Urban flood forecasting method based on rainfall threshold

Abstract

The invention discloses an urban flood forecasting method based on a rainfall threshold, and relates to the field of numerical simulation and calculation in hydrology, and the method comprises the following steps: 1, collecting a continuous flood event record of a certain ponding point, arranging the record into a format required by a method provided in a patent, and estimating model parameters a, b and c by writing Python codes, or calculating by utilizing a linear regression function of statistical software. According to the urban flood forecasting method based on the rainfall threshold value, the rainfall threshold value relation is introduced into urban inland inundation forecasting by limiting application conditions. The waterlogging forecasting technology only depending on the rainfall condition not only can provide a reliable urban waterlogging forecasting result, but also has very high operation efficiency; the rainfall threshold relation is applied to urban flood forecasting, and the previous law is generally applied to disaster events caused by rainfall with binary characteristics such as landslide and debris flow.

Description

Technical Field

[0001] The invention relates to the technical field of numerical simulation and calculation in hydrology, and in particular to a method for urban flood forecasting based on rainfall threshold. Background Art

[0002] Urban flood disasters caused by heavy rains are increasingly becoming a major threat to the stable operation of cities. Managing urban flood risks has become an important aspect of ensuring the safety, resilience and sustainability of modern cities. Accurate and rapid forecasting and warning systems are an important part of urban flood risk management, providing crucial preparation time for emergency and disaster reduction efforts. In disaster prediction and warning, rainfall thresholds are often used to assess the possibility of natural disasters such as landslides or mudslides. The rainfall threshold refers to the minimum rainfall or intensity required to trigger natural disasters such as landslides or mudslides within a specific period of time. When the rainfall exceeds this threshold, the possibility of a disaster increases greatly, while when the rainfall is below this threshold, the risk is relatively low. One of the most widely used methods to determine these thresholds is the "intensity-duration (ID)" relationship and its variant "cumulative event rainfall-duration (ED)" model, using a power law model: express.

[0003] However, this approach has not been used for flood forecasting, despite the close relationship between flood and rainfall conditions. However, several factors have led to the limited use of rainfall thresholds in flood prediction. First, floods often develop continuously, with no clear boundary between occurrence and non-occurrence; Second, flood risk is not only affected by rainfall intensity and duration. Other key factors, such as watershed size, topography, soil type and land use, play an important role in flood formation. In addition, landslides and debris flows are local events, usually occurring in small areas with minimal geological and hydrological changes; In contrast, floods involve more complex dynamics and delayed processes. These factors introduce time lags in flood formation, making it difficult to predict flood events based solely on rainfall thresholds. Summary of the invention

[0004] The purpose of the present invention is to provide an urban flood forecasting method based on rainfall thresholds to solve the problem raised in the above background technology that floods often continue to develop, and there is no clear boundary between occurrence and non-occurrence; secondly, flood risk is not only affected by rainfall intensity and duration. Other key factors, such as watershed size, topography, soil type and land use, play an important role in flood formation. In addition, landslides and mudslides are local events, usually occurring in small areas with minimal geological and hydrological changes. In contrast, floods involve more complex changes and delayed processes. These factors introduce time lags in flood formation, making it difficult to predict flood events based solely on rainfall thresholds.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for urban flood forecasting based on rainfall threshold, comprising the following steps: Step 1: Collect the continuous flood event records of a certain water accumulation point and organize them into the format required by the method proposed in the patent. The specific format is shown in Table 1; Table 1 Data format required for flood event recording

[0006] Step 2: Perform logarithmic transformation and establish a multiple log-log regression model between flood peak value P and rainfall duration D and total rainfall E. The expression is as follows; (1) The estimation of model parameters a, b, and c can be calculated by writing Python code or using the linear regression function of statistical software.

[0007] Step 3: Verify the model. The collected flood events are randomly divided into a training set and a validation set in a ratio of 7:3. The parameters a, b, and c are obtained using the training set data according to formula (1). Subsequently, the validation set data is substituted into the formula to calculate the results and compared with the measured data to evaluate the model accuracy. If the model accuracy does not meet expectations, it may be due to insufficient sample size; New flood events can be simulated under designed rainfall conditions using a verified hydrological model, and an extended data set consisting of a training set and a validation set can be constructed for modeling to improve model accuracy. In addition, actual flood events at waterlogging points can be continuously collected, and the model can be corrected when the data volume is sufficient.

[0008] Furthermore, by breaking down the overall flood forecast of the city into smaller parts, rainfall threshold relationships are established for each of the waterlogging points dispersed in the city, thereby ensuring that the impact of rainfall can be controlled in areas with minimal geological and hydrological changes.

[0009] Furthermore, the proposed method does not completely copy the power law model currently used in debris flows and landslides, but improves it to match the characteristics of floods that continue to develop without a clear boundary between occurrence and non-occurrence.

[0010] Furthermore, by restricting the application conditions, the rainfall threshold relationship is introduced into the urban waterlogging forecast. This waterlogging forecasting technology that only relies on rainfall conditions can not only provide reliable urban waterlogging forecast results, but also has a very high operating efficiency.

[0011] Furthermore, taking a waterlogging point on a road in a city as an example, 70 measured flood events and 680 flood events simulated using a calibrated flood model were collected, which includes the following steps: Step 1: According to the method described in the patent, the data set is randomly divided into a training set and a validation set in a ratio of 7:3; Step 2: Use the data from the training set to establish a multivariate double logarithmic regression model, and obtain the values ​​of parameters a, b, and c as -0.387, 1.278, and -6.142, respectively. The coefficient of determination R2 is 0.970, and the residual is 6.639; Step 3: Substitute the data of the validation set into the obtained multivariate double logarithmic regression model and compare it with the measured data. Use the determination coefficient R 2 And the root mean square error RMSE is used to evaluate the model accuracy.

[0012] Compared with the prior art, the present invention has the following beneficial effects: This urban flood forecasting method based on rainfall threshold introduces the rainfall threshold relationship into urban waterlogging forecasting by restricting the application conditions. This waterlogging forecasting technology that relies solely on rainfall conditions can not only provide reliable urban waterlogging forecasting results, but also has very high operating efficiency; Applying rainfall threshold relationship to urban flood forecasting. Previously, this law was usually applied to landslides and debris flows, which are rain-induced disasters with binary characteristics. Furthermore, based on the analysis of the characteristics of local urban floods, the application of the power law model was improved. By establishing a multivariate logarithmic regression model between flood peak value and total rainfall and rainfall duration, the model can not only predict the occurrence of flood events but also predict the flood peak value of each flood event. Furthermore, compared with the hydrological model, this model has the characteristics of not requiring too many physical parameters, being easy to update and self-improve in real time, and having fast calculation speed; Furthermore, it is suitable for large-scale promotion and application, and has good applicability in different geographical regions and time scales; Furthermore, by breaking down the overall flood forecast of the city into smaller parts, rainfall threshold relationships are established for each of the scattered waterlogging points in the city, thereby ensuring that the impact of rainfall can be controlled in areas with minimal geological and hydrological changes. Secondly, the method proposed in the patent does not completely copy the power law model currently used in debris flows and landslides, but improves it to match the characteristics of floods that continue to develop and have no clear boundaries between occurrence and non-occurrence. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the original data set of the present invention; Figure 2 It is a schematic diagram of the training data set of the present invention; Figure 3 This is a schematic diagram of a test data set of the present invention; Figure 4 This is a schematic diagram of the verification results of the model of the present invention. DETAILED DESCRIPTION

[0014] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] The present invention introduces the rainfall threshold relationship into urban waterlogging forecasting by limiting the application conditions. This waterlogging forecasting technology that only relies on rainfall conditions can not only provide reliable urban waterlogging forecasting results, but also has very high operating efficiency.

[0016] The present invention first breaks down the overall flood forecast of the city into smaller parts, and establishes rainfall threshold relationships for each of the scattered waterlogging points in the city, thereby ensuring that the impact of rainfall can be controlled in areas with minimal geological and hydrological changes. Secondly, the method proposed in the patent does not completely copy the power law model currently used in debris flows and landslides, but improves it to match the characteristics of floods that continue to develop and there is no clear boundary between occurrence and non-occurrence; Example 1: Please refer to Figure 1-4 The present invention provides the following technical solution: a method for urban flood forecasting based on rainfall threshold, comprising the following steps: Step 1: Collect the continuous flood event records of a certain water accumulation point and organize them into the format required by the method proposed in the patent. The specific format is shown in Table 1; Table 1 Data format required for flood event recording

[0017] Step 2: Perform logarithmic transformation and establish a multiple log-log regression model between flood peak value P and rainfall duration D and total rainfall E. The expression is as follows; (1) The estimation of model parameters a, b, and c can be calculated by writing Python code or using the linear regression function of statistical software.

[0018] Step 3: Verify the model. The collected flood events are randomly divided into a training set and a validation set in a ratio of 7:3. The parameters a, b, and c are obtained using the training set data according to formula (1). Subsequently, the validation set data is substituted into the formula to calculate the results and compared with the measured data to evaluate the model accuracy. If the model accuracy does not meet expectations, it may be due to insufficient sample size; New flood events can be simulated under designed rainfall conditions using a verified hydrological model, and an extended data set consisting of a training set and a validation set can be constructed for modeling to improve model accuracy. In addition, actual flood events at waterlogging points are continuously collected, and the model can be modified when the data volume is sufficient.

[0019] By breaking down the overall flood forecast of the city into smaller parts, rainfall threshold relationships are established for each of the scattered waterlogging points in the city, thereby ensuring that the impact of rainfall can be controlled in areas with minimal geological and hydrological changes. The proposed method does not completely copy the power law model currently used in debris flows and landslides, but improves it to match the characteristics of continuous development of floods, with no clear boundary between occurrence and non-occurrence. By restricting the application conditions, the rainfall threshold relationship is introduced into the urban waterlogging forecast. This waterlogging forecasting method that relies solely on rainfall conditions can not only provide reliable urban waterlogging forecast results, but also has very high operating efficiency; Based on the analysis of the characteristics of local urban floods, the application of the power law model was improved. By establishing a multivariate logarithmic regression model between flood peak value, total rainfall and rainfall duration, the model can not only predict the occurrence of flood events but also predict the flood peak value of individual flood events. Compared with the hydrological model, this model does not require too many physical parameters, is easy to update and self-improve in real time, and has a fast calculation speed.

[0020] Example 2: Based on Example 1, taking a waterlogging point on a road in a city as an example, 70 measured flood events and 680 flood events simulated using a calibrated flood model were collected. The original data is shown in the scatter plot. Figure 1 , which comprises the following steps: Step 1: According to the method described in the patent, the data set is randomly divided into a training set and a validation set in a ratio of 7:3. See the scatter plot for details. Figure 2 and Figure 3 ; Step 2: Use the data from the training set to establish a multivariate double logarithmic regression model, and obtain the values ​​of parameters a, b, and c as -0.387, 1.278, and -6.142, respectively. The coefficient of determination R2 is 0.970, and the residual is 6.639; Step 3: Substitute the data of the validation set into the calculated results of the multivariate double logarithmic regression model and compare them with the measured data. Use the determination coefficient R2 and root mean square error (RMSE) to evaluate the accuracy of the model. For specific validation results, see Figure 4 ; By breaking down the overall flood forecast of the city into smaller parts, rainfall threshold relationships are established for each of the scattered waterlogging points in the city, thereby ensuring that the impact of rainfall can be controlled in areas with minimal geological and hydrological changes. Secondly, the method proposed in the patent does not completely copy the power law model currently used in debris flows and landslides, but improves it to match the characteristics of floods that continue to develop and there is no clear boundary between occurrence and non-occurrence.

[0021] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for urban flood forecasting based on rainfall threshold, characterized in that: The following steps are involved: Step 1: Collect the continuous flood event records of a certain water accumulation point and organize them into the format required by the method proposed in the patent. The specific format is shown in Table 1; Table 1 Data format required for flood event recording ； Step 2: Perform logarithmic transformation and establish a multiple log-log regression model between flood peak value P and rainfall duration D and total rainfall E. The expression is as follows; （1） The estimation of model parameters a, b, and c can be calculated by writing Python code or using the linear regression function of statistical software; Step 3: Verify the model. The collected flood events are randomly divided into a training set and a validation set in a ratio of 7:

3. The parameters a, b, and c are obtained using the training set data according to formula (1). Subsequently, the validation set data is substituted into the formula to calculate the results and compared with the measured data to evaluate the model accuracy. If the model accuracy does not meet expectations, it may be due to insufficient sample size; New flood events can be simulated under designed rainfall conditions using a verified hydrological model, and an extended data set consisting of a training set and a validation set can be constructed for modeling to improve model accuracy. In addition, actual flood events at waterlogging points can be continuously collected, and the model can be corrected when the data volume is sufficient.

2. The urban flood forecasting method based on rainfall threshold according to claim 1 is characterized by: By breaking down the overall flood forecast of the city into smaller parts, rainfall threshold relationships are established for each of the waterlogging points dispersed in the city, thereby ensuring that the impact of rainfall can be controlled in areas with minimal geological and hydrological changes.

3. The urban flood forecasting method based on rainfall threshold according to claim 1 is characterized in that: The proposed method does not completely copy the power law model currently used in debris flows and landslides, but improves it to match the characteristics of floods that continue to develop without a clear boundary between occurrence and non-occurrence.

4. The urban flood forecasting method based on rainfall threshold according to claim 1 is characterized in that: By restricting the application conditions, the rainfall threshold relationship is introduced into the urban waterlogging forecast. This waterlogging forecasting technology that only relies on rainfall conditions can not only provide reliable urban waterlogging forecast results, but also has very high operating efficiency.

5. The urban flood forecasting method based on rainfall threshold according to claim 1 is characterized in that: Taking a waterlogging point on a road in a certain city as an example, 70 measured flood events and 680 flood events simulated using a calibrated flood model were collected, which includes the following steps: Step 1: According to the method described in the patent, the data set is randomly divided into a training set and a validation set in a ratio of 7:3; Step 2: Use the training set data to establish a multivariate double logarithmic regression model, and obtain the values ​​of parameters a, b, and c as -0.387, 1.278, and -6.142, respectively. The coefficient of determination R 2 is 0.970, and the residual is 6.639; Step 3: Substitute the data of the validation set into the obtained multivariate double logarithmic regression model and compare it with the measured data. Use the coefficient of determination (R 2 , Coefficient of Determination) and root mean square error (RMSE, Root Mean Square Error) were used to evaluate the model accuracy.

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