Method, device and medium for identifying sudden drought in a watershed based on water-heat coupling balance

Abstract

The present invention discloses a method, device and medium for identifying sudden drought in a watershed based on water-heat coupling balance, the method comprising: obtaining basic data, the basic data comprising meteorological observation data, hydrological data, soil moisture data and vegetation data; calculating the potential evapotranspiration of the watershed based on the basic data; constructing a hydrothermal coupling balance model at a phenological scale based on the Budyko equation; estimating the parameters of the hydrothermal coupling balance model at a phenological scale using vegetation and land use data; determining the hydrothermal coupling state space of the watershed based on the constructed hydrothermal coupling balance model at a phenological scale; calculating the duration and drought intensity of the sudden drought using the development curve of the sudden drought in the hydrothermal coupling state space at a phenological scale of the watershed. The present invention can accurately and appropriately characterize the characteristics of the duration and drought intensity of the sudden drought, and will enrich and improve the method system for identifying sudden drought.

Description

Technical Field

[0001] The present invention relates to the technical field of drought monitoring and prediction, and in particular to a method, device and medium for identifying sudden drought in a watershed based on water-heat coupling balance. Background Art

[0002] Sudden drought refers to the phenomenon that soil moisture content decreases rapidly due to temperature increase or precipitation decrease, which quickly triggers drought. Unlike seasonal drought, which develops slowly and lasts for a long time, sudden drought only lasts for a few seasons (one season is 5 days) or a few weeks, but its high intensity and rapid outbreak cause great harm to water resources, ecological environment and agriculture. Studying the occurrence mechanism of sudden drought and accurately identifying the characteristics of sudden drought such as duration, intensity and coverage are very important links in sudden drought assessment and watershed drought prevention and disaster reduction management, which are of great significance for reducing the impact of sudden drought and watershed disaster prevention and reduction.

[0003] The development of sudden drought is mainly due to the fact that strong solar radiation enhances the evapotranspiration capacity of the basin. At the same time, the reduction of precipitation in the basin also exacerbates the rapid decline of soil moisture, leading to the rapid development of sudden drought. When the soil moisture content drops rapidly to a certain threshold, the contribution of energy to evapotranspiration gradually weakens, water control begins to become dominant, and evapotranspiration will also decrease, thereby slowing down the rate of decline of soil moisture content. Therefore, the occurrence and development of sudden drought are closely related to factors such as temperature, precipitation, and soil moisture. However, there is no unified conclusion on how to effectively identify sudden drought at home and abroad. The main methods for identifying sudden drought at present include: (1) identifying sudden drought and its characteristics based on the change amplitude and change rate of hydrological elements represented by soil moisture content; (2) characterizing sudden drought based on the change in the ratio of potential evapotranspiration to actual evapotranspiration in the basin; (3) constructing composite indicators such as standardized rainfall evapotranspiration index and standardized soil moisture index to identify sudden drought.

[0004] In summary, the current definition and identification techniques of sudden droughts are mainly based on calculating the statistical value changes of specific factors, which fail to describe the occurrence and development of sudden droughts from the physical mechanism level. The leading role of controlling factors in different development stages of sudden droughts is obviously insufficient, and the current technical methods have a certain degree of subjectivity in the standards for sudden drought identification. Therefore, it is necessary to establish a sudden drought identification method that can systematically explain the synergistic effects of multiple factors such as energy and water in the process of sudden drought development and evolution in the basin from the physical mechanism level, and can also reflect the characteristics of sudden drought events such as intensity and duration. Summary of the invention

[0005] In view of the shortcomings of the prior art mentioned above, and aiming at the difficulty of coordinating the energy and hydrological factors in the sudden drought identification process, the purpose of the present invention is to provide a method, device and medium for identifying sudden drought in a watershed based on water-thermal coupling balance, so as to quantify the dominant role of controlling factors in different development stages of sudden drought from the physical mechanism level.

[0006] The present invention adopts the following technical solution:

[0007] According to a first aspect of the present invention, a method for identifying sudden drought in a watershed based on water-heat coupling balance is provided, the method comprising:

[0008] Acquiring basic data, including meteorological observation data, hydrological data, soil moisture data, and vegetation data;

[0009] Based on the basic data, the potential evapotranspiration of the watershed is calculated;

[0010] A climatic-scale hydrothermal coupled balance model was constructed based on the Budyko equation;

[0011] The parameters of the phenological scale hydrothermal coupled balance model are estimated using vegetation and land use data;

[0012] According to the constructed phenological-scale hydrothermal coupling balance model, the hydrothermal coupling state space of the basin is determined;

[0013] The duration and intensity of sudden drought are calculated using the development curve of sudden drought in the water-heat coupling state space at the basin climatic scale.

[0014] Furthermore, based on the basic data, the potential evapotranspiration of the basin is calculated by the following formula:

[0015]

[0016] Where: ET0 is the reference crop evaporation, Δ is the gradient of the saturated water vapor pressure-temperature curve, R n is the net radiation of the crop surface, G is the heat flux into the soil, γ is the air humidity constant, T is the average temperature at a height of 2m, U2 is the average wind speed at a height of 2m, e s and e a are the saturated water vapor pressure of air and the actual water vapor pressure of air respectively.

[0017] Furthermore, a climatic-scale hydrothermal coupling balance model is constructed based on the Budyko equation, which specifically includes:

[0018] The available water volume Q for a given period of time is calculated by the following formula:

[0019] Q=P+I+S (2)

[0020] Where: P represents the rainfall in the period, I represents the external water diversion, and S represents the soil water availability at the initial moment of the period;

[0021] The actual evapotranspiration E is a function of the available water Q and available energy in a given period of time and is expressed as:

[0022] E=f(Q,E0,E) (3)

[0023] Where: E0 represents the commonly used potential evapotranspiration;

[0024] Derivatives of Q and E0 are taken respectively, and the differential equations are solved under 0th-order boundary conditions and 1st-order boundary conditions. The differential equations are expressed as:

[0025]

[0026] According to formula (4), we can get:

[0027]

[0028] Wherein, n and C both represent parameters to be determined.

[0029] Furthermore, the parameters of the phenological scale hydrothermal coupling balance model are estimated using vegetation and land use data, including:

[0030] The polynomial function shown in the following formula is used to estimate the parameter n to be determined:

[0031] n=a+bx+cx 2 +....+nx n (6)

[0032] Where: a, b, c, ..., n are the parameters of the polynomial function, estimated by the least square method or linear distance method; x is the value of the leaf area index LAI in a given period; according to the characteristics of the underlying surface in different watersheds, the total primary productivity or solar induced chlorophyll fluorescence is used to replace LAI;

[0033] Based on meteorological observation data, rainfall, soil moisture content and other data, the least squares method or linear distance method is used to estimate the parameter C to be determined.

[0034] Furthermore, based on the constructed phenological scale hydrothermal coupling balance model, the basin hydrothermal coupling state space is determined, including:

[0035] When the parameters n and C to be determined are determined, the value of E / E0 is used as the ordinate and the value of Q / E0 is used as the abscissa to construct the watershed water-heat coupling state space, wherein the watershed water-heat coupling state space includes the water control boundary OA, the energy control boundary AB and the boundary line OC of the watershed water-heat coupling state space;

[0036] When the meteorological conditions are determined, the sudden drought development curve moves in the space formed by the boundary line OC of the water-heat coupling state space of the basin and the horizontal axis. The meteorological conditions include precipitation, temperature, wind speed, and air humidity.

[0037] Furthermore, the development curve of sudden drought in the water-heat coupling state space at the basin climatic scale is determined by the following method:

[0038] Based on the water-heat coupling state space of the watershed, when the temperature is low and the soil moisture content is sufficient, it is determined that the sudden drought development curve is located at the t0 position;

[0039] When a sudden drought occurs, the sudden drought development curve stays at t4 after passing t3. When the horizontal coordinate is greater than 1, the sudden drought is controlled by energy; when the horizontal coordinate is less than 1, it enters the water control stage.

[0040] According to the soil moisture threshold, the position THR of the soil moisture threshold on the horizontal axis is calculated. When the motion trajectory exceeds the THR position, it indicates that the sudden drought has ended.

[0041] Furthermore, the duration and severity of sudden drought are calculated by the following method:

[0042] The moment when the absolute value of the slope of the motion trajectory suddenly increases due to the temperature rise is recorded as the start time of the sudden drought, and the moment when the motion trajectory exceeds THR is recorded as the end time of the sudden drought. The calculation formula for the duration of the sudden drought is as follows:

[0043] FD=(T-1)·t (7)

[0044] Where: FD is the duration of sudden drought, T is the total number of moments of sudden drought development curve, and t is the time scale;

[0045] The vertical coordinate values ​​at each moment are added together to represent the intensity of the entire sudden drought event. The calculation formula for the sudden drought intensity is as follows:

[0046]

[0047] Where: FI is the sudden drought intensity, It represents the ordinate value of the water-heat coupling state space of the sudden drought development curve at time i, where i is the time number.

[0048] According to a second aspect of the present invention, a watershed drought identification device based on water-heat coupling balance is provided, the device comprising:

[0049] A data acquisition unit is configured to acquire basic data, wherein the basic data includes meteorological observation data, hydrological data, soil moisture data, and vegetation data;

[0050] A first calculation unit is configured to calculate the potential evapotranspiration of the watershed based on the basic data;

[0051] A model building unit, configured to build a climatological-scale hydrothermal coupled balance model based on the Budyko equation;

[0052] A parameter estimation unit is configured to estimate the parameters of the phenological scale water-heat coupling balance model using vegetation and land use data;

[0053] A space determination unit is configured to determine a water-thermal coupling state space of a watershed according to a constructed phenological-scale water-thermal coupling balance model;

[0054] The second calculation unit is configured to calculate the duration and drought intensity of the sudden drought by using the development curve of the sudden drought in the water-thermal coupling state space at the basin climatic scale.

[0055] According to a third aspect of the present invention, a non-transitory computer-readable storage medium storing instructions is provided. When the instructions are executed by a processor, the method for identifying sudden drought in a watershed based on water-thermal coupling balance as described above is executed.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] 1. Starting from the physical mechanism level, the present invention constructs a method for identifying sudden drought in a watershed based on the water-heat coupling balance equation. While identifying sudden drought events, it can systematically explain the synergistic effect of "energy-water" in the development process of sudden drought, and can accurately and appropriately characterize the duration, drought intensity and other characteristics of sudden drought, which will enrich and improve the method system for identifying sudden drought.

[0058] 2. By establishing a composite correlation between sudden drought and multiple factors such as meteorology, hydrology, and underlying surface conditions, it is possible to quantify the dominant role of controlling factors at different development stages of sudden drought and the degree of influence of each factor on the characteristic variables of sudden drought, thereby minimizing the subjective influence in the process of sudden drought identification.

[0059] 3. The method of the present invention has the advantages of simple structure, easy acquisition of input data, and efficient calculation, and can be applied to the prediction, early warning, and drought prevention and drought relief decision-making of river basin sudden droughts. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In the drawings, which are not necessarily drawn to scale, the same reference numerals may describe similar parts in different views. The same reference numerals with letter suffixes or different letter suffixes may represent different instances of similar parts. The accompanying drawings generally illustrate various embodiments by way of example and not limitation, and together with the specification and claims, are used to illustrate the embodiments of the invention. When appropriate, the same reference numerals are used throughout the drawings to refer to the same or similar parts. Such embodiments are illustrative and are not intended to be exhaustive or exclusive embodiments of the present apparatus or method.

[0061] Figure 1 The present invention is a flowchart of a method for identifying sudden drought in a watershed based on water-heat coupling balance according to an embodiment of the present invention.

[0062] Figure 2 Schematic diagram of the water-heat coupling state space and sudden drought development curve at the climatic scale of the watershed according to an embodiment of the present invention.

[0063] Figure 3 The distribution of the water-heat balance state of the Fu River Basin in the water-heat coupling state space at each calculation time from 2016 to 2017 according to an embodiment of the present invention.

[0064] Figure 4 1 is a development curve of a typical sudden drought event in the Fujiang River Basin in the water-heat coupling state space according to an embodiment of the present invention.

[0065] Figure 5 4 is a structural diagram of a watershed drought identification device based on water-heat coupling balance according to an embodiment of the present invention. DETAILED DESCRIPTION

[0066] The following examples are only for better explanation of the present invention, but the content of the present invention is not limited to the application in the examples. Therefore, those skilled in the art can make non-essential improvements and adjustments to the implementation scheme according to the above content of the invention and apply them to other examples, which are still within the protection scope of the present invention.

[0067] The present invention will now be further described with reference to the accompanying drawings.

[0068] The embodiment of the present invention provides a method for identifying sudden drought in a watershed based on water-heat coupling balance. In the specific implementation, one pentad (5 days) is used as the time scale, and the sub-basins divided according to the similarity of terrain, soil type, and land use are used as the spatial scale. The time scale of the present invention can be extended to different time scales such as weeks, ten days, months, and quarters, and the spatial scale can be extended to grid or pixel scales. It should be understood that the specific implementation methods described here are only used to explain the present invention and do not limit the scope of protection of the present invention.

[0069] like Figure 1 As shown, it is a flow chart of a method for identifying sudden drought in a watershed based on water-heat coupling balance, and the method includes the following steps 1 to 6.

[0070] Step 1, obtaining basic data, which includes meteorological observation data, hydrological data, soil moisture data, and vegetation data.

[0071] In this embodiment, meteorological observation data, hydrology, soil moisture, vegetation data, topographic soil and land use data required for calculation are collected and downloaded from the National Meteorological Science Data Center, the Resource and Environmental Science Data Center of the Chinese Academy of Sciences and other units. The meteorological observation data include precipitation, average temperature, wind speed, relative humidity, air pressure and net radiation. Resampling, interpolation and other methods are used to regularize data with inconsistent time scales or spatial scales.

[0072] Step 2: Based on the basic data obtained, select the potential evapotranspiration calculation method and calculate the potential evapotranspiration of the basin.

[0073] Based on the regularized basic data, the potential evapotranspiration calculation formula (as shown in formula (1)) is selected to calculate the potential evapotranspiration.

[0074]

[0075] Where: ET0 is the reference crop evapotranspiration (mmd -1 ), Δ is the gradient of the saturated water vapor pressure-temperature curve de / dT (kPa℃ -1 ), R n is the net radiation on the crop surface (MJm -2 d -1 ), G is the heat flux into the soil (MJm -2 d -1 ), γ is the air humidity constant (kPa℃ -1 ), T is the average temperature at 2m height (℃), U2 is the average wind speed at 2m height (ms -1 ), e s and e a are the saturated water vapor pressure of air and the actual water vapor pressure of air (kPa) respectively.

[0076] Step 3: Construct a climatic-scale hydrothermal coupling equilibrium model based on the Budyko equation.

[0077] Budyko believes that on a longer time scale, the main controlling factors of the actual evapotranspiration of the basin are available water and available energy. When the time scale is multi-year average, the multi-year average precipitation and multi-year average potential evapotranspiration in the Budyko equation can represent the available water and available energy, respectively. However, sudden droughts develop rapidly and generally last for 20 to 40 days. If we want to use it to construct a hydrothermal coupled balance model on a synoptic scale (5 days), we need to improve the parameters of the Budyko equation.

[0078] The available water volume Q for a given period can be approximately considered to be composed of the rainfall P in the period, the external water diversion volume I and the soil available water volume at the initial moment of the period (which can be approximately considered to be the soil water content at the initial moment) S, that is:

[0079] Q=P+I+S (2)

[0080] At this time, the actual evapotranspiration E is a function of the available water Q and available energy (usually expressed as potential evapotranspiration, E0) during this period, that is:

[0081] E=f(Q,E0,E) (3)

[0082] Derivatives of Q and E0 are taken respectively, and the equations are solved under 0th-order boundary conditions and 1st-order boundary conditions. According to relevant research, the differential equation can be expressed as:

[0083]

[0084] In particular, for smaller time scales, the boundary condition Q→0 may lead to Then the equation will be expressed as:

[0085]

[0086] Analyzing formula (5), potential evapotranspiration E0 can be calculated by formula (1), rainfall P and external water diversion I can be determined by meteorological observation data and hydrological data, and soil moisture content S can be determined by soil moisture content data. Therefore, the parameters to be determined include n and C.

[0087] Step 4: Use vegetation and land use data to estimate the parameters of the phenological scale hydrothermal coupled balance model.

[0088] Based on literature research, parameter n is closely related to the underlying surface conditions in the study area. Existing studies have used decadal and daily scale data for calibration and verification, and the results show that parameter n has a good correlation with the Leaf Area Index (LAI). Therefore, parameter n can be estimated using a polynomial function related to LAI, as shown in formula (6).

[0089] n=a+bx+cx 2 +....+nx n (6)

[0090] Where a, b, c, ..., n are the parameters of the polynomial function, which can be estimated using the least squares method or the linear distance method, and x is the value of LAI for a given period. According to the characteristics of the underlying surface in different watersheds, indicators such as gross primary productivity (GPP) or solar-induced chlorophyll fluorescence (SIF) can be used to replace LAI.

[0091] Parameter C is related to the given analysis period. When the time scale of the study increases, the influence of parameter C becomes smaller. When the study scale is long enough, the influence of parameter C can be ignored. Parameter C in formula (5) can be estimated based on meteorological observation data, rainfall, soil moisture content and other data using the least squares method or linear distance method.

[0092] Step 5: Based on the constructed phenological-scale hydrothermal coupling balance model, clarify the basin hydrothermal coupling state space.

[0093] When the parameters n and C are determined according to the underlying surface conditions of the basin, the water-heat coupling state space of the basin can be constructed with the value of E / E0 as the ordinate and the value of Q / E0 as the abscissa, as shown in the following figure. Figure 2 As shown in the figure, OA is the water control boundary, AB is the energy control boundary, and OC is the boundary line of the water-heat coupling state space of the basin. When the meteorological conditions such as precipitation, temperature, wind speed, and air humidity are determined, the sudden drought development curve will move in the space formed by OC and the horizontal axis, and then the sudden drought characteristics and dominant factors can be analyzed. Figure 3 This is the distribution of the water-heat balance state of the Fu River Basin in the water-heat coupling state space at each calculation moment from 2016 to 2017.

[0094] Step 6: Use the development curve of sudden drought in the water-heat coupling state space at the basin climatic scale to define the duration, drought intensity and other characteristics of sudden drought.

[0095] Attach Figure 2 Taking this as an example, the whole process of a sudden drought event shifting from energy control to water control and finally ending is described.

[0096] When the temperature is low and the soil moisture content is sufficient, the sudden drought development curve is at position t0. When a sudden drought occurs, the temperature rises, causing the actual evapotranspiration to increase and the soil moisture content to decrease. Figure 2In the equation, the vertical axis increases while the horizontal axis decreases, and the sudden drought development curve moves from t0 to t1. Subsequently, the sudden drought continues to develop, and the sudden drought development curve stays at t4 after t3. When the horizontal axis (Q / E0) is greater than 1, the sudden drought is controlled by energy; when the horizontal axis is less than 1, it enters the moisture control stage. Thereafter, as rainfall occurs, the soil moisture content gradually increases, and the sudden drought development curve moves from t4 to t5. Because the end of a sudden drought is usually determined by the soil moisture content exceeding a certain threshold (the current technical method uses the soil moisture content greater than 20% as the judgment standard). According to this soil moisture threshold, its position on the horizontal axis can be calculated, as shown in THR. When the motion trajectory exceeds the THR position, it indicates that the sudden drought ends. At this time, the moment when the absolute value of the slope of the motion trajectory suddenly increases due to the temperature rise at the beginning (t1 in the figure) can be recorded as the start time of the sudden drought, and the moment when the motion trajectory exceeds THR (t5 in the figure) can be recorded as the end time of the sudden drought. The duration of the sudden drought is as shown in formula (7).

[0097] FD=(T-1)·t (7)

[0098] Wherein: FD is the duration of sudden drought, n is the total number of moments of the sudden drought development curve, and t is the time scale, which is 5 days in the specific embodiment.

[0099] The vertical coordinate value (E / E0) at each moment is added together to represent the intensity of the entire sudden drought event. The sudden drought intensity is as shown in formula (8).

[0100]

[0101] Where: FI is the sudden drought intensity, (E / E0) i It represents the ordinate value of the water-heat coupling state space of the sudden drought development curve at time i, i is the time number, and T is the total number of calculated moments.

[0102] The change value of the horizontal axis (ΔQ / E0) in each period is added together to characterize the development speed of the entire sudden drought event. The development speed of the sudden drought is as shown in formula (9).

[0103]

[0104] Where: FS is the speed of sudden drought development, x i+1 and x i are the horizontal coordinate values ​​of the sudden drought development curve in the water-heat coupling state space at time i+1 and time i, respectively, and i is the time number.

[0105] Figure 4 Taking the Fujiang River Basin as an example, a specific implementation example of a typical sudden drought event is given, and the duration, intensity and development speed of the sudden drought are calculated, as shown in Table 1.

[0106] Table 1 Characteristics of typical sudden drought events in the Fujiang River Basin

[0107]

[0108] The embodiment of the present invention provides a watershed drought identification device based on water-heat coupling balance, such as Figure 5 As shown, the device 500 includes:

[0109] The data acquisition unit 501 is configured to acquire basic data, wherein the basic data includes meteorological observation data, hydrological data, soil moisture data, and vegetation data;

[0110] A first calculation unit 502 is configured to calculate the potential evapotranspiration of the watershed based on the basic data;

[0111] A model building unit 503 is configured to build a climatological scale hydrothermal coupling balance model based on the Budyko equation;

[0112] The parameter estimation unit 504 is configured to estimate the parameters of the phenological scale water-heat coupling balance model using vegetation and land use data;

[0113] The space determination unit 505 is configured to determine the water-heat coupling state space of the watershed according to the constructed phenological scale water-heat coupling balance model;

[0114] The second calculation unit 506 is configured to calculate the duration and drought intensity of the sudden drought by using the development curve of the sudden drought in the water-thermal coupling state space at the basin climatic scale.

[0115] In some embodiments, the first calculation unit is further configured to calculate the potential evapotranspiration of the watershed based on the basic data by the following formula:

[0116]

[0117] Where: ET0 is the reference crop evaporation, Δ is the gradient of the saturated water vapor pressure-temperature curve, R n is the net radiation of the crop surface, G is the heat flux into the soil, γ is the air humidity constant, T is the average temperature at a height of 2m, U2 is the average wind speed at a height of 2m, e s and e a are the saturated water vapor pressure of air and the actual water vapor pressure of air respectively.

[0118] In some embodiments, the model building unit is further configured to:

[0119] The available water volume Q for a given period of time is calculated by the following formula:

[0120] Q=P+I+S (2)

[0121] Where: P represents the rainfall in the period, I represents the external water diversion, and S represents the soil water availability at the initial moment of the period;

[0122] The actual evapotranspiration E is a function of the available water Q and available energy in a given period of time and is expressed as:

[0123] E=f(Q,E0,E) (3)

[0124] Where: E0 represents the commonly used potential evapotranspiration;

[0125] Derivatives of Q and E0 are taken respectively, and the differential equations are solved under 0th-order boundary conditions and 1st-order boundary conditions. The differential equations are expressed as:

[0126]

[0127] According to formula (4), we can get:

[0128]

[0129] Wherein, n and C both represent parameters to be determined.

[0130] In some embodiments, the parameter estimation unit is further configured to:

[0131] The polynomial function shown in the following formula is used to estimate the parameter n to be determined:

[0132] n=a+bx+cx 2 +....+nx n (6)

[0133] Where: a, b, c, ..., n are the parameters of the polynomial function, estimated by the least square method or linear distance method; x is the value of the leaf area index LAI in a given period; according to the characteristics of the underlying surface in different watersheds, the total primary productivity or solar induced chlorophyll fluorescence is used to replace LAI;

[0134] Based on meteorological observation data, rainfall, soil moisture content and other data, the least squares method or linear distance method is used to estimate the parameter C to be determined.

[0135] In some embodiments, the space determination unit is further configured to:

[0136] When the parameters n and C to be determined are determined, the value of E / E0 is used as the ordinate and the value of Q / E0 is used as the abscissa to construct the watershed water-heat coupling state space, wherein the watershed water-heat coupling state space includes the water control boundary OA, the energy control boundary AB and the boundary line OC of the watershed water-heat coupling state space;

[0137] When the meteorological conditions are determined, the sudden drought development curve moves in the space formed by the boundary line OC of the water-heat coupling state space of the basin and the horizontal axis. The meteorological conditions include precipitation, temperature, wind speed, and air humidity.

[0138] In some embodiments, the second computing unit is further configured to:

[0139] Based on the water-heat coupling state space of the watershed, when the temperature is low and the soil moisture content is sufficient, it is determined that the sudden drought development curve is located at the t0 position;

[0140] When a sudden drought occurs, the sudden drought development curve stays at t4 after passing t3. When the horizontal coordinate is greater than 1, the sudden drought is controlled by energy; when the horizontal coordinate is less than 1, it enters the water control stage.

[0141] According to the soil moisture threshold, the position THR of the soil moisture threshold on the horizontal axis is calculated. When the motion trajectory exceeds the THR position, it indicates that the sudden drought has ended.

[0142] In some embodiments, the second computing unit is further configured to:

[0143] The moment when the absolute value of the slope of the motion trajectory suddenly increases due to the temperature rise is recorded as the start time of the sudden drought, and the moment when the motion trajectory exceeds THR is recorded as the end time of the sudden drought. The calculation formula for the duration of the sudden drought is as follows:

[0144] FD=(T-1)·t (7)

[0145] Where: FD is the duration of sudden drought, T is the total number of moments of sudden drought development curve, and t is the time scale;

[0146] The vertical coordinate values ​​at each moment are added together to represent the intensity of the entire sudden drought event. The calculation formula for the sudden drought intensity is as follows:

[0147]

[0148] Where: FI is the sudden drought intensity, It represents the ordinate value of the water-heat coupling state space of the sudden drought development curve at time i, where i is the time number.

[0149] In some embodiments, the second computing unit is further configured to:

[0150]

[0151] Where: FS is the speed of sudden drought development, x i+1 and x i are the horizontal coordinate values ​​of the sudden drought development curve in the water-heat coupling state space at time i+1 and time i, respectively, and i is the time number.

[0152] It should be noted that the various device structures described in this embodiment belong to the same technical concept as the previously described method, and achieve the same technical effect through the same principle, which will not be repeated here.

[0153] An embodiment of the present invention further provides a non-transitory computer-readable storage medium storing instructions, and when the instructions are executed by a processor, the method for identifying sudden drought in a watershed based on water-thermal coupling balance as described in any of the above embodiments is executed.

[0154] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and should all be included in the scope of the claims and specification of the present invention.

Claims

1. A method for identifying sudden drought in a watershed based on water-heat coupling balance, characterized in that: The method comprises: Acquiring basic data, including meteorological observation data, hydrological data, soil moisture data, and vegetation data; Based on the basic data, the potential evapotranspiration of the watershed is calculated; A climatic-scale hydrothermal coupled balance model was constructed based on the Budyko equation; The parameters of the phenological scale hydrothermal coupled balance model are estimated using vegetation and land use data; According to the constructed phenological-scale hydrothermal coupling balance model, the hydrothermal coupling state space of the basin is determined; The duration and severity of sudden drought are calculated by using the development curve of sudden drought in the water-heat coupling state space at the basin climatic scale. Based on the Budyko equation, a climatic-scale hydrothermal coupling balance model is constructed, including: The available water volume Q for a given period of time is calculated by the following formula: Q=P+I+S (2) Where: P represents the rainfall in the period, I represents the external water diversion, and S represents the soil water supply at the initial moment of the period; The actual evapotranspiration E is a function of the available water Q and available energy in a given period of time and is expressed as: E=f(Q,E0,E) (3) Where: E0 represents the commonly used potential evapotranspiration; Derivatives of Q and E0 are taken respectively, and the differential equations are solved under 0th-order boundary conditions and 1st-order boundary conditions. The differential equations are expressed as: According to formula (4), we can get: Among them, n and C both represent parameters to be determined; The parameters of the hydrothermal coupled equilibrium model at the phenological scale are estimated using vegetation and land use data, including: The parameter n to be determined is estimated using the polynomial function shown in the following formula: n=a+bx+cx 2 +....+nx n (6) Where: a, b, c, ..., n are the parameters of the polynomial function, estimated by the least square method or linear distance method; x is the value of the leaf area index LAI in a given period; according to the characteristics of the underlying surface in different watersheds, the total primary productivity or solar induced chlorophyll fluorescence is used to replace LAI; Based on meteorological observation data and soil moisture data, the parameter C to be determined is estimated using the least squares method or linear distance method.

2. The method according to claim 1, characterized in that Based on the basic data, the potential evapotranspiration of the basin is calculated by the following formula: Where: ET0 is the reference crop evaporation, Δ is the gradient of the saturated water vapor pressure-temperature curve, R n is the net radiation of the crop surface, G is the heat flux into the soil, γ is the air humidity constant, T is the average temperature at a height of 2m, U2 is the average wind speed at a height of 2m, e s and e a are the saturated water vapor pressure of air and the actual water vapor pressure of air respectively.

3. The method according to claim 1, characterized in that Based on the constructed phenological scale hydrothermal coupling balance model, the basin hydrothermal coupling state space is determined, including: When the parameters n and C to be determined are determined, the value of E / E0 is used as the ordinate and the value of Q / E0 is used as the abscissa to construct the watershed water-heat coupling state space, wherein the watershed water-heat coupling state space includes the water control boundary OA, the energy control boundary AB and the boundary line OC of the watershed water-heat coupling state space; When the meteorological conditions are determined, the sudden drought development curve moves in the space formed by the boundary line OC of the water-heat coupling state space of the basin and the horizontal axis. The meteorological conditions include precipitation, temperature, wind speed, and air humidity.

4. The method according to claim 3, characterized in that The development curve of sudden drought in the water-heat coupling state space at the basin climatic scale is determined by the following method: Based on the water-heat coupling state space of the watershed, when the temperature is low and the soil moisture content is sufficient, it is determined that the sudden drought development curve is located at the t0 position; When a sudden drought occurs, the sudden drought development curve stays at t4 after passing t3. When the horizontal coordinate is greater than 1, the sudden drought is controlled by energy; when the horizontal coordinate is less than 1, it enters the water control stage. According to the soil moisture threshold, the position THR of the soil moisture threshold on the horizontal axis is calculated. When the motion trajectory exceeds the THR position, it indicates that the sudden drought has ended.

5. The method according to claim 4, characterized in that The duration and severity of sudden drought are calculated by the following method: The moment when the absolute value of the slope of the motion trajectory suddenly increases due to the temperature rise is recorded as the start time of the sudden drought, and the moment when the motion trajectory exceeds THR is recorded as the end time of the sudden drought. The calculation formula for the duration of the sudden drought is as follows: FD=(T-1)·t(7) Where: FD is the duration of sudden drought, T is the total number of moments of sudden drought development curve, and t is the time scale; The vertical coordinate values ​​at each moment are added together to represent the intensity of the entire sudden drought event. The calculation formula for the sudden drought intensity is as follows: Where: FI is the sudden drought intensity, It represents the ordinate value of the water-heat coupling state space of the sudden drought development curve at time i, where i is the time number.

6. The method according to claim 5, characterized in that The method further includes: using the development curve of sudden drought in the water-heat coupling state space of the basin climatic scale to calculate the development speed of sudden drought by the following formula: Where: FS is the speed of sudden drought development, x i+1 and x i are the horizontal coordinate values ​​of the sudden drought development curve in the water-heat coupling state space at time i+1 and time i, respectively, and i is the time number.

7. A watershed drought identification device based on water-heat coupling balance, characterized in that: The device comprises: A data acquisition unit is configured to acquire basic data, wherein the basic data includes meteorological observation data, hydrological data, soil moisture data, and vegetation data; A first calculation unit is configured to calculate the potential evapotranspiration of the watershed based on the basic data; A model building unit, configured to build a climatological-scale hydrothermal coupled balance model based on the Budyko equation; A parameter estimation unit is configured to estimate the parameters of the phenological scale water-heat coupling balance model using vegetation and land use data; A space determination unit is configured to determine a water-thermal coupling state space of a watershed according to a constructed phenological-scale water-thermal coupling balance model; The second calculation unit is configured to calculate the duration and drought intensity of the sudden drought by using the development curve of the sudden drought in the water-heat coupling state space at the basin climatic scale; The model building unit is further configured to: The available water volume Q for a given period of time is calculated by the following formula: Q=P+I+S (2) Where: P represents the rainfall in the period, I represents the external water diversion, and S represents the soil water supply at the initial moment of the period; The actual evapotranspiration E is a function of the available water Q and available energy in a given period of time and is expressed as: E=f(Q,E0,E) (3) Where: E0 represents the commonly used potential evapotranspiration; Derivatives of Q and E0 are taken respectively, and the differential equations are solved under 0th-order boundary conditions and 1st-order boundary conditions. The differential equations are expressed as: According to formula (4), we can get: Among them, n and C both represent parameters to be determined; The parameter estimation unit is further configured to: The parameter n to be determined is estimated using the polynomial function shown in the following formula: n=a+bx+cx 2 +....+nx n (6) Where: a, b, c, ..., n are the parameters of the polynomial function, estimated by the least square method or linear distance method; x is the value of the leaf area index LAI in a given period; according to the characteristics of the underlying surface in different watersheds, the total primary productivity or solar induced chlorophyll fluorescence is used to replace LAI; Based on meteorological observation data and soil moisture data, the parameter C to be determined is estimated using the least squares method or linear distance method. 8 . A non-transitory computer-readable storage medium storing instructions, which, when executed by a processor, executes the method according to claim 1 .

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