Grain virtual water flow evaluation method considering irrigation yield increase effect

Abstract

The invention discloses a grain virtual water flow evaluation method considering an irrigation yield increase effect. The method comprises the following steps: S1, acquiring per unit yield and crop production water footprint data of grain crops in a measurement and calculation area in irrigation cultivated land and rain-fed cultivated land in a measurement and calculation time period; s2, acquiring consumption data of various types of grains, and collecting grain yield data to calculate an inter-provincial grain trade network; s3, calculating the amount of water resources needing to be consumed when the grains participating in the trade produce in the output province and the input province respectively through a preset condition that no grain trade occurs; and S4, in combination with the grain trade circulation data and the grain production water footprint data, calculating inter-provincial grain virtual water flow momentum in the year and performing benefit evaluation. According to the method, a more rational grain virtual water flow evaluation method is realized, and reference can be provided for regional grain safety and water resource management.

Description

Technical Field

[0001] This invention belongs to the field, specifically, relates to. Background Technology

[0002] Ensuring food security amidst water scarcity has become a critical global challenge. China faces the challenge of continuously increasing agricultural water demand due to economic growth and changes in dietary structure. Given the uneven distribution of water resources and the mismatch between water and land resources, inter-regional food trade has emerged to address regional food security, accompanied by virtual water flows. Unlike managing water resources through engineering measures, virtual water flows offer a new perspective on addressing resource pressures in agricultural production and consumption. A sound assessment of virtual water resources is a prerequisite and foundation for agricultural water resource management, providing support for policymakers in formulating resource reallocation and sustainable resource development and utilization strategies.

[0003] Virtual water trade is evaluated by comparing the impact of food trade on local water resources before and after it occurs. Most current studies assess the impact of trade on regional water resources based on the water consumption of both trading parties producing the same quantity of food. While this identifies regional differences in water use for food production, it fails to accurately reflect the actual impact of food trade on regional water resources. This evaluation method assumes that the virtual water composition of food (i.e., the ratio of blue water to green water) and water use efficiency remain unchanged before and after trade, which is inconsistent with actual agricultural production and water resource management decisions. Specifically, in resource-constrained environments, managers typically focus on increasing "food yield per unit of water" when facing the need to increase food production. Therefore, as food yields are increased through measures such as efficient irrigation and supplemental irrigation, the amount of virtual water resources contained in crops will also change. The existing evaluation framework ignores three facts: (1) China’s arable land resources are strictly limited, making it impossible to increase grain production by directly expanding the arable land area; (2) Irrigation can significantly increase grain production, and expanding the arable land area under the limited arable land constraints is an effective way to alleviate food shortages; (3) Green water is a water resource derived from precipitation, which has a low opportunity cost, and the effective use of green water helps to optimize resource allocation. Summary of the Invention

[0004] To address the problem that existing virtual water flow evaluation methods for grain lack consideration of arable land constraints and irrigation yield-increasing effects in agricultural production, leading to inconsistencies between these methods and actual agricultural production and water resource management decisions, this invention provides a virtual water flow evaluation method for grain that considers irrigation yield-increasing effects.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for evaluating virtual water flow in grain that considers the yield-increasing effect of irrigation, comprising the following steps:

[0007] S1. Obtain data on the yield per unit area and crop production water footprint of grain crops in irrigated and rain-fed farmland within the measurement period;

[0008] S2. Obtain data on the consumption of various types of grain and combine grain production data to calculate the inter-provincial grain trade network;

[0009] S3. By assuming no grain trade occurs, calculate the amount of water resources required for the production of grain in the exporting and importing provinces.

[0010] S4. Combine grain trade and circulation data with grain production water footprint data to calculate the virtual water flow of grain between provinces within the year and conduct a benefit evaluation.

[0011] Furthermore, the detailed steps of step S1 include:

[0012] Obtain data on grain yield (kg / ha), irrigation area (ha), rain-fed farmland area (ha) within the province, and blue water consumption (m³) for large-scale irrigation areas. 3 Green water volume (m) 3 ;

[0013] Calculate the grain yield per unit area in irrigated farmland and rain-fed farmland separately;

[0014] Calculate the blue water footprint and green water footprint data of grain production.

[0015] Furthermore, the grain yield Y per unit of irrigated cultivated land within the measurement area was calculated. I,i The following formula:

[0016]

[0017] Calculate the grain yield Y per unit of rain-fed cultivated land within the measurement area. R,i The data is shown in the following formula:

[0018]

[0019] Among them, A I,i and A R,i These represent the areas of irrigated and rain-fed farmland in province i, respectively, in ha; A ID,x Y represents the irrigated area of ​​large irrigation district x in province i, in ha; ID,x TY represents the crop yield per unit area of ​​large irrigation district x in province i, expressed in kg / ha; i This represents the total grain output of province i, expressed in kg.

[0020] Furthermore, the blue water footprint (PBWF) of grain production in irrigated farmland within the region was calculated. I,i Green Footprint of Grain Production (PGWF) I,iGreen Water Footprint in Grain Production and Rain-Nourished Farmland (PGWF) G,i The calculation expression is as follows:

[0021]

[0022] In the above formula, BWC I,i GWC I,i GWC G,i These represent the blue water consumption, green water consumption, and green water consumption in rain-fed farmland for grain production in province i, respectively, in m³. 3 ;TY I,i and TY R,i These represent the total grain output in irrigated and rain-fed farmland of province i, respectively, in kg.

[0023] Furthermore, the data on grain consumption by category includes consumption of staple food, feed grain, industrial consumption, seed retention demand, and grain loss.

[0024] Furthermore, the difference between grain production and grain demand within the region is used to calculate the quantity of grain involved in trade, as shown in the following formula:

[0025] T i =TY i -TR i

[0026] Among them, T i This represents the amount of grain traded by province i. A value > 0 indicates participation in grain exports, and a value < 0 indicates participation in grain imports. The unit is kg. i This represents the grain demand of province i, expressed in kg.

[0027] Furthermore, the calculation of the inter-provincial grain trade network adopts a linear optimization method with the objective of minimizing freight costs, implemented using the Linprog function in MATLAB software. The calculation formula is as follows:

[0028]

[0029] Among them, c ij The lowest transportation cost between province i and province j, expressed in yuan / t; T ij S represents the amount of grain exported from province i to province j, in kg; S and D represent the total surplus of all provinces with grain surpluses and the total deficit of all provinces with grain deficits, respectively, in kg; s i and d jThese represent the grain surplus of province J and the grain deficit of province J, respectively, in kg. Since China's grain self-sufficiency rate is less than 1 during the calculation period, and without considering overseas grain imports, to ensure the rational distribution of grain among provinces, it is assumed that the ratio of grain input to demand in all deficit provinces is greater than 80% of China's grain self-sufficiency rate.

[0030] Furthermore, by assuming no grain trade occurs, the water resources required for producing traded grain in both the exporting and importing provinces are calculated. It is important to distinguish that, under the assumption of no trade, to achieve rational resource utilization, grain-exporting regions will prioritize reducing irrigation to conserve blue water resources, while grain-importing regions, given limited arable land, will prioritize increasing irrigation to achieve higher grain production.

[0031] For grain-exporting province i, assuming no grain trade occurs, there are two calculation scenarios: ① By reducing irrigation, it is possible to stop producing grain T that participates in trade. i ② In addition to reducing irrigation, it is also necessary to reduce the area of ​​cultivated land in order to stop producing grain for trade. i .

[0032] In the above situation ①, the production and trade of grain in province i is T i The process only consumed blue water resources (BWF). i The calculation formula is shown below:

[0033] BWF i =A IS,i ×Y I,i ×PBWF I,i

[0034]

[0035] In the formula, A IS,i Assuming no trade occurs, province i can reduce its irrigated area by, in units of ha.

[0036] In the above situation ②, the production and trade of grain in province i is T i The process also consumed blue water BWF. i and Green Water GWF i The calculation formula is shown below:

[0037] BWF i =A IS,i ×Y I,i ×PBWF I,i

[0038] GWF i =A AS,i ×Y R,i ×PGWF R,i

[0039]

[0040] A IS,i =A I,i -A AS,i

[0041] In the formula, A AS,i Let's assume no trade occurs and calculate the area of ​​arable land that province i can reduce, in ha.

[0042] For grain-importing province j, assuming no grain trade occurs, there are two scenarios: ① Grain self-sufficiency can be achieved by supplementing irrigation to existing rainfed farmland; ② Even after supplementing irrigation to all existing rainfed farmland, new farmland is still needed to achieve grain production.

[0043] In the above situation ①, province J produces and trades its own grain T. j Only consumed blue water resources BWF j The calculation formula is shown below:

[0044] BWF j =A IE,j ×Y I,j ×PBWF I,j

[0045]

[0046] In the formula, A AS,i Let's assume that province j produces and trades T of its own grain. j The area of ​​cultivated land requiring supplemental irrigation, in ha;

[0047] In situation ② above, province J produces and trades its own grain T. j New arable land needs to be added, and to maximize resource utilization, this new land must be irrigated. At this time, the production and trade of grain in province J requires the simultaneous consumption of Blue Water (BWF). j and Green Water GWF j The calculation formula is as follows:

[0048] BWF j =(A IE,j +A NA,j )×Y I,j ×PBWF I,j

[0049] GWF j =A NA,j ×PGWF I,j ×Y I,j

[0050] A IE,j =A R,j

[0051]

[0052] In the formula, A R,j The area of ​​rain-fed arable land in province J is expressed in ha; A NA,j This represents the area of ​​newly added arable land required in province J, expressed in ha.

[0053] Furthermore, in step S4, the inter-provincial virtual water trade volume (VWT) for grain... ig Calculate the water resources consumed per unit of traded grain produced in grain-exporting province i, and the corresponding grain trade volume T. ij The product is calculated as follows:

[0054] VWT ij =VBWT ij +VGWT ij =T ij ×(PBWF T,i +PGWF T,i )

[0055] Among them, VBWT ij and VGWT ij These represent the virtual water flow from province i to province j, in meters (m³). 3 ;PBWF T,i and PGWF T,i These represent the amount of blue water and green water resources required to produce one unit of grain trade volume in province i, respectively, in m³. 3 / kg.

[0056] Furthermore, the formula for evaluating the benefits of virtual water flow in grain production between provinces within the year is as follows:

[0057]

[0058] In the formula, n is the number of grain-exporting provinces i; VWS is the virtual water resource saved by grain trade, in m³. 3 .

[0059] The virtual water trade benefit evaluation method aims to assess the impact of virtual water trade on regional resources. Virtual water trade achieves a water-saving effect when it transports water from areas with high water resource utilization efficiency to areas with relatively low efficiency; conversely, it results in waste. Water resource utilization efficiency is the reciprocal of the amount of virtual water contained in each unit of traded food.

[0060] Compared with the prior art, the present invention has the following advantages:

[0061] By considering the constraints of arable land and the effects of irrigation on yield increase in actual agricultural production, this study calculates the inter-provincial grain trade network by combining grain production data and grain production water footprint data. It then calculates the virtual water flow of grain between provinces within the year and conducts a benefit evaluation, thus realizing a more rational evaluation method for virtual water flow of grain, which can provide a reference for regional food security and water resource management. Attached Figure Description

[0062] Figure 1 This is an overall flowchart of a virtual water flow evaluation method for grain considering the yield-increasing effect of irrigation, as described in an embodiment of the present invention. Detailed Implementation

[0063] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0064] like Figure 1 As shown, this embodiment provides a method for evaluating virtual water flow in grain that considers the yield-increasing effect of irrigation, including the following steps:

[0065] S1. Obtain data on the yield per unit area and crop production water footprint of grain crops in irrigated and rain-fed farmland within the measurement period;

[0066] S2. Obtain data on the consumption of various types of grain and combine grain production data to calculate the inter-provincial grain trade network;

[0067] S3. By assuming no grain trade occurs, calculate the amount of water resources required for the production of grain in the exporting and importing provinces.

[0068] S4. Combine grain trade and circulation data with grain production water footprint data to calculate the virtual water flow of grain between provinces within the year and conduct a benefit evaluation.

[0069] The detailed steps of step S1 include:

[0070] Obtain data on grain yield (kg / ha), irrigation area (ha), rain-fed farmland area (ha) within the province, and blue water consumption (m³) for large-scale irrigation areas. 3 Green water volume (m) 3 ;

[0071] Calculate the grain yield per unit area in irrigated farmland and rain-fed farmland separately;

[0072] Calculate the blue water footprint and green water footprint data of grain production.

[0073] Calculate the grain yield Y per unit of irrigated cultivated land in the measurement area. I,i The following formula:

[0074]

[0075] Calculate the grain yield Y per unit of rain-fed cultivated land within the measurement area. R,i The data is shown in the following formula:

[0076]

[0077] Among them, A I,i and A R,i These represent the areas of irrigated and rain-fed farmland in province i, respectively, in ha; A ID,x Y represents the irrigated area of ​​large irrigation district x in province i, in ha; ID,x TY represents the crop yield per unit area of ​​large irrigation district x in province i, expressed in kg / ha; i This represents the total grain output of province i, expressed in kg.

[0078] Calculate the blue water footprint (PBWF) of grain production in irrigated farmland within the region. I,i Green Footprint of Grain Production (PGWF) I,i Green Water Footprint in Grain Production and Rain-Nourished Farmland (PGWF) G,i The calculation expression is as follows:

[0079]

[0080]

[0081] In the above formula, BWC I,i GWC I,i GWC G,i These represent the blue water consumption, green water consumption, and green water consumption in rain-fed farmland for grain production in province i, respectively, in m³. 3 ;TY I,i and TY R,i These represent the total grain output in irrigated and rain-fed farmland of province i, respectively, in kg.

[0082] Furthermore, the data on grain consumption by category includes consumption of staple food, feed grain, industrial consumption, seed retention demand, and grain loss.

[0083] The difference between grain production and grain demand within the region is used to determine the quantity of grain involved in trade, calculated as follows:

[0084] T i =TY i -TR i

[0085] Among them, T iThis represents the amount of grain traded by province i. A value > 0 indicates participation in grain exports, and a value < 0 indicates participation in grain imports. The unit is kg. i This represents the grain demand of province i, expressed in kg.

[0086] The calculation of the inter-provincial grain trade network adopts a linear optimization method with the objective of minimizing freight costs, implemented using the Linprog function in MATLAB software. The calculation formula is as follows:

[0087]

[0088] Among them, c ij The lowest transportation cost between province i and province j, expressed in yuan / t; T ij S represents the amount of grain exported from province i to province j, in kg; S and D represent the total surplus of all provinces with grain surpluses and the total deficit of all provinces with grain deficits, respectively, in kg; s i and d j These represent the grain surplus of province J and the grain deficit of province J, respectively, in kg. Since China's grain self-sufficiency rate is less than 1 during the calculation period, and without considering overseas grain imports, to ensure the rational distribution of grain among provinces, it is assumed that the ratio of grain input to demand in all deficit provinces is greater than 80% of China's grain self-sufficiency rate.

[0089] By assuming no grain trade, the water resources required for producing traded grain in both exporting and importing provinces are calculated. It's important to distinguish that, under the assumption of no trade, to optimize resource utilization, grain-exporting regions will prioritize reducing irrigation to conserve blue water resources, while grain-importing regions, with limited arable land, will prioritize increasing irrigation to boost grain production.

[0090] For grain-exporting province i, assuming no grain trade occurs, there are two calculation scenarios: ① By reducing irrigation, it is possible to stop producing grain T that participates in trade. i ② In addition to reducing irrigation, it is also necessary to reduce the area of ​​cultivated land in order to stop producing grain for trade. i .

[0091] In the above situation ①, the production and trade of grain in province i is T i The process only consumed blue water resources (BWF). i The calculation formula is shown below:

[0092] BWF i =A IS,i ×Y I,i ×PBWF I,i

[0093]

[0094] In the formula, A IS,i Assuming no trade occurs, province i can reduce its irrigated area by, in units of ha.

[0095] In the above situation ②, the production and trade of grain in province i is T i The process also consumed blue water BWF. i and Green Water GWF i The calculation formula is shown below:

[0096] BWF i =A IS,i ×Y I,i ×PBWF I,i

[0097] GWF i =A AS,i ×Y R,i ×PGWF R,i

[0098]

[0099] A IS,i =A I,i -A AS,i

[0100] In the formula, A AS,i Let's assume no trade occurs and calculate the area of ​​arable land that province i can reduce, in ha.

[0101] For grain-importing province j, assuming no grain trade occurs, there are two scenarios: ① Grain self-sufficiency can be achieved by supplementing irrigation to existing rainfed farmland; ② Even after supplementing irrigation to all existing rainfed farmland, new farmland is still needed to achieve grain production.

[0102] In the above situation ①, province J produces and trades its own grain T. j Only consumed blue water resources BWF j The calculation formula is shown below:

[0103] BWF j =A IE,j ×Y I,j ×PBWF I,j

[0104]

[0105] In the formula, A AS,i Let's assume that province j produces and trades T of its own grain. j The area of ​​cultivated land requiring supplemental irrigation, in ha;

[0106] In situation ② above, province J produces and trades its own grain T.j New arable land needs to be added, and to maximize resource utilization, this new land must be irrigated. At this time, the production and trade of grain in province J requires the simultaneous consumption of Blue Water (BWF). j and Green Water GWF j The calculation formula is as follows:

[0107] BWF j =(A IE,j +A NA,j )×Y I,j ×PBWF I,j

[0108] GWF j =A NA,j ×PGWF I,j ×Y I,j

[0109] A IE,j =A R,j

[0110]

[0111] In the formula, A R,j The area of ​​rain-fed arable land in province J is expressed in ha; A NA,j This represents the area of ​​newly added arable land required in province J, expressed in ha.

[0112] In step S4, the inter-provincial virtual water trade volume (VWT) for grain is... ig Calculate the water resources consumed per unit of traded grain produced in grain-exporting province i, and the corresponding grain trade volume T. ij The product is calculated as follows:

[0113] VWT ij =VBWT ij +VGWT ij =T ij ×(PBWF T,i +PGWF T,i )

[0114] Among them, VBWT ij and VGWT ij These represent the virtual water flow from province i to province j, in meters (m³). 3 ;PBWF T,i and PGWF T,i These represent the amount of blue water and green water resources required to produce one unit of grain trade volume in province i, respectively, in m³. 3 / kg.

[0115] Formula for evaluating the benefits of virtual water flow in grain production between provinces within the year:

[0116]

[0117] In the formula, n is the number of grain-exporting provinces i; VWS is the virtual water resource volume that grain trade can save for China, in meters. 3 .

[0118] The virtual water trade benefit evaluation method aims to assess the impact of virtual water trade on regional resources. Virtual water trade achieves a water-saving effect when it transports water from areas with high water resource utilization efficiency to areas with relatively low efficiency; conversely, it results in waste. Water resource utilization efficiency is the reciprocal of the amount of virtual water contained in each unit of traded food.

[0119] Compared with the prior art, the present invention has the following advantages:

[0120] By considering the constraints of arable land and the effects of irrigation on yield increase in actual agricultural production, this study calculates the inter-provincial grain trade network by combining grain production data and grain production water footprint data. It then calculates the virtual water flow of grain between provinces within the year and conducts a benefit evaluation, thus realizing a more rational evaluation method for virtual water flow of grain, which can provide a reference for regional food security and water resource management.

[0121] The above provides a detailed description of a virtual water flow evaluation method for grain that considers the yield-increasing effect of irrigation, as provided in this application. The specific embodiments are described only to aid in understanding the method and its core ideas. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims.

Claims

1. A method for evaluating virtual water flow of grain considering the effect of irrigation yield increase, characterized in that, The method comprises the steps of: S1, obtaining the yield of grain crops in irrigated farmland and rain-fed farmland and the water footprint data of crop production in the calculation period and calculation area; S2, obtaining the consumption data of various types of grain, and calculating the inter-provincial grain trade network by combining the grain production data; S3, under the condition that no grain trade occurs, the water resources consumed by the grain trade in the output province and the input province are calculated respectively; S4, combining the grain trade circulation data and the grain production water footprint data, the inter-provincial grain virtual water flow quantity in the year is calculated and the benefit is evaluated.

2. The method for evaluating virtual water flow of grain considering the effect of irrigation yield increase according to claim 1, characterized in that, The detailed steps of step S1 include: Obtaining the grain yield data, irrigated area, rain-fed farmland area, blue water consumption and green water consumption of grain in the province; Calculating the grain yield data in irrigated farmland and rain-fed farmland respectively; Calculating the blue water footprint and green water footprint data of grain production.

3. The method for evaluating virtual water flow of grain considering the effect of irrigation yield increase according to claim 2, characterized in that, The grain yield per unit of irrigated farmland in the calculation area is calculated as follows: The grain yield per unit of rain-fed farmland in the calculation area is calculated as follows: Wherein, A I,i and A R,i are the area of irrigated farmland and rain-fed farmland in i province respectively, A ID,x is the irrigated area of large irrigation area x in i province, Y ID,x is the crop yield per unit of large irrigation area x in i province, TY i is the total grain output of i province, Y I,i is the grain yield per unit of irrigated farmland in the calculation area, Y R,i is the grain yield per unit of rain-fed farmland in the calculation area.

4. The method for evaluating virtual water flow of grain considering the effect of irrigation yield increase according to claim 3, characterized in that, The calculation expressions of the blue water footprint of grain production in irrigated farmland, the green water footprint of grain production in irrigated farmland and the green water footprint of grain production in rain-fed farmland in the calculation area are as follows: Where BWC I,i , GWC I,i , and GWC G,i are the blue water consumption, green water consumption in irrigated cropland, and green water consumption in rain-fed cropland of grain production in i province, respectively, TY I,i and TY R,i are the total grain yield in irrigated cropland and rain-fed cropland in i province, respectively, PBWF I,i is the blue water footprint of grain production in irrigated cropland in the region, PGWF I,i is the green water footprint of grain production, and PGWT G,i is the green water footprint of grain production in rain-fed cropland.

5. The method for virtual water flow evaluation of grain considering the effect of irrigation yield increase according to claim 4, characterized in that, The difference between the grain yield and the grain demand in the calculation area is the amount of grain involved in trade, and the calculation formula is as follows: T i = TY i - TR i Wherein, T i is the amount of grain that i province participates in trade, T i the value > 0 represents participating in grain export, T i the value < 0 represents participating in grain import, TR i is the grain demand of i province.

6. The method for virtual water flow evaluation of grain considering the effect of irrigation yield increase according to claim 5, characterized in that, The inter-provincial grain trade network is calculated by using the linear optimization method with the minimum transportation cost as the target, and the calculation formula is as follows: where c ij is the minimum transportation cost between i and j provinces, T ij is the amount of grain exported from i to j, S and D are the total surplus of all surplus provinces and the total deficit of all deficit provinces, respectively, s i and d j are the surplus of i and the deficit of j, respectively.

7. The method for evaluating virtual water flow of grain considering the effect of irrigation yield increase according to claim 6, characterized in that, For the grain output province i, under the condition that no grain trade occurs, there are two calculation cases: ① by reducing irrigation, the grain involved in trade is no longer produced, and ② the cultivated land area is reduced; In the above case ①, the process of producing trade grain in i province only consumes blue water resources, and the calculation formula is as follows: BWF i = A IS,i x Y I,i x PBWF I,i In the formula, A IS,i is the irrigation area that i province can reduce under the assumption that no trade occurs, BWF i is the blue water resource, T i is the tradeable grain produced by i province; In the above case ②, the process of producing trade grain in i province consumes blue water resources and green water resources, and the calculation formula is as follows: BWF i = A IS,i x Y I,i x PBWF I,i GWF i = A AS,i x Y R,i x PGWF R,i A IS,i = A I,i - A AS,i wherein A AS,i is the reduced arable land area of i province under the assumption that no trade occurs, BWF i is blue water resources, GWF i is green water resources; For the grain input province j, under the condition that no grain trade occurs, there are also two cases: ① by supplementing irrigation in the existing rain-fed farmland, the grain is self-sufficient; ② after supplementing irrigation in the existing rain-fed farmland, new cultivated land is still needed to realize grain production; In the above case ①, the process of producing trade grain in j province only consumes blue water resources, and the calculation formula is as follows: BWF j = A IE,j × Y I,j × PBWF I,j In the formula, A AS,i is the amount of self-produced trade grain T j the area of farmland that needs supplemental irrigation; In the above case ②, j province self-produced trade grain T j When new farmland area needs to be increased, j province produces trade grain, which needs to consume blue water resources and green water resources at the same time. The calculation formula is as follows: BWF j = (A IE,j + A NA,j ) x Y I,j x PBWF I,j GWF j = A NA,j x PGWF I,j x Y I,j A IE,j = A R,j In the formula, A R,j is the existing rain-fed farmland area in j province, A NA,j is the farmland area that needs to be newly added in j province.

8. The method for evaluating virtual water flow of grain considering the effect of irrigation yield increase according to claim 7, characterized in that, In step S4, the inter-provincial grain virtual water trade quantity is calculated as the product of the water resources consumed by the production of unit trade grain in the grain output province i and the corresponding grain trade quantity, and the calculation formula is as follows: VWT ij = VBWT ij + VGWT ij = T ij × (PBWF T,i + PGWF T,i ) where VBWT ij and VGWT ij are the virtual water amounts of i province flowing to j province, PBWF T,i and PGWF T,i are the blue water and green water amounts consumed by i province to produce one unit of grain trade, VWT ig is the inter-provincial grain virtual water trade amount, and T ij is the corresponding grain trade amount.

9. The method for evaluating virtual water flow of grain considering the effect of irrigation yield increase according to claim 8, characterized in that, The benefit evaluation formula of inter-provincial grain virtual water flow quantity in the year is as follows: In the formula, n is the number of grain output provinces i; VWS is the virtual water resource quantity that can be saved by grain trade.

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