A large-scale soil erosion assessment method based on hydrological station data

Abstract

The present invention discloses a large-scale soil erosion evaluation method based on hydrological station data, comprising: merging or migrating basin evaluation units according to the relative relationship between the station distribution location and the location of the river section in the basin to establish a "station-controlled basin" evaluation unit; determining outliers in the station observation data caused by local extreme climate events based on the station observation data, and screening and eliminating outliers in the time series; judging the data quality of the hydrological station in the "station-controlled basin" basic evaluation unit according to the spatial location distribution of the hydrological observation station relative to the overall basin and the local river section, and selecting appropriate hydrological stations for soil erosion results evaluation. The method of the present invention can optimize the sediment time series data observed by the hydrological station in combination with the distribution pattern of the basin units and stations, making up for the current shortcomings of simply and directly using statistical data to evaluate and verify large-scale basin soil erosion results.

Description

Technical Field

[0001] The present invention relates to the fields of GIS and soil and water conservation, and in particular to a large-area-scale soil erosion evaluation method based on hydrological station data. Background Art

[0002] Soil erosion is not only a major form of land degradation globally, but soil intrusion into water bodies can also lead to river siltation and exacerbated flooding (Shi Zhihua and Song Changqing, 2016). Current soil erosion estimation methods, represented by empirical models like the Revised Universal Soil Loss Equation (RUSLE), are widely used due to their relatively simple data acquisition and high operability, making them suitable for simulating soil erosion over long periods of time and over large areas (Xu et al., 2013). However, verification techniques for these large-scale soil erosion results remain relatively traditional and qualitative.

[0003] Traditional validation methods for soil erosion research are mostly conducted at the scale of small watersheds and experimental fields. Zhao Ziyuan et al. (2022) used observations from runoff plots in small watersheds to validate local soil erosion model simulations. Liu Dianmin et al. (2022) directly validated soil erosion results using field observations from soil troughs in experimental fields. However, due to the high spatial heterogeneity of soil erosion and the significant human and material resources required for field observations, these methods are not applicable at large regional scales.

[0004] Currently, there are numerous studies on large-scale soil erosion simulation based on models such as RUSLE. However, most of these results are validated using simple evaluation methods based on traditional large-scale watershed site and regional classification statistics. Meusburger et al. (2010) used a simple classification method to categorize soil erosion estimates and then combined them with high-resolution satellite data to conduct qualitative visual verification of areas with severe soil erosion. Borrelli et al. (2014) calculated sediment content values ​​based on sediment volume changes in lakes downstream of rivers to characterize soil erosion in the upstream watershed of lakes. They then combined this with sediment transport ratios calculated from topography to validate the RUSLE-based watershed soil erosion results. Gu Zhijia et al. (2019) compared interpolated results based on the average modulus of survey units with grid moduli calculated from remote sensing to verify the accuracy of remotely sensed erosion moduli. Zhao Mengen et al. (2022) simply classified their soil erosion estimates, which was insufficient for direct verification of the reliability of their results. Alewell et al. (2019) pointed out that due to the temporal and spatial limitations of current monitoring data, absolutely accurate verification is difficult to achieve. Models should be used as tools to more accurately examine the status, spatial variability, and time series changes of soil erosion within limited observational data.

[0005] Currently, significant progress has been made in estimating soil erosion at a large regional scale. However, due to the lack of validation methods and the coarseness of the models used in all studies, the quality of erosion data products is difficult to guarantee. Consequently, only indirect verification of the rationality of the results or the erosion grade can be used. Due to the uneven temporal and spatial distribution of hydrological stations and the limited availability of historical data, river water and sediment observation data cannot be well matched with large-scale soil erosion results, making it difficult to meet the current computational verification requirements for quantitative soil erosion. Therefore, selecting appropriate river sediment hydrological observation data that is compatible with the watershed unit from the limited and coarse hydrological station observation data is particularly important for verifying and evaluating large-scale watershed soil erosion estimation results.

[0006] The present invention combines the distribution pattern of watershed units and stations to optimize the time series data of sediment volume observed by hydrological stations, and makes a reasonable evaluation of the remote sensing estimation results of soil erosion in large watersheds. It has a certain universality and makes up for the shortcomings of the current simple and direct use of statistical data to evaluate and verify the results of soil erosion in large-scale watersheds. It can provide effective scientific reference and theoretical basis for the quantitative estimation of soil erosion by remote sensing in large-scale watersheds and further for watershed soil and water conservation and ecological environment assessment. Summary of the Invention

[0007] The purpose of the present invention is to provide a large-scale soil erosion evaluation method based on hydrological station data. It can optimize the sediment time series data observed by hydrological stations in combination with the distribution pattern of watershed units and stations, and reasonably evaluate the remote sensing estimation results of soil erosion in large watersheds.

[0008] In order to achieve the above object, the technical solutions adopted by the present invention are as follows:

[0009] Large-scale soil erosion assessment methods based on hydrological station data include:

[0010] Based on the basin vector boundary, multiple basin units are obtained, and a single basin unit is used as the initial assessment unit of the basin;

[0011] Based on the relative relationship between the distribution location of hydrological stations and the location of river sections in the basin and the controlled basin area corresponding to the stations, the initial basin evaluation units are merged or relocated to establish a basin evaluation unit with one station for one basin unit or one station for multiple basin units;

[0012] For each evaluation unit, a scatter plot was established with the annual sediment transport measured at the site as the horizontal axis and the total soil erosion in the basin calculated using the soil erosion estimation model as the vertical axis. Outliers were removed in combination with climate change data.

[0013] When there are multiple sites in a watershed unit, based on the spatial distribution of the sites relative to the overall watershed and local river sections, the watershed evaluation units containing the watershed unit are screened using the correlation and root mean square error between the annual sediment discharge measured at the sites and the total soil erosion amount in the watershed calculated using the soil erosion estimation model as the judgment indicators to determine the watershed evaluation unit to be used.

[0014] As a preferred implementation, the watershed vector boundary uses a third-level watershed or a finer watershed division level.

[0015] As a preferred embodiment, the method of merging or migrating the initial watershed evaluation units according to the relative relationship between the distribution positions of the stations and the positions of the river sections and the controlled watershed areas corresponding to the stations includes:

[0016] When the station is located upstream of a river reach, the watershed is merged upstream until the area of ​​the merged watershed approaches the area of ​​the watershed controlled by the station;

[0017] When the station is located at the confluence of the main and tributary streams, the main stream basin and the tributary basin are simultaneously merged upstream until the area of ​​the merged basin approaches the area of ​​the station's controlled basin;

[0018] When the control basin of a site does not include the basin in which it is located, the basin it controls is corrected to its upstream basin.

[0019] As a preferred embodiment, for a river basin containing multiple rivers, the rivers controlled by the stations are determined based on their longitude and latitude, and the relative relationship between the river sections and the station distribution locations is determined based on the river sections.

[0020] As a preferred embodiment, the soil erosion estimation model is a soil erosion estimation model that takes into account factors such as topography, precipitation, vegetation conditions, soil properties and soil and water conservation measures, and has a time resolution of 1 year.

[0021] As a preferred implementation, the soil water erosion estimation model uses a RUSLE model or a CSLE model.

[0022] As a preferred implementation, the step of removing outliers in combination with climate change data includes:

[0023] Candidate outliers are identified based on the scatter plot and then verified against climate change data to identify extreme climate events. If an extreme climate event is present, the data for the corresponding station and year are removed from the candidate outliers based on the impact of the extreme climate event. Furthermore, extreme climate events are defined as those that cause changes in water and sediment levels in the downstream basin, including extreme localized precipitation, levee breaches along riverbanks, landslides along and upstream riverbanks, and ecological changes along and upstream riverbanks.

[0024] As a preferred embodiment, the projection coordinate system, geographic coordinate system and spatial resolution of the hydrological station data and the watershed data used for calculating the total soil water erosion amount are kept consistent.

[0025] As a preferred embodiment, when there are multiple sites in a watershed unit, the sites located in the middle of the watershed are first eliminated;

[0026] Secondly, when the station is located at the head of the river basin, the upstream station of the basin is selected. In this case, the basin controlled by the station is the upstream basin. When the station is located at the end of the downstream river basin, the downstream station is selected. In this case, the basin controlled by the station is the basin where the station is located. When the station is located at the confluence node of the main stream of the water system, the station controls the basin of the upstream tributary that converges.

[0027] Based on the above principles, the judgment indicators are used to judge the size of the data spatial error of the station in the basic evaluation unit in turn, so as to screen suitable hydrological stations for evaluating soil water erosion results.

[0028] With the support of multi-source remote sensing data products, the present invention first compiles the correspondence between observation stations and watershed units based on the spatial distribution of hydrological observation stations in the public hydrological data, the controlled watershed area, and the relative position relationship with the watershed unit. Secondly, the annual sediment transport measured by the hydrological observation station is compared with the sum of the soil erosion modulus calculated in the controlled watershed to draw a scatter plot, and the data time series is screened in combination with local hydrological events and extreme climate events in the public data. Finally, the optimal station is selected based on the upstream, midstream and downstream positions of the hydrological station in the main and tributary basins of the overall watershed and the local river section to conduct accuracy verification on the watershed unit scale, which makes up for the current shortcoming of simply using statistical data to evaluate and verify the results of soil erosion in large-scale watersheds, and can provide effective scientific reference and theoretical basis for quantitative estimation of soil erosion in large-scale watersheds by remote sensing, and further for watershed soil and water conservation and ecological environment assessment.

[0029] It can be seen from the above technical solutions of the present invention that the soil erosion evaluation method based on hydrological station data optimization of the present invention is different from other large-scale soil erosion estimation studies that lack measured data verification or rough site verification methods. This evaluation method optimizes the sediment time series data observed by the hydrological station by combining the distribution pattern of watershed units and stations, and reasonably evaluates the remote sensing estimation results of soil erosion in large watersheds, thereby improving the level of soil erosion monitoring and providing technical support for land management and soil degradation control.

[0030] It should be understood that all combinations of the foregoing concepts and the additional concepts described in more detail below, as long as such concepts are not mutually inconsistent, can be considered part of the inventive subject matter of this disclosure. In addition, all combinations of the claimed subject matter are considered part of the inventive subject matter of this disclosure.

[0031] The foregoing and other aspects, embodiments, and features of the present invention will be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the present invention, such as features and / or beneficial effects of the exemplary embodiments, will become apparent from the following description or through practice of specific embodiments according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings are not intended to be drawn to scale. In the accompanying drawings, each identical or approximately identical component shown in the various figures may be represented by the same reference numeral. For clarity, not every component is labeled in each figure.

[0033] Embodiments of various aspects of the present invention will now be described by way of example and with reference to the accompanying drawings, in which:

[0034] Figure 1 It is a flow chart of the soil water erosion evaluation method based on the optimization of hydrological station data.

[0035] Figure 2 It is the three-level basin division and numbering of a certain basin in the embodiment.

[0036] Figure 3 This is the soil erosion estimation result diagram of a certain watershed based on the RUSLE model.

[0037] Figure 4 This is a modified schematic diagram of a third-level watershed evaluation unit in the embodiment (taking Site 4 as an example).

[0038] Figure 5 This is a comparison chart of the accuracy of a certain third-level watershed evaluation unit before and after correction in the embodiment.

[0039] Figure 6 This is a comparison chart of site accuracy before and after the evaluation unit correction (taking Site 4 as an example).

[0040] Figure 7 This is a scatter plot of outlier removal in step 2 of a certain river basin site in the embodiment (taking Site 4 as an example).

[0041] Figure 8 This is a comparison chart of the verification accuracy of main and tributary river stations in step three of a certain basin in the embodiment.

[0042] Figure 9 This is a schematic diagram of the locations of upstream, midstream and downstream stations in a typical local river section of a certain river basin in the embodiment.

[0043] Figure 10 This is a comparison chart of the verification accuracy of relative position stations in different river sections in step three of the embodiment for a certain river basin.

[0044] The coordinates, symbols or other expressions in English in the above-mentioned Figures 1-10 are well known in the art and will not be described in detail in this example. DETAILED DESCRIPTION

[0045] In order to better understand the technical content of the present invention, specific embodiments are given below in conjunction with the accompanying drawings.

[0046] Various aspects of the present invention are described in this disclosure with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to include all aspects of the present invention. It should be understood that the various concepts and embodiments introduced above, as well as those described in more detail below, can be implemented in any of many ways, and that the concepts and embodiments disclosed herein are not limited to any implementation. In addition, some aspects of the present disclosure may be used alone or in any appropriate combination with other aspects of the present disclosure.

[0047] Example 1

[0048] Since large-scale soil erosion calculations require a large amount of data, a long computation time, and a complex processing flow, this embodiment takes a large-scale watershed as an example to further describe the technical solution of the present invention.

[0049] The present invention first compiles the correspondence between the observation stations and the third-level basins based on the spatial distribution of the hydrological observation stations in the public data, the controlled basin area, and the relative position relationship with the third-level basin. Secondly, the annual sediment transport measured by the hydrological observation station is compared with the sum of the soil erosion modulus calculated in the third-level basin to draw a scatter plot, and the data time series is screened in combination with the local hydrological events and extreme climate events in the public data. Finally, the optimal station is selected based on the upstream, midstream and downstream positions of the hydrological station in the main and tributary basins of the overall basin and the local river sections to conduct accuracy verification at the basin unit scale, which makes up for the current shortcoming of simply and directly using statistical data to evaluate and verify the results of soil erosion in large-scale basins. It can provide effective scientific reference and theoretical basis for quantitative estimation of soil erosion in large-scale basins by remote sensing and further for watershed soil and water conservation and ecological environment assessment. The technical flow chart is as follows Figure 1 shown.

[0050] As an exemplary description, the implementation of the above method is described in detail below with reference to the accompanying drawings.

[0051] Step 1: Determine the evaluation unit. Based on the watershed vector boundary, determine the available watershed vector data and obtain multiple watershed units. In this example, the obtained vector level 3 watershed data is used. For example, watershed number F0101 is a watershed unit, which is used as the initial evaluation unit.

[0052] Secondly, the initial watershed evaluation units are merged or migrated according to the relative relationship between the site distribution location and the location of the river section in the basin and the controlled watershed area corresponding to the site.

[0053] The merging is based on the principle of merging upstream, because sediment generally flows from upstream to downstream.

[0054] For example, if the station is located upstream of a river section, the watershed it controls includes the adjacent watersheds through which the upstream river passes. The watersheds are merged and migrated upward one by one until the area of ​​the corresponding control unit is close to the area of ​​the watershed controlled by the station in the data.

[0055] When the station is located at the confluence of the main and tributary rivers, because the sediment from the tributaries is introduced, it is necessary to merge upward not only in the main river basin but also in the tributary basin until the area of ​​the corresponding control unit is close to the area of ​​the station control basin in the data.

[0056] The migration mainly refers to the fact that sometimes the modified controlled basin does not include the basin in which it is located, but is instead moved to an adjacent basin upstream. For example, if a station is located upstream of basin F0102, its controlled basin will be revised to its upstream basin F0101, thus migrating from F0102 to F0101.

[0057] Establish a one-to-one or one-to-many evaluation unit of "site-control basin" such as Figure 4 As shown, a list of evaluation units is established, as shown in Table 1, where one row in the table represents one evaluation unit.

[0058] Table 1. Matching table of evaluation units of “site-controlled basin” in watershed

[0059]

[0060]

[0061] Due to the temporal and spatial differences in the distribution of stations within the basin and the soil erosion estimation results, the spatial and temporal resolutions of the stations and raster data used in the example need to be limited. The source of the hydrological station observation data must be the data published by the local water conservancy department and the spatial location of the hydrological observation stations and the annual sediment discharge monitored by each station extracted from it. The temporal resolution is 1 year, and the observation data must include the annual sediment discharge. The basin vector data must use the third-level basin divided by the basin or more detailed basin data, such as Figure 2 As shown in the figure, the soil erosion result data to be verified must be an existing soil erosion estimation model (such as RUSLE and CSLE models) that considers five factors: topography, precipitation, vegetation conditions, soil properties, and soil and water conservation measures, and the time resolution must be 1 year. Figure 3The following is a 1km result map of large-scale watershed soil erosion estimation based on the RUSLE model in 2021. In terms of spatial reference, the projection coordinate system and geographic coordinate system of each data must be consistent for subsequent calculations. After the correction of the evaluation unit, the verification results of the hydrological station have been significantly improved compared with those before the correction. Figure 5 and Figure 6 At the same time, the revised basin must have a clear division of main and tributary basins, and a clear distribution of river sections in the basic basin units.

[0062] Step 2: Screening and Eliminating Anomalies. Based on a scatter plot of the regional statistics of the observed sediment content and soil erosion results at the station and climate change data, identify outliers in the station's observation data caused by local extreme climate events. Specifically, candidate outliers are first identified based on the scatter plot. Then, the data are compared with climate change data to verify the presence of an extreme climate event in that year. If an extreme climate event did occur, the data for the corresponding station and year are removed from the candidate outliers based on the impact range of the extreme climate event. If there was no extreme climate event, the data is not considered an anomaly.

[0063] A list of abnormal years was established, and abnormal data in the time series were screened and removed, as shown in Table 2.

[0064] Table 2. Table of years with abnormal data removed from hydrological observation stations of tributaries in a certain basin

[0065]

[0066] The scatter plot of the sediment content observed at the site and the regional statistics of soil erosion results needs to use the annual sediment discharge of the site and the total amount of soil erosion in the control basin as the horizontal and vertical coordinates, respectively, such as Figure 7 Extreme climate events are determined based on publicly available records, such as abnormal meteorological events released by meteorological departments and extreme hydrological events published by water conservancy departments. Extreme climate events must include extreme local precipitation, levee breaches along river sections, landslides along river sections and upstream, and ecological changes along river sections and upstream, leading to changes in water and sediment elements in the downstream basin.

[0067] Step 3: Optimize the spatial location of the station. The annual sediment transport measured by the main hydrological monitoring stations in the public basin of the local water conservancy department is used for verification. According to the spatial distribution of the hydrological observation stations relative to the overall basin and local river sections, that is, the locations of the hydrological stations in the main and tributary basins of the overall basin and the upper, middle and lower reaches of the local river sections are shown in Table 3 and Figure 9As shown. When there are multiple stations in a three-level watershed, three situations are considered. First, stations located in the middle section of the watershed are eliminated first, because due to the limitations of the watershed vector data, midstream stations will introduce large spatial errors. Secondly, when the station is located in the river section at the head of the watershed, the upstream station of the watershed is selected. At this time, the watershed controlled by the station is the upstream watershed. Finally, when the station is located in the river section at the downstream end of the watershed, the downstream station is selected. At this time, the watershed controlled by the station is the watershed where the station is located. When the station is located at the confluence node of the main stream of the water system, the station controls the upstream tributary watershed it converges. According to the above principles, the data spatial error size of the hydrological station in the basic evaluation unit of "station-controlled watershed" is judged in turn, and suitable hydrological stations are screened for the evaluation of soil water erosion results.

[0068] Table 3 Basic information of hydrological observation stations in a river basin and relative position distribution of river sections

[0069]

[0070]

[0071] The validation method used in this example is based on a three-level watershed zoning. Because the correspondence between the locations of hydrological observation stations and the controlled watershed area varies between different levels of watershed zoning, the correlation between the annual sediment load measured at the hydrological observation stations and the sum of the soil erosion moduli calculated within the three-level watershed was calculated as a criterion for optimal combination selection. Because annual sediment load is the most intuitive indicator of soil erosion at the observation station scale, annual sediment load was used as validation data.

[0072] Finally, the verification accuracy of each "site-controlled watershed" evaluation unit of the soil erosion estimation results of the watershed is obtained. As shown in the figure, the verification results are compared. Figure 8 and Figure 10 As shown, the spatial errors between the tributary stations and the stations located upstream and downstream of the basin are relatively small due to the mismatch between the stations and the basin levels. Figure 9 As shown, the verification effect is better, so when selecting site verification data, the tributary sites of the basin and the sites located upstream and downstream are given priority.

[0073] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Those skilled in the art will appreciate that various modifications and variations can be made without departing from the spirit and scope of the present invention.

Claims

1. A large-scale soil erosion assessment method based on hydrological station data, characterized by: include: Based on the basin vector boundary, multiple basin units are obtained, and a single basin unit is used as the initial assessment unit of the basin; Based on the relative relationship between the distribution location of hydrological stations and the location of river sections in the basin, as well as the controlled basin area corresponding to the stations, the initial evaluation units of the basin are merged or relocated to establish a basin evaluation unit with one station for one basin unit or one station for multiple basin units; For each watershed evaluation unit, a scatter plot was constructed with the annual sediment transport measured at the site as the horizontal axis and the total soil erosion in the watershed calculated by the soil erosion estimation model as the vertical axis. In addition, outliers were removed in combination with climate change data. When there are multiple sites in a watershed unit, based on the spatial distribution of the sites relative to the overall watershed and local river sections, the watershed evaluation units containing the watershed unit are screened using the correlation and root mean square error between the annual sediment discharge measured at the sites and the total soil erosion amount in the watershed calculated using the soil erosion estimation model as the judgment indicators to determine the watershed evaluation unit to be used.

2. The method according to claim 1, characterized in that The watershed vector boundary adopts a third-level watershed or a finer watershed division level.

3. The method according to claim 1, characterized in that The method of merging or migrating the initial evaluation units of the watershed according to the relative relationship between the distribution positions of the stations and the positions of the river sections in the watershed and the controlled watershed areas corresponding to the stations includes: When the station is located upstream of a river reach, the watershed is merged upstream until the area of ​​the merged watershed approaches the area of ​​the watershed controlled by the station; When the station is located at the confluence of the main and tributary streams, the main stream basin and the tributary basin are simultaneously merged upstream until the area of ​​the merged basin approaches the area of ​​the station's controlled basin; When the control basin of a site does not include the basin in which it is located, the basin it controls is corrected to its upstream basin.

4. The method according to claim 1 or 3, characterized in that For a basin containing multiple rivers, the river it controls is determined based on the latitude and longitude of the station, and the relative relationship between the river section and the station distribution location is determined based on the location of the river.

5. The method according to claim 1, wherein The soil erosion estimation model is a soil erosion estimation model that takes into account factors such as topography, precipitation, vegetation conditions, soil properties and soil and water conservation measures, and has a time resolution of 1 year.

6. The method according to claim 1 or 5, characterized in that The soil water erosion estimation model uses the RUSLE model or the CSLE model.

7. The method according to claim 1, characterized in that The removal of outliers by combining climate change data includes: Candidate outliers are determined based on the scatter plot, and then compared with climate change data to determine whether there are extreme climate events. If there are extreme climate events, the data for the corresponding year at the corresponding station are removed from the candidate outliers based on the impact range of the extreme climate event.

8. The method according to claim 7, characterized in that The extreme climate events mentioned above are abnormal events that lead to changes in water and sediment elements in the downstream basin, including extreme local precipitation, dike breaches along river sections, landslides along river sections and upstream, and ecological transformation along river sections and upstream.

9. The method according to claim 1, characterized in that The projection coordinate system, geographic coordinate system and spatial resolution of the hydrological station data and the watershed data used for total soil water erosion calculation were kept consistent.

10. The method according to claim 1, characterized in that When there are multiple sites in a watershed unit, the following principles are followed: sites located in the middle of the watershed are eliminated first; Secondly, when the station is located at the head of the basin, the upstream station is selected. In this case, the control basin of the station is the upstream basin. When the station is located at the end of the downstream basin, the downstream station is selected. In this case, the control basin of the station is the basin where the station is located. When the station is located at the confluence node of the main stream of the river system, the station controls the upstream tributary basin that it confluences; Based on the above principles, the judgment indicators are used to judge the data spatial error of the site in the watershed evaluation unit in turn, so as to screen suitable hydrological sites for evaluating soil water erosion results.

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