Method and device for obtaining tension water and free water capacity of seasonal frozen soil basin

Abstract

The present invention proposes a method and device for obtaining the tension water and free water capacity of a seasonal frozen soil basin, the method comprising obtaining the underlying surface data of the basin through satellite remote sensing; obtaining the spatial distribution of the tension water capacity and free water capacity in the non-frozen soil period according to the obtained elevation data and vegetation type of the basin; calculating the spatial distribution of the maximum freezing depth and melting depth of the basin soil according to the determined soil freeze-thaw period and the obtained soil type and soil moisture content of the basin; interpolating and calculating the soil freezing depth time series during the freeze-thaw period; and obtaining the spatial distribution of the tension water capacity and free water capacity in the frozen soil period. The method takes into account the influence of soil freeze-thaw cycles on tension water and free water capacity, determines the spatiotemporal dynamic distribution of tension water and free water capacity in seasonal frozen soil basins from the perspective of the physical meaning of parameters, and provides support for the input of soil intermediate variables of distributed hydrological models.

Description

Technical Field

[0001] The invention belongs to the field of hydrological technology, and in particular relates to a method for obtaining the temporal and spatial dynamic distribution of tension water and free water capacity in a seasonal frozen soil basin. Background Art

[0002] As a key tool for studying complex hydrological phenomena in a watershed, the basin hydrological model has always been a frontier field of hydrological research. Compared with the traditional lumped hydrological model, the distributed hydrological model has more advantages. It can better consider the spatial variability of rainfall and underlying surface conditions, and make full use of spatial information such as GIS technology and remote sensing to simulate the rainfall-runoff response of the basin. As the core parameters in the runoff generation module of the domestic distributed hydrological model, the rationality of the spatial distribution of tension water capacity and free water capacity has a direct impact on the final runoff generation of the basin. However, the current methods for determining these two parameters are mostly subjective and empirical, and lack a determination method based on physical properties. In addition, existing studies often assume that the tension water and free water capacity of the basin are evenly distributed, ignoring their spatial variability, which constitutes an obstacle to the development of distributed hydrological models.

[0003] In cold regions, seasonal freeze-thaw cycles of near-surface soils can affect the hydrological characteristics of the surface, thereby changing the hydrological process. Soil freezing reduces soil water storage capacity, forms a relatively impermeable layer near the surface, and changes the runoff generation and confluence mechanism of the hydrological process. This impact is directly or indirectly reflected in annual runoff, seasonal distribution of runoff, and runoff composition. The melting of frozen soil increases soil water storage capacity, resulting in a slower winter water withdrawal process and a more even distribution of runoff throughout the year. At present, there is still a research gap in the determination of tensile water capacity and free water capacity in seasonally frozen soil areas. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method and device for obtaining the temporal and spatial dynamic distribution of tension water and free water capacity in a seasonal frozen soil basin, which takes into account the water loss caused by soil freezing during the permafrost period and realizes the temporal and spatial dynamic changes of tension water and free water capacity.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] The present invention first provides a method for obtaining the temporal and spatial dynamic distribution of tension water and free water capacity in a seasonally frozen soil basin, comprising:

[0007] Obtain the underlying surface data of the watershed through satellite remote sensing, where the underlying surface data includes elevation data, soil type, soil moisture content and vegetation type;

[0008] According to the obtained watershed elevation data and vegetation types, the spatial distribution of tension water capacity and free water capacity in the non-frozen period is obtained;

[0009] Define the soil freezing start date, maximum freezing depth date and complete thawing date, and then determine the soil freezing and thawing period:

[0010] According to the determined soil freezing and thawing period and the obtained soil type and soil moisture content of the basin, the spatial distribution of the maximum freezing depth and thawing depth of the basin soil is calculated;

[0011] Based on the time series of distributed surface temperature and the calculated spatial distribution of the maximum freezing depth and thawing depth of the watershed soil, the time series of soil freezing depth during the freeze-thaw period is obtained by interpolation calculation.

[0012] Based on the spatial distribution of tensile water capacity and free water capacity in the non-frozen soil period and the time series of soil freezing depth during the freeze-thaw period obtained by interpolation calculation, the spatial distribution of tensile water capacity and free water capacity in the frozen soil period was obtained.

[0013] According to the time series of distributed surface temperature, combined with the calculated spatial distribution of the maximum freezing depth and thawing depth of the basin soil, the interpolation calculation is performed to obtain the time series of soil freezing depth during the freeze-thaw period.

[0014] During the period from the start date of soil freezing to the day of maximum freezing depth, the soil freezing depth time series calculation formula is:

[0015] D i =D i-1 +λ i ×SFD, i=1,2,3…N F

[0016]

[0017] λ i =0, T i >0

[0018] D0=0

[0019] D NF =SFD

[0020] Where D i and D i-1 is the soil freezing depth on the i-th day and the i-1-th day, λ i represents the ratio of the new soil freezing depth to the maximum freezing depth on the i-th day, SFD is the maximum soil freezing depth, FI is the freezing index, T i is the daily average surface temperature on the ith day, N F is the calculation time from the soil freezing start date to the maximum freezing depth date, D0 represents the freezing depth one day before the soil freezing start date, and D NF Indicates the freezing depth on the day of maximum freezing depth;

[0021] During the period from the day after the maximum freezing depth to the day of complete melting, the soil freezing depth time series calculation formula is:

[0022] D j =D NF -μ j ×STD, j=1,2,3…N T

[0023]

[0024] μ j =0, T j <0

[0025] D NT =0

[0026] Where D NF represents the freezing depth on the day of maximum freezing depth, μ j It represents the ratio of soil melting depth on day j to the maximum melting depth, STD is the maximum soil melting depth, N T is the calculation time from the day after the maximum freezing depth to the day of complete melting, TI is the melting index, d NT Indicates the freezing depth on a complete thaw day.

[0027] The calculation formulas for freezing index FI and melting index TI are:

[0028]

[0029] Where, T i / T j is the daily average surface temperature on the i / j day, N F N is the calculation time from the beginning date of soil freezing to the maximum freezing depth date. T It is the calculation time from the day after the maximum freezing depth to the day of complete melting;

[0030] The calculation formula for the maximum freezing depth and melting depth is:

[0031]

[0032] Where, SFD and STD are the maximum soil freezing depth and thawing depth respectively; E is the soil freeze-thaw parameter, which is determined according to the soil type and soil moisture content of the calculation unit;

[0033] In the freezing calculation period of seasonally frozen ground basins, STD = SFD, and N is calculated based on the temperature time series. F and N T , and then determine the maximum freezing depth day and complete melting day.

[0034] According to the spatial distribution of tensile water capacity and free water capacity in the non-frozen soil period and the soil freezing depth time series obtained by interpolation calculation during the freeze-thaw period, the spatial distribution steps of tensile water capacity and free water capacity in the frozen soil period are obtained.

[0035] During the period from the beginning of soil freezing to the maximum freezing depth, i=1,2,3…N F , the calculation formula for tension water and free water capacity on day i is:

[0036] When L h >D i hour:

[0037] W′ Mi =W M -(θ fc -θ wp )×D i

[0038] S′ Mi =S M -(θ s -θ fc )×D i

[0039] When L h ≤D i <L a hour:

[0040] W′ Mi =W M -(θ fc -θ wp )×D i

[0041] S′ Mi =0

[0042] When L a ≤D i hour:

[0043] W′ Mi =0

[0044] S′ Mi =0

[0045] During the period from the day after the maximum freezing depth to the day of complete melting, j = 1, 2, 3…N T , the calculation formula for tension water and free water capacity on day j is:

[0046] When L h >D NF -D j hour:

[0047] W′ Mj=(θ fc -θ wp )×(D NF -D j )

[0048] S′ Mj =(θ s -θ fc )×(D NF -D j )

[0049] When L h ≤D NF -D j <L a hour:

[0050] W′ Mj =(θ fc -θ wp )×(d NF -d j )

[0051] S′ Mj =S M

[0052] When L a ≤D NF -D k hour:

[0053] W′ Mj =n M

[0054] S′ Mj =S M

[0055] Where, L a and L h Indicates the thickness of the aeration zone and the humus layer, W′ Mi / W′ Mj and S′ Mi / S′ Mj They represent the tensile water capacity and free water capacity of frozen soil during freezing / thawing period, W M and S M represent the tensile water capacity and free water capacity in the non-frozen soil period, θ fc is the field water capacity, θ wp is the wilting water content, θ s is the saturated water content.

[0056] During the freezing calculation time, the first day when the average daily temperature is below 0℃ for three consecutive days is taken as the starting day of soil freezing, the date with the lowest cumulative temperature is taken as the maximum freezing depth day, the date when the soil freezing depth is completely melted is taken as the complete melting day, and the period from the starting day of soil freezing to the complete melting day is the soil freeze-thaw period.

[0057] The freezing index and thawing index were calculated using the surface temperature, and the spatial distribution of the maximum freezing depth and thawing depth of the soil in the basin was calculated based on the Stefan approximate solution.

[0058] According to the obtained watershed elevation data and vegetation type, the spatial distribution of tensile water capacity and free water capacity in the non-frozen period is obtained, including:

[0059] Based on the elevation data, the spatial distribution of the basin terrain index is extracted, and the calculation formula of the terrain index TPI is:

[0060]

[0061] In the formula, a represents the single-width catchment area, tanβ represents the local surface slope, A is the upstream cumulative catchment area of ​​the calculated terrain unit, and tanβ k is the gradient with the kth downslope grid, L k is the length of the contour line perpendicular to the kth downslope direction, and n is the total number of upslope directions;

[0062] Based on the spatial distribution of vegetation types, the thickness of the vadose zone and the thickness of the humus soil layer are calculated according to the quantitative relationship between the thickness of the vadose zone and the terrain index, and the quantitative relationship between the thickness of the humus soil layer and the thickness of the vadose zone. The calculation formula is:

[0063] L a =ξ a ×TPI+ξ b

[0064]

[0065] Where, L a and L h represents the thickness of the aeration zone and the thickness of the humus layer, ξ a and b To calculate the two coefficients of the thickness of the vadose zone, It indicates the soil thickness conversion coefficient, which is mainly determined by the vegetation type of the calculation unit;

[0066] Based on the spatial distribution of soil types, the spatial distribution of tensile water capacity and free water capacity in the non-frozen soil period is calculated according to the thickness of the vadose zone and the thickness of the humus soil layer:

[0067] W M =(θ fc -θwp )×L a

[0068] S M =(θ s -θ fc )×L h

[0069] Where W M and S M represent the tension water capacity and free water capacity in the non-frozen soil period, θ fc is the field water capacity, θ wp is the wilting water content, θ s is the saturated water content, θ fc ,θ wp ,θ s Both can be determined according to the soil type of the calculation unit.

[0070] The present invention also provides a device for obtaining the spatiotemporal dynamic distribution of tension water and free water capacity in a seasonal frozen soil basin, comprising a processor and a memory; the memory stores a program or instruction, and the program or instruction is loaded and executed by the processor to implement the steps of the above-mentioned method for obtaining the spatiotemporal dynamic distribution of tension water and free water capacity in a seasonal frozen soil basin.

[0071] The present invention also provides a computer-readable storage medium, on which a program or instruction is stored. When the program or instruction is executed by a processor, the steps of the above-mentioned method for obtaining the spatiotemporal dynamic distribution of tension water and free water capacity in a seasonal frozen soil basin are implemented.

[0072] In order to more accurately describe the spatiotemporal dynamic distribution of tension water and free water, the maximum freezing depth and thawing depth of the basin soil are calculated with the help of the Stefan approximate solution, and then the soil freezing depth time series during the freeze-thaw period is calculated by time interpolation method to deduct the water loss caused by soil freezing. This method takes into account the impact of freeze-thaw cycles on the spatiotemporal distribution of tension water and free water, and effectively improves the accuracy of these two parameters.

[0073] Beneficial results of the present invention:

[0074] The present invention provides a method for obtaining the spatiotemporal dynamic distribution of tension water and free water capacity in a seasonally frozen soil basin. First, the thickness of the watershed aeration zone and the thickness of the humus soil layer are calculated to obtain the spatial distribution of the tension water capacity and free water capacity of the soil in the non-frozen soil period; then, the spatial distribution of the maximum freezing depth and thawing depth of the watershed soil is calculated according to the Stefan approximate solution; the time series of the soil freezing depth in the frozen soil period is interpolated and calculated in combination with the time series of the distributed surface temperature; the water loss caused by soil freezing is deducted from the tension water capacity and free water capacity in the non-frozen soil period to obtain the spatiotemporal dynamic distribution of the tension water and free water capacity in the frozen soil period. This method takes into account the influence of soil freeze-thaw cycles on tension water and free water capacity, determines the spatiotemporal dynamic distribution of tension water and free water capacity in seasonally frozen soil basins from the perspective of the physical meaning of parameters, and provides support for the input of soil intermediate variables of distributed hydrological models. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 It is a schematic diagram of the process of the present invention;

[0076] Figure 2 Schematic diagram of the spatial distribution of tension water capacity and free water capacity in the non-frozen soil period of the present invention; (a) is the tension water capacity, and (b) is the free water capacity;

[0077] Figure 3 This is a schematic diagram of the spatial distribution of the maximum freezing depth of soil in the present invention;

[0078] Figure 4 Schematic diagram of spatial distribution of tension water capacity and free water capacity during the frozen soil period on January 1, 2015 of the present invention, wherein (a) is tension water capacity and (b) is free water capacity. DETAILED DESCRIPTION

[0079] The technical method of the present invention is further described below in conjunction with the accompanying drawings and specific examples.

[0080] Example 1

[0081] This embodiment provides a method for obtaining the spatiotemporal dynamic distribution of tension water and free water capacity in a seasonally frozen soil basin. The Yalong River Basin is used as the application basin, the spatial resolution is 0.1°, and the freezing calculation time is from July 1, 2014 to June 30, 2015. The flowchart is shown in Figure 1. The specific implementation includes the following steps:

[0082] Step 1: Obtain basin elevation data, soil type, soil moisture content, vegetation type and other underlying surface data through satellite remote sensing, extract the spatial distribution of basin terrain index with the help of digital watershed technology, calculate the thickness of the vadose zone based on the quantitative relationship between the thickness of the vadose zone and the terrain index, calculate the thickness of the humus soil layer based on the quantitative relationship between the thickness of the humus soil layer and the thickness of the vadose zone, and obtain the spatial distribution of tensile water capacity and free water capacity in the non-frozen period based on the spatial distribution of soil type and vegetation type.

[0083] Obtaining the spatial distribution of tension water capacity and free water capacity includes:

[0084] Step 11, based on the elevation data, the spatial distribution of the basin terrain index is extracted with the help of digital watershed technology. The calculation formula of the terrain index TPI is:

[0085]

[0086] In the formula, a represents the single-width catchment area, tanβ represents the local surface slope, A is the upstream cumulative catchment area of ​​the calculated terrain unit, and tanβ k is the gradient with the kth downslope grid, L k is the length of the contour line perpendicular to the kth downslope direction, and n is the total number of upslope directions.

[0087] Step 12, based on the spatial distribution of vegetation types, the thickness of the vadose zone and the thickness of the humus soil layer are calculated according to the quantitative relationship between the thickness of the vadose zone and the terrain index and the quantitative relationship between the thickness of the humus soil layer and the thickness of the vadose zone. The calculation formula is:

[0088] L a =ξ a ×TPI+ξ b

[0089]

[0090] Where, L a and L h represents the thickness of the aeration zone and the thickness of the humus layer, ξ a and b To calculate the two coefficients of the thickness of the vadose zone, It represents the soil thickness conversion coefficient, which is mainly determined according to the vegetation type of the calculation unit.

[0091] Step 13, based on the spatial distribution of soil types, calculate the spatial distribution of tensile water capacity and free water capacity in the non-frozen soil period according to the thickness of the vadose zone and the thickness of the humus soil layer:

[0092] W M =(θ fc -θ wp )×L a

[0093] S M =(θ s -θ fc )×L h

[0094] Where W M and S M represent the tension water capacity and free water capacity in the non-frozen soil period, θ fc is the field water capacity, θ wp is the wilting water content, θ s is the saturated water content, θ fc ,θ wp ,θ s Both can be determined according to the soil type of the calculation unit. Figure 2 is the tensile water capacity of the non-frozen soil period calculated by the present invention in the Yalong River Basin ( Figure 2 (a)) and free water capacity ( Figure 2 (b) Schematic diagram of the spatial distribution of tension water capacity in the basin. The range of tension water capacity is between 0-206 mm, and the range of free water capacity is between 0-33 mm. The minimum value always appears in the river channel.

[0095] Step 2: Define the soil freezing start date, maximum freezing depth date, and complete melting date, and then determine the soil freeze-thaw period: within the freezing calculation time, the first day when the average daily temperature is below 0°C for three consecutive days is taken as the soil freezing start date, the date with the lowest cumulative temperature is taken as the maximum freezing depth date, and the date when the soil freezing depth is completely melted is taken as the complete melting date. The soil freeze-thaw period is from the soil freezing start date to the complete melting date.

[0096] Step 3: Calculate the freezing index and melting index using the surface temperature, and calculate the spatial distribution of the maximum freezing depth and melting depth of the watershed soil according to the Stefan approximate solution;

[0097] The calculation formulas for the freezing index and melting index are:

[0098]

[0099] Where, T i / T j is the daily average surface temperature on the i / j day, N F N is the calculation time from the beginning date of soil freezing to the maximum freezing depth date. T It is the calculation time from the day after the maximum freezing depth to the day of complete melting.

[0100] The calculation formula for the maximum freezing depth and melting depth is:

[0101]

[0102] Where SFD and STD are the maximum soil freezing depth and thawing depth, respectively, and E is the soil freeze-thaw parameter, which can be determined according to the soil type and soil moisture content of the calculation unit. Figure 3 This is a schematic diagram of the spatial distribution of the maximum freezing depth of the soil obtained by the present invention. It can be seen that the maximum freezing depth in the upstream of the basin is the deepest, reaching 1.5 meters, and the freezing depth in the downstream is shallower, between 0-0.5 meters.

[0103] In the freezing calculation period of seasonally frozen ground basins, STD = SFD, and N is calculated based on the temperature time series. F and N T , and then determine the maximum freezing depth day and complete melting day.

[0104] Step 4: Based on the time series of distributed surface temperature, combined with the maximum freezing depth and thawing depth of the soil, the time series of soil freezing depth during the freeze-thaw period is interpolated and calculated;

[0105] During the period from the start date of soil freezing to the day of maximum freezing depth, the soil freezing depth time series calculation formula is:

[0106] D i =D i-1 +λ i ×SFD, i=1,2,3…N F

[0107]

[0108] λ i =0, T i >0

[0109] D0=0

[0110] D NF =SFD

[0111] Where D i and D i-1 is the soil freezing depth on the i-th day and the i-1-th day, λ i represents the ratio of the new soil freezing depth to the maximum freezing depth on the i-th day, D0 represents the freezing depth one day before the start of soil freezing, and D NF Indicates the freezing depth on the day of maximum freezing depth.

[0112] During the period from the day after the maximum freezing depth to the day of complete melting, the soil freezing depth time series calculation formula is:

[0113] D j =D NF -μ j ×STD, j=1,2,3…N T

[0114]

[0115] μ j =0, T j <0

[0116] D NT =0

[0117] In the formula, μ j represents the ratio of soil melting depth on day j to the maximum melting depth, D NT Indicates the freezing depth on a complete thaw day.

[0118] Step 5. Finally, deduct the water loss caused by soil freezing from the soil tension water capacity and free water capacity in the non-frozen period to obtain the spatiotemporal dynamic distribution of the tension water and free water capacity of the basin in the frozen period: during the period from the start date of soil freezing to the maximum freezing depth, the soil gradually freezes from the surface downward to the maximum freezing depth; during the period from the day after the maximum freezing depth to the complete melting day, the frozen soil gradually melts from the surface downward until it is completely melted.

[0119] During the period from the beginning of soil freezing to the maximum freezing depth, i=1,2,3…N F , the calculation formula for tension water and free water capacity on day i is:

[0120] When L h >D i hour:

[0121] W′ Mi =W M -(θ fc -θ wp )×D i

[0122] S′ Mi =S M -(θ s -θ fc )×D i

[0123] When L h ≤D i <L a hour:

[0124] W′ Mi =W M -(θ fc -θ wp )×D i

[0125] S′ Mi =0

[0126] When L a ≤Di hour:

[0127] W′ Mi =0

[0128] S′ Mi =0

[0129] During the period from the day after the maximum freezing depth to the day of complete melting, j = 1, 2, 3…N T , the calculation formula for tension water and free water capacity on day j is:

[0130] When L h >D NF -D j hour:

[0131] W′ Mj =(θ fc -θ wp )×(D NF -D j )

[0132] S′ Mj =(θ s -θ fc )×(D NF -D j )

[0133] When L h ≤D NF -D j <L a hour:

[0134] W′ Mj =(θ fc -θ wp )×(D NF -D j )

[0135] S′ Mj =S M

[0136] When L a ≤D NF -D j hour:

[0137] W′ Mj =W M

[0138] S′ Mj =S M

[0139] Figure 4 The tensile water capacity of the frozen soil on January 1, 2015 ( Figure 4 (a)) and free water capacity ( Figure 4(b) Schematic diagram of the spatial distribution of frozen soil in the upstream, the tension water capacity and free water capacity are reduced compared with the non-frozen period.

[0140] The method for obtaining the spatiotemporal dynamic distribution of tensile water and free water capacity in seasonal frozen soil watersheds proposed in the present invention obtains watershed elevation data, soil type, soil moisture content, vegetation type and other underlying surface data through satellite remote sensing, extracts the spatial distribution of watershed terrain index with the help of digital watershed technology, calculates the thickness of the vadose zone based on the quantitative relationship between the thickness of the vadose zone and the terrain index, calculates the thickness of the humus soil layer based on the quantitative relationship between the thickness of the humus soil layer and the thickness of the vadose zone, and obtains the spatial distribution of tensile water capacity and free water capacity in the non-frozen soil period based on the spatial distribution of soil type and vegetation type; defines soil The freezing start date, the maximum freezing depth date, and the complete melting date are used to determine the soil freezing and thawing period; the freezing index and melting index are calculated using the surface temperature, and the spatial distribution of the maximum freezing depth and melting depth of the basin soil is calculated according to the Stefan approximate solution; according to the time series of the distributed surface temperature, combined with the maximum freezing depth and melting depth of the soil, the soil freezing depth time series during the freezing and thawing period is interpolated and calculated; finally, the soil tension water capacity and free water capacity in the non-frozen soil period are deducted from the water loss caused by soil freezing to obtain the spatiotemporal dynamic distribution of the tension water and free water capacity of the basin during the frozen soil period. The present invention takes into account the influence of soil freeze-thaw cycles on tension water and free water capacity, determines the spatiotemporal dynamic distribution of tension water and free water capacity in seasonal frozen soil basins from the perspective of the physical meaning of parameters, and provides support for the input of soil intermediate variables of the distributed hydrological model.

[0141] Example 2

[0142] The present embodiment provides a device for obtaining the spatiotemporal dynamic distribution of tension water and free water capacity in a seasonal frozen soil basin, comprising a processor and a memory; the memory stores a program or instruction, and the program or instruction is loaded and executed by the processor to implement the steps of the method for obtaining the spatiotemporal dynamic distribution of tension water and free water capacity in a seasonal frozen soil basin provided in Example 1.

[0143] Example 3

[0144] This embodiment provides a computer-readable storage medium, on which a program or instruction is stored. When the program or instruction is executed by a processor, the steps of the method for obtaining the spatiotemporal dynamic distribution of tension water and free water capacity in a seasonal frozen soil basin provided in Example 1 are implemented.

[0145] The above is only a preferred embodiment of the present invention. The protection scope of the present invention is not limited to the above embodiment. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for obtaining the temporal and spatial dynamic distribution of tension water and free water capacity in seasonally frozen soil basins, characterized in that: include: Obtain the underlying surface data of the watershed through satellite remote sensing, where the underlying surface data includes elevation data, soil type, soil moisture content and vegetation type; According to the acquired watershed elevation data and vegetation types, the spatial distribution of tensile water capacity and free water capacity in the non-frozen period is obtained; Define the soil freezing start date, maximum freezing depth date and complete thawing date, and then determine the soil freezing and thawing period: According to the determined soil freezing and thawing period and the obtained soil type and soil moisture content of the basin, the spatial distribution of the maximum freezing depth and thawing depth of the basin soil is calculated; Based on the time series of distributed surface temperature and the calculated spatial distribution of the maximum freezing depth and thawing depth of the watershed soil, the time series of soil freezing depth during the freeze-thaw period is obtained by interpolation calculation. Based on the spatial distribution of tensile water capacity and free water capacity in the non-frozen soil period and the soil freezing depth time series obtained by interpolation calculation during the freeze-thaw period, the spatial distribution of tensile water capacity and free water capacity in the frozen soil period is obtained; According to the time series of distributed surface temperature, combined with the calculated spatial distribution of the maximum freezing depth and thawing depth of the basin soil, the interpolation calculation is performed to obtain the time series of soil freezing depth during the freeze-thaw period. During the period from the start date of soil freezing to the day of maximum freezing depth, the soil freezing depth time series calculation formula is: D i =D i-1 +λ i ×SFD,i=1,2,3…N F l i =0,T i >0 D0＝0 D NF =SFD Where D i and D i-1 is the soil freezing depth on the i-th day and the i-1-th day, λ i represents the ratio of the new soil freezing depth to the maximum freezing depth on the i-th day, SFD is the maximum soil freezing depth, FI is the freezing index, T i / T j is the daily average surface temperature on the i / j day, N F is the calculation time from the soil freezing start date to the maximum freezing depth date, D0 represents the freezing depth one day before the soil freezing start date, and D NF Indicates the freezing depth on the day of maximum freezing depth; During the period from the day after the maximum freezing depth to the day of complete melting, the soil freezing depth time series calculation formula is: D j =D NF -μ j ×STD,j=1,2,3…N T m j =0,T j <0 D NT ＝0 Where D NF Indicates the freezing depth on the day of maximum freezing depth, μ j It represents the ratio of soil melting depth on day j to the maximum melting depth, STD is the maximum soil melting depth, N T is the calculation time from the day after the maximum freezing depth to the day of complete melting, TI is the melting index, and D NT Indicates the freezing depth on a complete thaw day.

2. The method for obtaining the temporal and spatial dynamic distribution of tension water and free water capacity in seasonal frozen soil basins according to claim 1, characterized in that: The calculation formulas for freezing index FI and melting index TI are: Where, T i / T j is the daily average surface temperature on the i / j day, N F N is the calculation time from the beginning date of soil freezing to the maximum freezing depth date. T It is the calculation time from the day after the maximum freezing depth to the day of complete melting; The calculation formula for the maximum freezing depth and melting depth is: Where, SFD and STD are the maximum soil freezing depth and thawing depth respectively; E is the soil freeze-thaw parameter, which is determined according to the soil type and soil moisture content of the calculation unit; In the freezing calculation period of seasonally frozen ground basins, STD = SFD, and N is calculated based on the temperature time series. F and N T , and then determine the maximum freezing depth day and complete melting day.

3. The method for obtaining the temporal and spatial dynamic distribution of tension water and free water capacity in seasonal frozen soil basins according to claim 2, characterized in that: According to the spatial distribution of tensile water capacity and free water capacity in the non-frozen soil period and the soil freezing depth time series obtained by interpolation calculation during the freeze-thaw period, the spatial distribution steps of tensile water capacity and free water capacity in the frozen soil period are obtained. During the period from the beginning of soil freezing to the maximum freezing depth, i=1,2,3…N F , the calculation formula for tension water and free water capacity on day i is: When L h >D i hour: W′ Mi =W M -(θ fc -θ wp )×D i S′ Mi =S M -(θ s -θ fc )×D i When L h ≤D i <L a hour: W′ Mi =W M -(θ fc -θ wp )×D i S′ Mi ＝0 When L a ≤D i hour: W′ Mi ＝0 S′ Mi ＝0 During the period from the day after the maximum freezing depth to the day of complete melting, j = 1, 2, 3…N T , the calculation formula for tension water and free water capacity on day j is: When L h >D NF -D j hour: W′ Mj =(θ fc -θ wp )×(D NF -D j ) S′ Mj =(θ s -θ fc )×(D NF -D j ) When L h ≤D NF -D j <L a hour: W′ Mj =(θ fc -θ wp )×(D NF -D j ) S′ Mj =S M When L a ≤D NF -D j hour: IN' Mj =In M S′ Mj =S M Where, L a and L h Indicates the thickness of the aeration zone and the humus layer, W′ Mi / W′ Mj and S′ Mi / S′ Mj They represent the tensile water capacity and free water capacity of frozen soil during freezing / thawing period, W M and S M represent the tensile water capacity and free water capacity in the non-frozen soil period, θ fc is the field water capacity, θ wp is the wilting water content, θ s is the saturated water content.

4. The method for obtaining the temporal and spatial dynamic distribution of tension water and free water capacity in seasonal frozen soil basins according to claim 1, characterized in that: During the freezing calculation time, the first day when the average daily temperature is below 0℃ for three consecutive days is taken as the starting day of soil freezing, the date with the lowest cumulative temperature is taken as the maximum freezing depth day, the date when the soil freezing depth is completely melted is taken as the complete melting day, and the period from the starting day of soil freezing to the complete melting day is the soil freeze-thaw period.

5. The method for obtaining the temporal and spatial dynamic distribution of tension water and free water capacity in seasonal frozen soil basins according to claim 1, characterized in that: The freezing index and thawing index were calculated using the surface temperature, and the spatial distribution of the maximum freezing depth and thawing depth of the soil in the basin was calculated based on the Stefan approximate solution.

6. The method for obtaining the temporal and spatial dynamic distribution of tension water and free water capacity in seasonal frozen soil basins according to claim 1, characterized in that: Based on the acquired watershed elevation data and vegetation types, the spatial distribution of tensile water capacity and free water capacity in the non-frozen soil period is obtained, including: Based on the elevation data, the spatial distribution of the basin terrain index is extracted, and the calculation formula of the terrain index TPI is: In the formula, a represents the single-width catchment area, tanβ represents the local surface slope, A is the upstream cumulative catchment area of ​​the calculated terrain unit, and tanβ k is the gradient with the kth downslope grid, L k is the length of the contour line perpendicular to the kth downslope direction, and n is the total number of upslope directions; Based on the spatial distribution of vegetation types, the thickness of the vadose zone and the thickness of the humus soil layer are calculated according to the quantitative relationship between the thickness of the vadose zone and the terrain index, and the quantitative relationship between the thickness of the humus soil layer and the thickness of the vadose zone. The calculation formula is: L a =ξ a ×TPI+ξ b Where, L a and L h represents the thickness of the aeration zone and the thickness of the humus layer, ξ a and b To calculate the two coefficients of the thickness of the vadose zone, Indicates the soil layer thickness conversion coefficient, which is determined according to the vegetation type of the calculation unit; Based on the spatial distribution of soil types, the spatial distribution of tensile water capacity and free water capacity in the non-frozen soil period is calculated according to the thickness of the vadose zone and the thickness of the humus soil layer: W M =(θ fc -θ wp )×L a S M =(θ s -θ fc )×L h Where W M and S M represent the tensile water capacity and free water capacity in the non-frozen soil period, θ fc is the field water capacity, θ wp is the wilting water content, θ s is the saturated water content, θ fc ,θ wp ,θ s Both can be determined according to the soil type of the calculation unit.

7. A device for obtaining the temporal and spatial dynamic distribution of tension water and free water capacity in seasonal frozen soil basins, characterized in that: It comprises a processor and a memory; the memory stores a program or instruction, and the program or instruction is loaded and executed by the processor to implement the steps of the method for obtaining the spatiotemporal dynamic distribution of tension water and free water capacity in a seasonal frozen soil basin as described in any one of claims 1 to 6.

8. A computer-readable storage medium storing a program or instruction, wherein the program or instruction, when executed by a processor, implements the steps of the method for obtaining the spatiotemporal dynamic distribution of tension water and free water capacity in a seasonal frozen soil basin as described in any one of claims 1 to 6.

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