Hydrothermal coupling numerical model to identify the distribution of permafrost type index

Abstract

The application discloses a water-heat coupling numerical model melting depth discrimination permafrost type index distribution method, and relates to a soil index distribution method, which comprises the following processes: determining a melting area spatial distribution according to a melting depth process obtained through water-heat coupling simulation; combining a three-dimensional soil temperature field to discriminate permafrost and seasonal frozen soil grids, and obtaining spatial distributions of the two types of frozen soil; and according to the two types of frozen soil, solving and determining a permafrost depth spatial distribution of a permafrost area and a maximum frozen soil depth spatial distribution of a seasonal frozen soil area. The application effectively expands the application range of the water-heat coupling numerical model; compared with the prior art, the application has obvious improvement in the aspects of strong experience, insufficient mapping range, accuracy and fineness in frozen soil mapping, and is unable to discriminate frozen soil types, and overcomes the defect that the prior art fails to consider the melting area in permafrost mapping.

Description

TECHNICAL FIELD

[0001] The application relates to a permafrost type index distribution method based on a water-heat coupling numerical model. BACKGROUND

[0002] Permafrost is a soil body in which solid water (ice) and soil particles are tightly interlocked, and has great differences from conventional soil in terms of water permeability, hardness, compressibility, fluidity and the like. The volume, buried depth and existence time of permafrost are objects of attention in many industries such as resource environment, water conservancy, civil engineering and agriculture. Distinguishing and identifying perennial frozen soil (permafrost) that does not thaw for many years and seasonal frozen soil that thaws in the warm season within a year is the main content of permafrost mapping, and the accuracy and fineness of calculating the characteristic indexes and spatial distribution of the two types of permafrost are of great significance to the study of hydrological processes.

[0003] At present, the methods for permafrost mapping mainly include air temperature correlation method, multi-factor correlation method, remote sensing inversion method, geophysical prospecting method, Stefan method, and frozen soil top plate temperature method (TTOP). However, these methods and their derived lumped and distributed models are highly empirical, have insufficient physical mechanisms, do not consider unfrozen water below the freezing point, and have limited frozen soil detection range, resulting in insufficient range, accuracy and fineness. With the emergence of water-heat coupling numerical models based on the principle of convection and diffusion, it is possible to directly determine the soil freezing-thawing state using unfrozen water content, and to obtain the daily thawing depth of soil and the three-dimensional temperature field of soil, but the two cannot directly obtain permafrost type classification and its characteristic indexes. Therefore, it is crucial to obtain a method for identifying the spatial distribution of permafrost types and their characteristic indexes based on the thawing depth of a water-heat coupling numerical model. SUMMARY

[0004] The purpose of the present application is to provide a water-heat coupling numerical model thawing depth permafrost type index distribution method, which is a method for identifying the spatial distribution of permafrost types and their characteristic indexes based on a water-heat coupling numerical model. The present application solves the deficiencies in permafrost mapping, and uses a water-heat coupling numerical model to realize permafrost type index distribution, which has the characteristics of high empiricality, high mapping range, high accuracy and high fineness.

[0005] The purpose of the present application is achieved by the following technical solutions:

[0006] The water-heat coupling numerical model thawing depth permafrost type index distribution method comprises the following processes:

[0007] S1, determining the spatial distribution of thawing zones based on the thawing depth process obtained by water-heat coupling simulation;

[0008] S2, combined with three-dimensional soil temperature field, identify multi-year frozen soil and seasonal frozen soil grid, get the spatial distribution of two types of frozen soil;

[0009] S3, according to two types of frozen soil, solve the spatial distribution of frozen soil depth in permafrost region and the spatial distribution of maximum frozen depth in seasonal frozen soil region.

[0010] The water-heat coupling numerical model melting depth discriminates frozen soil type index distribution method, in step S1, with day as a scale, record the melting depth of a point of model output as d i,j,t , wherein i represents the i row, j represents the j column, t represents the t day; according to the value, directly judge whether it is a melting area, if it meets the following conditions, it is determined to be a melting area;

[0011] d i,j,t < 0, 0<t<366 (1)

[0012] By traversing all values of i,j , the judgment of all points is obtained, and the spatial distribution of the melting area is obtained.

[0013] The water-heat coupling numerical model melting depth discriminates frozen soil type index distribution method, in step S2, considering the points which are not melting areas in step S1; record the soil temperature of a point i,j,z ) in the three-dimensional soil temperature field in summer as T i,j,z,240 , wherein z represents the depth of the point, and the serial number of the soil discrete layer from the ground to the ground is used to represent, and the total number of soil discrete layers is set to n ; 240 represents the 240th day from January 1st in a year, and represents the end of August;

[0014] Record the total depth of the simulated soil as D m , d i,j,t The corresponding soil layer is z d ; for the points determined to be not melting areas in step S1, if the following two conditions are met at the same time, it is determined to be permafrost; otherwise, it is determined to be seasonal frozen soil;

[0015] (2).

[0016] The water-heat coupling numerical model melting depth discriminates the permafrost type index distribution method, the discrimination is to divide the melting area into permafrost, and the spatial distribution of permafrost is obtained, and points that are not permafrost are seasonal frozen soil; thus, the spatial distribution of the two types of frozen soil is obtained through discrimination.

[0017] The water-heat coupling numerical model melting depth discriminates the permafrost type index distribution method, the step S3 is to solve the characteristic indexes of the two types of frozen soil, the characteristic index of permafrost is frozen soil depth (DPT), and the characteristic index of seasonal frozen soil is maximum frozen depth (MFD); wherein the frozen soil depth is not equal to the traditional active layer thickness (ALT), because the former considers the existence of the melting area; for the point of the permafrost type, the annual maximum melting depth is taken as the frozen soil depth, that is:

[0018] DPT= max{d i,j,t }, t=1…366 , permafrost area (3)

[0019] For the point of the seasonal frozen soil type, the annual maximum melting depth is taken as the maximum frozen depth, that is:

[0020] MFD= max{d i,j,t }, t=1…366 , seasonal frozen soil area (4)

[0021] Thus, the spatial distribution of the characteristic indexes of permafrost and seasonal frozen soil is obtained.

[0022] The advantages and effects of the present application are:

[0023] The present application proposes a water-heat coupling numerical model melting depth discriminates permafrost type and its characteristic index spatial distribution method, effectively overcomes the shortcomings that the melting depth and three-dimensional soil temperature cannot directly determine the frozen soil type, combines the advantages of the two, effectively expands the application range of the water-heat coupling numerical model; compared with the existing method, the present application has obvious improvement in the aspects of strong experience, mapping range, accuracy and fineness in permafrost mapping, and cannot discriminate the permafrost type, and overcomes the shortcomings that the existing method cannot consider the melting area in permafrost mapping. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is the annual process of the melting depth of the present application embodiment for a point;

[0025] Figure 2 It is a method flowchart of the present application embodiment;

[0026] Figure 3 It is a three-dimensional coordinate positioning schematic diagram of the present application embodiment. DETAILED DESCRIPTION

[0027] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings.

[0028] The soil melting depth output by the hydrothermal coupling numerical model of this invention typically divides its annual process at a given point into the following categories: Figure 1 The diagram shows three scenarios. Scenario 1 and 2 involve abrupt changes when the thawing depth reaches 0, which is not a natural process of soil thawing depth. For scenario 1, the dotted line 5 represents the freezing depth before thawing; for scenario 2, the dashed line 4 represents the bidirectional thawing process. This abrupt change is a common problem in numerical models when using unfrozen water content to determine freeze-thaw conditions. Therefore, it is difficult to distinguish between scenarios 1 and 2, which represent the thawing process of perennial permafrost and which represent the thawing process of seasonal permafrost. Scenario 3 is a typical thawing zone.

[0029] Of the three thawing depth scenarios, scenario 3 is the easiest to determine the type of permafrost, so we'll start with scenario 3. In scenario 3, the thawing depth never reaches 0 throughout the year, indicating it's not seasonal permafrost but perennial permafrost. Since it's not 0 throughout the year, it means the shallow soil cannot reach that thawing depth, meaning the winter soil freezing depth cannot reach it. In other words, the soil cannot completely freeze in winter, and the maximum winter freezing depth is less than the thawing depth at that point. Therefore, there is a thawing zone between these two depths, classifying this point as a thawing zone in perennial permafrost. In other words, a point meeting the following conditions is classified as a thawing zone.

[0030] d i,j,t < 0, 0<t<366 (5)

[0031] Where i and j represent the position of the point, located using row and column numbers, such as Figure 3 As shown. This completes the determination of the fusion zone in step S1, as follows. Figure 2 As shown in S1.

[0032] If the above conditions are not met, then the remaining scenarios are 1 and 2. The type of permafrost in these two scenarios can be determined from the characteristics of the intra-annual hydrothermal hydrograph, but not quantitatively, because both scenarios contain zero values ​​and exhibit freeze-thaw cycles in the shallow soil. Therefore, we introduce another result from the hydrothermal coupled numerical model: the three-dimensional soil temperature field, to determine the type of permafrost by utilizing the temperature of the deep soil layers.

[0033] First, a special case needs to be addressed: the annual maximum thawing depth equals the maximum soil depth simulated by the model. This indicates that the entire soil layer remains unfrozen throughout the year, and is therefore classified as seasonally frozen soil. For cases where the annual maximum thawing depth is less than the soil layer thickness, if there is soil below the annual maximum thawing depth with a temperature below 0 degrees Celsius... Figure 3There is any soil temperature less than 0 degree between the layer depth z where the maximum thawing depth shown and the maximum simulated layer thickness n. This indicates that there is permafrost in the deep layer that does not thaw for many years, and it is identified as permafrost. If there is no soil less than 0 degree, it indicates that there is no soil that does not thaw for many years, and it is identified as seasonal frozen soil. That is, it is determined as permafrost if it meets the following conditions, and otherwise it is determined as seasonal frozen soil.

[0034] (6)

[0035] Thus, the permafrost type determination is achieved when the annual thawing depth is 0 meters, and the thawing area determined in step S1 is classified as permafrost. The spatial distribution of permafrost and seasonal frozen soil can be obtained by identifying each point in the study area. Figure 2 S2.

[0036] The permafrost type of the three types of thawing depth annual process has been determined. Then, the next step S3 is performed. First, the annual maximum thawing depth of all points is obtained, and according to the permafrost type determined in the foregoing part, the annual maximum thawing depth of the permafrost area point is the permafrost depth DPT, and the annual maximum thawing depth of the seasonal frozen soil area point is the maximum frozen depth MFD.

[0037] In summary, the spatial distribution of the thawing area, the spatial distribution of different permafrost types, and the spatial distribution of corresponding characteristic indexes are obtained through the logical analysis and the determination and calculation process constructed.

Claims

1. A method for identifying the distribution of permafrost type indicators using numerical models of hydrothermal coupling to determine thaw depth, characterized in that, The method Comprise the following process: S1, melt depth process is determined to the space distribution of thawing area obtained by hydrothermal coupling simulation; S2, combined with three-dimensional soil temperature field, identify permafrost and seasonal frozen soil grid, obtain the spatial distribution of two types of frozen soil; S3, according to two types of frozen soil, solve to determine the spatial distribution of permafrost buried depth in permafrost area and the spatial distribution of maximum frozen depth in seasonal frozen soil area; In step S1, the melt depth of a certain point of the model output is recorded as di,j,t, where i represents the ith row, j represents the jth column, and t represents the tth day; According to the value, it is directly judged whether it is a thawing area, if it meets the following conditions, it is determined to be a thawing area: di,j,t < 0, 0<t<366 (1) By traversing all values of i,j, the judgment of all points is obtained, and the spatial distribution of the thawing area is obtained; In step S2, consider the points that are not thawing areas in step S1; Record the soil temperature of a certain point (i,j,z) in the three-dimensional soil temperature field in summer as Ti,j,z,240, where z represents the depth of the point, and the serial number of the soil discrete layer from the surface to the underground is used to represent, and the total number of soil discrete layers is n; 240 represents the 240th day from January 1st in a year, which represents the end of August; Record the simulated soil total depth as Dm, di,j,t corresponds to the soil layer zd; For the points that are not determined as thawing areas in step S1, if the following two conditions are met at the same time, it is determined to be permafrost; Otherwise, it is determined to be seasonal frozen soil; (2) The identification is to classify the thawing area into permafrost, and the spatial distribution of permafrost is obtained, and the points that are not permafrost are seasonal frozen soil; In this way, the spatial distribution of the two types of frozen soil is obtained through identification; The step S3 is to solve the characteristic indexes of the two types of frozen soil. The characteristic index of permafrost is frozen soil buried depth DPT, and the characteristic index of seasonal frozen soil is maximum frozen depth MFD; The frozen soil buried depth is not equal to the traditional active layer thickness ALT, because the former considers the existence of the thawing area; For the points of permafrost type, take the annual maximum thawing depth as the frozen soil buried depth, that is: DPT= max{di,j,t}, t=1…366, permafrost area (3) For the points of seasonal frozen soil type, take the annual maximum thawing depth as the maximum frozen depth, that is: MFD= max{di,j,t}, t=1…366, seasonal frozen soil area (4) In this way, the spatial distribution of the characteristic indexes of permafrost and seasonal frozen soil is obtained.

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