A method for calculating and evaluating minimum ecological water requirement of lakes based on aeolian sandy land

Abstract

This invention discloses a method for calculating and evaluating the minimum ecological water requirement of a sandy lake in a wind-blown sandy area. The lake is a truncated cone-shaped lake. The method includes the following steps: 1) collecting meteorological and lake data, constructing a lake water level-area relationship function, and calculating the lake's water volume; 2) analyzing the relationship between lake water level and surface area, and determining the inflection point of the lake's surface area change with water level; 3) constructing a mathematical equation for groundwater-lake exchange and determining the recharge and discharge relationship between groundwater and the lake; 4) estimating the lake's minimum ecological water requirement; 5) finally, evaluating whether the lake's ecological function meets the standards by comparing the measured area of ​​the lake with the minimum surface area. This invention can achieve the evaluation and early warning of the ecological function of a lake ecosystem. It is applicable to typical sandy lakes in wind-blown sandy areas where field parameter acquisition is difficult and hydrogeological conditions are complex. The method is simple to operate and easy to promote and apply.

Description

Technical Field

[0001] This invention belongs to the field of eco-hydrology, specifically relating to a method for calculating and evaluating the minimum ecological water demand of lakes in sandy and windy areas. Background Technology

[0002] Lakes are an important component of the terrestrial hydrosphere and water cycle, especially inland lakes in arid regions. Their unique hydrological, hydrochemical, and aquatic ecological properties play a crucial role in maintaining local lake ecosystems and regional balance. Arid-region lake ecosystems are complex entities composed of lake basins, lake water, water properties, and aquatic organisms; they are also known as water purification ecosystems within aquatic ecosystems. In recent years, affected by climate change and human activities, lakes in the Mu Us Desert have been continuously drying up and shrinking, with severe water pollution. The ecological crisis of lakes and the resulting resource-based and water quality-based water shortages are becoming increasingly serious. Maintaining reasonable water levels in lakes and reservoirs has become a fundamental guarantee for the scientific allocation and sustainable use of water resources. However, how to determine reasonable lake water levels, ensure the minimum ecological water demand of lake ecosystems, and balance the contradiction between water supply and demand are urgent problems to be solved in lake ecological environmental protection.

[0003] Currently, the main methods for calculating the minimum ecological water requirement of lakes include: the curve correlation method, the functional method, the minimum water level method, and the water exchange cycle method. All of these methods have the following drawbacks: the functional method, while comprehensively considering the water resource functions of lakes, neglects the influence of hydrological conditions; the curve correlation method fully reflects the relationship between the lake ecosystem status and water volume, but its limitation lies in requiring a large amount of continuous ecological function index data and corresponding hydrological data; the minimum water level method, while considering the dynamic impact of hydrological conditions on the lake system, requires the collection of a large amount of natural water level data for establishing a dynamic model in practical applications; and the water exchange cycle method is suitable for closed lakes with minimal human interference or lakes with abundant flow and requires corresponding historical hydrological data.

[0004] In summary, for areas like the Mu Us Desert, where hydrological data is scarce and long-sequence data collection is difficult, it is necessary to propose a method for calculating the minimum ecological water demand and evaluating the ecological function of typical lakes in sandy deserts, in order to maintain the allocation and sustainable use of lake water resources.

[0005] In view of this, the present invention provides a method for calculating and evaluating the minimum ecological water demand of lakes in sandy and windy areas, in order to overcome the shortcomings of the prior art. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for calculating and evaluating the minimum ecological water demand of lakes in sandy and aeolian sandy areas. This method is applicable to frustum-shaped lakes with difficult parameter acquisition and complex hydrogeological conditions, such as frustum-shaped lakes in the Mu Us Desert. The principle of this invention can also be applied to other lake morphologies. At the same time, the operation method of this invention is simple and easy to promote and apply.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for calculating and evaluating the minimum ecological water requirement of lakes in sandy wastelands, wherein the sandy wasteland lakes are truncated cone-shaped lakes, specifically includes the following steps:

[0009] Step S1: Collect meteorological data in the study area, interpret the lake water area distribution based on remote sensing images, and construct a lake water level-area relationship function with the measured lake water level data; at the same time, calculate the volume of typical lake water bodies in sandy areas based on the lake water surface area interpreted by remote sensing.

[0010] Step S2: Based on the lake water level-area relationship function constructed in Step S1, draw a lake water level-area relationship map over the years. Based on the trend of the lake water level-area relationship map, determine the turning point of the lake water surface area changing with the lake water level. This turning point corresponds to the lowest ecological water level of the lake system.

[0011] Step S3: Construct a mathematical equation for the exchange between groundwater and lake based on the groundwater level and lake surface area, and determine the recharge and discharge relationship between groundwater and lake;

[0012] Step S4: Based on steps S2-S3 and in accordance with the principle of water balance, estimate the minimum ecological water demand of the lake;

[0013] Step S5: Calculate the minimum ecological water surface area of ​​the lake based on the minimum ecological water requirement of the lake determined in Step S4. Use this as the basis for the ecological environment assessment of the lake ecosystem and evaluate whether the lake's ecological function meets the standards.

[0014] Furthermore, the specific process of constructing the lake water level-area relationship function in step S1 is as follows:

[0015] First, the normalized water index is calculated for the remote sensing image covering the lake area. The formula is: NDWI=(p(Green)-p(NIR)) / (p(Green)+p(NIR)); where NDWI is the normalized water index, and p(Green) and p(NIR) are the pixel values ​​of the green band and near-infrared band of the remote sensing image, respectively.

[0016] Then, select a reasonable threshold for NDWI (e.g., 0 < NDWI < 1) to extract the lake water area, calculate its total area, and correspond it with the lake water level data on the observation date of the remote sensing image one by one. Use the lake water surface area as a functional index to establish a lake water level-area relationship function S(h).

[0017] Further, the lake water volume in step S1 is as follows:

[0018] Then H A is:

[0019] In the formula: V is the lake water volume, with the unit of m 3 ; A is the lake water surface area obtained by remote sensing interpretation in the current year; B is the lake bottom area obtained by consulting historical data; R1 is the lake water surface radius, with the unit of m; R2 is the lake bottom radius, with the unit of m; H A is the lake water level elevation, with the unit of m; H B is the height from the lake bottom to the cone, with the unit of m.

[0020] Further, for each unit increase or decrease in the water level corresponding to the turning point in step S2, the lake water surface area will change significantly, that is, the lake ecological function will also change significantly. If this water level is near the multi-year average water level of the lake, then this maximum value is considered to be the lowest ecological water level H min of the lake, and the lowest ecological water level H min is used as the ecological function warning water level of the lake ecosystem.

[0021] Further, the specific process of step S3 is as follows:

[0022] Take the top of the cone formed by the lake water surface and the lake bottom as (0,0), the direction perpendicular to the lake water surface as the ordinate, and the direction parallel to the lake water surface as the abscissa to establish a rectangular coordinate system, and construct a mathematical model of the groundwater-lake exchange volume, that is, the groundwater-lake recharge and discharge relationship equation:

[0023] Among them, W q (t) is the exchange volume between the lake and groundwater in year t, H(t) is the average elevation of the groundwater level around the lake in year t, with the unit of m; M is the average thickness of the lake bottom silt layer, with the unit of m; H A (t) is the lake water level elevation in year t, with the unit of m; K is the vertical permeability coefficient of the lake silt layer, with the unit of m / d; B(t) is the lake bottom area in year t.

[0024] Further, if the groundwater-lake recharge and discharge relationship is: H > H A , groundwater recharges the lake; if H ≤ H AThe lake replenishes groundwater; among which, H A H represents the lake's water level elevation, and H represents the groundwater level elevation around the lake.

[0025] Furthermore, the specific process for estimating the minimum ecological water requirement of the lake in S4 is as follows:

[0026] Assuming zero change in lake water volume, the replenishment of the lake ecosystem equals the consumption, which is the minimum water volume required to maintain the lake's normal ecological functions. Under natural conditions, the ecological water requirement of the lake area equals the sum of lake evaporation and groundwater-lake exchange, minus the lake area's precipitation. When evaporation is high or rainfall is low, evaporation and exchange are approximated as the lake's minimum ecological water requirement, i.e., the formula is: W min (t)=W q (t)+A(t)E(t);

[0027] Among them, W min (t) represents the minimum ecological water demand of the lake at time t, W q (t) represents the amount of water exchanged between the lake and groundwater in year t, A(t) represents the minimum ecological water surface area of ​​the lake in year t, and E(t) represents the annual evaporation in year t.

[0028] Furthermore, the specific process of step S5 is as follows:

[0029] Based on the minimum ecological water requirement of the lake estimated in step S4, and the minimum water level required to maintain the various components of the lake ecosystem and meet the main ecological functions of the lake, the minimum ecological water surface area of ​​the lake is determined, namely:

[0030]

[0031] Among them, H min To maintain the minimum water level required to sustain all components of the lake ecosystem and meet the lake's main ecological functions; W min (t) represents the minimum ecological water demand of the lake at time t; A(t) represents the minimum ecological water surface area of ​​the lake in year t.

[0032] The criteria for evaluating whether a lake's ecological function meets the standards are: the measured value of the lake area and the average value f of the minimum ecological water surface area. If the ratio f ≥ 1, the lake's ecological function is considered to meet the standards; if the ratio 0.5 ≤ f < 1, the lake's ecological function is considered to be relatively poor; if the ratio f < 0.5, the lake's ecological function is considered to be poor.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] This invention provides a method for calculating and evaluating the minimum ecological water requirement of lakes in sandy desert areas. Primarily targeting the Mu Us Desert sandy desert region, where hydrological data is scarce and long-sequence data collection is difficult, this method constructs a lake water level-area relationship function and calculates the lake's water volume based on remote sensing image interpretation. Finally, it estimates the minimum ecological water requirement of the lake and calculates the minimum ecological water surface area from this requirement, serving as the basis for evaluating the ecological environment of the lake's ecosystem, thereby maintaining the sustainable use of lake water resources. This method is applicable to truncated cone-shaped lakes where parameter acquisition is difficult and hydrogeological conditions are complex. Furthermore, the method is simple to operate and easy to promote and apply. Attached Figure Description

[0035] The accompanying drawings are incorporated in and form part of this specification, and together with the description serve to explain the principles of the invention.

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the process of this invention;

[0038] Figure 2 This is a schematic diagram of the typical lake water volume of the present invention;

[0039] Figure 3 This is a schematic diagram illustrating the concept of groundwater-lake interaction in this invention;

[0040] Figure 4 This is a schematic diagram illustrating the relationship between the lake surface area and water level in an embodiment of the present invention;

[0041] Figure 5 This is a schematic diagram illustrating the relationship between lake and groundwater replenishment and discharge in an embodiment of the present invention. Detailed Implementation

[0042] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses consistent with some aspects of the invention as detailed in the appended claims.

[0043] See Figure 1As shown, this invention provides a method for calculating and evaluating the minimum ecological water requirement of sandy lakes, which are generally truncated cone-shaped lakes. The method specifically includes the following steps:

[0044] Step S1: Collect meteorological data in the study area, interpret the lake water area distribution based on remote sensing images, and construct a lake water level-area relationship function with the measured lake water level data; at the same time, calculate the volume of typical lake water bodies in sandy areas based on the lake water surface area interpreted by remote sensing.

[0045] Specifically, based on the interpretation of remote sensing imagery, the distribution area of ​​lake water bodies is as follows:

[0046] First, the Normalized Difference Water Index (NDWI) is calculated for the Landsat image covering the lake area. The formula is: NDWI = (p(Green) - p(NIR)) / (p(Green) + p(NIR)); where NDWI is the normalized water index, and p(Green) and p(NIR) are the pixel values ​​of the green band and near-infrared band of the remote sensing image, respectively.

[0047] Then, a reasonable threshold for NDWI (e.g., NDWI>0) is selected to extract the lake's water area, its total area is calculated, and it is matched one-to-one with the lake water level data of the remote sensing image observation date. The lake water surface area is used as a functional indicator to establish the lake water level-area relationship curve S(h).

[0048] Calculation of the volume of a typical lake in a sandy beach area based on the lake surface area interpreted by remote sensing: Then H A for:

[0049] ∵

[0050]

[0051] ∴

[0052] Furthermore, according to the principle of similar triangles,

[0053]

[0054] That is, to obtain the final result

[0055] In the formula: V is the volume of lake water, in meters. 3 A represents the lake's surface area obtained from remote sensing interpretation in that year; B represents the lake's bottom area obtained from historical data; R1 is the lake's surface radius in meters; R2 is the lake's bottom radius in meters; H ALake water level elevation, in meters (m); H B The height from the lake bottom to the cone is in meters (m).

[0056] Step S2: Based on the lake water level-area relationship function constructed in Step S1, draw the lake water level-area relationship map over the years. Based on the trend of the lake water level-area relationship map, determine the turning point of the lake water surface area change with the lake water level, which corresponds to the lowest ecological water level of the lake system.

[0057] Specifically, in step S2, for every unit increase or decrease in the water level corresponding to the turning point, the lake's surface area will change significantly, meaning the lake's ecological function will also change significantly. If this water level is near the lake's multi-year average water level, then this maximum value is considered the lake's minimum ecological water level H. min The lowest ecological water level H of the lake min This serves as an early warning level for the ecological function of the lake's ecosystem.

[0058] Step S3: Construct a mathematical equation for the exchange between groundwater and lake based on the groundwater level and lake surface area, and determine the recharge and discharge relationship between groundwater and lake;

[0059] Specifically, based on the schematic diagram of the lake's water volume, a rectangular coordinate system is established with the top of the cone formed by the lake surface and bottom as (0, 0), the direction perpendicular to the lake surface as the ordinate, and the direction parallel to the lake surface as the abscissa. A mathematical model of the groundwater-lake exchange rate is then constructed based on this system, namely, the equation governing the recharge and discharge relationship between groundwater and the lake:

[0060]

[0061] Among them, W q H(t) represents the amount of water exchanged between the lake and groundwater in year t; H(t) represents the average elevation of the groundwater level around the lake in year t, in meters; M represents the average thickness of the silt layer at the bottom of the lake, in meters; H A (t) represents the lake water level elevation in year t, in meters; K represents the vertical permeability coefficient of the lake silt layer, in m / d; B(t) represents the lake bottom area in year t.

[0062] When the recharge and discharge relationship between groundwater and lakes is: H > H A If groundwater replenishes the lake; if H ≤ H A The lake replenishes groundwater.

[0063] Step S4: Based on steps S2-S3 and in accordance with the principle of water balance, estimate the minimum ecological water demand of the lake;

[0064] Specifically, lakes in arid regions are all closed-flow lakes, mainly replenished by precipitation and groundwater, with no surface runoff in or out, and discharge mainly through evaporation and seepage; they are not used for industrial or agricultural purposes, and saline lakes are unsuitable for livestock drinking water. Therefore, by substituting the lake surface area into the equation, the lake water balance formula can be rewritten as: dV / dt=A(t)P(t)-A(t)E(t)-W q (t),

[0065] Assuming zero change in lake water volume, the replenishment of the lake ecosystem equals the consumption, which is the minimum water volume required to maintain the lake's normal ecological functions. Under natural conditions, the ecological water requirement of the lake area equals the sum of lake evaporation and groundwater-lake exchange, minus the lake area's precipitation. When evaporation is high or rainfall is low, evaporation and exchange are approximated as the lake's minimum ecological water requirement, i.e., the formula is: W min (t)=W q (t)+A(t)E(t);

[0066] Among them, W min (t) represents the minimum ecological water demand of the lake at time t, W q (t) represents the amount of water exchanged between the lake and groundwater in year t, A(t) represents the minimum ecological water surface area of ​​the lake in year t, and E(t) represents the annual evaporation in year t.

[0067] Step S5: Calculate the minimum ecological water surface area of ​​the lake based on the minimum ecological water requirement of the lake determined in Step S4. Use this as the basis for the ecological environment assessment of the lake ecosystem and evaluate whether the lake's ecological function meets the standards.

[0068] Specifically, based on the minimum ecological water requirement of the lake estimated in step S4 and the minimum water level required to maintain the various components of the lake ecosystem and meet the main ecological functions of the lake, the minimum ecological water surface area of ​​the lake is determined, that is:

[0069]

[0070] Among them, H min To maintain the minimum water level required to sustain all components of the lake ecosystem and meet the lake's main ecological functions; W min (t) represents the minimum ecological water demand of the lake at time t; A(t) represents the minimum ecological water surface area of ​​the lake in year t.

[0071] The criteria for evaluating whether a lake's ecological function meets the standards are: the measured value of the lake area and the average value f of the minimum ecological water surface area. If the ratio f ≥ 1, the lake's ecological function is considered to meet the standards; if the ratio 0.5 ≤ f < 1, the lake's ecological function is considered to be relatively poor; if the ratio f < 0.5, the lake's ecological function is considered to be poor.

[0072] Example

[0073] To better understand the specific principles of the method for calculating the minimum ecological water requirement and evaluating the ecological function of lake ecosystems in this invention, a representative year following the implementation of desertification control measures in the 1970s, using a typical lake in the Mu Us Desert in northern Shaanxi, my country, is selected as an example. The invention is illustrated in conjunction with the accompanying drawings. Based on local meteorological data, the high-water season is determined to be from June to September each year. Remote sensing data is collected from August each year. Given the existing data, the details of the basic data collection and investigation will not be elaborated upon.

[0074] The application of this invention is illustrated by analyzing the known groundwater level and lake water level of a typical lake in a sandy desert in Northwest my country. The minimum ecological water requirement of the lake is determined based on the known data in Table 1 below.

[0075] Table 1. Known data for a typical lake in a sandy desert area in Northwest my country.

[0076]

[0077] The typical lake in this embodiment is a frustum-shaped lake, and its water volume is expressed as follows:

[0078]

[0079] H A With H B The relation is:

[0080]

[0081] Equations relating groundwater recharge and drainage to lakes:

[0082]

[0083] In this embodiment, the lake water level H A (t) are all less than the groundwater level H(t) around the lake, meaning that groundwater replenishes the lake, such as Figure 5 As shown.

[0084] Due to the high evaporation rate in the northwest wind-blown sandy area, the minimum ecological water requirement equation for the lake at time t is as follows:

[0085] W min (t)=W q (t)+A(t)E(t)

[0086] Reference Figure 4The diagram shows a clear inflection point. After this point, each unit increase or decrease in water level will significantly alter the lake's surface area, meaning its function will also change significantly. If this water level is near the lake's multi-year average water level, then this maximum value is considered the lake's minimum ecological water level. This determines the minimum ecological water level H for the lake's ecosystem. min The water level is 1.64m, which can be used as an early warning level for the ecological function of the lake's ecosystem.

[0087] Based on the lowest ecological water level H of the lake ecosystem min The minimum water surface area of ​​the lake ecosystem over the years was determined, i.e.

[0088]

[0089] Substituting the known data from Table 1 into the above formula yields Table 2, which shows that the lake's water volume V is always less than the minimum ecological water requirement W. min The lake's water volume is insufficient to maintain the normal ecological functions of its ecosystem. The minimum water surface area of ​​the lake ecosystem over the years was ultimately determined. This minimum water surface area can be used as an indicator for evaluating the ecological functions of the lake ecosystem.

[0090] Table 2. Projected data for a typical lake in a sandy desert area in Northwest my country.

[0091]

[0092] The average minimum ecological water surface area for the selected representative years is: 2.41 × 10⁻⁶. 6 m 2 .

[0093] Evaluation criteria:

[0094] The lake's ecological function can be evaluated based on the evaluation criteria. The evaluation results are as follows: except for 2008 (measured water surface area 2.39) and 2011 (measured water surface area 2.31), when the lake's ecological function was relatively poor, the other representative years all met the criteria.

[0095] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0096] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for calculating and evaluating the minimum ecological water requirement of a sandy lake, wherein the sandy lake is a truncated cone-shaped lake, characterized in that... Specifically, the following steps are included: Step S1: Collect meteorological data in the study area, interpret the lake water area distribution based on remote sensing images, and construct a lake water level-area relationship function with the measured lake water level data; at the same time, calculate the volume of typical lake water bodies in sandy areas based on the lake water surface area interpreted by remote sensing. Step S2: Based on the lake water level-area relationship function constructed in Step S1, draw a lake water level-area relationship map over the years. Based on the trend of the lake water level-area relationship map, determine the turning point of the lake water surface area changing with the lake water level. This turning point corresponds to the lowest ecological water level of the lake system. Step S3: Construct a mathematical equation for the exchange between groundwater and lake based on the groundwater level and lake surface area, and determine the recharge and discharge relationship between groundwater and lake; The specific process of step S3 is as follows: A rectangular coordinate system is established with the top of the cone formed by the lake surface and the lake bottom as (0,0), the direction perpendicular to the lake surface as the ordinate, and the direction parallel to the lake surface as the abscissa. A mathematical model of the groundwater-lake exchange is then constructed based on this system, namely, the equation governing the recharge and discharge relationship between groundwater and the lake: in, for t Annual exchange rate between lakes and groundwater for t Average elevation of groundwater level around the lake in a given year, in meters; The average thickness of the silt layer at the bottom of the lake, in meters; for t Lake water level elevation for the year, in meters; The vertical permeability coefficient of the lake silt layer is expressed in m / d. for t The lake's bottom surface area in a given year; Step S4: Based on steps S2-S3 and in accordance with the principle of water balance, estimate the minimum ecological water demand of the lake; The specific process for estimating the minimum ecological water requirement of the lake in S4 is as follows: Assuming zero change in lake water volume, the replenishment of the lake ecosystem equals the consumption, which is the minimum water volume required to maintain the lake's normal ecological functions. Under natural conditions, the ecological water requirement of the lake area equals the sum of lake evaporation and groundwater-lake exchange, minus the lake area precipitation. When evaporation is high or rainfall is low, evaporation and exchange are taken as the minimum ecological water requirement of the lake, i.e., the formula is: in, for t The minimum ecological water requirement of a lake at any given time. for t Annual exchange rate between lakes and groundwater for t The minimum ecological water surface area of ​​a lake in a given year for t Annual evaporation rate for a given year; Step S5: Calculate the minimum ecological water surface area of ​​the lake based on the minimum ecological water requirement of the lake determined in Step S4. Use this as the basis for the ecological environment assessment of the lake ecosystem and evaluate whether the lake's ecological function meets the standards. The specific process of step S5 is as follows: Based on the minimum ecological water requirement of the lake estimated in step S4, and the minimum water level required to maintain the various components of the lake ecosystem and meet the main ecological functions of the lake, the minimum ecological water surface area of ​​the lake is determined, namely: in, The minimum water level required to maintain all components of the lake ecosystem and meet the lake's main ecological functions; for t Minimum ecological water requirement of a lake at any given time; for t The minimum ecological water surface area of ​​a lake in a given year; The criterion for evaluating whether a lake's ecological function meets the standards is the ratio of the measured lake area to the minimum ecological water surface area. f If the ratio f If the ratio is ≥1, the lake's ecological function is considered to meet the standard; if the ratio is 0.5≤ f If the ratio is less than 1, the lake is considered to have poor ecological function; if the ratio is less than 1, the lake is considered to have poor ecological function. f If the value is less than 0.5, the lake is considered to have poor ecological function.

2. The method for calculating and evaluating the minimum ecological water requirement of lakes in sandy wastelands according to claim 1, characterized in that, The specific process of constructing the lake water level-area relationship function in step S1 is as follows: First, the normalized water index is calculated from the remote sensing images covering the lake area, using the following formula: ; where NDWI is the normalized water index, and p(Green) and p(NIR) are the pixel values ​​of the green band and near-infrared band of the remote sensing image, respectively. Then, a reasonable threshold for NDWI was selected to extract the lake's water area, its total area was calculated, and it was mapped one-to-one with the lake water level data of the remote sensing image observation date. The lake water surface area was used as a functional indicator to establish a lake water level-area relationship function. S(h) .

3. The method for calculating and evaluating the minimum ecological water requirement of lakes in sandy wastelands according to claim 2, characterized in that, The volume of lake water in step S1 is: ,but for: ; In the formula: V The volume of the lake is expressed in meters (m). 3 ; The lake surface area for that year, as interpreted by remote sensing. The lake bottom area was obtained by consulting historical data; R 1 The radius of the lake's surface is in meters. R 2 The radius of the lake's bottom surface is in meters. The elevation of the lake is in meters (m). The height from the lake bottom to the cone is in meters (m).

4. The method for calculating and evaluating the minimum ecological water requirement of lakes in sandy wastelands according to claim 3, characterized in that, In step S2, for every unit increase or decrease in the water level corresponding to the inflection point, the lake's surface area will change significantly, meaning the lake's ecological function will also change significantly. If this water level is near the lake's multi-year average water level, then this maximum value is considered the lake's minimum ecological water level. H min The lowest ecological water level of the lake H min This serves as an early warning level for the ecological function of the lake's ecosystem.

5. The method for calculating and evaluating the minimum ecological water requirement of lakes in sandy wastelands according to claim 1, characterized in that, If the relationship between groundwater replenishment and drainage in lakes is as follows: Groundwater replenishes lakes; if Lakes replenish groundwater; among them, H A (t) is t Lake water level elevation for the year, in meters; H (t) is t Average elevation of groundwater level around the lake in a given year, in meters.

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