CN119849764A

CN119849764A - Method for determining small-drainage-basin non-point source pollution key source area

Info

Publication number: CN119849764A
Application number: CN202510016562.3A
Authority: CN
Inventors: 赵洪涛; 黄甜; 朱昊; 苏静君
Original assignee: Research Center for Eco Environmental Sciences of CAS
Current assignee: Research Center for Eco Environmental Sciences of CAS
Priority date: 2025-01-06
Filing date: 2025-01-06
Publication date: 2025-04-18

Abstract

The present disclosure provides a method for determining the key source area of non-point source pollution in a small watershed, which can be applied to the fields of pollutant analysis technology and environmental science. The method for determining the key source area of non-point source pollution in a small watershed includes: obtaining multiple sets of precipitation runoff process information corresponding to the geographical area to be investigated; generating N sets of theoretical values of pollutant output based on multiple sets of precipitation runoff process information and N sets of land information; generating N sets of pollutant transmission resistance values based on N sets of pre-collected geographical information corresponding to N geographical grid units one by one; generating N actual values of pollutant output corresponding to N geographical grid units one by one based on N theoretical values of pollutant output and N pollutant transmission resistance values; and selecting at least one target geographical grid unit from the N geographical grid units based on the N actual values of pollutant output as the key source area of non-point source pollution in the small watershed.

Description

Method for determining small-drainage-basin non-point source pollution key source area

Technical Field

The disclosure relates to the technical field of pollutant analysis and the field of environmental science, and more particularly relates to a method for determining a small-drainage-basin non-point source pollution key source region.

Background

In order to effectively manage and control the surface source pollution, it is generally necessary to precisely determine the critical source region of the surface source pollution. The area source pollution key source area comprises an area which contributes to the area source pollution load in the river basin greatly. The related method mainly identifies geographical areas such as a non-point source pollution key source area through models such as a mechanism model, an experience model, an index model and the like.

In the process of realizing the conception of the disclosure, the inventor finds that at least the following problems exist in the related technology, namely, the related method for identifying the geographical areas such as the key source area polluted by the surface source is mainly focused on analyzing the output potential of the pollution source, but the important influence of the dynamic characteristics and the hydrologic connectivity of the precipitation and the production flow process on the surface source pollution process is usually ignored, so that the key source area is not accurately identified and the feasibility is low. In addition, when the existing mechanism model, experience model, index model and other models are used for identifying the geographical areas such as the non-point source pollution key source area, the problems of high data requirement, insufficient model precision, difficulty in adapting to complex land utilization types, terrain conditions, insufficient dynamic property and the like exist respectively.

Disclosure of Invention

In view of the above, the disclosure provides a method for determining a small-river basin surface source pollution key source area, which comprises the steps of obtaining multiple sets of precipitation runoff process information corresponding to a geographical area to be examined, wherein the multiple sets of precipitation runoff process information correspond to multiple water-lowering flow events occurring in the geographical area to be examined, the geographical area to be examined comprises N geographic grid units, generating N sets of pollutant output theoretical values corresponding to the N geographic grid units one by one based on the multiple sets of precipitation runoff process information and the N sets of land information which is obtained in advance and corresponds to the N geographic grid units one by one, wherein pollutants are generated by precipitation flow events, generating N sets of pollutant transmission resistance values corresponding to the N geographic grid units one by one based on the N sets of pollutant output theoretical values and the N pollutant transmission resistance values, and screening at least one target geographic grid unit from the N geographic grid units based on the N pollutant output actual values to serve as the key source area to be examined.

According to an embodiment of the present disclosure, the geographic grid cells correspond to at least one land use type, and the land information includes land use type information, and land coverage areas corresponding to the respective land use types.

According to the embodiment of the disclosure, each set of pollutant output theoretical values comprises K pollutant output theoretical values, generating N sets of pollutant output theoretical values corresponding to N geographic grid units one by one based on multiple sets of rainfall runoff process information and N sets of land information obtained in advance and corresponding to the N geographic grid units one by one comprises determining K rainfall types corresponding to the multiple sets of rainfall runoff process information based on a preset rainfall threshold value, calculating K sets of pollutant average concentration values corresponding to the K rainfall types one by one based on the K sets of rainfall runoff process information corresponding to the K rainfall types one by one and land utilization type information corresponding to the geographic grid units, and calculating K sets of total runoff depth values corresponding to the K rainfall types one by one based on the K sets of pollutant average concentration values, the K sets of total runoff depth values and land coverage areas corresponding to the land utilization output types one by one for each geographic grid unit.

According to the embodiment of the disclosure, land utilization type information comprises runoff parameter values corresponding to land utilization types, calculating K groups of total runoff depth values corresponding to K precipitation types one by one comprises determining at least one runoff parameter value corresponding to a geographic grid unit based on at least one land utilization type corresponding to the geographic grid unit, determining at least one accumulated precipitation amount corresponding to the geographic grid unit based on at least one land utilization type corresponding to the geographic grid unit, and calculating the total runoff depth value corresponding to the precipitation type based on the at least one runoff parameter value corresponding to the geographic grid unit and the at least one accumulated precipitation amount for each precipitation type.

According to the embodiment of the disclosure, the geographic information comprises geographic grid cell distance information and geographic characteristic indexes, and the geographic grid cell distance information comprises a distance value from a geographic grid cell to a pollutant collecting area.

According to the embodiment of the disclosure, generating N groups of pollutant transmission resistance values corresponding to N geographic grid cells one by one based on N groups of geographic information acquired in advance and corresponding to the N geographic grid cells one by one comprises determining at least one geographic characteristic index corresponding to the geographic grid cells and determining a weight value corresponding to the at least one geographic characteristic index for each geographic grid cell, and obtaining the pollutant transmission resistance value corresponding to the geographic grid cell based on the distance value from the geographic grid cell to a pollutant collecting area and the weight value corresponding to the at least one geographic characteristic index for each geographic grid cell.

According to the embodiment of the disclosure, the geographic characteristic index comprises a landscape type index, a soil type index and a geographic information index, wherein the geographic information index comprises at least one of an altitude index, a distance index, a gradient index, a humidity index and a vegetation coverage index.

According to the embodiment of the disclosure, generating N pollutant output actual values in one-to-one correspondence with N geographic grid units based on N pollutant output theoretical values and N pollutant transmission resistance values comprises generating N hydrologic connectivity standard values in one-to-one correspondence with N geographic grid units based on the N pollutant transmission resistance values, and calculating to obtain the pollutant output actual values based on the N pollutant output theoretical values and the N hydrologic connectivity standard values.

According to the embodiment of the disclosure, calculating the actual pollutant output value based on the N pollutant output value theoretical values and the N hydrologic connectivity standard values comprises calculating the product of the pollutant output value theoretical values and the hydrologic connectivity standard values corresponding to the geographic grid units for each geographic grid unit to obtain the actual pollutant output value.

According to the embodiment of the disclosure, screening at least one target geographic grid cell from N geographic grid cells based on N pollutant output quantity actual values comprises carrying out preset grading treatment on the N pollutant output quantity actual values to obtain grading treatment results, and screening at least one target geographic grid cell from the N geographic grid cells based on the grading treatment results.

According to the embodiment of the disclosure, the theoretical value of the pollutant output is determined based on the rainfall type and other rainfall runoff process information, and the actual value of the pollutant output is determined based on the geographic information, so that the influence of the whole process of the rainfall runoff generation event and the pollutant transmission to the pollutant sink into the water body on the actual output of the pollutant can be comprehensively analyzed, the influence of various geographic information such as topography, land utilization and vegetation coverage is comprehensively considered, and therefore the small-river basin surface source pollution key source area can be dynamically identified under different rainfall conditions, and the identification accuracy is improved.

Drawings

The foregoing and other objects, features and advantages of the disclosure will be more apparent from the following description of embodiments of the disclosure with reference to the accompanying drawings, in which:

FIG. 1 schematically illustrates a flow chart of a method for determining a critical source region for small-basin area source contamination in accordance with an embodiment of the present disclosure;

FIG. 2 schematically illustrates a flow, production analysis results graph for different land utilization types, in accordance with an embodiment of the present disclosure;

3 (a), 3 (b), 3 (c) schematically illustrate a schematic diagram of a plurality of theoretical pollutant output values at different precipitation types according to an embodiment of the disclosure;

FIG. 4 schematically illustrates a schematic view of landscape types included in different land utilization types according to an embodiment of the present disclosure;

5 (a), 5 (b), 5 (c) schematically illustrate schematic diagrams of standard values of hydrologic connectivity under different precipitation types according to embodiments of the disclosure;

Fig. 6 (a), 6 (b), 6 (c) schematically illustrate diagrams of actual values of pollutant output under different precipitation types according to embodiments of the disclosure.

Detailed Description

For the purposes of promoting an understanding of the principles and advantages of the disclosure, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same.

The endpoints of the ranges and any values disclosed in this disclosure are not limited to the precise range or value, and such range or value should be understood to encompass values approaching those range or value. For numerical ranges, one or more new numerical ranges may be obtained in combination with each other between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, and are to be considered as specifically disclosed in this disclosure.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The terms "comprises," "comprising," and/or the like, as used herein, specify the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components. All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. It should be noted that the terms used herein should be construed to have meanings consistent with the context of the present specification and should not be construed in an idealized or overly formal manner.

In the process of realizing the method, the identification method of the relevant non-point source pollution key source area is mainly focused on analyzing the output potential of the pollution source, but the important influence of the dynamic characteristics of precipitation and the flow production process and the hydrologic connectivity on the non-point source pollution process is usually ignored, so that the identification of the key source area is not accurate enough and the feasibility is low. And the related non-point source pollution recognition technology mainly depends on a mechanism model, an experience model and an index model. The mechanism model needs a large amount of actual measurement data to support, the data dependence is high, and experience and index models are difficult to adapt to space-time variation of the river basin characteristics due to parameter simplification, so that the recognition accuracy and applicability are limited. In particular, although the mechanism model can accurately simulate hydrologic process and pollutant transmission, the mechanism model has strong dependence on high-resolution and long-time sequence data and complex calculation, so that the mechanism model is difficult to be widely applied in small watershed with data shortage. The empirical model generally simply estimates pollution load through an empirical formula, and is difficult to reflect the complex landscape structure and pollutant output under the dynamic hydrologic condition due to the dependence of fixed parameters, so that the recognition accuracy is low. While the exponential model is suitable for risk assessment of specific pollutants, it is mostly limited to single pollutants, lacking comprehensive analysis of multiple pollutants and diverse land utilization. In addition, the problem of insufficient dynamics exists in the related model generally, the space-time variation of pollutant output in the precipitation and the production process cannot be accurately captured, for example, the distribution and migration modes of the pollutants in time and space can be changed due to different factors such as the intensity, duration and precipitation amount of the precipitation, and the related model generally cannot capture the space-time variation. And meanwhile, although partial methods consider hydrologic connectivity, the simulation of a pollutant transmission path is not accurate enough, and the resistance influence of factors such as topographic vegetation on pollutant transmission is ignored. In view of this, embodiments of the present disclosure provide a method for determining a critical source region of small-basin area source pollution.

Fig. 1 schematically illustrates a flowchart of a method for determining a critical source region of small-basin area source contamination in accordance with an embodiment of the present disclosure. The method for determining the small-river-basin non-point source pollution key source region in the embodiment comprises operations S110-S150.

In operation S110, a plurality of sets of precipitation runoff process information corresponding to a geographical area to be examined is acquired, wherein the plurality of sets of precipitation runoff process information correspond to a plurality of precipitation runoff events occurring in the geographical area to be examined, and the geographical area to be examined includes N geographical grid cells.

According to the embodiment of the disclosure, pollutants can enter environments such as soil through runoff and the like under the action of natural conditions such as rainfall and snowfall and the like, so that non-point source pollution is generated, for example, the pollutants can flow through runoff formed by rainfall, flow through different geographic areas on the ground and finally enter rivers. The non-point source pollution load contribution of different geographical areas is different due to different precipitation conditions and the natural condition that runoff flows through the geographical areas can be different. The geographical area which contributes to the pollution load of the non-point source in the geographical area through which the runoff flows can be used as the key source area of the non-point source pollution.

In accordance with an embodiment of the present disclosure, in operation S110, a geographical area to be inspected includes a plurality of geographical areas through which runoff flows. In order to accurately determine the non-point source pollution key source area in the geographical area to be examined, the geographical area to be examined can be divided into N geographical grid units in advance, and the non-point source pollution load contribution of each geographical grid unit is evaluated respectively, so that the geographical area with larger non-point source pollution load contribution is screened from the N geographical grid units, and the non-point source pollution key source area is obtained.

The geographic area to be examined may be divided into N geographic grid cells using geographic information system technology (Geographic Information System, abbreviated GIS). Basic geographical data of the N geographical grid cells may be collected in advance, including but not limited to a digital elevation model, a land utilization/vegetation cover map, a soil type distribution map, a vegetation index image, etc., and time consistency and quality reliability of the basic geographical data may be ensured in advance.

According to the embodiment of the disclosure, the geographical area to be examined is divided into N geographical grid units in advance, and the non-point source pollution load contribution conditions of the N geographical grid units are respectively analyzed, instead of directly analyzing the whole geographical area to be examined, so that the requirements of calculation efficiency and spatial resolution can be comprehensively considered, and the calculation efficiency and calculation accuracy are improved.

According to the embodiment of the disclosure, a plurality of precipitation runoff events which occur in a geographical area to be inspected within a predetermined period of time can be determined, the precipitation runoff events can include events for generating surface runoff through precipitation such as rainfall and snowfall, and precipitation runoff process information corresponding to each precipitation runoff event in different land utilization types of the area to be inspected is collected respectively, and the precipitation runoff process information includes precipitation information such as precipitation amount, precipitation duration time, precipitation intensity and the like, and runoff information such as runoff time, runoff rate, runoff amount and pollutant concentration at each runoff time.

According to embodiments of the present disclosure, the overall process of contaminant transport includes the arrival of contaminants by precipitation at the ground, the flow of contaminants through different geographical areas of the ground by runoff, the collection of contaminants by runoff into a receiving body of water such as a river or lake. The load of contaminants into the receiving body of water is ultimately affected by the precipitation conditions and the geographic conditions of the geographic grid elements. Specifically, for each geographic grid cell, the precipitation condition and the geographic condition corresponding to the geographic grid cell influence the non-point source pollutant output potential of the geographic grid cell, and the geographic condition also influences the resistance of the output pollutant to radial flow transmission. The non-point source pollutant output potential and the resistance of the pollutant to the radial flow transmission can jointly influence the non-point source pollution load contribution of each geographic grid cell.

In operation S120, N sets of theoretical pollutant output values corresponding to N geographic grid cells one-to-one are generated based on the sets of precipitation runoff process information and the N sets of land information corresponding to the N geographic grid cells one-to-one acquired in advance, wherein the pollutants are generated by precipitation runoff events.

In accordance with embodiments of the present disclosure, the pollutant output quantity theoretical value may represent the non-point source pollutant output potential, which may represent the maximum amount of pollutant that one geographic grid cell may release into the environment. The rainfall runoff process information may include an accumulated rainfall. The land information may include land usage types corresponding to the geographic grid cells, which may include woodland, garden land, road, etc., and may include other land usage types, which are not limited herein.

Both precipitation runoff process information and geographical information can influence the theoretical value of the pollutant output. In particular, the cumulative rainfall required for different land use types to be able to form runoff may be different, for example, roads may start to produce flow earlier due to more watertight surfaces, while forests may start to produce flow later due to good soil permeability. In the case where the precipitation flow event is rainfall, the content of the pollutants corresponding to different rainfall types may be different, for example, because the precipitation amount of heavy rain is more, the pollutants are more carried, and the concentration of the pollutants corresponding to the heavy rain may be larger. For each geographic grid cell, a land utilization type included in the geographic grid cell may be determined, and a rainfall type corresponding to the geographic grid cell may be determined, where the rainfall type may include light rain, medium rain, heavy rain. The theoretical pollutant output value corresponding to each geographic grid cell can be calculated based on the rainfall runoff process information and the land information corresponding to each geographic grid cell.

According to embodiments of the present disclosure, for each geographic grid cell, which corresponds to at least one rainfall type and at least one land utilization type, a set of theoretical pollutant output values corresponding to the geographic grid cell may be calculated for each rainfall type. Specifically, the theoretical value of the output of the pollutant corresponding to each rainfall type may be calculated based on the average concentration of the pollutant in the geographical grid cell corresponding to each rainfall type, the total runoff depth corresponding to different land utilization types within a predetermined period of time, and the land coverage area corresponding to each land utilization type.

In operation S130, N sets of contaminant transmission resistance values corresponding to the N geographic grid cells one-to-one are generated based on N sets of geographic information corresponding to the N geographic grid cells one-to-one acquired in advance.

According to embodiments of the present disclosure, the contaminant transport resistance value may be indicative of the amount of resistance encountered by the contaminant during transport. The hydrologic connectivity of the geographic grid cells may be assessed based on the contaminant transport resistance values, which may characterize how convenient the contaminant is to be transported through runoff. The geographic information may include, for example, landscape morphology, soil type, and the like. The geographical information can affect the pollutant transmission resistance values of the geographical grid cells, for example, the hydrologic connectivity of yellow soil is poor for different soil types, and the hydrologic connectivity of the overburden soil is good. The resistance coefficient of each geographic grid cell can be determined based on the geographic information such as landscape morphology, soil type, vegetation coverage type and the like, and pollutant transmission resistance values of each geographic grid cell are calculated based on the resistance coefficient.

In operation S140, N actual contaminant output values are generated in one-to-one correspondence with the N geographic grid cells based on the N theoretical contaminant output values and the N contaminant transmission resistance values.

According to embodiments of the present disclosure, for each geographic grid cell, an actual value of the contaminant output corresponding to the geographic grid cell may be generated based on the theoretical value of the contaminant output and the contaminant transfer resistance value of the geographic grid cell. The actual value of the pollutant output is used for representing the non-point source pollution load contribution. The larger the actual value of the pollutant output, the higher the non-point source pollution load contribution.

At operation S150, at least one target geographic grid cell is selected from the N geographic grid cells as a key source of small-basin area source pollution in the geographic area to be examined based on the N actual values of the pollutant output quantity.

According to the embodiment of the disclosure, after determining the actual value of the pollutant output quantity of each geographic grid cell, the geographic grid cell with a larger actual value of the pollutant output quantity can be used as a small-river basin area source pollution key source area, and the small-river basin area source pollution key source area is used for representing a geographic area needing to be focused on or treated in a geographic area to be examined.

According to the embodiment of the disclosure, the pollutant output actual value is obtained by calculating the pollutant output theoretical value and the pollutant output actual value of each geographic grid unit, so that the influence of the whole process of generating a precipitation flow event, transmitting pollutants through runoff and converging the pollutants into a water body on the pollutant actual output value can be comprehensively analyzed, and the small-river basin surface source pollution key source area can be accurately determined. The pollutant output theoretical value is determined based on the rainfall type and other rainfall runoff process information, and the pollutant output characteristics of different rainfall types can be determined, so that the pollution load under different rainfall conditions can be dynamically evaluated, and the problem that the rainfall dynamics is ignored in the related method is solved. By comprehensively considering the influence of various geographic information such as terrain, land utilization, vegetation coverage and the like, the transmission path and resistance of pollutants from the source to the water body can be simulated, so that the influence of hydrologic connectivity on pollutant output is fully considered, and the depicting precision of the pollutant transmission process under a complex landscape structure is improved. The pollutant output actual value is determined based on the pollutant output theoretical value and the pollutant output actual value, so that the small-river basin surface source pollution key source area can be dynamically identified under different rainfall conditions, and the identification accuracy of the small-river basin surface source pollution key source area determination process in space and time is improved.

According to the embodiment of the disclosure, when the area of the non-point source pollution source in the small watershed is determined through the related mechanism model, the related mechanism model generally needs a larger data volume to output an accurate result, and because the watershed is smaller, the related data is also less, so that the accuracy of applying the related model to identifying the area of the non-point source pollution key source in the small watershed is lower. Compared with the related model, the method can reduce the difficulty of data acquisition and simplify the data acquisition requirement by combining the geographic information system technology and short-term rainfall observation, thereby being applicable to small watershed with limited data. In addition, the method for determining the small-river-basin surface-source pollution key source area simultaneously considers the influence of precipitation flow-producing events and hydrologic connectivity, so that the small-river-basin surface-source pollution key source area can be accurately and dynamically identified, and the accuracy and the efficiency of pollution control are improved.

According to an embodiment of the present disclosure, the geographic grid cells correspond to at least one land use type. The land information includes land use type information and land coverage areas corresponding to the respective land use types.

According to an embodiment of the present disclosure, each set of pollutant output theoretical values includes K pollutant output theoretical values. Based on the multiple sets of rainfall runoff process information and N sets of land information which are obtained in advance and are in one-to-one correspondence with the N geographic grid units, generating N sets of pollutant output quantity theoretical values which are in one-to-one correspondence with the N geographic grid units comprises operations 11-13.

And 11, determining K precipitation types corresponding to the multiple groups of precipitation runoff process information based on a preset precipitation amount threshold.

According to embodiments of the present disclosure, the predetermined precipitation threshold may be preset. The rainfall types can comprise light rain, medium rain and heavy rain, wherein the rainfall thresholds corresponding to the light rain, medium rain and heavy rain can be determined according to the accumulated rainfall corresponding to different land utilization types when the production flow starts. Daily precipitation data of the geographical area to be examined in a preset time period and surface flow data corresponding to rainfall events of different land utilization types in the geographical area to be examined can be collected in advance, the daily precipitation data comprise daily accumulated precipitation amount, precipitation type, duration time of each precipitation event, precipitation intensity and the like, and the surface flow data comprise runoff amount, runoff rate, pollutant concentration and the like corresponding to each 5 minutes, 10 minutes and 30 minutes in the rainfall process and flow.

Operation 12, calculating K groups of pollutant average concentration values corresponding to the K precipitation types one by one and K groups of total runoff depth values corresponding to the K precipitation types one by one according to K groups of precipitation runoff process information corresponding to the K precipitation types one by one and land utilization type information corresponding to the geographic grid units.

According to embodiments of the present disclosure, the theoretical value of the pollutant output for different precipitation types may be different for the same geographic grid cell. The average concentration and total runoff depth values of the pollutants corresponding to the various precipitation types can be calculated respectively, and the theoretical pollutant output values corresponding to the various precipitation types can be obtained. For the same rainfall runoff event, the accumulated rainfall corresponding to the beginning of the runoff and the pollution production of different land utilization types can be determined, the rainfall duration, the rainfall intensity and other information can be determined, multiple sets of rainfall runoff process information are obtained, and the multiple sets of rainfall runoff process information can represent the runoff and the pollution production time sequence characteristics of different land utilization types.

According to the embodiment of the disclosure, for one geographic grid unit, the average concentration of pollutants and the total runoff depth value corresponding to different land use types are also different under the same precipitation type, and the influence of the land use types can be comprehensively considered based on a rainfall event average concentration model (EMC model) so as to calculate the average concentration of pollutants of different land use types under different precipitation types, for example, the average concentration of pollutants corresponding to different land use types under different precipitation types can be calculated by the following formula (1).

(1)

Wherein M is the pollutant mass, V is the total runoff, C is the pollutant concentration generated by precipitation current generation events, Q is the flow, t is the time interval, and EMC represents the pollutant average concentration.

And (13) calculating K pollutant output theoretical values corresponding to the K precipitation types one by one according to the K groups of pollutant average concentration values, the K groups of total runoff depth values and the land coverage areas corresponding to the land utilization types aiming at each geographic grid unit.

According to an embodiment of the present disclosure, the theoretical value of the pollutant output amount corresponding to each precipitation type may be calculated by the following formula (2).

(2)

Where L is the theoretical pollutant output value for each geographic grid cell, n is the nth land use type, a is the land coverage area, and R is the total runoff depth value.

According to the embodiment of the disclosure, by calculating the average concentration of the pollutants corresponding to different land utilization types under different precipitation types and the total runoff depth corresponding to each land utilization type, the influence of the precipitation factors on the pollutant output of the geographic grid unit and the influence of the land utilization types on the pollutant output can be considered, so that the rule between the total runoff depth value and the pollutant output quantity can be accurately and quantitatively described, and the accuracy of the calculation result of the theoretical value of the pollutant output quantity can be improved.

According to an embodiment of the present disclosure, land use type information includes runoff parameter values corresponding to respective land use types. Calculating K sets of runoff depth values corresponding to the K precipitation types one by one comprises operations 21-23.

Operation 21 determines at least one runoff parameter value corresponding to the geographic grid cell based on at least one land use type corresponding to the geographic grid cell.

According to embodiments of the present disclosure, the runoff parameter values include, for example, an initial loss rain value, an infiltration rain value, a loss coefficient, and a dimensionless curve number, wherein the dimensionless curve number sources corresponding to each land utilization type include, but are not limited to, empirical parameters, literature references, database searches. The initial loss rainfall value, the infiltration rainfall value, the loss coefficient and the dimensionless curve number can also be searched through a related recommendation table of a runoff curve number model (SCS-CN model) based on the accumulated rainfall corresponding to the producible flow of different land utilization types.

Operation 22 determines at least one cumulative precipitation amount corresponding to the geographic grid cells based on the at least one land utilization type corresponding to the geographic grid cells.

According to the embodiment of the disclosure, the accumulated rainfall of different rainfall types in the geographic area to be examined in the preset time period can be calculated based on different rainfall types and rainfall event distribution frequencies, for example, the accumulated daily rainfall data of the geographic area to be examined can be calculated.

Operation 23, for each precipitation type, calculates a total runoff depth value corresponding to the precipitation type based on at least one runoff parameter value corresponding to the geographical grid unit and at least one accumulated precipitation amount.

According to the embodiment of the disclosure, the total runoff depth values corresponding to different land utilization types under different precipitation types can be calculated by the following formula (3), the initial loss rainfall can be calculated by the following formula (4), and the infiltration rainfall can be calculated by the following formula (5).

(3)

(4)

(5)

Wherein R is the total runoff depth value, P is the accumulated precipitation,The initial loss rainfall is S, infiltration rainfall, lambda, loss coefficient and CN, and dimensionless curve number.

According to the embodiment of the disclosure, by generating the total runoff depth value based on the accumulated precipitation amount and the runoff parameter value at the same time, comprehensive factors influencing runoff generation can be considered, so that calculation accuracy of the total runoff depth value is improved.

According to embodiments of the present disclosure, the pollutant collection zone may be the water body into which the pollutant is ultimately collected as it is transported through the runoff. For example, the contaminants eventually sink into a river by runoff, which may be the contaminant collection area. The geographic characteristic index is used for representing landscape type, soil type and geographic information of each geographic grid unit.

According to the embodiment of the disclosure, generating N groups of pollutant transmission resistance values corresponding to N geographic grid cells one by one based on N groups of geographic information acquired in advance and corresponding to the N geographic grid cells one by one comprises determining at least one geographic characteristic index corresponding to the geographic grid cells and determining a weight value corresponding to the at least one geographic characteristic index for each geographic grid cell, and obtaining the pollutant transmission resistance value corresponding to the geographic grid cell based on the distance value from the geographic grid cell to a pollutant collecting area and the weight value corresponding to the at least one geographic characteristic index for each geographic grid cell. The contaminant transfer resistance value may characterize the efficiency of the transfer of the contaminant from each of the geocell grids to the receiving body of water, and may also determine a path of the transfer of the contaminant from each of the geocell grids to the receiving body of water based on the contaminant transfer resistance value.

According to embodiments of the present disclosure, determining the weight value corresponding to the at least one geographic characteristic index may be determining the weight value based on geographic factors such as landscape type, soil type, terrain, vegetation coverage, etc. of each geographic grid cell. Specifically, the weight value may be determined based on the magnitude of the impact of each geographic characteristic index on the hydrologic connectivity, the greater the impeding effect of each geographic characteristic index on the pollutant transmission, the higher the weight value.

According to the embodiment of the disclosure, the determined weight value may be connected to a pre-constructed weight table corresponding to each geographic grid cell through geographic information system software, and the weight table may include geographic characteristic indexes and weight values thereof included in each geographic grid cell. And different resistance surfaces can be established by geographic information system software based on the landscape type, the soil type, the geographic information and other geographic characteristic indexes, and pollutant transmission resistance values are calculated by a minimum cumulative resistance model (Minimum Cumulative Resistance Model, abbreviated as MCR). The geographic information system software may be software for map creation and spatial data analysis, for example. Specifically, the calculation of the contaminant transport resistance value by the MCR model can be calculated by the following formula (6).

(6)

The MCR is a pollutant transmission resistance value, and can represent the minimum resistance value which is needed to be overcome when the pollutant starts from a geographical grid unit where a precipitation flow-producing event occurs, passes through different types of landscapes, soil types and different geographical factors, and reaches a pollutant collecting area. D is a distance value from the pollutant collecting region j to each geographic grid cell i, and R _i is a weight value corresponding to at least one geographic characteristic index.

According to embodiments of the present disclosure, the hydrologic connectivity of each geographic grid cell may be determined by calculating the contaminant transmission resistance value for each geographic grid cell, with hydrologic connectivity generally better with less contaminant transmission resistance, and with enhanced hydrologic connectivity facilitating the transmission of the contaminant. By comprehensively considering the blocking effect of various geographic characteristic indexes such as landscape type, soil type, geographic information and the like on pollutant transmission, the transmission path and resistance of pollutants from the source to the water body can be simulated, the depicting precision of the pollutant transmission process under a complex landscape structure is improved, and therefore the pollutant transmission resistance value can be accurately determined.

According to embodiments of the present disclosure, each geographic grid cell includes a soil type including, for example, red soil, dark brown soil, and the like. The landscape type included in each geographic grid cell may be determined by landscape morphology spatial pattern analysis (MAPA), and the landscape type index may include at least one landscape morphology including, but not limited to, core areas, islands, etc. The landscape morphology and definition are shown in table 1.

TABLE 1

According to the embodiment of the disclosure, for the landscape morphology indexes, the resistance value between the target plaque and other landscapes can be defined based on the area size, boundary characteristics, connectivity and other morphological attributes of each landscape unit, and the weight value is determined based on the substance transmission capacity of the landscape unit in the ecological process. For example, a core region of larger area has a minimum weight due to the favour of mass exchange, which may be for example 0.2, whereas an isolated plaque of smaller size has the highest weight due to the limited mass transport, which may be for example 1.0. For soil type indicators, soil erosion coefficient values may be determined based on existing data and weight values determined based on the soil erosion coefficient values. For the indexes such as altitude, distance, gradient and the like in the geographic information indexes, the indexes can be divided into 5 grades by a natural breakpoint method, and weight values are determined based on the grades. For the humidity index, its weight is set to 0 or 1 according to whether it generates runoff. The weight value of the vegetation coverage index may be determined from the index coverage percentage.

According to the embodiment of the disclosure, by combining the rainfall event average concentration model, the landscape morphology space pattern analysis and the minimum accumulated resistance model, various factors such as terrain, land utilization, vegetation coverage and the like can be comprehensively considered, the transmission path and resistance of pollutants from the source to the water body are simulated, and the depicting precision of the pollutant transmission process under a complex landscape structure is improved.

The small-river-basin non-point source pollution has the characteristics of wide distribution, spatial variability, randomness and delay effect, for example, the spatial variability shows that pollution loads corresponding to different land utilization types can be different, the randomness and the wide distribution show that the water-lowering flow events occur randomly in time and space respectively, and the delay effect shows that the pollutants cannot influence the water body immediately and are gradually released into the water body through processes such as runoff, soil erosion and the like after a certain time.

The related static model is difficult to capture the characteristics, such as space-time dynamics of pollutant generation and transportation under different rainfall conditions, so that the effectiveness of the model in accurate river basin management is limited, and the accuracy of identifying a small river basin non-point source pollution key source area is low. In addition, the related method is difficult to realize the integrated application of combining the rainfall event average concentration model, the landscape morphology space pattern analysis and the minimum accumulated resistance model, particularly, the event average concentration application model needs high-precision rainfall data support, the existing observation means is difficult to meet the fine simulation requirement of small watershed dimensions, the morphology space pattern analysis lacks a theoretical basis for transformation for pollutant migration analysis, and the coupling of the minimum accumulated resistance and the morphology space pattern analysis involves complex dimensional conversion and parameter matching problems.

According to the embodiment of the disclosure, by generating the theoretical value of the pollutant output quantity and the pollutant transmission resistance value corresponding to the geographic grid unit and generating the actual value of the pollutant output quantity based on the theoretical value of the pollutant output quantity and the pollutant transmission resistance value, an integrated framework combining a rainfall event average concentration model, a landscape morphology space pattern analysis and a minimum accumulation resistance model can be formed, so that a small-river-area-source pollution key source area (Critical Source Areas, abbreviated as CSAs) can be dynamically and accurately identified, a relatively accurate and adaptable tool is provided for specific rainfall pollution control and accurate river-area management, and subsequent water quality improvement on the small-river-area-source pollution key source area is facilitated. Compared with a related static model, an agricultural pollution source recognition theoretical framework based on morphological space mode analysis is constructed, so that the space-time variability of pollutant generation and transmission can be dynamically captured, the accuracy of rainfall event average concentration model application in a small watershed scale is improved, and a minimum accumulated resistance model-morphological space mode analysis parameter transfer algorithm is constructed, so that agricultural small watershed pollutant dynamic simulation can be performed.

According to the embodiment of the disclosure, based on N pollutant transmission resistance values, generating N hydrologic connectivity standard values corresponding to N geographic grid units one by one comprises calculating the inverse value of the pollutant transmission resistance value for each pollutant transmission resistance value to obtain a hydrologic connectivity initial value, and carrying out standardization processing on the hydrologic connectivity initial value to obtain the hydrologic connectivity standard value. The initial value of the hydrologic connectivity can be calculated by the following formula (7), and the standard value of the hydrologic connectivity can be calculated by the following formula (8).

(7)

(8)

Wherein MCR is a pollutant transmission resistance value, CI is a hydrologic connectivity initial value, CI _min、CI_max is the minimum value and the maximum value in N hydrologic connectivity initial values respectively, CI ₁ is a hydrologic connectivity standard value, and the range of the hydrologic connectivity standard value is between 0 and 1.

According to the embodiment of the disclosure, calculating the actual pollutant output value based on the N pollutant output value theoretical values and the N hydrologic connectivity standard values comprises calculating the product of the pollutant output value theoretical values and the hydrologic connectivity standard values corresponding to the geographic grid units for each geographic grid unit to obtain the actual pollutant output value. The actual contaminant output can be calculated by the following equation (9).

(9)

Wherein Pr is the actual pollutant output value of each geographic grid unit, L is the theoretical pollutant output value corresponding to the geographic grid unit, and CI ₁ is the hydrologic connectivity standard value corresponding to the geographic grid unit.

According to the embodiment of the disclosure, the pollution source-flow-sink characteristics of the small-basin surface source are analyzed based on the whole chain of the rainfall process, the average concentration model of rainfall events, the analysis of the landscape morphology space pattern and the minimum accumulation resistance model are introduced, the GIS data and the short-term rainfall observation data are used for running, the physical distance and the topography are considered, the factors such as land utilization and vegetation coverage are integrated, the potential pollution load and hydrologic connectivity are combined, the pollutant transmission path is accurately simulated, the pollutant output characteristics and the key source areas can be dynamically identified in different rainfall events and time periods according to different rainfall events, the pollution change under rainfall driving can be reflected more accurately than the traditional method, the dependence on long-time sequence data is reduced, the identification precision under the complex landscape condition is obviously improved, the method is suitable for the complex small-basin with mosaic distribution of agriculture, living and natural land, the complex structure with coexistence of various land types can be effectively applied, the defect under the complex land use condition is avoided, and the method has higher practicability.

According to an embodiment of the present disclosure, the predetermined classification process includes, for example, performing a natural breakpoint method process on the N actual contaminant output values, resulting in a plurality of categories of actual contaminant output values. The screening of at least one target geographic grid cell from the N geographic grid cells may be, for example, determining a geographic grid cell corresponding to the target contaminant output actual value by using the predetermined type of contaminant output actual value as the target contaminant output actual value, and obtaining the target geographic grid cell. For example, the geographic information system software can be used for carrying out natural breakpoint method processing to obtain the actual value of the class 5 pollutant output quantity, and the actual values of the class 4 pollutant output quantity and the class 5 pollutant output quantity can be used as the actual values of the target pollutant output quantity. The actual values of class 4 and class 5 contaminant output are higher among the N actual values of contaminant output. Based on the preset grading process, the target grid cells are screened out from the geographic grid cells, so that the small-river basin area source pollution key source area can be accurately determined.

The disclosure is further illustrated by the following examples and related test experiments. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. It may be evident, however, that one or more embodiments may be practiced without these specific details. Moreover, the details of the various embodiments below may be arbitrarily combined into other viable embodiments without conflict.

Example 1

In the embodiment, a reservoir is used as a small river basin, and a small river basin surface source pollution key source area in the reservoir is determined, wherein the small river basin surface source pollution key source area can be the surface source pollution key source area of the reservoir. Specifically, rainfall data and runoff observation data of the reservoir region in 20XX years can be collected, the average concentration model of rainfall events is utilized to calculate the non-point source pollutant load under different rainfall events, and the hydrologic connectivity of the reservoir region is analyzed by combining the landscape morphology space pattern analysis and the minimum accumulated resistance model, so that the small-river-basin non-point source pollution key source region is determined. The reservoir region can be subdivided into geographical unit grids with the size of 30m multiplied by 30m based on a geographical information system technology, and weight values are given to geographical property indexes such as geographical property, soil property and vegetation coverage of each geographical unit grid according to data such as a Digital Elevation Model (DEM), a land utilization type, a soil type and vegetation coverage, so that subsequent analysis is facilitated. And collecting rainfall runoff process information of different land utilization types in each geographic grid unit within a preset time period, and generating a rainfall information acquisition table of the research area. Land use types include, for example, road traffic land, living land, cultivated land, garden land, woodland, and the like. The rainfall information acquisition table of the study area is shown in table 2.

TABLE 2

According to the embodiment of the disclosure, the flow and pollution production processes of different land utilization types can be analyzed aiming at the same water-lowering flow event. Fig. 2 schematically illustrates a flow, production analysis results graph for different land use types, in accordance with an embodiment of the present disclosure. The contaminant may be, for example, phosphorus. As shown in fig. 2, the total phosphorus concentration and total phosphorus load corresponding to different land utilization types are different.

According to the embodiment of the disclosure, a preset precipitation threshold value is determined by combining meteorological and hydrological data of the reservoir area and monitoring station management measures, a rainfall event occurring in the reservoir area within a preset time period is divided into a plurality of rainfall types based on the preset precipitation threshold value, the rainfall types comprise small rain, medium rain and heavy rain, wherein the rainfall of 11.4mm is more than or equal to 1.4mm, the rainfall of 24mm is more than or equal to 11.4mm, the rainfall of heavy rain is more than or equal to 24mm, and the average concentration value of pollutants of different land utilization types under different rainfall types is calculated for each geographic grid unit. The average concentration values for the contaminants for the different land use types for the different rainfall types are shown in table 3.

TABLE 3 Table 3

According to the embodiment of the disclosure, the runoff curve number model can be queried based on the accumulated rainfall corresponding to the producible flow of different land utilization types to determine the initial loss rainfall value, the infiltration rainfall value, the loss coefficient and the dimensionless curve number corresponding to each land utilization type, wherein the initial loss rainfall value corresponding to each land utilization type is @) The value of the infiltration rain (S), the loss coefficient (lambda) and the dimensionless number of Curves (CN) are shown in Table 4.

TABLE 4 Table 4

According to embodiments of the present disclosure, total runoff depth values per unit area for different land use types at different precipitation types for 20XX years may be calculated based on the accumulated precipitation amount and the runoff parameter values, as shown in table 5.

TABLE 5

Among other types of precipitation may include light rain, medium rain and heavy rain. The precipitation amount corresponding to small rain is 2-10mm, the precipitation amount corresponding to medium rain is 10-25mm, and the precipitation amount corresponding to large rain is more than 25 mm. The total annual total runoff depth value is the total value of the total runoff depth values of the same rainfall type and the same land utilization type in 20XX years, and can be obtained by adding the total runoff depth value in the high water period, the total runoff depth value in the flat water period and the total runoff depth value in the dead water period, which correspond to the same rainfall type and the same land utilization type in 20XX years. The total runoff depth value of the precipitation can be obtained by calculating the sum of the total runoff depth values of the high water period under each precipitation type, the sum of the total runoff depth values of the flat water period under each precipitation type and the sum of the total runoff depth values of the dead water period under each precipitation type.

According to the embodiment of the disclosure, for each geographic grid cell, a plurality of theoretical pollutant output values corresponding to each geographic grid cell under different precipitation types can be calculated according to the land coverage area, the average pollutant concentration value and the total runoff depth value corresponding to the included land utilization type. Fig. 3 (a), 3 (b), 3 (c) schematically illustrate a schematic diagram of a plurality of theoretical pollutant output values at different precipitation types according to an embodiment of the disclosure. Specifically, fig. 3 (a) -3 (c) schematically show a plurality of theoretical pollutant output values corresponding to a certain geographic grid cell under different precipitation types. The pollutant may be phosphorus and the theoretical value of total phosphorus concentration may be indicative of the theoretical value of output of the pollutant, the theoretical value of total phosphorus concentration being in mg/L. As can be seen from fig. 3, the theoretical pollutant output values for different precipitation types may be different for the same geographical grid cell.

According to embodiments of the present disclosure, landscape types of different land use type patches within each geographic grid cell may be identified using landscape Morphology Spatial Pattern (MSPA) analysis.

Fig. 4 schematically illustrates a schematic view of landscape types for different land utilization types according to an embodiment of the present disclosure. In particular, fig. 4 schematically shows a schematic view of the landscape types of different land use types comprised by a certain geographical grid cell. As shown in fig. 4, the landscape types included in different land use types may be different for the same geographic grid cell.

According to the embodiment of the disclosure, weight values can be given to the view type index, the soil type index and the geographic information index, and the assignment result is connected to the attribute table of each grid through the geographic information system software, and the assignment basis is that the influence of each factor on hydrologic connectivity is large, the larger the blocking effect of each factor on the source pollutant is, the higher the assignment is, and the specific table is shown in table 6. The weight values corresponding to the respective geographic characteristic indexes are shown in table 6, for example, and the geographic characteristic index types and weight values in table 6 are only illustrative, and the specific weight values are not limited thereto. The geographic information system software can be used for data management, map making, space analysis and the like.

TABLE 6

Different resistance surfaces can be established through geographic information system software according to the weight values, each geographic grid unit is a 'sink' by taking a water body in a certain reservoir flow field as a 'source', and a minimum accumulated resistance model (MCR model) is applied to calculate pollutant transmission resistance values of each geographic grid unit. The method can calculate the hydrologic connectivity initial value of each geographic grid unit based on the pollutant transmission resistance value of each geographic grid unit, and perform standardization processing on the hydrologic connectivity initial value to obtain a hydrologic connectivity standard value, wherein the range of the hydrologic connectivity standard value is between 0 and 1.

Fig. 5 (a), 5 (b), 5 (c) schematically illustrate schematic diagrams of the standard values of hydrologic connectivity under different precipitation types according to embodiments of the disclosure. As shown in fig. 5, the hydrologic connectivity standard values corresponding to the same geographic grid cell under different precipitation types may be different.

According to the embodiment of the disclosure, the actual pollutant output value of each geographic grid cell is calculated based on the theoretical pollutant output value and the hydrologic connectivity standard value. The method can divide the actual pollutant output values of the geographic grid cells into 5 categories by using geographic information system software through a natural breakpoint method, wherein the actual pollutant output values of the 4 th category and the 5 th category are higher, and the geographic grid cells corresponding to the actual pollutant output values of the 4 th category and the 5 th category can be used as a small-river basin surface source pollution key source area in a certain reservoir flow field. And the key source area of the small-river-area non-point source pollution can be subjected to key investigation and analysis.

Fig. 6 (a), 6 (b), 6 (c) schematically illustrate diagrams of actual values of pollutant output under different precipitation types according to embodiments of the disclosure. The actual pollutant output can be expressed by the actual total phosphorus concentration in mg/L. As shown in fig. 6, the actual value of the pollutant output at different precipitation types may be different for the same geographical grid cell. The greater the amount of rainfall, the greater the actual value of the pollutant output may be.

The foregoing embodiments have been provided for the purpose of illustrating the general principles of the present disclosure, and are not meant to limit the disclosure to the particular embodiments disclosed, but to limit the scope of the disclosure to the particular embodiments disclosed.

Claims

1. The method for determining the small-river-basin non-point source pollution key source area is characterized by comprising the following steps:

Acquiring a plurality of sets of rainfall runoff process information corresponding to a geographical area to be examined, wherein the plurality of sets of rainfall runoff process information correspond to a plurality of times of rainfall runoff events occurring in the geographical area to be examined, and the geographical area to be examined comprises N geographical grid units;

generating N groups of pollutant output quantity theoretical values corresponding to the N geographic grid units one by one based on the multiple groups of rainfall runoff process information and N groups of land information which are acquired in advance and correspond to the N geographic grid units one by one, wherein the pollutants are generated by the rainfall runoff events;

generating N groups of pollutant transmission resistance values corresponding to the N geographic grid cells one by one based on N groups of geographic information which is acquired in advance and corresponds to the N geographic grid cells one by one;

generating N pollutant output actual values in one-to-one correspondence with the N geographic grid units based on the N pollutant output theoretical values and the N pollutant transmission resistance values;

And screening at least one target geographic grid unit from the N geographic grid units based on the N pollutant output quantity actual values, wherein the target geographic grid unit is used as a small-river basin area source pollution key source area in the geographic area to be examined.

2. The method of claim 1, wherein the step of determining the position of the substrate comprises,

The geographic grid cells correspond to at least one land utilization type;

the land information includes land use type information, and land coverage areas corresponding to the respective land use types.

3. The method of claim 2, wherein each set of the theoretical pollutant output values comprises K theoretical pollutant output values;

The generating N groups of pollutant output quantity theoretical values corresponding to the N geographic grid units one by one based on the multiple groups of rainfall runoff process information and the N groups of land information which is acquired in advance and corresponds to the N geographic grid units one by one comprises:

Determining K precipitation types corresponding to the plurality of groups of precipitation runoff process information based on a preset precipitation threshold;

For each geographic grid unit, calculating K groups of pollutant average concentration values corresponding to the K precipitation types one by one and K groups of total runoff depth values corresponding to the K precipitation types one by one based on K groups of precipitation runoff process information corresponding to the K precipitation types one by one and the land utilization type information corresponding to the geographic grid unit;

And calculating K pollutant output theoretical values corresponding to the K precipitation types one by one based on the K groups of pollutant average concentration values, the K groups of total runoff depth values and the land coverage areas corresponding to the land utilization types aiming at the geographic grid units.

4. The method of claim 3, wherein the step of,

The land use type information comprises runoff parameter values corresponding to the land use types;

the calculating of the K groups of total runoff depth values corresponding to the K precipitation types one by one comprises:

determining at least one runoff parameter value corresponding to the geographic grid cell based on at least one land use type corresponding to the geographic grid cell;

determining at least one cumulative precipitation amount corresponding to the geographic grid cells based on at least one land use type corresponding to the geographic grid cells;

for each precipitation type, calculating a total runoff depth value corresponding to the precipitation type based on at least one runoff parameter value corresponding to the geographic grid unit and at least one accumulated precipitation amount.

5. The method of claim 1, wherein the step of determining the position of the substrate comprises,

The geographic information comprises geographic grid cell distance information and geographic characteristic indexes;

The geographical grid cell distance information includes a distance value of the geographical grid cell to a pollutant collecting area.

6. The method of claim 5, wherein generating N sets of contaminant transfer resistance values corresponding one-to-one to the N geographic grid cells based on the pre-acquired N sets of geographic information corresponding one-to-one to the N geographic grid cells comprises:

Determining, for each of the geographic grid cells, at least one geographic characteristic index corresponding to the geographic grid cell, and determining a weight value corresponding to the at least one geographic characteristic index;

And obtaining a pollutant transmission resistance value corresponding to each geographic grid cell based on the distance value from the geographic grid cell to a pollutant collecting area and a weight value corresponding to the at least one geographic characteristic index.

7. The method of claim 6, wherein the geographic characteristic index comprises a landscape type index, a soil type index, a geographic information index;

The geographic information index comprises at least one of an altitude index, a distance index, a gradient index, a humidity index and a vegetation coverage index.

8. The method of claim 1, wherein the generating N actual contaminant output values in one-to-one correspondence with the N geographic grid cells based on the N theoretical contaminant output values, the N contaminant transfer resistance values comprises:

Generating N hydrologic connectivity standard values in one-to-one correspondence with the N geographic grid units based on the N pollutant transmission resistance values;

And calculating the actual pollutant output value based on the N pollutant output value theoretical values and the N hydrologic connectivity standard values.

9. The method of claim 8, wherein said calculating the actual value of the contaminant output based on the N theoretical values of contaminant output and the N standard values of hydrographic connectivity comprises:

and calculating the product of the theoretical value of the pollutant output quantity corresponding to the geographic grid cells and the standard value of the hydrologic connectivity for each geographic grid cell to obtain the actual value of the pollutant output quantity.

10. The method of claim 1, wherein the screening at least one target geographic grid cell from the N geographic grid cells based on the N actual contaminant output values comprises:

carrying out preset grading treatment on the N pollutant output quantity actual values to obtain grading treatment results;

And screening at least one target geographic grid cell from the N geographic grid cells based on the grading processing result.