Evaluation method of dual risks of water quality and quantity and their cascade transmission in agriculture

Abstract

The application discloses an agricultural water quality and water quantity dual risk and cascade transmission evaluation method, belongs to the technical field of water resource management, and aims at solving the problem that traditional methods only stay in water quantity depletion caused water resource pressure accounting and ignore the risk caused by substandard water quality; the application comprises the following steps: based on a farmland soil nitrogen budget and hydrodynamics coupling model, quantifying the pollution emission list of subdivided sources in the growth process of specific crops, simulating agricultural pollution dilution water consumption; using a crop water requirement model to calculate the irrigation water consumption of specific crops in the whole growth period; using a source and sink corrected physical flow trade model to analyze the virtual water transfer path hidden in each agricultural product trade link; integrating the production end and the consumption end results to realize high-precision grid agricultural water resource supply and demand imbalance risk evaluation and cascade effect analysis; and the cascade transmission effect of the application in evaluating the water resource risk provides strong support for reasonable allocation of agricultural water resources and improvement of nitrogen fertilizer utilization efficiency.

Description

Technical Field

[0001] This invention relates to the field of water resource management technology, specifically to an assessment method for the dual risks of agricultural water quality and quantity and their cascading transmission. Background Technology

[0002] Currently, more than half of the world's population faces a severe dual water shortage dilemma: quantitative shortage caused by insufficient water volume and qualitative shortage caused by the functional degradation (pollution) of water bodies. This phenomenon is primarily caused by the contradiction between ever-increasing water demand and limited supply, coupled with the environmental pressures from the spread of agricultural non-point source pollution and lagging point source wastewater treatment capacity. These adverse trends further exacerbate regional water supply and demand imbalances, highlighting the urgency of comprehensive water quantity and quality management at the watershed and even global scales. Irrigated agriculture, as the world's largest water user sector, consumes over 85% of freshwater resources and contributes nearly 75% of nitrogen water pollution load, becoming a core driving factor in the dual water shortage of both quantity and quality.

[0003] However, previous assessment systems have primarily focused on physical water scarcity caused by water depletion, paying insufficient attention to functional water scarcity caused by water quality deterioration. Even recent studies that have begun to incorporate water pollution dimensions are typically limited to localized analyses at the production end, lacking life-cycle accounting based on the consumption end. This makes it difficult to reveal the virtual water transfer pathways hidden in agricultural trade and the resulting cross-regional cascading effects of water resource risks. Furthermore, existing research often fails to clearly distinguish the heterogeneous impact mechanisms of water depletion and water pollution. For example, some measures aimed at alleviating water shortages may actually exacerbate water quality deterioration. This trade-off severely restricts the formulation of precise and synergistic adaptive strategies, making it difficult for managers to effectively address the combined challenges of water resource depletion and quality degradation. Summary of the Invention

[0004] To address the limitations of the aforementioned background technologies, the present invention aims to construct a complete assessment system for the dual risks of agricultural water quality and quantity, and their cascading transmission. This system can not only accurately quantify the water requirements for pollution dilution and irrigation consumption throughout the entire growth process of a specific crop, but also comprehensively and dynamically assess the cascading transmission effects of agricultural water shortage risks across regions from both production and consumption perspectives. It can also identify specific driving factors contributing to these risks (such as specific crop types, water depletion or pollution, local consumption, or trade-driven factors). Through the methods of this invention, a scientific basis for the sustainable management of agricultural water resources can be provided, significantly improving water resource utilization efficiency, optimizing global and regional water resource allocation, helping to alleviate water shortages caused by the dual pressures of water quantity and quality, ensuring the stable development of agricultural production and the virtuous cycle of the ecological environment, thereby effectively solving the problems of existing technologies' inability to coordinate responses to dual risks and the lack of cross-regional cascading effect assessment.

[0005] To achieve the above objectives, the present invention provides the following technical solution: Assessment methods for the dual risks of agricultural water quality and quantity and their cascading transmission include: Based on a coupled model of nitrogen budget and hydrodynamics in farmland soil, the pollution emission inventory of specific sources during the growth process of a particular crop is quantified, and the water consumption for dilution of agricultural pollution is simulated. Calculate the irrigation water consumption of a specific crop throughout its entire growth period using crop water requirement models; Using the modified physical flow trade model, we analyze the virtual water transfer path implied in each agricultural product trade link, revealing the trade-off and synergistic effect between "water conservation" and "pollution control" implied in cross-regional trade of water quality and quantity risks. By integrating data from both the production and consumption ends, a multi-level water shortage risk tracing system is constructed to achieve a refined analysis of risk sources: at the micro level, the water use characteristics of specific crops are distinguished; at the meso level, the contribution of water quantity and water quality risks is analyzed; and at the macro level, the effects of local consumption-driven and cross-regional trade-driven factors are separated, thereby supporting a high-precision gridded risk assessment and cascading effect analysis of agricultural water supply and demand imbalance. By integrating the results from both the production and consumption ends, this invention achieves high-precision grid-based risk assessment and cascading effect analysis of agricultural water resource supply and demand imbalance. It evaluates the cascading transmission effect of water resource risks, providing strong support for the rational allocation of agricultural water resources and the improvement of nitrogen fertilizer utilization efficiency.

[0006] Preferably, based on a coupled hydrodynamic model of nitrogen budget in farmland soil, the water consumption for pollution dilution during the growth process of 26 specific crops is quantified, and the water consumption for agricultural pollution dilution of specific crops is simulated. The following operations are performed: The 26 crops include staple crops, other cereals, oil crops, sugar crops, starch crops, and other crops; Among them, staple crops include wheat, corn, and rice; Other grains include barley, rye, millet, and sorghum; Oilseed crops include soybeans, sunflowers, peanuts, oil palm fruit, and castor beans; Sugar crops include sugarcane and sugar beets; Starch crops include potatoes and cassava; Other crops include legumes, forage grasses, perennial crops, and annual crops.

[0007] High-precision grid-scale nitrogen pollution in farmland was simulated using computer simulations of 26 crops, and the amount of water used to dilute the pollution was measured using the grey water footprint. The amount of nitrogen entering the water body from crop j in grid i is calculated based on the nitrogen budget of farmland. The formula is as follows: ; In the formula, Indicates fertilizer; Indicates organic fertilizer; This indicates that straw has been returned to the field. Indicates irrigation water; Indicates biological nitrogen fixation; Indicates atmospheric deposition; Indicates crop harvest; This indicates denitrification in air; It indicates that it remains in the soil; The main nitrogen input point of farmland Including fertilizers Organic fertilizer Straw return to the field Irrigation water Biological nitrogen fixation and atmospheric deposition ; Nitrogen output from farmland Including crop harvesting ; The difference between input and output Loss to the environment through denitrification in the air Or leaching runoff into water bodies Or remain in the soil ; Will As input to the reaction kinetic equations to simulate nitrogen pollution from agricultural diffusion sources, the convection-diffusion-dispersion equations are as follows: ; In the formula, This indicates nitrogen concentration, expressed in mg / L. This indicates the velocity of water flow, measured in m / s. This represents the effective diffusion coefficient, with units of m. 2 / s, including mechanical dispersion and molecular diffusion; Indicates source or sink, unit is mg / (L·s); The amount of water used for pollution dilution during the growth of 26 crops was simulated using a computer, and the formula is as follows: ; In the formula, Indicates crops The amount of nitrogen entering the water body during growth, expressed in kg N / ha, is calculated using formulas 1.2 and 1.3. and They are grids The maximum permissible concentration and natural concentration are determined by the World Health Organization and the European Union. The maximum acceptable concentration in freshwater is 10 mg N / L, and the natural concentration of nitrogen in water is approximately 0.4 mg / L.

[0008] Preferably, the irrigation water consumption of a specific crop throughout its entire growth period is calculated using a crop water requirement model, and the following operations are performed: Computer simulations were used to measure the global grid-scale irrigation water consumption of 26 crops. Irrigation water consumption is determined by the portion of crop evapotranspiration that is not effectively replenished by precipitation. Reference crop evapotranspiration This refers to the evapotranspiration of a specific reference crop with adequate water supply and uniform growth, avoiding the need to define separate evapotranspiration levels for each crop and growth stage, and the need to measure or calculate evapotranspiration at different locations or in different seasons. The values ​​are comparable, calculated using the FAO Penman-Monteith formula, which comprehensively considers various meteorological factors, including air temperature, humidity, wind speed, and solar radiation. The formula is as follows: In the formula, This represents the slope of the saturated water vapor pressure curve, in kPa / ℃. This represents the net radiation emitted by the crop surface, expressed in MJ / (m·d). This represents soil heat flux, expressed in MJ / (m·d). This represents the temperature and humidity constant, with units of kPa / ℃; This represents the average daily temperature at a height of 2m, expressed in °C. This indicates the wind speed at a height of 2m, expressed in m / s. This represents the saturated vapor pressure, expressed in kPa. This represents the actual vapor pressure, expressed in kPa. Crop evapotranspiration under standard conditions This is the evapotranspiration measured for crops that are free from pests and diseases, properly fertilized, grown in the field, with optimal soil moisture, and growing vigorously under given climatic conditions. The calculation method is based on the evapotranspiration of a reference crop. And multiply by a coefficient that varies with crop type and growth stage. The formula is as follows: Secondly, crop evapotranspiration under non-standard conditions This refers to the evapotranspiration of crops grown under management or environmental conditions that deviate from standard conditions. In actual field cultivation, adverse factors such as pests and diseases, soil salinization, low soil fertility, water shortage, or waterlogging can lead to a decrease in the actual evapotranspiration of crops compared to standard conditions. This deviation affects crop growth, resulting in insufficient plant density and reduced transpiration, causing it to fall below the required level. At this point, by introducing a water stress coefficient ,exist Based on the calculation, the following is obtained The formula is as follows: In the formula, p represents the ratio of the maximum amount of water that the crop can extract in the rhizosphere to the maximum effective water capacity Smax of the rhizosphere without water stress. It is a function of crop type and potential crop evapotranspiration. Soil moisture content simulated by the soil water balance equation with a time step of days; Based on soil water balance, changes in soil moisture content in the crop root zone are understood by monitoring influent and effluent fluxes. The formula is as follows: In the formula, and express Time and Soil moisture content in the root zone at any given time; Indicates precipitation; Indicates surface runoff; Indicates irrigation water; Indicates capillary rise of water; This indicates soil evaporation; Indicates crop transpiration; Indicates deep infiltration loss; The main sources of water entering the soil include precipitation. Irrigation water Capillary rise Outflow includes surface runoff. Soil evaporation Crop transpiration And deep infiltration losses that will occur if the soil moisture in the root zone exceeds field capacity after heavy rainfall or over-irrigation. ; Among them, deep infiltration loss is equal to the maximum field water holding capacity of the soil, i.e., the reservoir capacity minus the current stored water volume. The maximum water holding capacity in the field is closely related to different soil types; Due to the impact of interannual and intra-annual climate variability on irrigation water consumption, and the lack of annually updated irrigation area data, a fixed irrigation area based on the MIRCA2000 dataset was used. To account for the impact of changes in irrigation area on irrigation water demand, a computer was used to adjust the simulation results using irrigation facility area data, estimating the ratio of annual irrigation facility area to the reference year for each region. This ratio was then applied to each grid cell of the corresponding region to scale the simulated monthly irrigation water consumption, as shown in the following formula: In the formula, This represents the adjusted irrigation water usage for region c in year t for crop j; This represents the simulated irrigation water consumption for the crop in that year; and These represent the irrigation facility coverage area of ​​region c in year t and the reference year, respectively.

[0009] Preferably, a source-sink modified physical flow trade model is used to analyze virtual water transfer, reveal the cross-regional cascading effect of "water quality-water quantity", and perform the following operations: Based on the calculated agricultural irrigation water consumption and polluted water dilution at the production end, the amount and quality of all crop-related water used for final consumption in the region are calculated. By employing a source tracing algorithm to adjust the matrix, crop water use from production to consumption is calculated using the following formula: In the formula, and It is an (i×1) matrix, representing the amount and quality of water consumed by crop j in a region in year t; and It is an (i×1) matrix, representing the amount and quality of water used for crop j planted in a region in year t; It is an (i×i) matrix, representing the proportion of production in region j in year t that is ultimately consumed by region s; The spatial distribution of water consumption at the crop production end is supplemented to each grid. In short, the spatial distribution of water consumption at the grid level based on the consumption end is consistent with the spatial distribution of local crop production. However, due to the differences in the spatial distribution of water consumption and trade ratios in different regions and for different crops, the resulting spatial distribution of water consumption based on the consumption end and the production end will also be different.

[0010] Preferably, this involves controlling water resource consumption caused by grid-scale water quantity and quality. and With available water resources Combining these factors, we can calculate the water resource pressure caused by water depletion and water pollution at the grid scale. and The formula is as follows: In the formula, and These are agricultural water consumption caused by water quantity and water quality, respectively. and These are industrial water consumption caused by water quantity and water quality, respectively. and These are household water consumption caused by water quantity and water quality, respectively. Indicates total runoff. This represents the environmental flow demand, taking into account the environmental flow demand under different scales and flow conditions to ensure river baseflow, wetland recharge, and critical groundwater depth. The calculation formula is as follows: In the formula, Indicates the total amount of available water; It represents the 25th percentile of total available water; when WSI>1, water resources are being used in an unsustainable manner, leading to the depletion of groundwater or runoff.

[0011] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention breaks through the limitations of traditional methods that only focus on macroscopic water allocation. By constructing a coupled hydrodynamic model of farmland soil nitrogen budget and a crop water requirement model, it can accurately simulate and distinguish irrigation water consumption (physical water consumption) and pollution dilution water demand (functional water demand) from specific sources (chemical fertilizers, organic fertilizers, irrigation water, etc.) throughout the entire growth process of a particular crop. This high-precision micro-quantification method enables managers to accurately identify the specific driving factors leading to water shortages (such as specific crop types, simple water depletion, or water pollution), providing a scientific basis for implementing refined water resource management.

[0012] 2. This invention innovatively introduces a source-sink modified physical flow trade model, combining water resource pressures at the production end (local consumption) and the consumption end (virtual water trade). It not only assesses local water shortage risks but also reveals the hidden water resource risk transfer paths embedded in agricultural trade and their cross-regional cascading effects. Through this two-dimensional assessment perspective, this invention can effectively identify which trade links alleviate pressure on one side while exacerbating risks on the other, thus providing decision support for optimizing the global agricultural trade pattern and preventing the cascading spread of risks.

[0013] 3. This invention can quantitatively assess the complex relationship between "water conservation" and "pollution control" objectives for each trade link, identify optimized paths with synergistic effects (both water conservation and pollution reduction), and avoid the trade-offs caused by blindly pursuing a single objective (such as water conservation but increased pollution). This comprehensive assessment system significantly enhances the systematicness and foresight of water resource management, and helps to achieve efficient utilization and rational allocation of water resources, as well as the coordinated development of agricultural production and the ecological environment. Attached Figure Description

[0014] Figure 1 This is a flowchart of the assessment method for the dual risks of agricultural water quality and quantity and their cascading transmission according to the present invention. Figure 2 A schematic diagram of the nitrogen cycle in farmland for assessing the dual risks of agricultural water quality and quantity and their cascading transmission, as presented in this invention. Figure 3 This is a schematic diagram of the soil water balance of irrigated crops, illustrating the assessment method for the dual risks of agricultural water quality and quantity and their cascading transmission according to the present invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] To address the existing challenges posed by both quantitative and qualitative water scarcity, please refer to [link / reference]. Figure 1-3 This embodiment provides the following technical solution: Assessment methods for the dual risks of agricultural water quality and quantity and their cascading transmission include: Based on the coupled hydrodynamic model of nitrogen budget in farmland soil, the amount of water used for pollution dilution during the growth process of specific crops is quantified, and the amount of water used for agricultural pollution dilution is simulated.

[0017] The study employed computer simulations to measure the water consumption for pollutant dilution in 26 crops, and used grey water footprint to measure this consumption. Grey water footprint reflects the amount of freshwater required to absorb pollutant loads in freshwater bodies, taking into account both natural background concentrations and current environmental water quality standards. This method of measurement enables a comparable assessment of water resource risks arising from both quantity and quality. Agricultural activities, such as fertilizers and atmospheric nitrogen inputs, can pollute freshwater bodies through runoff or infiltration.

[0018] The 26 crops include staple crops, other cereals, oil crops, sugar crops, starch crops, and other crops. Among them, staple crops include wheat, corn, and rice; other cereals include barley, rye, millet, and sorghum; oil crops include soybeans, sunflowers, peanuts, oil palm fruit, and castor beans; sugar crops include sugarcane and sugar beets; starch crops include potatoes and cassava; and other crops include legumes, forage grasses, other perennial crops, and other annual crops.

[0019] See Figure 2 A diagram illustrating the nitrogen budget of farmland, where downward arrows represent nitrogen inputs and upward arrows represent nitrogen outputs; The amount of nitrogen entering the water body from crop j in grid i is calculated based on the nitrogen budget of farmland. The formula is as follows: In the formula, Indicates fertilizer; Indicates organic fertilizer; This indicates that straw has been returned to the field. Indicates irrigation water; Indicates biological nitrogen fixation; Indicates atmospheric deposition; Indicates crop harvest; This indicates denitrification in air; It indicates that it remains in the soil; The main nitrogen input point of farmland Including fertilizers Organic fertilizer Straw return to the field Irrigation water Biological nitrogen fixation and atmospheric deposition ; Nitrogen output from farmland Including crop harvesting ; The difference between input and output Loss to the environment through denitrification in the air Or leaching runoff into water bodies Or remain in the soil ; This calculation quantifies water pollution by source, which helps to more accurately identify the main contributing crops to agricultural water quality. j； Will As input to the reaction kinetic equations to simulate nitrogen pollution from agricultural diffusion sources, the convection-diffusion-dispersion equations are as follows: In the formula, This indicates nitrogen concentration, expressed in mg / L. This indicates the velocity of water flow, measured in m / s. This represents the effective diffusion coefficient, with units of m. 2 / s, including mechanical dispersion and molecular diffusion; Indicates the source (such as non-point source pollution input) or sink (such as sediment adsorption), with units of mg / (L·s); The amount of water used for pollution dilution during the growth of 26 crops was simulated using a computer, and the formula is as follows: In the formula, Indicates crops The amount of nitrogen entering the water body during growth, expressed in kg N / ha, is calculated using formulas 1.2 and 1.3. and They are grids The maximum permissible concentration and natural concentration are determined by the World Health Organization and the European Union. The maximum acceptable concentration in freshwater is 10 mg N / L, and the natural concentration of nitrogen in water is approximately 0.4 mg / L.

[0020] By using crop water requirement models, the amount of irrigation water required during the growth process of a specific crop can be calculated, and agricultural irrigation water consumption can be simulated.

[0021] Among them, computer simulations were used to calculate the global grid-scale irrigation water consumption of 26 crops. The irrigation water consumption was determined by the portion of crop evapotranspiration that was not effectively replenished by precipitation. Reference crop evapotranspiration This refers to the evapotranspiration of a specific reference crop with adequate water supply and uniform growth, avoiding the need to define separate evapotranspiration levels for each crop and growth stage, and the need to measure or calculate evapotranspiration at different locations or in different seasons. The values ​​are comparable, calculated using the FAO Penman-Monteith formula, which comprehensively considers various meteorological factors, including air temperature, humidity, wind speed, and solar radiation. The formula is as follows: In the formula, This represents the slope of the saturated water vapor pressure curve, in kPa / ℃. This represents the net radiation emitted by the crop surface, expressed in MJ / (m·d). This represents soil heat flux, expressed in MJ / (m·d). This represents the temperature and humidity constant, with units of kPa / ℃; This represents the average daily temperature at a height of 2m, expressed in °C. This indicates the wind speed at a height of 2m, expressed in m / s. This represents the saturated vapor pressure, expressed in kPa. This represents the actual vapor pressure, expressed in kPa. Crop evapotranspiration under standard conditions This is the evapotranspiration measured for crops that are free from pests and diseases, properly fertilized, grown in the field, with optimal soil moisture, and growing vigorously under given climatic conditions. The calculation method is based on the evapotranspiration of a reference crop. And multiply by a coefficient that varies with crop type and growth stage. The formula is as follows: Secondly, crop evapotranspiration under non-standard conditions This refers to the evapotranspiration of crops grown under management or environmental conditions that deviate from standard conditions. In actual field cultivation, adverse factors such as pests and diseases, soil salinization, low soil fertility, water shortage, or waterlogging can lead to a decrease in the actual evapotranspiration of crops compared to standard conditions. This deviation affects crop growth, resulting in insufficient plant density and reduced transpiration, causing it to fall below the required level. At this point, by introducing a water stress coefficient ,exist Based on the calculation, the following is obtained The formula is as follows: In the formula, p represents the ratio of the maximum amount of water that the crop can extract in the rhizosphere to the maximum effective water capacity Smax of the rhizosphere without water stress. It is a function of crop type and potential crop evapotranspiration. Soil moisture content simulated by the soil water balance equation with a time step of days; Based on soil water balance, changes in soil moisture content in the crop root zone are understood by monitoring influent and effluent fluxes. The formula is as follows: In the formula, and express Time and Soil moisture content in the root zone at any given time; Indicates precipitation; Indicates surface runoff; Indicates irrigation water; Indicates capillary rise of water; This indicates soil evaporation; Indicates crop transpiration; Indicates deep infiltration loss; The main sources of water entering the soil include precipitation. Irrigation water Capillary rise Outflow includes surface runoff. Soil evaporation Crop transpiration And deep infiltration losses that will occur if the soil moisture in the root zone exceeds field capacity after heavy rainfall or over-irrigation. ; Among them, deep infiltration loss is equal to the maximum field water holding capacity of the soil, i.e., the reservoir capacity minus the current stored water volume. The maximum water holding capacity in the field is closely related to different soil types. For example, sandy soil particles are larger and have larger gaps, so water will quickly penetrate into the deeper soil layers or be lost into groundwater, resulting in poor water holding capacity. On the other hand, clay particles are smaller and have strong adhesion, which can better retain water, resulting in a higher maximum water holding capacity. In this study, considering the impact of interannual and intra-annual climate variability on irrigation water consumption, a fixed irrigated area based on the MIRCA2000 dataset (monthly irrigated and rain-fed crop area from 1998 to 2002) was used due to the lack of annually updated irrigated area data. To account for the impact of changes in irrigated area on irrigation water demand, the simulation results were adjusted using irrigation facility area data (FAO database) to estimate the ratio of annual irrigated facility area to the reference year (average from 1998 to 2002) for each region. This ratio was then applied to each grid cell of the corresponding region to scale the simulated monthly irrigation water consumption, as shown in the following formula: In the formula, This represents the adjusted irrigation water usage for region c in year t for crop j; This represents the simulated irrigation water consumption for the crop in that year; and These represent the irrigation facility coverage area of ​​region c in year t and the reference year (1998-2002), respectively.

[0022] By integrating data from both the production and consumption ends, a multi-level water shortage risk tracing system is constructed to achieve a refined analysis of risk sources: at the micro level, the water use characteristics of specific crops are distinguished; at the meso level, the contribution of water quantity and water quality risks is analyzed; and at the macro level, the effects of local consumption-driven and cross-regional trade-driven factors are separated, thereby supporting a high-precision gridded risk assessment and cascading effect analysis of agricultural water supply and demand imbalance.

[0023] Among them, based on the calculated agricultural irrigation water consumption and pollution water dilution at the production end, the amount and quality of all crop-related water used for regional consumption are calculated. By employing a source tracing algorithm to adjust the matrix, crop water use from production to consumption is calculated using the following formula: In the formula, and It is an (i×1) matrix, representing the amount and quality of water consumed by crop j in a region in year t; and It is an (i×1) matrix, representing the amount and quality of water used for crop j planted in a region in year t; It is an (i×i) matrix, representing the proportion of production in region j in year t that is ultimately consumed by region s; The spatial distribution of water consumption at the crop production end is supplemented to each grid. In short, the spatial distribution of water consumption at the grid level based on the consumption end is consistent with the spatial distribution of local crop production. However, due to the differences in the spatial distribution of water consumption and trade ratios in different regions and for different crops, the resulting spatial distribution of water consumption based on the consumption end and the production end will also be different.

[0024] Water consumption caused by grid-scale water quantity and quality and With available water resources By combining natural runoff with environmental flow required to sustain the ecosystem, the water resource pressure caused by water quantity and quality at the grid scale can be calculated. and The formula is as follows: In the formula, and These are agricultural water consumption caused by water quantity and water quality, respectively. and These are industrial water consumption caused by water quantity and water quality, respectively. and These are household water consumption caused by water quantity and water quality, respectively. Indicates total runoff. This represents the environmental flow demand; considering the environmental flow demand under different scales and flow conditions to ensure river baseflow, wetland recharge, and critical groundwater depth, the calculation formula is as follows: In the formula, Indicates the total amount of available water; It represents the 25th percentile of total available water; when WSI>1, water resources are being used in an unsustainable manner, leading to the depletion of groundwater or runoff.

[0025] This section constructs a dual-dimensional assessment of production and consumption based on the perspective of virtual water flow, reveals the risk pattern, and provides a scientific basis for the formulation of differentiated regulation strategies (Table 1). On this basis, it further identifies the causes of water shortage, including unsustainable water quantity (i.e., water supply cannot meet the minimum rigid demand) and unsustainable water quality (the amount of water meeting the standards is insufficient to support the water quality demand).

[0026] Table 1 Water Resources Risk Zoning

[0027] In summary, based on the coupled model of nitrogen budget and hydrodynamics in farmland soil, this study quantifies the pollution emission inventory from various sources during the growth of specific crops and simulates the water consumption for agricultural pollution dilution. It also uses a crop water requirement model to calculate the irrigation water consumption of specific crops throughout their entire growth period. Furthermore, it employs a source-sink modified physical flow trade model to analyze the virtual water transfer paths implicit in each agricultural product trade link, revealing the trade-offs and synergistic effects between "water conservation" and "pollution control" in cross-regional trade involving water quality and quantity risks. Finally, it integrates the results from both the production and consumption ends to achieve a high-precision gridded risk assessment and cascading effect analysis of agricultural water resource supply and demand imbalance.

[0028] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0029] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An assessment method for the dual risks of agricultural water quality and quantity and their cascading transmission, characterized in that, include: Based on a coupled model of nitrogen budget and hydrodynamics in farmland soil, the pollution emission inventory of specific sources during the growth process of a particular crop is quantified, and the water consumption for dilution of agricultural pollution is simulated. Calculate the irrigation water consumption of a specific crop throughout its entire growth period using crop water requirement models; Using the source-source-convergence modified physical trade flow model, we analyze the virtual water transfer path implicit in each agricultural product trade link, revealing the trade-off and synergistic effect between "water conservation" and "pollution control" implied in cross-regional trade of water quality and quantity risks; By integrating data from both the production and consumption ends, a multi-level water shortage risk tracing system is constructed to achieve a refined analysis of risk sources: at the micro level, the water use characteristics of specific crops are distinguished; at the meso level, the contribution of water quantity and water quality risks is analyzed; and at the macro level, the effects of local consumption-driven and cross-regional trade-driven factors are separated, thereby supporting a high-precision gridded risk assessment and cascading effect analysis of agricultural water supply and demand imbalance.

2. The assessment method for the dual risks of agricultural water quality and quantity and their cascading transmission as described in claim 1, characterized in that, Based on a coupled hydrodynamic model of nitrogen budget in farmland soil, the water consumption for pollution dilution during the growth process of 26 specific crops was quantified. Simulations of agricultural pollution dilution water consumption for specific crops were conducted, and the following operations were performed: The 26 crops include staple crops, other cereals, oil crops, sugar crops, starch crops, and other crops; Among them, staple crops include wheat, corn, and rice; Other grains include barley, rye, millet, and sorghum; Oilseed crops include soybeans, sunflowers, peanuts, oil palm fruit, and castor beans; Sugar crops include sugarcane and sugar beets; Starch crops include potatoes and cassava; Other crops include legumes, forage grasses, perennial crops, and annual crops; High-precision grid-scale nitrogen pollution in farmland was simulated using computer simulations of 26 crops, and the amount of water used to dilute the pollution was measured using the grey water footprint. The amount of nitrogen entering the water body from crop j in grid i is calculated based on the nitrogen budget of farmland. The formula is as follows: ； In the formula, Indicates fertilizer; Indicates organic fertilizer; This indicates that straw has been returned to the field. Indicates irrigation water; Indicates biological nitrogen fixation; Indicates atmospheric deposition; Indicates crop harvest; This indicates denitrification in air; It indicates that it remains in the soil; The main nitrogen input point of farmland Including fertilizers Organic fertilizer Straw return to the field Irrigation water Biological nitrogen fixation and atmospheric deposition ; Nitrogen output from farmland Including crop harvesting ; The difference between input and output Loss to the environment through denitrification in the air Or leaching runoff into water bodies Or remain in the soil ; Will As input to the reaction kinetic equations to simulate nitrogen pollution from agricultural diffusion sources, the convection-diffusion-dispersion equations are as follows: ； In the formula, This indicates nitrogen concentration, expressed in mg / L. This indicates the velocity of water flow, measured in m / s. It represents the effective diffusion coefficient, with units of m² / s, and includes mechanical dispersion and molecular diffusion; Indicates source or sink, unit is mg / (L·s); The amount of water used for pollution dilution during the growth of 26 crops was simulated using a computer, and the formula is as follows: ； In the formula, Indicates crops The amount of nitrogen entering the water body during growth, expressed in kg N / ha, is calculated using formulas 1.2 and 1.

3. and They are grids The maximum permissible concentration and natural concentration are determined by the World Health Organization and the European Union. The maximum acceptable concentration in freshwater is 10 mg N / L, and the natural concentration of nitrogen in water is approximately 0.4 mg / L.

3. The assessment method for the dual risks of agricultural water quality and quantity and their cascading transmission as described in claim 2, characterized in that, To calculate the irrigation water consumption of a specific crop throughout its entire growth period using a crop water requirement model, perform the following operations: Computer simulations were used to measure the global grid-scale irrigation water consumption of 26 crops. Irrigation water consumption is determined by the portion of crop evapotranspiration that is not effectively replenished by precipitation. The calculation uses the FAO Penman-Monteith formula, which incorporates various meteorological factors, including air temperature, humidity, wind speed, and solar radiation. The formula is as follows: ； In the formula, This represents the slope of the saturated water vapor pressure curve, in kPa / ℃. This represents the net radiation emitted by the crop surface, expressed in MJ / (m·d). This represents soil heat flux, expressed in MJ / (m·d). This represents the temperature and humidity constant, with units of kPa / ℃; This represents the average daily temperature at a height of 2m, expressed in °C. This indicates the wind speed at a height of 2m, expressed in m / s. This represents the saturated vapor pressure, expressed in kPa. This represents the actual vapor pressure, expressed in kPa. Crop evapotranspiration under standard conditions This is the evapotranspiration measured for crops that are free from pests and diseases, properly fertilized, grown in the field, with optimal soil moisture, and growing vigorously under given climatic conditions. The calculation method is based on the evapotranspiration of a reference crop. And multiply by a coefficient that varies with crop type and growth stage. The formula is as follows: ； Secondly, crop evapotranspiration under non-standard conditions This refers to the evapotranspiration of crops grown under management or environmental conditions that deviate from standard conditions, by introducing the water stress coefficient. ,exist Based on the calculation, the result is obtained The formula is as follows: ； ； In the formula, p represents the ratio of the maximum amount of water extracted by the crop in the root zone to the maximum effective water capacity Smax of the root zone, which is a function of crop type and potential crop evapotranspiration. Soil moisture content simulated by the soil water balance equation with a time step of days; Based on soil water balance, changes in soil moisture content in the crop root zone are understood by monitoring influent and effluent fluxes. The formula is as follows: ； In the formula, and express Time and Soil moisture content in the root zone at any given time; Indicates precipitation; Indicates surface runoff; Indicates irrigation water; Indicates capillary rise of water; This indicates soil evaporation; Indicates crop transpiration; Indicates deep infiltration loss; Soil water inflow includes precipitation Irrigation water Capillary rise Outflow includes surface runoff. Soil evaporation Crop transpiration And deep infiltration losses that will occur if the soil moisture in the root zone exceeds field capacity after heavy rainfall or over-irrigation. ; Among them, deep infiltration loss is equal to the maximum field water holding capacity of the soil, i.e., the reservoir capacity minus the current stored water volume. The maximum water holding capacity in the field is closely related to different soil types; The ratio of annual irrigation facility area to a reference year in each region was estimated using a computer. This ratio was then applied to each grid cell in the corresponding region to scale the simulated monthly irrigation water consumption. The formula is as follows: ； In the formula, This represents the adjusted irrigation water usage for region c in year t for crop j; This represents the simulated irrigation water consumption for the crop in that year; and These represent the irrigation facility coverage area of ​​region c in year t and the reference year, respectively.

4. The assessment method for the dual risks of agricultural water quality and quantity and their cascading transmission as described in claim 3, characterized in that, Using a source-sink modified physical flow trade model, this study analyzes the virtual water transfer paths implicit in each agricultural product trade link, revealing the trade-offs and synergistic effects between "water conservation" and "pollution control" implied in cross-regional trade involving water quality and quantity risks. The following operations are performed: Based on the calculated agricultural irrigation water consumption and polluted water dilution at the production end, the amount and quality of all crop-related water used for final consumption in the region are calculated. By employing a source tracing algorithm to adjust the matrix, crop water use from production to consumption is calculated using the following formula: ； ； In the formula, and It is an (i×1) matrix, representing the amount and quality of water consumed by crop j in a region in year t; and It is an (i×1) matrix, representing the amount and quality of water used for crop j planted in a region in year t; It is an (i×i) matrix, representing the proportion of production in region j in year t that is ultimately consumed by region s.

5. The assessment method for the dual risks of agricultural water quality and quantity and their cascading transmission as described in claim 4, characterized in that, Constructing a multi-level water scarcity risk tracing system enables refined analysis of risk sources: at the micro level, distinguishing water usage characteristics of specific crops; at the meso level, differentiating the contribution of water quantity and water quality risks; and at the macro level, separating the effects of local consumption and cross-regional trade. This supports high-precision grid-based risk assessment and cascading effect analysis of agricultural water supply and demand imbalances, by analyzing water consumption caused by water quantity and quality at the grid scale. and With available water resources This involves combining natural runoff with the environmental flow required to maintain the ecosystem to calculate water resource pressure caused by water depletion and pollution at the grid scale. and The formula is as follows: ； ； In the formula, and These are agricultural water consumption caused by water quantity and water quality, respectively. and These are industrial water consumption caused by water quantity and water quality, respectively. and These are household water consumption caused by water quantity and water quality, respectively. Indicates total runoff. This represents the environmental flow demand, taking into account the environmental flow demand under different scales and flow conditions to ensure river baseflow, wetland recharge, and critical groundwater depth. The calculation formula is as follows: ； In the formula, Indicates the total amount of available water; This represents the 25th percentile of total available water; when WSI > 1, water resources are being used in an unsustainable manner.

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