An assessment method for the impact of urbanization process on rainfall

Abstract

The present invention discloses a method for evaluating the impact of urbanization on rainfall. The method includes: 1) data collection and preprocessing in the study area; 2) division of urban and suburban areas; 3) construction of a comprehensive rainfall index for urban rainfall; 4) quantification of the impact of urbanization on regional rainfall changes. The present invention proposes a method for evaluating the impact of urbanization on rainfall. The method first proposes a comprehensive rainfall index for urban rainfall based on the characteristics of individual rainfall events, solves the problem of lacking targeted indicators in the study of the impact of urbanization on rainfall, and accurately divides the urban and suburban areas based on impervious surface data. Then, based on the difference between the comprehensive rainfall indices of the urban and suburban areas, the impact of urbanization on regional rainfall changes is quantified. The method for evaluating the impact of urbanization on rainfall realizes the quantitative study of the impact of urbanization on rainfall, improves the understanding of the impact law of urbanization on rainfall changes, and is of great significance for guiding future urban planning and development and evaluating its potential impact on rainfall.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantifying the impact of urbanization on rainfall, and particularly relates to a calculation method for quantitatively evaluating the impact of urbanization on rainfall changes. Background Art

[0002] With the continuous deepening of the urbanization process, the urban area shows a gradually increasing trend, which changes the energy budget relationship and water vapor distribution on the ground surface, resulting in the formation of a unique regional microclimate in the city, and significant changes have occurred in urban rainfall. Exploring the impact of urbanization on rainfall has become one of the hot issues in the study of urbanization effects. Quantitative research on the impact of urbanization on rainfall can deepen the understanding of the law of the impact of urbanization on rainfall changes, and is of great significance for guiding future urban planning and development and evaluating its potential impact on rainfall.

[0003] The method of mathematical statistics is often used to quantify the impact of urbanization on rainfall changes due to its simple principle and strong operability. By calculating the differences in rainfall indicators and their change rates between urban areas and suburban areas, the impact of urbanization on rainfall changes is quantified. However, this method requires accurate division of the study area into urban and suburban areas, and the impervious surface area is a representative indicator for dividing cities and suburbs. However, affected by the scale effect, it is necessary to specifically determine the threshold of the impervious surface area at a specific scale, and then distinguish the scope of urban and suburban areas and quantify the impact of urbanization on rainfall changes.

[0004] At the same time, many scholars have carried out research on quantifying the impact of urbanization on rainfall changes, and a large number of indicators related to daily rainfall have been proposed in existing research. However, most of these indicators only reflect one aspect of urban rainfall, which leads to obvious one-sidedness when using these indicators to quantify the impact of urbanization on rainfall changes, and it is impossible to fully reveal the overall impact of urbanization on rainfall changes. Therefore, it is necessary to propose a comprehensive indicator to reflect the comprehensive characteristics of urban rainfall, and then quantify the impact of urbanization on rainfall from an overall perspective. Summary of the Invention

[0005] The present invention provides an evaluation method for the impact of urbanization on rainfall, aiming to specifically determine the threshold of the impervious surface area, accurately divide the scope of urban and suburban areas, and at the same time propose an indicator that can comprehensively reflect the characteristics of urban rainfall, achieve the purpose of quantifying the overall impact of urbanization on rainfall, deepen the understanding of the law of the impact of urbanization on rainfall changes, and provide help for guiding future urban planning and development and evaluating its potential impact on rainfall.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] The present invention proposes an evaluation method for the impact of urbanization on rainfall, including the following steps:

[0008] Step 1), Data collection and preprocessing in the study area:

[0009] Collect and download satellite rainfall data, meteorological station data, impervious surface data, and land use data in the study area; correct the satellite rainfall data using the linear scaling method based on the meteorological station data, extract the individual rainfall events in the study area based on the corrected satellite rainfall data, and extract the impervious surface area in the study area by clipping the global impervious surface data (GISA); divide grids with the same spatial resolution as the satellite rainfall data and aligned;

[0010] Step 2), Division of urban and suburban areas:

[0011] Resample the impervious surface data in the study area to the grids corresponding to the resolution of the satellite rainfall data; calculate the impervious surface percentage of each grid in the study area, where the impervious surface percentage is the ratio of the impervious surface area to the grid area, and divide the urban and suburban areas by setting different impervious surface percentage thresholds within the grids; based on the comparison between the obtained division results and the land use data of the same period, determine the optimal impervious surface percentage threshold for dividing the urban and suburban areas;

[0012] Step 3), Construction of comprehensive rainfall indicators for urban rainfall:

[0013] Based on the extracted individual rainfall event data, calculate the characteristics of the rainfall amount and time course distribution of the individual rainfall events, and construct comprehensive rainfall indicators that can comprehensively reflect urban rainfall changes;

[0014] The indicators of the rainfall amount characteristics of the individual rainfall events include: the maximum rainfall intensity i max , the total rainfall amount R of the individual rainfall event events , and the indicators of the time course distribution characteristics include: the proportion R of the duration before the peak rainfall amount to the total rainfall duration max , the proportion T of the duration when 50% of the total rainfall amount appears to the total rainfall duration 50 , the proportion T of the duration when 75% of the total rainfall amount appears to the total rainfall duration 75 , and the proportion T of the duration when 95% of the total rainfall amount appears to the total rainfall duration 95 .

[0015] The comprehensive rainfall indicators are constructed by combining the rainfall amount and time course distribution characteristics. The calculation formula for the comprehensive rainfall indicators is:

[0016]

[0017] In the formula: CPI is the comprehensive rainfall indicator, with the unit of mm 2 / h; i max is the maximum rainfall intensity, with the unit of mm / h; R events is the total rainfall amount of the individual rainfall event, with the unit of mm; R maxis the ratio of the duration when the total rainfall before the peak occurs to the total rainfall duration, dimensionless; T 50 represents the ratio of the duration when 50% of the total rainfall occurs to the total rainfall duration; T 75 represents the ratio of the duration when 75% of the total rainfall occurs to the total rainfall duration; T 95 represents the ratio of the duration when 95% of the total rainfall occurs to the total rainfall duration;

[0018] CPI is the comprehensive rainfall index; i max and R events are the rainfall components of the event rainfall; R max and are the time - course distribution components of the event rainfall; i max ×R max The physical meaning of is the distribution of the maximum rainfall intensity during the rainfall duration; The physical meaning of is the distribution of the total rainfall amount during the rainfall duration.

[0019] Step 4), Quantification of the impact of urbanization on rainfall changes:

[0020] Compare and analyze the comprehensive rainfall indices and their change trends of the urban and suburban areas divided within the region, and use the difference between the indices of the two regions to characterize the impact of urbanization on rainfall changes; the difference represents the impact of urbanization on rainfall changes after removing the influence of climate change.

[0021] The indices for quantifying the impact of urbanization on rainfall are CR mean and CR slope , where CR mean is defined as the contribution rate of urbanization to the average rainfall, which is the ratio of the difference between the average CPI of the urban grid and the average CPI of the suburban grid to the average CPI of the suburban grid; CR slope is defined as the difference between the slope k urban of the average CPI sequence of the urban grid and the slope k rural of the average CPI sequence of the suburban grid, divided by k urban , which can be regarded as a measure of the contribution of urbanization to precipitation changes.

[0022]

[0023] In the formula: CR mean is the average contribution rate of urbanization to rainfall, with the unit of 1; CPI urban is the average CPI of the urban grid; CPI rural is the average CPI of the suburban grid; CR slope is the contribution rate of urbanization to rainfall changes, with the unit of %; k urban is the slope of the average CPI sequence of the urban grid; k ruralis the slope of the average CPI sequence of the suburban grid.

[0024] Further, the satellite rainfall data described in step 1) is CMORPH (Climate Prediction Center MORPHing technique)-CDR, with a time resolution of 30 minutes and a spatial resolution of 8 km; the rainfall data of meteorological stations has a time resolution of days, the impervious surface data is GISA (Global Impervious Surface Area), with a time resolution of years and a spatial resolution of 30 m, and the land use data is CLCD (China Land Cover Dataset), with a time resolution of years and a spatial resolution of 30 m.

[0025] Further, the spatial resolution of the grid described in step 1) is 8 km and is aligned with the rainfall grid.

[0026] Further, the rainfall extracted in step 1) is the rainfall of grid scale in the study area, and the extracted rainfall events require that the time interval between every two adjacent rainfall events is greater than 6 hours.

[0027] Further, the extraction process of the rainfall events described in step 1) is as follows:

[0028] S11, preliminary selection of rainfall events. According to the meteorological definition, rainfall with an hourly rainfall exceeding 0.1 mm is effective rainfall. Continuous effective rainfall is recorded as a rainfall event.

[0029] S12, elimination of rainfall events. Urban rainfall with a duration of 6 hours or more can fully reflect the rise and fall of the rainfall process. Therefore, rainfall events with a duration of less than 6 hours are first selected. If the total rainfall of a rainfall event is not less than 30.0 mm (heavy rain), then the rainfall event is retained, otherwise it is eliminated.

[0030] S13, merging of rainfall events. If the time interval between two rainfall events is less than 6 hours, then the two rainfall events are merged into one rainfall event.

[0031] Further, in step 2), the impervious surface data is resampled to the same spatial resolution of 8 km as the rainfall, and at the same time, the impervious surface grid is aligned with the rainfall grid.

[0032] Further, the different impervious surface percentage thresholds in the grid described in step 2) include 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% and 10%, a total of 10 thresholds.

[0033] Further, the optimal impervious surface percentage threshold described in step 2) is determined by referring to the spatial distribution of land use. The specific process is as follows:

[0034] S21, extract the building and road layers based on land use data;

[0035] S22, divide the study area into urban and suburban areas based on different impervious surface percentage thresholds, where areas with an impervious surface percentage greater than or equal to the threshold are identified as urban areas, and areas with an impervious surface percentage less than the threshold are identified as suburban areas.

[0036] S23, in Arcgis, overlay the building and road layers in land use with the urban and suburban layers of the study area in one layer, and select the best-matching impervious surface percentage threshold among 10 thresholds as the optimal percentage threshold by comparing the areas and spatial distributions of the two layers.

[0037] The beneficial effects of the present invention compared with the prior art are as follows:

[0038] Based on an evaluation method of the impact of urbanization on rainfall, the present invention first proposes a comprehensive urban rainfall index based on the characteristics of individual rainfall events, solves the problem of lacking targeted indicators in the study of the impact of urbanization on rainfall, and accurately divides the urban and suburban areas based on impervious surface data. Then, based on the difference between the comprehensive rainfall indices of urban and suburban areas, it quantifies the impact of urbanization on regional rainfall changes, achieving the purpose of quantifying the overall impact of urbanization on rainfall, which is beneficial to the study of the impact law of urbanization on rainfall changes. It provides help for guiding future urban planning and development and evaluating its potential impact on rainfall. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is the flowchart of the method of the present invention;

[0040] Figure 2 is the distribution map of urban and suburban areas under the impervious surface percentage threshold in the embodiment;

[0041] Figure 3 is the annual change diagram of CPI in the embodiment;

[0042] Figure 4 is the annual change diagram of CR mean in the embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] To enable those skilled in the art to better understand this method, the technical solution of the present invention will be described below in conjunction with the drawings and embodiments.

[0044] Embodiment 1

[0045] The present invention provides a method for evaluating the impact of urbanization on rainfall. Taking a certain city as a case study area, the specific implementation of the technical solution of the present invention will be further described below. The main content of the method flow of the present invention is summarized as Figure 1 shown, and the specific application includes the following steps:

[0046] Step 1), data collection and preprocessing in the study area:

[0047] Collect and download satellite rainfall data, meteorological station data, impervious surface data, and land use data in the study area. Based on the meteorological station data, the satellite rainfall data is corrected using a linear scaling method. Based on the corrected satellite rainfall data, the rainfall events in the study area are extracted. Based on the global impervious surface data, the impervious surface area in the study area is cropped and extracted; grids with the same spatial resolution as the rainfall data and aligned are divided;

[0048] In this embodiment, the satellite rainfall data in the study area is CMORPH (Climate Prediction Center MORPHing technique)-CDR, with a time resolution of 30 minutes and a spatial resolution of 8 km; the rainfall data of meteorological stations is from the China Meteorological Network, with a time resolution of one day; the impervious surface data is GISA (Global Impervious Surface Area), with a time resolution of one year and a spatial resolution of 30 m; the land use data is CLCD (China Land Cover Dataset), with a time resolution of one year and a spatial resolution of 30 m.

[0049] In Arcgis, the study unit grids are divided by Create Fishnet, with a spatial resolution of 8 km and aligned with the rainfall grids. In the divided study unit grids, the rainfall events and the impervious surface area are extracted.

[0050] Based on the corrected satellite rainfall, the rainfall events are extracted, and the extraction process is as follows:

[0051] S11, preliminary selection of rainfall events. According to the meteorological definition, rainfall with an hourly rainfall exceeding 0.1 mm is effective rainfall. Continuous effective rainfall is recorded as a rainfall event.

[0052] S12, elimination of rainfall events. Urban rainfall with a duration of 6 hours or more can fully reflect the rise and fall of the rainfall process. Therefore, rainfall events with a duration of less than 6 hours are first selected. If the total rainfall of a rainfall event is not less than 30.0 mm (heavy rain), the rainfall event is retained, otherwise it is eliminated.

[0053] S13, merging of rainfall events. If the time interval between two rainfall events is less than 6 hours, the two rainfall events are merged into one rainfall event.

[0054] Step 2), Division of urban and suburban areas:

[0055] Calculate the percentage of impervious surface for each grid in the study area, set different percentage thresholds of impervious surface within the grid (1%-10%) to divide it into urban and suburban areas, and determine the optimal percentage threshold of impervious surface for dividing urban and suburban areas by referring to and comparing with the land use data of the same period;

[0056] Based on the grid of the study unit, calculate the percentage of impervious surface of the grid, and its value is the ratio of the impervious surface area to the grid area;

[0057] Set the percentage thresholds of impervious surface for the grid of the study unit, including 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% and 10%, a total of 10 thresholds;

[0058] Based on the 10 percentage thresholds of impervious surface and the land use data, determine the optimal threshold for dividing urban and suburban areas, and its process is as follows:

[0059] S21, Extract the building and road layers based on the land use data;

[0060] S22, Divide the study area into urban and suburban areas based on different percentage thresholds of impervious surface. Among them, the area where the percentage of impervious surface is greater than or equal to the threshold is identified as the urban area, and the area where the percentage of impervious surface is less than the threshold is identified as the suburban area;

[0061] S23, In Arcgis, overlay the building and road layers in the land use with the urban and suburban area layers of the study area in one layer, and select the optimal percentage threshold of impervious surface that best matches among the 10 thresholds as the optimal percentage threshold by comparing the areas and spatial distributions of the two layers.

[0062] Through comparative analysis, the optimal threshold for the study area is determined to be 6%. The ranges of urban and suburban areas divided according to this threshold are shown in Figure 2 .

[0063] Step 3), Construction of the comprehensive rainfall index for urban rainfall:

[0064] Based on the rainfall event data extracted in Step 1, calculate the characteristics of the rainfall amount and time course distribution of the rainfall event, and construct a comprehensive rainfall index that can comprehensively reflect the urban rainfall variation accordingly;

[0065] The comprehensive rainfall index is constructed by combining the rainfall amount and the characteristics of the time course distribution. The calculation formula of the comprehensive rainfall index is:

[0066]

[0067] Where: CPI is the comprehensive rainfall index, with the unit of mm 2 / h; i max is the maximum rainfall intensity, with the unit of mm / h; R events is the total rainfall amount of a rainfall event, with the unit of mm; R max is the proportion of the duration of the total rainfall amount before the peak in the total rainfall duration, dimensionless; T 50 represents the proportion of the duration of 50% of the total rainfall amount in the total rainfall duration; T 75 represents the proportion of the duration of 75% of the total rainfall amount in the total rainfall duration; T 95 represents the proportion of the duration of 95% of the total rainfall amount in the total rainfall duration;

[0068] Step 4), quantification of the impact of urbanization on rainfall change:

[0069] Compare and analyze the comprehensive rainfall indices and their change trends of the urban and suburban areas divided within the region, and use the difference between the indices of the two regions to characterize the impact of urbanization on rainfall change;

[0070] Their calculation formulas are respectively:

[0071]

[0072] Where: CR mean is the average contribution rate of urbanization to rainfall, with the unit of 1; CPI urban is the average value of CPI of the urban grid; CPI rural is the average value of CPI of the suburban grid; CR slope is the contribution rate of urbanization to rainfall change, with the unit of %; k urban is the slope of the sequence of the average value of CPI of the urban grid; k rural is the slope of the sequence of the average value of CPI of the suburban grid.

[0073] Among them, the CPI changes of the urban and suburban areas over the years are as Figure 3 shown. Based on formula (2), the CR over the years has been calculated mean as Figure 4 shown. Based on formula (3), the CR has been calculated slope to be 109.4%.

[0074] The above description is only for the implementation of the examples of the present invention and is not used to limit the present invention. The number of levels of the waterlogging resilience in the present invention can be set according to requirements and specific research areas. Any modification, equivalent replacement, improvement, etc. made within the scope defined by the claims of the present invention shall be within the protection scope of the present invention.

Claims

1. A method for evaluating the impact of urbanization on rainfall, characterized in that: It includes the following steps: Step 1) Data collection and preprocessing: Collect and download satellite rainfall data, meteorological station data, impervious surface data and land use data of the study area; The satellite rainfall data were corrected based on the meteorological station data, and the rainfall data of the study area were extracted based on the corrected satellite rainfall data. Extract the impervious surface area of ​​the study area based on the impervious surface data; Divide the grids with the same spatial resolution and alignment with the satellite rainfall data; the satellite rainfall data is CMORPH-CDR, with a time resolution of 30 minutes and a spatial resolution of 8 km; the extracted rainfall is the grid-scale rainfall in the study area, and the extracted rainfall requires that the time interval between every two adjacent rainfall sessions is greater than 6 hours; The extraction process of rainfall events is as follows: S11, primary rainfall event: rainfall with an hourly rainfall exceeding 0.1 mm is considered effective rainfall, and continuous effective rainfall is recorded as one rainfall event; S12, remove rainfall events: select rainfall events with a rainfall duration of less than 6 hours. If the total rainfall of the rainfall event is not less than 30.0 mm, the rainfall event is retained, otherwise it is removed; S13, merging of rainfall events: if the time interval between two rainfall events is less than 6 hours, the two rainfall events are merged into one rainfall event; Step 2) Urban and suburban area division: resample the impervious surface data of the study area to a grid with a resolution corresponding to the satellite rainfall data; Calculate the percentage of impervious surface of each grid in the study area, the percentage of impervious surface is the ratio of the area of ​​impervious surface to the area of ​​the grid, and divide the urban area and suburbs by setting different thresholds of percentage of impervious surface in the grid; determine the optimal percentage threshold of impervious surface for dividing the urban area and suburbs based on the comparison of the division results with the land use data of the same period; the different percentage thresholds of impervious surface in the grid include 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% and 10%, a total of 10 thresholds; in step 2), divide the urban area and suburbs by setting different thresholds of percentage of impervious surface in the grid; determine the optimal percentage threshold of impervious surface for dividing the urban area and suburbs based on the comparison of the division results with the land use data of the same period, the specific process is: S21, extracting building and road layers based on land use data; S22, based on different thresholds of impervious surface percentage, the study area is divided into urban and suburban areas, where the area with an impervious surface percentage greater than or equal to the threshold is identified as urban, and the area with an impervious surface percentage less than the threshold is identified as suburban; S23, in ArcGIS, the building and road layers in land use were superimposed on the urban and suburban layers of the study area in one layer. By comparing the area and spatial distribution of the two layers, the best matching impervious surface percentage threshold was selected from the 10 thresholds as the optimal percentage threshold; Step 3) Construction of comprehensive rainfall index for urban rainfall: Based on the extracted rainfall data, the characteristics of rainfall and time distribution of each rainfall event are calculated, and a comprehensive rainfall index that can comprehensively reflect the change process of urban rainfall is constructed. The calculation formula of the comprehensive rainfall index is: Where: CPI is the comprehensive rainfall index, unit is mm 2 / h;i max is the maximum rainfall intensity, in mm / h; R events is the total rainfall in the event, in mm; R max T is the ratio of the total rainfall duration before the peak to the total rainfall duration; 50 It indicates the proportion of the duration of 50% of the total rainfall to the total rainfall duration; T 75 It indicates the proportion of the duration of 75% of the total rainfall to the total rainfall duration; T 95 It indicates the proportion of the duration of 95% of the total rainfall to the total rainfall duration; Step 4) Quantify the impact of urbanization on rainfall changes: Compare and analyze the comprehensive rainfall indicators and their changing trends of urban and suburban areas in the region to characterize the impact of urbanization on rainfall changes. The calculation formula is as follows: Where: CR mean is the average contribution rate of urbanization to rainfall, with the unit being 1; CPI urban is the average CPI of the urban grid; CPI rural is the average CPI of the suburban grid; CR slope is the contribution rate of urbanization to rainfall change, in %; k urban is the slope of the CPI average value series of the urban grid; k rural is the slope of the suburban grid CPI average series.

2. The method for evaluating the impact of urbanization on rainfall according to claim 1, characterized in that: In step 1), the temporal resolution of rainfall data from meteorological stations is day; the impervious surface data is GISA, with a temporal resolution of year and a spatial resolution of 30m; the land use data is CLCD, with a temporal resolution of year and a spatial resolution of 30m.

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