s), daily average value of air saturated water vapor pressure (kPa), daily average value of actual air water vapor pressure (kPa), daily scale G 0 Assuming it is 0, by day E gydP The value can be used to obtain the multi-year average potential evapotranspiration E of the whole basin. P value.

[0078] As a further preferred technical solution, in step S3, the expression of the photosynthetically active radiation absorbed by vegetation and the light energy utilization rate to study the multi-year average net primary productivity of vegetation in the entire basin includes:

[0079] Calculates the photosynthetically active radiation absorbed by vegetation, including:

[0080] The solar shortwave radiation flux received by the ground is calculated through the solar constant, sunshine hours, solar declination, day sequence, and daily solar radiation at the upper boundary of the atmosphere at different latitudes. Specifically:

[0081]

[0082]

[0083] d r =1+0.033cos(0.0172J)

[0084] rad=0.0409sin(0.0172J-1.39)

[0085]

[0086] In the formula, Rs is the solar shortwave radiation flux (MJ / (m 2 d)), that is, the solar radiation received by the ground, n is the actual sunshine hours, directly obtained from the meteorological station, N is the possible maximum sunshine hours, n / N is the sunshine percentage, J is the day sequence, lat is the latitude of the grid point, π is pi, and rad is the solar magnetic declination (rad);

[0087] Calculate the absorption ratio of the vegetation layer to the incident photosynthetically active radiation, specifically:

[0088]

[0089] Where, VI max To study the maximum value of the watershed vegetation index, VI min To study the minimum value of the vegetation index in the watershed, for a watershed covered by multiple vegetation, VI max and VI min In order to study the minimum and maximum values ​​of vegetation index of various vegetation types in the basin by area weight, VI max and VI min In order to study the minimum and maximum values ​​of vegetation index of various vegetation types in the basin by area weight, FPAR max In order to study the maximum value of the incident photosynthetically active radiation absorption ratio of the vegetation in the basin, FPAR min In order to study the minimum value of the incident photosynthetically active radiation absorption ratio of watershed vegetation, for watersheds covered by multiple vegetation types, FPAR max and FPAR min To study the minimum and maximum area-weighted values ​​of the incident photosynthetically active radiation absorption ratio of various vegetation types in the basin;

[0090] Calculate the photosynthetically active radiation absorbed by vegetation, specifically:

[0091] APAR=0.5R s FPAR

[0092] In the formula, the constant 0.5 means that the effective solar radiation that can be used by vegetation accounts for half of the total solar radiation;

[0093] Calculate the light energy utilization rate of vegetation, specifically:

[0094] ε=T ε1 T ε2 W ε ε max

[0095]

[0096] T ε2 =1.184(1+exp(0.2(T opt-10-T)) / exp(0.3(T opt -10+T)))

[0097] W ε =0.5+0.5ET / E P

[0098] Where ε is the light energy conversion rate of vegetation (gC / MJ), T ε1 and T ε2 is the temperature stress coefficient, ε max is the maximum light energy conversion rate of vegetation under ideal conditions (gC / MJ). When studying a watershed with multiple vegetation coverage, it can be obtained by weighting the maximum light energy conversion rate of each vegetation by area. opt The average temperature of the month when the vegetation index reaches the highest in the basin is considered to be the most suitable temperature for vegetation growth. When the average temperature of a month is less than or equal to -10℃, T opt is 0, that is, photosynthetic production is 0, T ε1 represents the limitation of plant sublimation on photosynthesis under low and high temperature conditions, T ε2 Indicates that the temperature changes from the most suitable temperature T opt The effect of changing to high and low temperatures on the gradual decrease in light energy conversion efficiency is that when the average temperature of a month is 10℃ higher or 13℃ lower than the most suitable temperature, the T ε2 Equal to the average temperature of the month when it is the most suitable temperature T ε2 Half of the value, W ε It represents the water stress coefficient, reflecting the effect of water conditions on the conversion of vegetation light energy. Its value range is 0.5-1, where 0.5 corresponds to extremely dry conditions and 1 corresponds to very wet conditions. ET is the average actual evapotranspiration of the study basin over many years (mm / year). P To study the multi-year average potential evapotranspiration of the basin (mm / year);

[0099] The average net primary productivity of vegetation in the whole basin over many years was obtained, specifically:

[0100]

[0101]

[0102] Where, NPP gym represents the average monthly vegetation net primary productivity (gC / (m 2 month)), NPP represents the average net primary productivity of vegetation in the whole basin over many years (gC / (m 2 year);

[0103] As a further preferred technical solution, in step S4, the Budyko formula developed taking into account the water use mechanism of vegetation is used to calculate the multi-year average actual evapotranspiration of the entire basin, including:

[0104] The Budyko formula considering the water use mechanism of vegetation is developed as follows:

[0105]

[0106] In the formula, ω represents the vegetation water use coefficient. Substituting ω = NPP / ET into the above formula, we can get:

[0107]

[0108]

[0109] Through mathematical derivation, the above formula can be converted into:

[0110]

[0111] The analytical solution of the above quadratic equation is:

[0112]

[0113] Where ET is the actual evapotranspiration of the whole basin averaged over many years (mm / year).

[0114] The beneficial effects of the present invention are as follows:

[0115] The present invention takes into account the water consumption mechanism in the process of producing the total amount of organic matter through photosynthesis of vegetation ecosystems, and expresses the vegetation contribution in the actual evapotranspiration estimation of the traditional Budyko formula as the ratio of the net primary productivity of vegetation to the water consumed by evapotranspiration, thereby improving the degree of vegetation participation in the actual evapotranspiration estimation of the traditional Budyko formula, and providing method support for the optimal allocation, accurate evaluation and efficient utilization of surface water resources in the basin.

[0116] This specification describes various embodiments in a progressive manner, and each embodiment focuses on describing the differences from other embodiments. Similar parts between the embodiments can be referenced to each other.

[0117] This specification explains the main ideas, technical features and practical methods of the present invention through specific examples. The above embodiments are only used to help understand the basic principles and core technologies of the present invention. At the same time, for ordinary technicians in this field, according to the ideas of the present invention, certain links of the method proposed in the present invention can be equivalently replaced and changed in terms of implementation steps and application scope. These changes do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and are all within the protection scope of the present invention.

Claims

1. A method for estimating actual evapotranspiration in a watershed taking into account the water use mechanism of vegetation, characterized in that: include: Obtain the input data set for the study period of the study basin and perform preprocessing; The input data set is used to calculate the multi-year average precipitation of the whole area, which represents the multi-year average actual evapotranspiration water supply of the study basin, and the multi-year average potential evapotranspiration of the whole area, which represents the multi-year average actual evapotranspiration energy supply of the study basin; The average net primary productivity of vegetation in the basin over many years is studied by expressing the photosynthetically active radiation absorbed by vegetation and the utilization rate of light energy. The Budyko formula considering the water use mechanism of vegetation is developed to calculate the actual evapotranspiration of the basin averaged over many years, including: The Budyko formula considering the water use mechanism of vegetation is developed as follows: In the formula, ω represents the vegetation water use coefficient. Substituting ω = NPP / ET into the above formula, we can get: Through mathematical derivation, the above formula can be converted into: The analytical solution of the above quadratic equation is: Where ET is the actual evapotranspiration of the whole basin averaged over many years, in mm / year.

2. The method according to claim 1, characterized in that The input data set of the study basin and the study period is obtained and preprocessed, and the input data set includes: digital elevation model, precipitation, air temperature, daily minimum temperature, daily maximum temperature, actual water vapor pressure, solar radiation at the top of the atmosphere, actual sunshine hours, maximum possible sunshine hours, surface albedo, surface air pressure, 2-meter wind speed above the ground, day sequence, latitude, vegetation index, and maximum light energy utilization rate; The preprocessing includes: using a digital elevation model to extract the boundary of the watershed, performing spatial interpolation on the meteorological data, using the watershed boundary to spatially clip the interpolated meteorological data and the surface albedo and vegetation index, and performing spatial averaging on the clipped input data set to obtain the multi-year average value of the entire study watershed.

3. The method according to claim 1, characterized in that The input data set is used to calculate the multi-year average precipitation of the whole area representing the multi-year average actual evapotranspiration water supply of the study basin and the multi-year average potential evapotranspiration of the whole area representing the multi-year average actual evapotranspiration energy supply of the study basin, including: The input data set is used to calculate the multi-year average precipitation of the whole area, which represents the multi-year average actual evapotranspiration water supply of the study basin, specifically: In the formula, G represents the number of grid points of input data after spatial interpolation in the study basin, Y represents the number of years of study time, and D y represents the number of days in year y, P gyd represents the daily precipitation at the g-th grid point in the study basin on the d-th day of the y-th year, in mm / d, and P represents the multi-year average precipitation of the entire study basin, in mm / year; The input data set is used to calculate the multi-year average potential evapotranspiration of the whole basin, which represents the multi-year average actual evapotranspiration energy supply of the study basin. Specifically, it is: In the formula, E gydP , R n ,G0,γ,Δ,T,u2,e s 、e a They represent the daily potential evapotranspiration at the g-th grid point in the study basin on the d-th day of the y-th year, in mm / d, and the daily net radiation on the crop surface, in MJ / (m 2 d) Daily soil heat flux, in MJ / (m 2 d) Daily average value of hygrometer constant, in kPa / ℃, daily average value of slope of saturated water vapor pressure and temperature relationship curve, in kPa / ℃, daily average value of air temperature, in ℃, daily average value of wind speed at 2m above ground, in m / s, daily average value of saturated water vapor pressure of air, in kPa, daily average value of actual water vapor pressure of air, in kPa, daily scale G0 is assumed to be 0, and the daily E gydP The value can be used to obtain the multi-year average potential evapotranspiration E of the whole basin. P value.

4. The method according to claim 1, characterized in that The above method of expressing the multi-year average net primary productivity of vegetation in the whole basin through the photosynthetically active radiation absorbed by vegetation and the utilization rate of light energy includes: Calculates the photosynthetically active radiation absorbed by vegetation, including: The solar shortwave radiation flux received by the ground is calculated through the solar constant, sunshine hours, solar declination, day sequence, and daily solar radiation at the upper boundary of the atmosphere at different latitudes. Specifically: d r =1+0.033cos(0.0172J) rad=0.0409sin(0.0172J-1.39) In the formula, R s is the solar shortwave radiation flux, in MJ / (m 2 d), that is, the solar radiation received by the ground, n is the actual sunshine hours, directly obtained from the meteorological station, N is the possible maximum sunshine hours, n / N is the sunshine percentage, J is the day sequence, lat is the latitude of the grid point, π is pi, and rad is the solar magnetic declination, the unit is rad; Calculate the absorption ratio of the vegetation layer to the incident photosynthetically active radiation, specifically: Where, VI max To study the maximum value of the watershed vegetation index, VI min To study the minimum value of the vegetation index in the watershed, for a watershed covered by multiple vegetation, VI max and VI min In order to study the minimum and maximum values ​​of vegetation index of various vegetation types in the basin by area weight, FPAR max In order to study the maximum value of the incident photosynthetically active radiation absorption ratio of the vegetation in the basin, FPAR min In order to study the minimum value of the incident photosynthetically active radiation absorption ratio of watershed vegetation, for watersheds covered by multiple vegetation types, FPAR max and FPAR min To study the minimum and maximum area-weighted values ​​of the incident photosynthetically active radiation absorption ratio of various vegetation types in the basin; Calculate the photosynthetically active radiation absorbed by vegetation, specifically: APAR=0.5R s FPAR In the formula, the constant 0.5 means that the effective solar radiation that can be used by vegetation accounts for half of the total solar radiation; Calculate the light energy utilization rate of vegetation, specifically: ε=T ε1 T ε2 W ε e max T ε2 =1.184(1+exp(0.2(T opt -10-T)) / exp(0.3(T opt -10+T))) W ε =0.5+0.5ET / E P Where ε is the light energy conversion rate of vegetation, in units of gC / MJ, T ε1 and T ε2 is the temperature stress coefficient, ε max is the maximum light energy conversion rate of vegetation under ideal conditions, in gC / MJ. When studying a watershed with multiple vegetation coverage, it can be obtained by weighting the maximum light energy conversion rate of each vegetation by area. opt The average temperature of the month when the vegetation index reaches the highest in the basin is considered to be the most suitable temperature for vegetation growth. When the average temperature of a month is less than or equal to -10℃, T opt is 0, that is, photosynthetic production is 0, T ε1 represents the limitation of plant sublimation on photosynthesis under low and high temperature conditions, T ε2 Indicates that the temperature changes from the most suitable temperature T opt The effect of changing to high and low temperatures on the gradual decrease in light energy conversion efficiency is that when the average temperature of a month is 10℃ higher or 13℃ lower than the most suitable temperature, the T ε2 Equal to the average temperature of the month when it is the most suitable temperature T ε2 Half of the value, W ε It represents the water stress coefficient, reflecting the effect of water conditions on the conversion of vegetation light energy. Its value range is 0.5-1, where 0.5 corresponds to extremely dry conditions and 1 corresponds to very wet conditions. ET is the average actual evapotranspiration of the study basin over many years, in mm / year. E P To study the multi-year average potential evapotranspiration of the basin, the unit is mm / year; The average net primary productivity of vegetation in the whole basin over many years was obtained, specifically: Where, NPP gym It represents the average monthly vegetation net primary productivity of the g-th grid point in the study basin in the m-th month of the y-th year, and the unit is gC / (m 2 month), NPP represents the average net primary productivity of vegetation in the whole basin over many years, and the unit is gC / (m 2 year).

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