A method for calculating water body heat change by combining net radiation and water-temperature difference

Abstract

The present invention relates to a method for calculating water body heat change by combining net radiation with the water-temperature difference. The method comprises the following steps: collecting basic data, calculating net radiation, calculating the net radiation change rate, calculating the water-temperature difference change process, calibrating the parameters of the calculation formula, and finally calculating the water body heat change. Compared to existing methods for calculating water body heat change that require water temperature data for the entire profile, the method described in the present invention not only eliminates the need for continuous observation or simulation of the entire water body temperature profile, but also simultaneously considers the hysteresis of water body heat change relative to net radiation, as well as heat exchange between the water body and the atmosphere above the water surface, significantly improving the efficiency and accuracy of water body heat change calculations.

Description

Technical Field

[0001] The present invention belongs to the field of hydrological analysis and calculation, and particularly relates to a method for calculating water body heat change by combining net radiation and water-air temperature difference. Background Art

[0002] Water has a high specific heat capacity and low thermal conductivity, resulting in significant heat storage and release potential. Reservoirs (lakes) absorb and store solar radiation in spring and summer, releasing it in autumn and winter. Variations in water heat affect their energy budget, which in turn influences water temperature and surface evaporation, significantly impacting aquatic ecosystems such as reservoirs and lakes. The impact of thermal variations is even more pronounced in deepwater bodies like the Three Gorges Reservoir. Accurately calculating these variations is key to accurately estimating reservoir (lake) water temperature and surface evaporation.

[0003] Currently, traditional methods for calculating water body heat changes require continuous observation or simulation of the entire water temperature profile, as well as data on outflow and inflow flow rates and water temperatures. This data observation is time-consuming and labor-intensive. Traditional empirical methods for calculating water body heat changes include the net radiation hysteresis method and the net heat exchange coefficient method, but neither fully considers the factors that influence water body heat changes. The net radiation hysteresis method only considers the effect of radiation energy lag, while the net heat exchange coefficient method only considers the difference between water and air temperatures, resulting in low calculation accuracy.

[0004] Therefore, how to effectively improve the calculation efficiency and accuracy of water body heat changes is a problem that needs to be solved. Summary of the Invention

[0005] To overcome the limitations of existing technologies, the present invention proposes a method for calculating water body heat changes that combines net radiation with the water-temperature difference. This method not only eliminates the need for continuous observation or simulation of the entire water body's temperature profile, but also accounts for the hysteresis of water body heat changes relative to net radiation, as well as heat exchange between the water body and the atmosphere above it, significantly improving the efficiency and accuracy of water body heat change calculations.

[0006] The object of the present invention is achieved like this:

[0007] A method for calculating water body heat change by combining net radiation and water-temperature difference comprises the following steps:

[0008] Step 1: Collection of basic data:

[0009] Determine the latitude and altitude of the target water body and the calculation period of water body heat change (above the daily scale), and collect the average water surface temperature T for each period. w , meteorological data and water surface evaporation data on the water surface;

[0010] The meteorological data on the water surface include: average temperature T a , average water vapor pressure e a , sunshine hours n, average wind speed u at 2 m above the water surface;

[0011] Step 2, calculation of net radiation:

[0012] Using the average water surface temperature T w , average temperature on the water surface T a , average water vapor pressure e a and sunshine hours n, calculate the net radiation R in each period n ;

[0013] Step 3, calculation of net radiation change rate:

[0014] The net radiation R calculated in step 2 is n , calculate the net radiation change rate

[0015] Step 4: Calculation of the water-temperature difference change process:

[0016] Calculate the water surface temperature T w and the water surface temperature T a , the difference between the two is T w -T a The period-by-period change process;

[0017] Step 5, calculate the calibration of the formula parameters:

[0018] Using the meteorological data and water surface evaporation data collected in step 1, the net radiation R calculated in step 2 n , the net radiation change rate calculated in step 3 and the water-temperature difference T calculated in step 4 w -T a , calibrate the parameters of the water surface evaporation simulation formula including the heat change of the water body;

[0019] Step 6, calculation of water body heat change:

[0020] The net radiation R calculated using steps 2-4 is n , net radiation change rate R n The difference between water temperature and air temperature T w -T a , and use the parameters calibrated in step 5 to calculate the heat change of the water body. The formula is:

[0021]

[0022] Where ΔQ is the change in water body heat, α HTare the parameters of the water surface evaporation calculation formula, and c1-c4 are empirical parameters.

[0023] Furthermore, in step 2, the net radiation R n The specific calculation steps include:

[0024] S21, calculate the solar declination δ and the correction parameter d of the distance between the sun and the earth according to the number of days J corresponding to the middle day of the calculated period in a year r :

[0025]

[0026] Where DOY is the total number of days in a year; the calculation step is day-time, J takes values ​​between 1 and DOY, and the step is the number of days in a year corresponding to the middle day of the calculation period;

[0027] S22, according to the latitude of the target water body Calculate the sunset angle ω using the solar declination δ s :

[0028]

[0029] S23, correct the parameter d according to the distance between the sun and the earth r 、sunset angle ω s ,latitude Calculate the solar sky total radiation R using the solar declination δ a :

[0030]

[0031] S24, according to the sunset angle ω s Calculate the maximum astronomical sunshine hours N:

[0032]

[0033] S25, based on the total solar radiation R a , calculate the net shortwave radiation R using the sunshine hours n collected in step 1 and the maximum astronomical sunshine hours N s :

[0034]

[0035] Where α is the albedo of the water surface, a s 、b s is a dimensionless empirical coefficient;

[0036] S26, based on the average water surface temperature T on the target water body collected in step 1 w 、Average water vapor pressure on the water surface e a , sunshine hours n, and the maximum astronomical sunshine hours N to calculate the net longwave radiation Rnl :

[0037]

[0038] Where σ is the Stefan-Boltzmann constant, ε is the emissivity of the water surface;

[0039] S27, based on the net shortwave radiation R s and net longwave radiation R nl Calculate radiation R n :

[0040] R n =R ns -R nl .

[0041] Furthermore, the net radiation change rate in step 3 is The specific calculation steps include:

[0042] S31, the net radiation R calculated in each time period according to step 2 n And calculate the number of days J corresponding to the middle day of the period in a year to calculate the net radiation R n The fitted regression equation is:

[0043]

[0044] Where a1, a2 and a3 are the fitting coefficients of the net radiation regression equation; DOY is the total number of days in a year;

[0045] S32, calculate the net radiation change rate based on the net radiation fitting regression equation calculated in S31

[0046]

[0047] Where M is the number of days included in the calculation period.

[0048] Furthermore, the parameter calibration of the water surface evaporation simulation formula in step 5 specifically includes the following steps:

[0049] S51, using the average temperature T a Calculate the saturated water vapor pressure e s , the slope Δ of the saturated water vapor pressure versus temperature curve, and the hygrometer constant γ:

[0050]

[0051] Where λ = 2501 - 2.361T a is the latent heat of vaporization, P a is the average atmospheric pressure, based on the water surface altitude H and temperature T a calculate:

[0052]

[0053] S52, calculate the aerodynamic term E for potential evaporation using the average wind speed u at 2 m above the water and the data obtained in S51 aero :

[0054]

[0055] S53, the average measured water surface evaporation E of group M2 in each period obs The simulated value E of water surface evaporation in each time period calculated using the following formula containing five parameters esti The goal is to minimize the mean absolute error MAE, and use the optimization algorithm to determine the parameter α HT , c1-c4, the optimized mean absolute error MAE is:

[0056]

[0057] Simulated value of water surface evaporation E at each time period esti By E obsi The corresponding aerodynamic term E of potential evaporation at each time period aero and the radiation term E containing the potential evaporation parameter rad The following formula is used for calculation:

[0058]

[0059] Where, α HT is the parameter of the water surface evaporation calculation formula, E rad Calculated by the following formula:

[0060]

[0061] Where, That is the change in water body heat, c1-c4 are empirical parameters.

[0062] The advantages and beneficial effects of the present invention are:

[0063] 1. Compared with the existing water body heat change calculation method which requires the water temperature data of the entire section, this patent application only requires the water surface temperature T w , conventional meteorological data and water surface evaporation data on the water surface. Since the data that are difficult to observe and simulate, such as water temperature profile and flow, are not required, the data required by the method of the present invention are easier to obtain; in particular, the water surface temperature T w Remote sensing data can be used to obtain data more accurately and conveniently. Conventional meteorological data on the water surface can be further obtained by converting data from meteorological stations in neighboring countries. After the parameters are clarified, water surface evaporation data can be omitted, and the data requirements can be further reduced.

[0064] 2. The present invention uses water surface temperature and conventional aquatic meteorological data to calculate and monitor changes in water body heat on a daily, ten-day, or monthly scale. This method takes into account both the hysteresis of water body heat changes relative to net radiation and the heat exchange between the water body and the atmosphere above the water surface. This method has the advantages of requiring less basic data, being easy to obtain, and a more comprehensive consideration of influencing factors with higher accuracy.

[0065] 3. Based on the method described in the present invention, it is possible to conveniently use the water surface temperature and conventional meteorological data on the water surface to establish a water body heat change monitoring system, which solves the problem in the existing technology that obtaining water body heat changes requires a large amount of observation of the water body temperature profile, which consumes manpower and material resources. At the same time, it greatly improves the calculation accuracy of the existing water body heat change. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The present invention will be further described below with reference to the accompanying drawings and examples.

[0067] Figure 1 It is a flow chart of the calculation process of the method for calculating the heat change of water body according to the present invention;

[0068] Figure 2 The figure shows the monthly variation of the net radiation calculated by the embodiment of the present invention;

[0069] Figure 3 The net radiation change rate calculated by the embodiment of the present invention is shown as follows: Monthly changes in

[0070] Figure 4 The water-temperature difference T calculated by the embodiment of the present invention is shown. w -T a Monthly changes in

[0071] Figure 5 The comparison results of the water body heat changes calculated by the method of the present invention and the measured values ​​are shown;

[0072] Figure 6 The comparison results of the monthly water body heat changes calculated by the existing net radiation hysteresis method and the measured values ​​are shown;

[0073] Figure 7 The comparison results of the monthly water body heat changes calculated by the existing net heat exchange method and the measured values ​​are given. DETAILED DESCRIPTION

[0074] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0075] like Figure 1 As shown, this embodiment provides a method for calculating water body heat change by combining net radiation and water-temperature difference, including the following steps:

[0076] Step 1: Collection of basic data:

[0077] Determine the latitude of the target water body ( The unit is rad) and the altitude (H, the unit is m), as well as the calculation period of water body heat change. Collect the daily average water surface temperature T during the calculation period w (unit is ℃) and the daily average temperature on the water surface T a (unit is ℃), daily average water vapor pressure e a (unit is kPa), sunshine hours n (unit is hour) and daily average wind speed u 2m above the water surface (unit is m / s) data.

[0078] If there is no sunshine hours data on the water surface, the data from the meteorological station of the neighboring country can be used instead. The monthly average data is obtained by arithmetic mean (if the monthly average data is collected, it can be used directly), the total number of data groups M1 is determined, and the monthly average water surface evaporation E of the M2 group corresponding to the partial calculation data is collected. obs The data (units are mm / day) are used for parameter calibration to ensure that the length of the water surface evaporation series is greater than one year, and that M1 ≥ M2 ≥ 12. Calculate the number of days J corresponding to the middle day of each data month (the average number of days in a year for this period, for example, January is the 15th day of the year). The values ​​are as follows:

[0079] Table 1 The number of days J corresponding to the middle day of different months in a year

[0080]

[0081] Step 2, calculation of net radiation:

[0082] Using the monthly average water surface temperature T w , water surface temperature T a , water vapor pressure e a and sunshine hours n, calculate the monthly net radiation R n .

[0083] S21, calculate the solar declination δ (in rad) and the sun-earth distance correction parameter d based on the number of days J in a year for the calculated day or the middle day of the month r :

[0084]

[0085] Where DOY is the total number of days in a year (366 in leap years and 365 in non-leap years); the calculation step is the number of days in a year corresponding to the middle day of the corresponding month;

[0086] S22, according to the latitude of the target water body Calculate the sunset angle ω using the solar declination δ s (unit is rad):

[0087]

[0088] S23, correct the parameter d according to the distance between the sun and the earth r 、sunset angle ω s ,latitude Calculate the solar sky total radiation R using the solar declination δ a (The unit is MJ / (m 2 d)):

[0089]

[0090] S24, according to the sunset angle ω s Calculate the maximum astronomical sunshine hours N (in hours):

[0091]

[0092] S25, based on the total solar radiation R a Calculate the net shortwave radiation R using the sunshine hours n (in hours) obtained in step 1 and the maximum astronomical sunshine hours N. s (The unit is MJ / (m 2 ·dayay)):

[0093]

[0094] Where α is the water surface albedo, which is determined based on actual measurements of the target water body. If there is no actual measurement data, the latitude of the water body can be used to determine the value for that month (unit: %), see Table 2.

[0095] Table 2 Water surface albedo at different latitudes in different months (unit %)

[0096] latitude January February March April May June July August September October November December 10° 8.76 8.4 8.03 7.67 7.95 8.13 8.09 7.83 7.88 8.3 8.79 8.89 20° 9.2 8.78 8.37 8.03 7.7 7.77 7.71 7.9 8.25 8.7 9.29 9.34 30° 9.67 9.19 8.75 8.43 8.02 7.9 7.99 8.35 8.66 9.15 9.82 9.84 40° 10.17 9.63 9.16 8.87 8.38 8.29 8.4 8.85 9.11 9.63 10.41 10.37 50° 10.72 10.11 9.61 9.35 8.79 8.72 8.87 9.4 9.6 10.15 11.05 10.95 60° 11.3 10.62 10.08 9.89 9.24 9.19 9.38 10 10.13 10.71 11.74 11.57

[0097] a s 、b sis a dimensionless empirical coefficient, which is determined based on the data of the radiation observation station near the research target water body. If there is no radiation observation station nearby, a s =0.25, b s =0.5.

[0098] S26, based on the daily average water surface temperature T on the observed target water body w 、Daily average water vapor pressure on the water surface e a , sunshine hours n, and the maximum astronomical sunshine hours N to calculate the net longwave radiation R nl :

[0099]

[0100] Where σ is the Stefan Boltzmann constant, 4.903×10 -9 MJ / (K 4 ·m 2 ·day); ε is the emissivity of the water surface, which is 0.97; a s 、b s The value is the same as that in the above step S25.

[0101] S27, based on the net shortwave radiation R s and net longwave radiation R nl Calculate radiation R n (The unit is MJ / (m 2 day)):

[0102] R n =R ns -R nl .

[0103] Step 3, calculation of net radiation change rate:

[0104] The monthly net radiation R calculated in step 2 n , calculate the net radiation change rate

[0105] S31, monthly net radiation R calculated according to step 2 n And the number of days J corresponding to the middle day of the corresponding month in a year to calculate the net radiation R n The fitted regression equation is:

[0106]

[0107] Where a1, a2 and a3 are dimensionless fitting coefficients of the net radiation regression equation; DOY is the total number of days in a year.

[0108] S32, calculate the net radiation change rate based on the net radiation fitting regression equation calculated in S31

[0109]

[0110] Where M is the number of days in a month.

[0111] Step 4: Calculation of the water-temperature difference change process:

[0112] Calculate the water surface temperature T w and the water surface temperature T a (Unit is ℃), the difference between the two is T w -T a Monthly changes in the process.

[0113] Step 5, calculate the calibration of the formula parameters:

[0114] Using the meteorological data and water surface evaporation data collected in step 1, the net radiation R calculated in step 2 n , the net radiation change rate calculated in step 3 and the water-temperature difference T calculated in step 4 w -T a , calibrate the parameters of the water surface evaporation simulation formula including the heat change of the water body.

[0115] S51, using the monthly average temperature T a Calculate the saturated water vapor pressure e monthly s (unit is kPa), the slope of the saturated water vapor pressure and temperature curve Δ (unit is kPa / ℃) and the hygrometer constant γ (unit is kPa / ℃):

[0116]

[0117] Where λ = 2501 - 2.361T a is the latent heat of vaporization (unit is J / g), P a is the average atmospheric pressure (kPa), which is determined by the water surface altitude H and the temperature T a calculate:

[0118]

[0119] S52, calculate the aerodynamic term E for potential evaporation using the monthly average wind speed u at 2 m above the water and the data obtained in S51 aero (Unit is mm / day):

[0120]

[0121] S53, the monthly average measured water surface evaporation E of group M2 obs(mm / day) and the simulated monthly water surface evaporation value E calculated using the following formula containing five parameters: esti The goal is to minimize the mean absolute error (MAE) between (mm / day) and use the optimization algorithm to determine the parameter α. HT , c1-c4, the optimized mean absolute error MAE is:

[0122]

[0123] Simulated values ​​of water surface evaporation E by month esti By E obsi The corresponding aerodynamic term E of potential evaporation on a monthly basis aero and the radiation term E containing the potential evaporation parameter rad (mm / day) is calculated using the following formula:

[0124]

[0125] Where, α HT is the parameter (dimensionless) in the water surface evaporation calculation formula, E rad (mm / day) is calculated using the following formula:

[0126]

[0127] Where, That is, the change in water body heat, c1-c4 are empirical parameters, where c1 is dimensionless, c2 is in days, and c3 is in MJ / (m 2 ·day·℃), the unit of c4 is MJ / (m 2 ·day).

[0128] Step 6, calculation of water body heat change:

[0129] The net radiation R calculated using steps 2-4 is n , net radiation change rate R n The water temperature difference T w -T a , and use the parameters calibrated in step 5 to calculate the heat change of the water body. The formula is:

[0130]

[0131] Where ΔQ is the change in water body heat (MJ / (m 2 ·day)), α HT are the parameters of the water surface evaporation calculation formula, and c1-c4 are empirical parameters.

[0132] Example:

[0133] This embodiment takes the Badong section of the Three Gorges Reservoir in the upper reaches of the Yangtze River as an example, and uses the method of the present invention to accurately calculate the heat changes in the water body of the Three Gorges Reservoir.

[0134] Step 1: Determine the latitude of the Badong section of the Three Gorges Reservoir as 31°03′N, the average water surface altitude as 162.2m, determine the calculation period as monthly, and collect the monthly average water surface temperature and the daily average temperature on the water surface T from August 2013 to July 2020. a (unit is ℃), daily average water vapor pressure e a (unit is kPa), sunshine hours n(unit is hour) and daily average wind speed u 2 m above the water surface(unit is m / s), totaling 84 sets of data. At the same time, a total of 60 water surface evaporation data were collected from August 2013 to July 2018.

[0135] Step 2: Use the monthly average water surface temperature T w (unit is ℃) and the temperature on the water surface T a (unit is ℃), water vapor pressure e a The monthly variation of net radiation can be calculated by using the unit of kPa and the number of sunshine hours n (in hours), as shown in the following example: Figure 2 shown.

[0136] Step 3: Calculate the rate of change of net radiation using the monthly net radiation data calculated in step 2 The monthly changes of Figure 3 shown.

[0137] Step 4: Use the monthly average water surface temperature T w (unit is ℃) and the temperature on the water surface T a (Unit is ℃) Calculate the monthly change process of the difference between the water surface temperature and the air temperature (water surface temperature difference), such as Figure 4 shown.

[0138] Step 5: Use the monthly observed and simulated values ​​of water surface evaporation to calibrate the parameters of the water body heat change calculation formula.

[0139] The α value was determined based on 60 data sets from August 2013 to July 2018. HT The optimal parameters c1-c4 in the water body heat change formula are shown in the table below:

[0140] Table 3 Optimal parameters for water body heat calculation formula

[0141]

[0142] In step 6, the net radiation, rate of change of net radiation, and water-temperature difference from August 2013 to July 2020 calculated in steps 2-4 are used, along with the parameters calibrated in step 5, to calculate the monthly water body heat change. Verification shows that the calculated results using the method described herein are highly consistent with the measured values.

[0143] Comparative Example

[0144] This comparative example uses the same data as the above embodiment, respectively using the existing net radiation hysteresis method and net heat exchange method (ΔQ=d3(T w -T a )+d4) calculation, and compare the calculation results with the results of the method of the present invention. Figure 6 、 Figure 7 It can be seen from the changing process of the water body heat change and various indicators that the calculation method of the present invention is significantly more accurate than the other two methods.

[0145] Table 4 Comparison of the calculation effect of the method of the present invention and the two existing methods on the change of water body heat

[0146]

[0147] In the table: RMSE is the root mean square error between the calculated value and the measured value, and NSE is the Nash efficiency coefficient.

[0148] In summary, the existing net radiation hysteresis method for calculating the change in water body heat only takes the net radiation R n and the rate of change of net radiation As input, the net heat exchange coefficient method only takes the water temperature difference T w -T a As input, the calculation input of the water body heat change in the present invention includes net radiation R n , the rate of change of net radiation The difference between water temperature and air temperature T w -T a , the input factors considered are more comprehensive and the calculation accuracy is higher.

[0149] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention and is not limiting. Although the present invention is described in detail with reference to the preferred arrangement scheme, ordinary technicians in this field should understand that the technical solution of the present invention (such as the use of various formulas, the sequence of steps, etc.) can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for calculating water body heat change by combining net radiation and water-temperature difference, characterized in that: The method comprises the following steps: Step 1: Collection of basic data: Determine the latitude and altitude of the target water body and the calculation period of water body heat change, and collect the average water surface temperature T for each period w , meteorological data and water surface evaporation data on the water surface; The meteorological data on the water surface include: average temperature T a , average water vapor pressure e a , sunshine hours n, average wind speed u at 2 m above the water surface; Step 2, calculation of net radiation: Using the average water surface temperature T w , average temperature on the water surface T a , average water vapor pressure e a and sunshine hours n, calculate the net radiation R in each period n ; Step 3, calculation of net radiation change rate: The net radiation R calculated in step 2 is n , calculate the net radiation change rate Step 4: Calculation of the water-temperature difference change process: Calculate the average water surface temperature T w The average temperature on the water surface T a , the difference between the two is T w -T a The period-by-period change process; Step 5, calculate the calibration of the formula parameters: Using the meteorological data and water surface evaporation data collected in step 1, the net radiation R calculated in step 2 n , the net radiation change rate calculated in step 3 and the water-temperature difference T calculated in step 4 w -T a , calibrate the parameters of the water surface evaporation simulation formula including the heat change of the water body; Step 6, calculation of water body heat change: The net radiation R calculated using steps 2-4 is n , net radiation change rate The difference between water temperature and air temperature T w -T a , and use the parameters calibrated in step 5 to calculate the heat change of the water body. The formula is: Where ΔQ is the change in water body heat, and c1-c4 are empirical parameters.

2. The method for calculating water body heat change by combining net radiation and water-temperature difference according to claim 1, characterized in that: The net radiation R in each time period in step 2 n The specific calculation steps include: S21, calculate the solar declination δ and the correction parameter d of the distance between the sun and the earth according to the number of days J corresponding to the middle day of the calculated period in a year r : Where DOY is the total number of days in a year; the calculation step is in days, the value of J ranges from 1 to DOY, and the step is the number of days in a year corresponding to the middle day of the calculated period; S22, according to the latitude of the target water body Calculate the sunset angle ω using the solar declination δ s : S23, correct the parameter d according to the distance between the sun and the earth r 、sunset angle ω s ,latitude Calculate the solar sky total radiation R using the solar declination δ a : S24, according to the sunset angle ω s Calculate the maximum astronomical sunshine hours N: S25, based on the total solar radiation R a , calculate the net shortwave radiation R using the sunshine hours n collected in step 1 and the maximum astronomical sunshine hours N s : Where α is the albedo of the water surface, a s 、b s is a dimensionless empirical coefficient; S26, based on the average water surface temperature T on the target water body collected in step 1 w 、Average water vapor pressure on the water surface e a , sunshine hours n, and the maximum astronomical sunshine hours N to calculate the net longwave radiation R nl : Where σ is the Stefan-Boltzmann constant, ε is the emissivity of the water surface; S27, based on the net shortwave radiation R s and net longwave radiation R nl Calculate radiation R n : R n =R s -R nl 。 3. The method for calculating water body heat change by combining net radiation and water-temperature difference according to claim 1, characterized in that: Net radiation change rate in step 3 The specific calculation steps include: S31, the net radiation R calculated in each time period according to step 2 n And calculate the number of days J corresponding to the middle day of the period in a year to calculate the net radiation R n The fitted regression equation is: Where a1, a2 and a3 are the fitting coefficients of the net radiation regression equation; DOY is the total number of days in a year; S32, calculate the net radiation change rate based on the net radiation fitting regression equation calculated in S31 Where M is the number of days included in the calculation period.

4. The method for calculating water body heat change by combining net radiation and water-temperature difference according to claim 1, characterized in that: The parameter calibration of the water surface evaporation simulation formula in step 5 specifically includes the following steps: S51, using the average temperature T a Calculate the saturated water vapor pressure e s , the slope Δ of the saturated water vapor pressure versus temperature curve, and the hygrometer constant γ: Where λ = 2501 - 2.361T a is the latent heat of vaporization, P a is the average atmospheric pressure, based on the water surface altitude H and the average temperature T a calculate: S52, calculate the aerodynamic term E for potential evaporation using the average wind speed u at 2 m above the water surface and the data obtained in S51 aero : S53, the average measured water surface evaporation E of group M2 in each period obsi The simulated value E of water surface evaporation in each time period calculated using the following formula containing five parameters esti The goal is to minimize the mean absolute error MAE, and use the optimization algorithm to determine the parameter α HT , c1-c4, the optimized mean absolute error MAE is: Simulated value of water surface evaporation E at each time period esti By E obsi The corresponding aerodynamic term E of potential evaporation at each time period aero and the radiation term E containing the potential evaporation parameter rad The following formula is used for calculation: Where, α HT is the parameter of the water surface evaporation simulation formula, E rad Calculated by the following formula: Where, That is the change in water body heat, c1-c4 are empirical parameters.

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