A multi-scale linkage flood risk early warning method for plain areas

Abstract

The application discloses a kind of face, block and point scale linkage flood warning method based on river forecast water level in plain area, according to the flood face scale early warning of plain representative site, for having face scale early warning area, using GIS technology and the spatial autocorrelation of plain area water level in flood forecast process, calculate submerged grid and depth, carry out block, point scale early warning.The method is a kind of simple, fast method.It includes the following steps: collecting plain area basic data;A kind of face, block and point multiscale linkage early warning mechanism;Compare regional representative site forecast water level and characteristic water level, dike elevation, and carry out face scale flood risk early warning;With face scale early warning area as unit, obtain regional forecast water level face data, generate the submerged grid and water depth of regional unit, and carry out block scale early warning;With face scale early warning area as unit, in combination with submerged face, submerged water depth and flood risk point data, utilize spatial analysis technique to carry out point scale early warning.

Description

Technical Field

[0001] This invention belongs to the field of flood risk early warning technology. Specifically, it relates to a flood risk early warning method that combines GIS technology and multi-source data, applicable to plain areas, and integrates area, block, and point scales. This method combines representative station water levels, characteristic water levels, and levee elevations for area-scale early warning. For areas with flood risk, it uses GIS technology to spatially interpolate water level data to quickly obtain the inundation range and water depth, enabling block-scale and point-scale flood risk early warning. This method is a simple, fast, and effective method for assessing urban flooding risk, capable of rapidly calculating the inundation range, inundation depth, and at-risk objects. Background Technology

[0002] Global warming and the increasing frequency of extreme weather events, including more frequent floods, are having a significant impact on human health and the environment. Southern my country, in particular, with its predominantly tropical and subtropical monsoon climate, is experiencing more severe flooding due to heavy rainfall and upstream snowmelt. Therefore, effective and rapid flood risk warnings and assessments, along with tailored risk alerts at different scales to meet diverse user needs, are of paramount importance.

[0003] Many flood warning methods exist, but there is insufficient coordination between warnings at different scales. These methods fail to adequately address the needs of managers, flood control personnel, and the general public, resulting in a lack of scale-linked flood risk warnings. Furthermore, rapid flood risk warning methods for large areas are lacking. While hydrological and hydrodynamic methods can quickly provide area-scale flood risk warnings by combining representative monitoring stations, small-scale flood risk assessments require comprehensive consideration of the impact between drainage networks and waterways, incorporating rich underlying surface information and numerous model calculation parameters. Combining hydrological and hydrodynamic methods for urban flooding warnings is time-consuming and costly. Therefore, to achieve rapid and efficient response, large-scale flood risk calculations using multi-source data are necessary. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-scale, interconnected flood risk early warning method for plain areas. This method is applicable to large-area flood risk early warning in plain areas and provides multi-scale early warning at the area, block, and point levels to meet the needs of various users, including managers, the general public, and flood control personnel. Specifically, it combines representative station water levels, characteristic water levels, and levee elevations for area-scale early warning. For areas with flood risk, the levee height of inland rivers is required to be equal to the land elevation. Assuming that the water flow within the local area is interconnected, spatial interpolation of river water levels can be used to form the inundation range of the local area, followed by block-scale and point-scale flood risk early warning.

[0005] Therefore, the present invention adopts the following technical solution:

[0006] A multi-scale coordinated flood risk early warning method for plain areas, characterized by the following steps:

[0007] Step (1): Obtain river vector data and river cross-section within the plain area, divide the area, determine the target time, collect the predicted water level of the river section at the target time, and collect the characteristic water level of the river section and the elevation value of the river embankment near the river section.

[0008] Step (2): Establish a multi-scale linkage early warning mechanism for surface, block, and point areas. For the plain area, flood orange, red, and purple early warnings are issued based on the target time forecast water level of the river section and multiple characteristic water levels. For the purple early warning area, block and point scale early warnings are activated.

[0009] Step (3): Compare the forecast water level and characteristic water level of the representative station at the target time in the region, and issue orange, red and purple area-scale warnings for the monitoring area according to the rules;

[0010] Step (4): Taking the purple warning area as a unit, spatial interpolation calculation is performed on the predicted water level of the inland river water point at the target time to obtain the regional predicted water level surface data, as well as spatial overlay analysis with DEM data, to generate the inundation grid and inundation depth of the regional unit, and to carry out block-scale flood risk warning.

[0011] Step (5): Using the purple warning area as a unit, combined with the inundation grid, inundation depth and flood risk point data, spatial analysis technology is used to carry out point-scale flood risk warning, and emergency linkage warning is carried out with relevant personnel.

[0012] Step (6): Steps (3)-(5) are executed sequentially for each monitoring area until all monitoring areas complete the early warning judgment.

[0013] In step (1), the following sub-steps are included: obtaining river vector data and river cross-sections within the plain area, dividing the region, determining the target time, collecting the predicted water level of the river section at the target time, collecting the characteristic water level of the river cross-section and the elevation values ​​of the river embankment near the river cross-section.

[0014] Step (11) Obtain river vector data within the plain area and river cross sections in each area, and make them have the same spatial coordinate system, and require that the number of river cross sections in each area is at least one.

[0015] Step (12): Divide the region according to the characteristics of river catchment in the plain area. It is required that the inland river system in the region is connected, the terrain is flat, and there are no dikes on both sides of the river in the region. It is assumed that the water level of the river at the target time in the monitoring area can be spatially interpolated to form the predicted water level surface of the corresponding area.

[0016] Step (13): Based on the predicted water level process of each section, confirm the target time in each area. The target time should be close to the predicted peak water level time, and obtain the predicted water level data at the target time.

[0017] Step (14) Obtain the guaranteed water level, warning water level and river embankment elevation near the river section (the river embankment elevation can be extracted from the DEM data).

[0018] In step (2), a multi-scale linkage early warning mechanism involving areas, blocks, and points is used to issue orange, red, and purple flood warnings at the area scale based on the target time forecast water level of the river cross-section and multiple characteristic water levels within the plain area. For the purple warning area, block-scale and point-scale early warnings are activated. Specifically, it includes the following sub-steps:

[0019] Step (21): Based on the predicted water level and characteristic water level of the river section at the target time in each monitoring area, issue orange, red and purple warnings at the surface scale. For the area-scale warning areas, promptly notify and contact the relevant management personnel.

[0020] Step (22): For the area under purple warning, activate block-scale warning, generate flood grid by combining GIS technology, target time forecast water level data and DEM elevation data, and promptly notify and contact relevant management personnel.

[0021] Step (23): For the area under purple warning, activate point-scale warning, calculate using GIS technology and risk point data, and promptly notify and contact relevant management personnel.

[0022] In step (3), the predicted water level and characteristic water level of the representative station at the target time in the region are compared, and the area-scale orange, red, and purple early warnings are issued for the monitoring area according to the rules. The specific steps include the following:

[0023] Step (31): Sequentially set the characteristic water levels of the corresponding river sections as warning water level, guaranteed water level, and approximate dike water level. The approximate dike water level is a value between the guaranteed water level and the dike water level, and close to the dike water level. Replacing the dike water level with the approximate dike water level is to improve the safety factor. The calculation formula is as follows:

[0024] H 近似堤防 =H 堤防 -(H 堤防 -H 保证 )*A (1)

[0025] Among them, H 近似堤防 To approximate the dike's water level, H 堤防 H represents the corresponding levee elevation for the river cross-section. 保证 To ensure the water level, A is a value between 0 and 1, and is taken as 0.10 here.

[0026] Step (32): Combine the forecast water level, warning water level, guaranteed water level and approximate dike water level at the target time to formulate early warning rules. If the forecast water level of at least one river section is greater than or equal to the elevation of the approximate dike water level, the area is given a purple flood warning. If the purple warning is not met and the forecast water level of at least one river section is greater than or equal to the guaranteed water level, the area is given a red warning. If the purple or red warning is not met and the forecast water level of at least one river section is greater than or equal to the warning water level, the area is given a yellow warning. If the forecast water level of all stations is less than the warning water level, the area is given no flood warning.

[0027] In step (4), the purple warning area is used as the unit. Spatial interpolation calculation is performed on the predicted water level of the inland river at the target time to obtain the regional predicted water level data. Spatial overlay analysis with DEM data is also performed to generate the inundation grid and inundation depth of the regional unit. Block-scale flood risk warning is then carried out. The specific sub-steps are as follows:

[0028] Step (41) determines whether there are abnormal water levels in the target time forecast water level within the area. Phenomena such as sluice gate closures can cause the water level at nearby river sections to be significantly higher than the water level data of other river sections in the area, thus reducing the applicability of the spatial interpolation algorithm and resulting in an excessively large inundation area. The formula for judging abnormal water levels is as follows:

[0029]

[0030] Where Y = 1 indicates that the water level at this point is abnormal, Y = 0 indicates that the water level at this point is abnormal, H i B represents the predicted water level of the i-th river section, and B represents the difference between the predicted water level of the i-th river section and the average predicted water level in the region, which is 0.5 in this case.

[0031] Step (42) Delineate the affected area for each river section based on various factors such as water catchment characteristics, historical inundation range, and human experience.

[0032] Step (43): If there are no abnormal areas, assuming that the water flow in the monitored area is connected, spatial interpolation calculation can be performed on the inland river water level forecast data at the target time in the area to obtain the regional forecast water level surface data. If there are abnormal areas, separate calculation is performed for the affected areas of the abnormal water level. The plane where the abnormal water level is located is the forecast water level surface. For other areas, spatial interpolation is performed on the inland river water level forecast point data in the area. The forecast water level surfaces of the abnormal areas and other areas are merged to obtain the forecast water level surface of the purple warning area.

[0033] Step (44) involves spatially overlaying the predicted water level and high-precision DEM data to generate the inundation grid and inundation depth for the area, and then performing block-scale early warning. This step includes the following sub-steps:

[0034] Step (441) involves spatially overlaying the predicted water level and high-precision DEM data in the same spatial coordinate system, with the predicted water level and high-precision DEM having the same grid size and spatial matching.

[0035] Step (442) calculates the inundation depth for each grid, i.e., using the predicted water level data (H). wl Subtract the elevation values ​​from the DEM data (H) dem If the former is greater than the latter, then the area is at risk of flooding, and a block-scale early warning is issued. The calculation formula is as follows:

[0036]

[0037] Where D represents the submerged water depth data, and H... wl Forecast water level data, H dem These are the elevation values ​​from the DEM data.

[0038] Step (5) uses the purple warning area as a unit, combines the inundation grid, inundation depth and flood risk point data, and uses spatial analysis technology to conduct point-scale flood risk warning, and conducts emergency linkage warning with relevant personnel. Specifically, it includes the following sub-steps:

[0039] Step (51) Obtain point vector data of the underlying surfaces of hazardous chemical enterprises, residential communities, shopping malls, agricultural and forestry land, villages, etc., and place them in the same spatial coordinate system as other data.

[0040] Step (52) determines whether the underlying surface point vector data and the flooding grid in step (4) intersect spatially. If they intersect, they are objects at risk of waterlogging and point-scale early warning is issued. Otherwise, there is no risk.

[0041] This invention employs a combined approach of area-scale, block-scale, and point-scale early warning systems. The area-scale system serves city and county-level management, the block-scale system can be used to quickly calculate the impact range and potential economic losses, and the point-scale system can provide rapid early warnings for key flood-prone areas, promptly notifying flood control management personnel. Furthermore, in many plain areas, the levee height of inland rivers is equal to the land level. During floods, not only is the river channel connected, but it can also be assumed that the water flow is connected throughout local areas. Therefore, spatial interpolation of river levels can be used to determine the inundation range of local areas. Based on this principle, rapid flood risk early warning at both the block and point scales can be achieved, and risk assessment can be conducted by combining sufficient surface information.

[0042] Compared with the prior art, the present invention has the following features and beneficial effects:

[0043] 1. This invention features rapid and efficient assessment of urban flooding risks. Combining the spatial linkage between points, lines, and areas, it proposes a multi-scale linkage early warning mechanism and proposes early warning methods for different scales. At the area scale, it combines multiple characteristic water levels for judgment and uses approximate dike water levels to further refine the early warning level, emphasizing the risk of flooding. At the block and point scales, it uses GIS technology for analysis and assessment, which can promptly communicate with flood control personnel, management personnel, and the public to respond to urban flooding risks and take swift measures to prevent urban flooding disasters.

[0044] 2. In block and point-scale early warning, considering the flat terrain of plain areas and the lack of obvious dikes in inland rivers, it is assumed that the water flow in the entire plain area is interconnected. Taking advantage of the strong autocorrelation of water levels in plain areas, spatial interpolation technology is used to interpolate the water level monitoring point data to quickly obtain water level surface scale data. Then, it is combined with high-precision topographic data for spatial overlay analysis, which is suitable for rapid urban flooding risk assessment in plain areas.

[0045] 3. Although it has been assumed that the water flow throughout the plain area is interconnected, the terrain is flat, and there are no obvious levees, thus satisfying the requirements for spatial interpolation of the predicted water level data, the closure of sluice gates can cause the water level at nearby river sections to be significantly higher than that of other river sections in the area, but not exceeding the elevation of the river levees. In this case, the applicability of the spatial interpolation algorithm will be reduced, and the inundation area will be larger than expected. Therefore, for areas with excessively high predicted water levels, separate calculations and risk analyses of the predicted water level surface are performed. Attached Figure Description

[0046] Figure 1 This is a flowchart illustrating the calculation process of a multi-scale linkage flood risk early warning method proposed in this invention.

[0047] Figure 2 This is a schematic diagram of a river channel, river cross-section, and nearby levee locations in a certain area.

[0048] Figure 3 (a) Figure 3 (b) Figure 3 (c) are respectively Figure 2 The diagram shows the predicted water level, DEM elevation, inundation grid, and water depth for the area shown, and provides block-scale early warning for the gray area.

[0049] Figure 4 for Figure 2 The diagram shows the flooding grid, water depth, and risk points in the area shown. Point-scale early warnings are provided for the locations of solid points. Detailed Implementation

[0050] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] This embodiment provides a multi-scale, coordinated flood risk early warning method for plain areas. It is applicable to large-area flood risk early warning in plain areas and provides multi-scale early warning at the area, block, and point levels to meet the needs of various users, including managers, the general public, and flood control personnel. Figure 1 The diagram shows the early warning method flow, which includes the following steps:

[0052] Step (1): Obtain river vector data and river cross-sections within the plain area, divide the region, determine the target time, collect the predicted water level of the river section at the target time, and collect the characteristic water level of the river cross-section and the elevation values ​​of the river embankment near the river cross-section (e.g., Figure 2 The image shows a river channel, river cross-section, and river embankment near the cross-section in a certain monitoring area. The specific steps include:

[0053] Step (11) Obtain river vector data and river cross-sections in each region within the plain (e.g., Haishu Plain in Ningbo City, or other similar flat plains), and make them have the same spatial coordinate system, and require that the number of river cross-sections in each region is at least one.

[0054] Step (12): Divide the area according to the characteristics of river catchment in the plain area. The area should have interconnected inland waterways, flat terrain, and no dikes on both banks of the river (e.g., the inland rivers in the Haishu Plain of Ningbo City have no dikes, which can be a separate monitoring area, or it can be further subdivided into more monitoring areas. This embodiment further divides it). Figure 2 (taking one of the monitoring areas), it is assumed that the river water level at the target time within the area can be spatially interpolated to form the corresponding area's forecast water level surface;

[0055] Step (13): Based on the predicted water level process of each section, confirm the target time in the monitoring area. The target time should be close to the predicted peak water level time, and obtain the predicted water level data of the target time. For example, Ningbo City uses a hydrological and hydrodynamic model to predict the water level of important inland river points in the Haishu Plain, and can obtain the time corresponding to the predicted peak water level in the monitoring area.

[0056] Step (14) obtains the guaranteed water level, warning water level, and elevation values ​​of the river embankment near the river cross-section. The elevation values ​​of the river embankment can be extracted from the DEM data or measured on-site.

[0057] Step (2) is to formulate a multi-scale linkage early warning mechanism for surface, block and point, and to issue orange, red and purple flood warnings for the plain area based on the target time forecast water level of the river section and multiple characteristic water levels. For the purple warning area, block and point scale early warnings are activated. The specific steps are as follows:

[0058] Step (21) involves issuing area-scale orange, red, and purple warnings based on the predicted and characteristic water levels at the river cross-sections within each monitoring area at the target time. For areas triggering area-scale warnings, relevant management personnel are promptly notified. This embodiment sets... Figure 2 The area is designated for monitoring, and a purple alert is issued for it.

[0059] Step (22): For the area under purple warning, activate block-scale warning, generate flood grid by combining GIS technology, target time forecast water level data and DEM elevation data, and promptly notify and contact relevant management personnel.

[0060] Step (23): For the area under purple warning, activate point-scale warning, calculate using GIS technology and risk point data, and promptly notify and contact relevant management personnel.

[0061] Step (3) compares the forecast water level and characteristic water level of representative stations at the target time within the region, and issues area-scale orange, red, and purple early warnings for the monitoring area according to the rules. The specific steps include the following:

[0062] Step (31): Sequentially set the characteristic water levels of the corresponding river sections as warning water level, guaranteed water level, and approximate dike water level. The approximate dike water level is a value between the guaranteed water level and the dike water level, and close to the dike water level. Replacing the dike water level with the approximate dike water level is to improve the safety factor. The calculation formula is as follows:

[0063] H 近似堤防 =H 堤防 -(H 堤防 -H 保证 )*A (1)

[0064] Among them, H 近似堤防 To approximate the dike's water level, H 堤防 H represents the corresponding levee elevation for the river cross-section. 保证 To ensure the water level, A is a value between 0 and 1, and is taken as 0.10 here.

[0065] Step (32): Combine the forecast water level, warning water level, guaranteed water level and approximate dike water level at the target time to formulate early warning rules. If the forecast water level of at least one river section is greater than or equal to the elevation of the approximate dike water level, the area is given a purple flood warning. If the purple warning is not met and the forecast water level of at least one river section is greater than or equal to the guaranteed water level, the area is given a red warning. If the purple or red warning is not met and the forecast water level of at least one river section is greater than or equal to the warning water level, the area is given a yellow warning. If the forecast water level of all stations is less than the warning water level, the area is given no flood warning.

[0066] Step (4) involves using the purple warning area as a unit to perform spatial interpolation calculations on the predicted water level of the inland river at the target time, obtaining the regional predicted water level data, and performing spatial overlay analysis with the DEM data to generate the inundation grid and inundation depth of the regional unit, and conducting block-scale flood risk warning. The specific steps include the following:

[0067] Step (41) determines whether there are abnormal water levels in the target time forecast water level within the area. Phenomena such as sluice gate closures can cause the water level at nearby river sections to be significantly higher than the water level data of other river sections in the area, thus reducing the applicability of the spatial interpolation algorithm and resulting in an excessively large inundation area. The formula for judging abnormal water levels is as follows:

[0068]

[0069] Where Y = 1 indicates that the water level at this point is abnormal, Y = 0 indicates that the water level at this point is abnormal, H i B represents the predicted water level of the i-th river section, and B represents the difference between the predicted water level of the i-th river section and the average predicted water level in the region, which is 0.5 in this case.

[0070] Step (42) Delineate the affected area for each river section based on various factors such as water catchment characteristics, historical inundation range, and human experience.

[0071] Step (43): If there are no abnormal areas, assuming that the water flow in the monitored area is connected, spatial interpolation calculation can be performed on the inland river water level forecast data at the target time in the area to obtain the regional forecast water level surface data. If there are abnormal areas, separate calculation is performed for the affected areas of the abnormal water level. The plane where the abnormal water level is located is the forecast water level surface. For other areas, spatial interpolation is performed on the inland river water level forecast point data in the area. The forecast water level surfaces of the abnormal areas and other areas are merged to obtain the forecast water level surface of the purple warning area.

[0072] Step (44) involves spatially overlaying the predicted water level and high-precision DEM data to generate the inundation grid and inundation depth (e.g., ...) for the area. Figure 3 As shown), for Figure 3(c) Block-scale early warning is performed in the gray area, which includes the following sub-steps:

[0073] Step (441) involves spatially overlaying the predicted water level and high-precision DEM data in the same spatial coordinate system, with the predicted water level and high-precision DEM having the same grid size and spatial matching.

[0074] Step (442) calculates the inundation depth for each grid, i.e., using the predicted water level data (H). wl Subtract the elevation values ​​from the DEM data (H) dem If the former is greater than the latter, then the area is at risk of flooding, and a block-scale early warning is issued. The calculation formula is as follows:

[0075]

[0076] Where D represents the submerged water depth data, and H... wl Forecast water level data, H dem These are the elevation values ​​from the DEM data.

[0077] Step (5) uses the purple warning area as a unit, combines the inundation grid, inundation depth and flood risk point data, and uses spatial analysis technology to conduct point-scale flood risk warning, and conducts emergency linkage warning with relevant personnel. The specific steps include the following:

[0078] Step (51) Obtain point vector data of the underlying surfaces of hazardous chemical enterprises, residential communities, shopping malls, agricultural and forestry land, villages, etc., and place them in the same spatial coordinate system as other data.

[0079] Step (52) determines whether the underlying surface point vector data and the inundation grid in step (4) spatially intersect. If they intersect, the object is at risk of urban flooding, and a point-scale early warning is issued; otherwise, there is no risk (e.g., ...). Figure 4 As shown, solid dots intersect with the flooded grid, requiring point-scale early warning.

[0080] Step (6): Steps (3)-(5) are executed sequentially for each monitoring area until all monitoring areas complete the early warning judgment.

[0081] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0082] The above specific embodiments are used to explain and illustrate the present invention, and are only preferred embodiments of the present invention, not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A multi-scale linkage flood risk early warning method for plain areas, characterized in that, Includes the following steps: Step (1): Obtain river vector data and river cross-section within the plain area, divide the monitoring area, determine the target time, collect the predicted water level of the river section at the target time, and collect the characteristic water level of the river section and the elevation value of the levee near the river section. Step (2): Establish a multi-scale linkage early warning mechanism for surface, block, and point areas. For the plain area, flood orange, red, and purple early warnings are issued based on the target time forecast water level of the river section and multiple characteristic water levels. For the purple early warning area, block-scale and point-scale early warnings are activated respectively. Step (3): Compare the forecast water level and characteristic water level of the representative station at the target time within the monitoring area, and issue orange, red, and purple area-scale early warnings for the monitoring area according to the rules; Step (4): Taking the purple warning area as a unit, spatial interpolation calculation is performed on the predicted water level of the inland river water point at the target time to obtain the predicted water level surface data of the monitoring area, as well as the spatial overlay analysis with the DEM data, to generate the inundation grid and inundation depth of the regional unit, and to carry out block-scale flood risk warning. Step (5): Using the purple warning area as a unit, combined with the inundation grid, inundation depth and flood risk point data, spatial analysis technology is used to carry out point-scale flood risk warning, and emergency linkage warning is carried out with relevant personnel. Step (6): Perform steps (3)-(5) sequentially on each monitoring area until all monitoring areas complete the early warning judgment; Step (2) includes the following sub-steps: Step (21): Based on the predicted water level and characteristic water level of the river section at the target time in each monitoring area, issue orange, red and purple warnings at the surface scale. For the area-scale warning areas, promptly notify and contact the relevant management personnel. Step (22): For the area under purple warning, activate block-scale warning, generate flood grid by combining GIS technology, target time forecast water level data and DEM elevation data, and promptly notify and contact relevant management personnel; Step (23): For the area under purple warning, activate point-scale warning, calculate using GIS technology and risk point data, and promptly notify and contact relevant management personnel. Step (4) includes the following sub-steps: Step (41) determines whether there is an abnormal water level in the target time forecast water level within the monitoring area; the closure of the sluice gate will cause the water level of the corresponding river section in the vicinity to be higher than that of other river sections in the area, thus reducing the applicability of the spatial interpolation algorithm and causing the flooding range to be too large; the formula for judging abnormal water levels is as follows: （2） wherein, equal to 1 indicates that the point is an abnormal water level, equal to 0 indicates that the point is an abnormal water level, represents the predicted water level of the i-th river section, and B represents the difference between the predicted water level of the i-th river section and the average predicted water level in the region. Step (42): Delineate the affected area for each river section based on various factors such as water catchment characteristics, historical inundation range, and human experience; Step (43): If there is no abnormal area, assuming that the water flow in the monitoring area is connected, spatial interpolation calculation can be performed on the inland river water level forecast data at the target time in the area to obtain the regional forecast water level surface data; if there is an abnormal area, the affected area of ​​the abnormal water level is calculated separately, and the plane where the abnormal water level is located is the forecast water level surface; for other areas, spatial interpolation is performed on the inland river water level forecast point data in the area, and the forecast water level surfaces of the abnormal area and other areas are merged to obtain the forecast water level surface of the purple warning area; Step (44) involves spatially overlaying the predicted water level and high-precision DEM data to generate the inundation grid and inundation depth for the area, and then conducting block-scale early warning. This step includes the following sub-steps: Step (441) involves spatially overlaying the predicted water level and high-precision DEM data in the same spatial coordinate system, with the predicted water level and high-precision DEM having the same grid size and spatial matching. Step (442), calculate the submerged water depth value of each grid, that is, subtract the DEM data elevation value ( ) from the predicted water level data ( ). If the former is greater than the latter, the area has a risk of submersion, and a block-scale warning is carried out, and the calculation formula is as follows: （3） in, For submerged water depth data, Forecast water level data, These are the elevation values ​​from the DEM data.

2. The multi-scale coordinated flood risk early warning method for plain areas as described in claim 1, characterized in that, Step (1) includes the following sub-steps: Step (11): Obtain river vector data within the plain area and river cross sections within each monitoring area, and ensure that they have the same spatial coordinate system, and require that the number of river cross sections within each monitoring area is at least one; Step (12): Divide the region according to the characteristics of river catchment in the plain area. It is required that the inland river system in the monitoring area is connected, the terrain is flat, and there are no dikes on both sides of the river in the monitoring area. It is assumed that the river water level at the target time in the monitoring area can be spatially interpolated to form the predicted water level surface of the corresponding area. Step (13): Based on the predicted water level process of each section, confirm the target time in each monitoring area. The target time should be close to the predicted peak water level time, and obtain the predicted water level data at the target time. Step (14): Obtain the guaranteed water level, warning water level and the elevation value of the dike near the river section. The elevation value of the river dike can be extracted from the DEM data.

3. The multi-scale coordinated flood risk early warning method for plain areas as described in claim 1, characterized in that, Step (3) includes the following sub-steps: Step (31): Sequentially set the characteristic water levels of the corresponding river sections as warning water level, guaranteed water level, and approximate dike water level. The approximate dike water level is a value between the guaranteed water level and the dike water level, and close to the dike water level. Replacing the dike water level with the approximate dike water level is to improve the safety factor. The calculation formula is as follows: （1） in, To approximate the dike water level, The corresponding levee elevation for the river cross-section. To ensure the water level, A is a value between 0 and 1; Step (32): Combine the forecast water level, warning water level, guaranteed water level and approximate dike water level at the target time to formulate early warning rules. If the forecast water level of at least one river section is greater than or equal to the elevation of the approximate dike water level, the monitoring area is given a purple flood warning. If the purple warning is not met and the forecast water level of at least one river section is greater than or equal to the guaranteed water level, the monitoring area is given a red warning. If the purple or red warning is not met and the forecast water level of at least one river section is greater than or equal to the warning water level, the monitoring area is given a yellow warning. If the forecast water level of all stations is less than the warning water level, there is no flood warning for the monitoring area.

4. The multi-scale coordinated flood risk early warning method for plain areas as described in claim 1, characterized in that, Step (5) includes the following sub-steps: Step (51): Obtain point vector data of the underlying surfaces of hazardous chemical enterprises, residential communities, shopping malls, agricultural and forestry land, and villages, and place them in the same spatial coordinate system as other data; Step (52) determines whether the underlying surface point vector data and the flooding grid in step (4) intersect spatially. If they intersect, they are objects at risk of waterlogging and point-scale early warning is issued. Otherwise, there is no risk.

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