An evaluation method and system for distribution and strength of freezing rain disasters in hilly areas

Abstract

The application discloses an evaluation method and system for distribution and strength of freezing rain disasters in hilly areas. The evaluation method comprises the following steps: collecting weather reanalysis grid data with fine vertical stratification in a freezing rain event influence period, calculating the freezing rain occurrence altitude and potential freezing rain amount of different grid points in the hilly area every hour, and reducing the scale to fine grid points; taking the potential freezing rain amount of a fine grid point at a moment when the freezing rain occurrence altitude is lower than the ground elevation as the freezing rain amount of the grid point at the moment, then accumulating the freezing rain amount of all fine grid points every hour, obtaining the cumulative freezing rain amount of all fine grid points in the influence period, and determining the distribution of freezing rain disasters in the hilly area; and combining the available partial regional freezing rain disaster information to determine the freezing rain risk grade. The application solves the problem of difficult evaluation of freezing rain disasters in the hilly area due to serious shortage of glaze data and incomplete freezing rain disaster information.

Description

Technical Field

[0001] This invention belongs to the field of meteorological disaster prevention and mitigation technology, specifically a method and system for assessing the distribution and intensity of freezing rain disasters in hilly areas. Background Technology

[0002] Freezing rain is liquid precipitation that occurs as supercooled water droplets. Upon contact with objects at or below 0°C, it immediately freezes (meteorologically known as rime). Freezing rain often severely impacts transportation, causing traffic paralysis, damage to power lines and pylons, and uprooting trees and plants. Its effects are often far more severe than those of equivalent snow or ice pellets. In southern China, there exists a freezing rain belt stretching from Guizhou, Hunan, and Jiangxi to Zhejiang, moving from west to east with decreasing frequency. This belt extends northward to Sichuan, Chongqing, Hubei, Anhui, and Henan, and southward to Yunnan, Guangxi, Guangdong, and northern Fujian. Its southern edge largely coincides with the orientation of the mountain ranges in southern my country. Guizhou, located on a plateau in the western part of the freezing rain belt, has abundant data on frost days and freezing rain disasters, sufficient for assessing the impact of freezing rain disasters. Meteorological stations in provinces with flat terrain in the eastern part of the freezing rain belt can also observe frost and other freezing rain-related data. However, in the hilly areas of the central and eastern parts of the freezing rain belt, the terrain is highly undulating, there are fewer mountain meteorological stations, and frost data is severely lacking, making it difficult to obtain information on freezing rain disasters. This leads to a significant underestimation of freezing rain in hilly areas. Taking Zhejiang Province as an example, of the province's 73 regular meteorological stations, 68 are below 200m in altitude, 3 are between 200 and 300m, and 2 are between 400 and 500m. However, approximately 23% of the province's area is mountainous terrain with an altitude of 500–1923m. During the freezing rain event in late February 2024, power transmission lines in several areas of Zhejiang Province experienced icing, with severe icing exceeding 30mm in places like Siming Mountain in Ningbo and Anji in Huzhou. However, meteorological stations recorded no days with icing during this period, and aside from records of power transmission line icing, there was little data on the extent of freezing rain damage. Similar phenomena are common in hilly and mountainous areas of Jiangxi, Anhui, Guangxi, and Guangdong provinces. This demonstrates that the number of days with icing fails to reflect the true freezing rain situation in hilly and mountainous areas. Furthermore, since freezing rain primarily occurs in mountainous regions, obtaining comprehensive data on freezing rain damage is difficult, significantly hindering the overall assessment of freezing rain disasters in hilly areas.

[0003] The severe icing in the mountainous areas, yet the absence of rime ice at weather stations, is a contradiction related to the local stratification characteristics. Changsha has a typical three-layer structure of "cold-warm-cold," with the weather station located in the cold layer, where freezing rain directly forms rime ice upon landing. Hangzhou, on the other hand, has a four-layer structure of "warm-cold-warm-cold," with the weather station located in the warm layer, where freezing rain falls as precipitation. However, the mountainous areas near Hangzhou have similar stratification characteristics to Changsha, where freezing rain forms rime ice upon reaching the mountains and then forms icing on power transmission lines. Because freezing rain in Hunan and Hubei provinces, represented by Changsha, is more easily detected by meteorological stations, and the warm layer center when freezing rain occurs in these provinces is mostly located at 700 hPa and the cold layer center is mostly located at 850 hPa, the range of the inversion layer formed by the two layers at 850 hPa and 700 hPa is often used as the main characteristic of freezing rain in operational practice. However, analysis of freezing rain stratification has revealed that the warm layer center and cold layer center of freezing rain caused by the encounter of warm and humid air currents with cold air from different sources are different, and even dynamically change according to the strength of the warm and cold air. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the difficulty in assessing freezing rain disasters in hilly areas due to the severe shortage of frost data and insufficient information on freezing rain disasters. This invention provides a method and system for assessing the distribution and intensity of freezing rain disasters in hilly areas. It estimates the amount of freezing rain based on the relative humidity at the height of freezing rain occurrence and constructs assessment indicators that can quantify the distribution and intensity of freezing rain disasters to assess the distribution and intensity of freezing rain disasters in hilly areas, thus providing a scientific basis for preventing freezing rain disasters in hilly areas.

[0005] Therefore, the present invention adopts the following technical solution: a method for assessing the distribution and intensity of freezing rain disasters in hilly areas, comprising:

[0006] First, based on the rime ice data from the meteorological station, the duration of an ice rain event is determined. Then, meteorological reanalysis grid data with fine vertical stratification of 5-25 km grid spacing are collected within the duration of the event. The altitude of ice rain occurrence and potential ice rain amount at different grid points in the hilly area are calculated hourly, and the scale is reduced to fine grid points with a grid spacing of less than 2.5 km.

[0007] Then, the potential freezing rain amount at a certain fine grid point at a certain moment, where the altitude of the freezing rain is lower than the ground elevation, is taken as the freezing rain amount at that grid point at that moment. Then, the freezing rain amounts at all moments are accumulated grid by grid to obtain the cumulative freezing rain amount of all fine grids during the period of influence, thereby determining the distribution of freezing rain disaster in a hilly and mountainous area.

[0008] Finally, by combining available data on freezing rain disasters in some areas, the risk level of freezing rain was determined, and a quantitative assessment of the severity of freezing rain disasters in the entire hilly region was conducted.

[0009] Furthermore, the determination of the duration of an ice rain event based on meteorological station rime data specifically involves: for hilly areas, collecting data on the number of days with rime observed by conventional meteorological stations in the area; selecting rime data observed by meteorological stations below 800m altitude from the collected rime day data, and determining the duration of an ice rain event based on two criteria: severe ice rain events and localized ice rain events.

[0010] Furthermore, the aforementioned severe freezing rain event is a freezing rain process with more than 70 daily frost stations and multiple stations experiencing freezing rain for more than 3 days; the localized freezing rain event is a freezing rain process with more than 5 daily frost stations and at least 3 stations experiencing freezing rain for more than 2 days.

[0011] Furthermore, the collection of meteorological reanalysis grid data with fine vertical stratification of 5-25 km grid spacing during the impact period specifically involves downloading meteorological reanalysis data with 5-25 km grid spacing and DEM data with 90 m grid spacing from relevant websites based on the impact period of the freezing rain event.

[0012] Furthermore, the hourly calculation of the freezing rain occurrence altitude and potential freezing rain amount for different grid points in the hilly area is specifically as follows: based on the typical temperature stratification characteristics of "cold-warm-cold" freezing rain, grid points that meet the freezing rain occurrence threshold conditions are identified hourly during the influence period of the freezing rain event, marked as 1, and the lower limit height of the bottom cold layer is recorded as the freezing rain occurrence altitude H1; those that do not meet the conditions are marked as 0; for grid points marked as 1, the potential freezing rain amount of the grid point is determined according to the relative humidity rh at its freezing rain occurrence altitude H1.

[0013] Furthermore, the formula for determining the potential freezing rain amount at grid points based on the relative humidity rh at the altitude H1 where freezing rain occurs is as follows:

[0014]

[0015] In the formula, the value of x ranges from 0.1 mm to 0.3 mm.

[0016] Furthermore, the specific process for obtaining the cumulative freezing rainfall for all fine grids within the affected period is as follows:

[0017] The potential freezing rain amount and freezing rain occurrence altitude data H1 calculated hourly are downscaled to fine grid points with a grid spacing of less than 2.5 kilometers in hilly areas to obtain freezing rain amount and freezing rain occurrence altitude data H2 at the fine grid points. Accordingly, the DEM is resampled to a grid spacing of less than 2.5 kilometers, and the ground elevation of each grid point is recorded as H3.

[0018] For grid points with a potential freezing rainfall greater than 0.0 mm, the difference between H3 and H2 is calculated. If H2 - H3 ≥ 0, the freezing rainfall at that grid point is assigned a value of 0.0 mm; otherwise, the potential freezing rainfall at that grid point is the freezing rainfall at the corresponding grid point. This process is repeated for all grid points in the study area to determine the hourly freezing rainfall at each grid point at the corresponding time. Similarly, the remaining time points are determined in the same way. Finally, the freezing rainfall at all times is accumulated for each grid point to obtain the cumulative freezing rainfall for all grid points during the affected period of a freezing rain event, thereby determining the distribution of freezing rain disasters in a hilly and mountainous area.

[0019] Furthermore, the freezing rain risk levels are as follows: Level 1 is slight icing with freezing rain <5mm; Level 2 is significant icing with freezing rain in the range of [5mm, 15mm); Level 3 is relatively heavy icing with freezing rain in the range of [15mm, 25mm); and Level 4 is severe icing with freezing rain ≥25mm.

[0020] Furthermore, a spatial distribution map is drawn based on the freezing rain risk level of each grid point to determine the impact range and intensity distribution of a freezing rain event.

[0021] This invention also provides an assessment system for the distribution and intensity of freezing rain disasters in hilly areas, used in the aforementioned assessment method for the distribution and intensity of freezing rain disasters in hilly areas, comprising:

[0022] Calculation Unit: Based on the rime ice data from the meteorological station, determine the duration of an impact event of freezing rain, collect meteorological reanalysis grid data with fine vertical stratification of 5-25 km grid spacing within the impact period, calculate the altitude of freezing rain occurrence and potential freezing rain amount of different grid points in the hilly area hourly, and downscale to fine grid points with a grid spacing of less than 2.5 km.

[0023] The cumulative freezing rain acquisition unit is used to take the potential freezing rain at a certain fine grid point at a certain moment when the freezing rain occurs at an altitude lower than the ground elevation as the freezing rain at that grid point at that moment. Then, the freezing rain at all moments is accumulated grid by grid to obtain the cumulative freezing rain of all fine grids during the period of influence.

[0024] Quantitative assessment unit: used to determine the freezing rain risk level by combining available data on freezing rain disasters in some areas, and to quantitatively assess the severity of freezing rain disasters in the entire hilly area.

[0025] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention combines DEM data of hilly and mountainous areas with detailed freezing rain disaster data of some areas to propose a freezing rain risk index for quantitatively assessing the impact of freezing rain disasters, evaluating the distribution and intensity of freezing rain disasters in the entire hilly area, and providing a scientific basis for preventing freezing rain disasters in hilly areas; This invention solves the problem of difficulty in assessing freezing rain disasters in hilly areas due to the severe shortage of frost data and insufficient freezing rain disaster data. Attached Figure Description

[0026] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the embodiments are briefly described below.

[0027] Figure 1 This is a flowchart of an assessment method for the distribution and intensity of freezing rain disasters in hilly areas according to the present invention;

[0028] Figure 2 This is a statistical chart showing the number of meteorological stations that observed rime ice daily in hilly areas during late February 2024, as described in a specific embodiment of the present invention.

[0029] Figure 3 The map shows the cumulative number of days with rime ice at meteorological stations from February 21 to 26, 2024, and the distribution of power transmission line icing accident sites in Zhejiang Province, as described in a specific embodiment of the present invention.

[0030] Figure 4 This is a typical stratification distribution characteristic diagram of freezing rain in January 2008, according to a specific embodiment of the present invention.

[0031] Figure 5 Spatial distribution map of freezing rain from February 21 to 26, 2024, calculated using the method of this invention (numbers represent the number of days with frost at meteorological stations);

[0032] Figure 6 This is a comparative analysis chart of ice accumulation accident sites and freezing rain volume in Zhejiang Province from February 21 to 26, 2024, according to a specific embodiment of the present invention.

[0033] Figure 7 Spatial distribution map of freezing rain risk levels from February 21 to 26, 2024, plotted using the method of the present invention;

[0034] Figure 8 This is a diagram illustrating the composition of a method for assessing the distribution and intensity of freezing rain disasters in hilly areas, as proposed in this invention. Detailed Implementation

[0035] The present invention will now be further described with reference to the accompanying drawings.

[0036] Example 1

[0037] This embodiment provides a method for assessing the distribution and intensity of freezing rain disasters in hilly areas, such as... Figure 1 As shown, the steps are as follows:

[0038] First, based on the rime ice data from the meteorological station, the duration of an ice rain event is determined. Then, meteorological reanalysis grid data with a fine vertical stratification of 25 km grid spacing is collected within the duration of the event. The altitude at which ice rain occurs and the potential amount of ice rain at different grid points in the hilly area are calculated hourly.

[0039] The method for determining the impact period of a freezing rain event based on meteorological station rime ice data specifically involves: for hilly areas (109°E-123°E, 24°N-35°N), collecting rime ice day data from conventional meteorological stations in the area; selecting rime ice data from meteorological stations below 800m altitude from the collected rime ice day data, and determining the impact period of a freezing rain event according to two criteria: severe freezing rain event and localized freezing rain event. A severe freezing rain event is defined as a freezing rain process with more than 70 rime ice stations per day and multiple stations experiencing freezing rain for more than 3 days; a localized freezing rain event is defined as a freezing rain process with more than 5 rime ice stations per day (stations close together) and at least 3 stations experiencing freezing rain for more than 2 days.

[0040] The collection of meteorological reanalysis gridded data with fine vertical stratification during the impact period is specifically as follows: based on the impact period of the freezing rain event, meteorological reanalysis data (here, the European Centre for Medium-Range Weather Forecasts' ERA5 is used, with a grid spacing of 25 kilometers, a time resolution of 1 hour, 37 vertical stratifications, and a data range of (109°E-123°E, 24°N-35°N)) is downloaded from relevant websites, along with DEM data with a grid spacing of 90 meters.

[0041] The hourly calculation of the freezing rain occurrence altitude and potential freezing rain amount for different grid points in the hilly area is as follows: Based on the typical temperature stratification characteristics of "cold-warm-cold" freezing rain, grid points that meet the freezing rain occurrence threshold conditions are identified hourly during the period of freezing rain event influence, marked as 1, and the lower limit height of the bottom cold layer is recorded as the freezing rain occurrence altitude H1. Those that do not meet the conditions are marked as 0. For grid points marked as 1, the potential freezing rain amount of the grid point is determined according to the relative humidity rh at its freezing rain occurrence altitude H1.

[0042] The formula for determining the potential freezing rain amount at grid points based on the relative humidity rh at the altitude H1 where freezing rain occurs is as follows:

[0043]

[0044] In the formula, the value of x ranges from 0.1 mm to 0.3 mm, and is determined based on the freezing rain disaster situation. It can be adjusted after more detailed freezing rain disaster data are available.

[0045] The specific process for obtaining the cumulative freezing rainfall of all fine grids during the affected period is as follows:

[0046] The potential freezing rain amount and freezing rain occurrence altitude data H1 calculated hourly are downscaled to a fine grid point with a grid spacing of 2.5 km in the hilly area to obtain the freezing rain amount and freezing rain occurrence altitude data H2 at the fine grid point. Accordingly, the DEM is resampled to a grid spacing of 2.5 km, and the ground elevation of each grid point is recorded as H3.

[0047] For grid points with a potential freezing rainfall greater than 0.0 mm, the difference between H3 and H2 is calculated. If H2 - H3 ≥ 0, the freezing rainfall at that grid point is assigned a value of 0.0 mm; otherwise, the potential freezing rainfall at that grid point is the freezing rainfall at the corresponding grid point. This process is repeated for all grid points in the study area to determine the hourly freezing rainfall at each grid point at the corresponding time. Similarly, the remaining time points are determined in the same way. Finally, the freezing rainfall at all times is accumulated for each grid point to obtain the cumulative freezing rainfall for all grid points during the affected period of a freezing rain event, thereby determining the distribution of freezing rain disasters in a hilly and mountainous area.

[0048] Finally, based on the available data on freezing rain disasters, the freezing rain risk level was determined, and the intensity of freezing rain disasters in hilly areas was quantitatively assessed.

[0049] The freezing rain risk levels are as follows: Level 1 is slight icing with freezing rain <5mm; Level 2 is significant icing with freezing rain in the range of [5mm, 15mm); Level 3 is relatively heavy icing with freezing rain in the range of [15mm, 25mm); and Level 4 is severe icing with freezing rain ≥25mm.

[0050] A spatial distribution map is drawn based on the freezing rain risk level of each fine grid point to determine the impact range and intensity distribution of a freezing rain event.

[0051] To verify the actual effect of the method described in this invention, this embodiment uses a large-scale heavy freezing rain event that occurred in a hilly area from February 21 to 26, 2024.

[0052] Step 1: Collect data on the number of days with rime ice observed at meteorological stations (below 800m altitude) in hilly areas (109°E-123°E, 24°N-35°N) in late February 2024, such as... Figure 2 As shown, the period from February 21st to 25th saw over 70 weather stations recording rime ice for five consecutive days, constituting a severe and widespread freezing rain event. Since over 10 weather stations still observed rime ice on February 26th (rime ice in the later stages of the freezing rain process is mostly distributed in the southern hilly and mountainous areas), the period of freezing rain impact is defined as February 21st to 26th. The spatial distribution of the cumulative number of rime ice days at each weather station from February 21st to 26th is plotted as follows: Figure 3 The map also shows data on freezing rain and icing damage to power transmission lines collected in Zhejiang Province. The lack of corresponding data on the number of days with frost in Zhejiang reflects the fact that freezing rain in hilly and mountainous areas is severely underestimated.

[0053] Step 2: Download the meteorological reanalysis data ERA5 from the European Centre for Medium-Range Weather Forecasts (ECMWF) website. The data covers a period of 144 hours, from 08:00 on February 21, 2024 to 08:00 on February 27, 2024, encompassing the region (109°E-123°E, 24°N-35°N). It has 37 vertical layers and includes meteorological elements such as temperature (t), relative humidity (r), and altitude (z). Download the DEM data with a 90-meter grid spacing from the StarMap Cloud Open Platform.

[0054] Step 3: Begin estimating freezing rainfall based on the downloaded reanalysis data. Typical stratification during freezing rainfall is shown below. Figure 4 As shown, the specific calculation method involves calculating vertically upwards from the bottom layer at each grid point whether a cold-warm layer junction is satisfied, and setting certain thresholds for the thickness of the intermediate warm layer and the bottom cold layer. The minimum threshold for the bottom cold layer thickness is 400m, and the maximum threshold is 3000m. The threshold for the intermediate warm layer thickness is also greater than 400m, and the maximum threshold for the warm layer thickness is 3600m. Based on the set thresholds, calculations are performed for each grid point. If the conditions are met, the grid point is considered to have freezing rain conditions at that moment. During the influence period of the freezing rain event, the grid points with freezing rain conditions are calculated hourly and recorded as 1, along with the altitude at which the freezing rain occurs. Grid points that do not meet the conditions are recorded as 0.

[0055] Step 4: For grid point marked as 1, determine the potential freezing rain amount (icerain) of the grid point based on the relative humidity (rh) at the altitude where freezing rain occurs (see Equation 1 for details).

[0056] Step 5: Downscale the potential freezing rain amount and freezing rain occurrence altitude data H1 of the coarse grid points calculated hourly to the hilly area to obtain the potential freezing rain amount and freezing rain occurrence altitude data H2 of the fine grid (2.5 km grid spacing or higher). Accordingly, resample the DEM to the same grid spacing, and record the DEM of each grid point as H3.

[0057] Step 6: For grid points with a potential freezing rainfall greater than 0.0 mm, calculate the difference between H2 and H3: If H2 - H3 ≥ 0, reassign the estimated freezing rainfall for that grid point to 0.0 mm; otherwise, the potential freezing rainfall for that grid point is the freezing rainfall for that grid point. The judgment of all grid points in the study area is used as the hourly freezing rainfall for each grid point at that time. Similarly, the judgment is performed for all times from February 21st to 26th, 2024. Finally, the judgment results for all times are accumulated for each grid point to obtain the total freezing rainfall for all grid points in the hilly area. Figure 5As shown in the figure, the calculated cumulative freezing rainfall distribution corresponds well with the distribution of the number of days with frost observed by the meteorological stations shown in the figure. Hunan, Hubei, Anhui, and Zhejiang provinces all experienced freezing rainfall exceeding 30mm, making them the provinces most severely affected by this freezing rain disaster. The following section uses the icing disaster on transmission lines in Zhejiang Province to verify the calculated results, and presents a comparative analysis chart of icing accident points and freezing rainfall in Zhejiang Province. Figure 6 Most icing incident locations correspond well to the 25mm freezing rainfall distribution, with a few exceptions (further analysis revealed that the low grid spacing in the data led to errors in the calculation results, which is reasonable; thicker icing is also common in some micro-topographical areas prone to icing). This indicates that the freezing rainfall distribution calculated by the method of this invention can effectively reflect the distribution and intensity of a single freezing rain disaster.

[0058] Step 7: Since the above analysis of freezing rainfall is based on meteorological data and may deviate from the actual freezing rainfall, and the amount of freezing rainfall cannot accurately reflect the extent of the impact of freezing rain disasters, this step combines a comprehensive analysis of freezing rainfall and freezing rain disaster conditions to convert freezing rainfall into a freezing rain risk level. Figure 7 As can be clearly seen from the figure, Hunan, Hubei, Anhui, and Zhejiang are the provinces most severely affected by freezing rain in this event, which is basically consistent with the extent of the freezing rain disaster. Hunan, Hubei, and Anhui all experienced large areas of relatively heavy and severe freezing rain risk levels, while in Zhejiang, relatively heavy and severe freezing rain occurred in more scattered areas. This indicates that the hilly terrain of Zhejiang Province had a more significant impact than other provinces, and also demonstrates that the method of this invention can better reflect the distribution and intensity of freezing rain risk in hilly areas.

[0059] Example 2

[0060] This embodiment provides an assessment system for the distribution and intensity of freezing rain disasters in hilly areas, used to implement the assessment method for the distribution and intensity of freezing rain disasters in hilly areas described in Embodiment 1, such as... Figure 8 As shown, it consists of a calculation unit, a cumulative freezing rain acquisition unit, and a quantitative assessment unit.

[0061] The computing unit: Based on the rime data from the meteorological station, it determines the period of impact of a freezing rain event, collects meteorological reanalysis grid data with fine vertical stratification of 25 km grid spacing (or smaller grid spacing) within the period of impact, calculates the altitude of freezing rain occurrence and potential freezing rain amount of different grid points in the hilly area hourly, and downscales to fine grid points of 2.5 km (or smaller grid spacing).

[0062] The cumulative freezing rain acquisition unit is used to take the potential freezing rain at a certain fine grid point at a certain moment when the altitude of the freezing rain is lower than the ground elevation as the freezing rain at that fine grid point at that moment, and then accumulate the freezing rain at all moments grid by grid to obtain the cumulative freezing rain of all fine grids in the affected period.

[0063] The quantitative assessment unit is used to classify the freezing rain risk level by combining the available freezing rain disaster data, and to quantitatively assess the intensity of freezing rain disasters in hilly areas.

[0064] It should be noted that each unit in the aforementioned assessment system for the distribution and intensity of freezing rain disasters in hilly areas can be implemented entirely or partially through software, hardware, or a combination thereof. These units can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the corresponding operations of each unit. For specific limitations regarding the assessment system for the distribution and intensity of freezing rain disasters in hilly areas, please refer to the limitations of the assessment method for the distribution and intensity of freezing rain disasters in hilly areas (i.e., Example 1) above; both have the same function and role, and will not be repeated here.

[0065] It will be apparent to those skilled in the art that various modifications can be made to the above embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A method for assessing the distribution and intensity of freezing rain disasters in hilly areas, characterized in that, First, based on the rime ice data from the meteorological station, the duration of an ice rain event is determined. Then, meteorological reanalysis grid data with fine vertical stratification of 5-25 km grid spacing are collected within the duration of the event. The altitude of ice rain occurrence and potential ice rain amount at different grid points in the hilly area are calculated hourly, and the scale is reduced to fine grid points with a grid spacing of less than 2.5 km. Then, the potential freezing rain amount at a certain fine grid point at a certain moment, where the altitude of the freezing rain is lower than the ground elevation, is taken as the freezing rain amount at that grid point at that moment. Then, the freezing rain amounts at all moments are accumulated grid by grid to obtain the cumulative freezing rain amount of all fine grids during the period of influence, thereby determining the distribution of freezing rain disaster in a hilly and mountainous area. Finally, based on the available data on freezing rain disasters in some areas, the freezing rain risk level was determined, and a quantitative assessment of the intensity of freezing rain disasters in the entire hilly area was conducted. The hourly calculation of the freezing rain occurrence altitude and potential freezing rain amount for different grid points in the hilly area is as follows: Based on the typical temperature stratification characteristics of "cold-warm-cold" freezing rain, grid points that meet the freezing rain occurrence threshold conditions are identified hourly during the influence period of the freezing rain event, marked as 1, and the lower limit height of the bottom cold layer is recorded as the freezing rain occurrence altitude H1. Those that do not meet the conditions are marked as 0. For grid points marked as 1, the potential freezing rain amount of the grid point is determined according to the relative humidity rh at its freezing rain occurrence altitude H1. The formula for determining the potential freezing rain amount at grid points based on the relative humidity rh at the altitude H1 where freezing rain occurs is as follows: In the formula, The value ranges from 0.1 mm to 0.3 mm.

2. The evaluation method according to claim 1, characterized in that, The method for determining the duration of a freezing rain event based on meteorological station rime data is as follows: For hilly areas, data on the number of days with rime observed by conventional meteorological stations in the area are collected; from the collected data on the number of days with rime observed, data on rime observed by meteorological stations below 800m in altitude are selected, and the duration of a freezing rain event is determined according to two criteria: severe freezing rain event and local freezing rain event.

3. The evaluation method according to claim 2, characterized in that, The aforementioned severe freezing rain event is a freezing rain process with more than 70 daily frost stations and multiple stations experiencing freezing rain for more than 3 days; the localized freezing rain event is a freezing rain process with more than 5 daily frost stations and at least 3 stations experiencing freezing rain for more than 2 days.

4. The evaluation method according to claim 1, characterized in that, The collection of meteorological reanalysis grid data with fine vertical stratification of 5-25 km grid spacing during the impact period specifically involves downloading meteorological reanalysis data with 5-25 km grid spacing and DEM data with 90 m grid spacing from relevant websites based on the impact period of the freezing rain event.

5. The evaluation method according to claim 1, characterized in that, The specific process for obtaining the cumulative freezing rainfall of all fine grids during the affected period is as follows: The potential freezing rain amount and freezing rain occurrence altitude data H1 calculated hourly are downscaled to fine grid points with a grid spacing of less than 2.5 kilometers in hilly areas to obtain freezing rain amount and freezing rain occurrence altitude data H2 at the fine grid points. Accordingly, the DEM is resampled to fine grid points with the same grid spacing, and the ground elevation of each grid point is recorded as H3. For grid points with a potential freezing rainfall greater than 0.0 mm, calculate the difference between H3 and H2. If H2-H3≥0, the freezing rainfall of that grid point is assigned a value of 0.0 mm; otherwise, the potential freezing rainfall of that grid point is the freezing rainfall of the corresponding fine grid point. Complete the judgment of all grid points in the study area to obtain the hourly freezing rainfall of each fine grid point at the corresponding time. Similarly, the remaining time intervals are determined, and finally, the freezing rain amounts at all times are accumulated for each fine grid point to obtain the cumulative freezing rain amount for all fine grids during the affected period of a freezing rain event, thereby determining the distribution of freezing rain disasters in a hilly and mountainous area.

6. The evaluation method according to claim 1, characterized in that, The freezing rain risk levels are as follows: Level 1 is slight icing with freezing rain <5mm; Level 2 is significant icing with freezing rain between [5mm and 15mm]; Level 3 is relatively heavy icing with freezing rain between [15mm and 25mm]; and Level 4 is severe icing with freezing rain ≥25mm.

7. The evaluation method according to claim 6, characterized in that, A spatial distribution map is drawn based on the freezing rain risk level of each grid point to determine the distribution range and intensity of a freezing rain event.

8. An assessment system for the distribution and intensity of freezing rain disasters in hilly areas, used to implement the assessment method described in any one of claims 1-7, characterized in that, include: Calculation Unit: Based on the rime ice data from the meteorological station, determine the duration of an impact event of freezing rain, collect meteorological reanalysis grid data with fine vertical stratification of 5-25 km grid spacing within the impact period, calculate the altitude of freezing rain occurrence and potential freezing rain amount of different grid points in the hilly area hourly, and downscale to fine grid points with a grid spacing of less than 2.5 km. The cumulative freezing rain acquisition unit is used to take the potential freezing rain at a certain fine grid point at a certain moment when the altitude of the freezing rain is lower than the ground elevation as the freezing rain at that grid point at that moment. Then, the freezing rain at all moments is accumulated grid by grid to obtain the cumulative freezing rain of all fine grids in the affected period. Quantitative assessment unit: used to determine the freezing rain risk level by combining available data on freezing rain disasters in some areas, and to quantitatively assess the severity of freezing rain disasters in the entire hilly area.

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