Model construction method and system for measuring and calculating farmland NEE variation caused by high temperature

Abstract

The invention discloses a model construction method and system for measuring and calculating farmland NEE variation caused by high temperature in the technical field of meteorological and farmland carbon source sink monitoring, and the method comprises the steps: dividing an observed farmland into research stages, recognizing high-temperature days and high-temperature events at different research stages, and constructing a corresponding high-temperature database; extracting a synchronous case corresponding to each high-temperature day and each high-temperature event, and taking an average value of NEE of all the synchronous cases of each high-temperature day and each high-temperature event as a final NEE value of the synchronous case of the high-temperature day and the high-temperature event; comparing the NEE values of the high-temperature day and the high-temperature event with the final NEE value of the case in the same period, determining the characterization form of the farmland high temperature in different research stages, and establishing a regression model for measuring and calculating the NEE variation caused by the high temperature in different research stages according to the characterization form of the farmland high temperature. According to the invention, quantitative estimation of farmland carbon source sink change caused by high temperature can be realized.

Description

Technical Field

[0001] The present invention relates to a model construction method and system for calculating the NEE change of farmland caused by high temperature, belonging to the technical field of meteorology and farmland carbon source and sink monitoring. Background Art

[0002] The high temperatures caused by global climate change are having a profound impact on agricultural production. Global warming has caused the expansion of high temperature events, which not only causes crop yield reduction and threatens food security, but also affects the carbon cycle process of farmland ecosystems. The farmland NEE (net ecosystem exchange) can generally be used to represent the carbon source and sink characteristics of farmland.

[0003] In previous technologies and research, the focus was mainly on measuring the changes in crop yields caused by extreme climate events, with less attention paid to the impact on farmland NEE. Although some studies have evaluated the interannual changes in farmland NEE at the growing season scale, there is currently a lack of research on the effects of extreme climate events on farmland NEE, especially the establishment of some quantitative relationships, which is not conducive to quantitatively evaluating the impact of climate change on farmland carbon sources and sinks. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a model construction method and system for measuring the change in NEE of farmland caused by high temperature, which can realize the quantitative estimation of the change in carbon source and sink of farmland caused by high temperature, and help understand the impact of climate change on carbon sequestration and emission reduction in farmland.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions: In a first aspect, the present invention provides a model construction method for calculating the change in NEE of farmland caused by high temperature, the method comprising: Obtain daily NEE values ​​and meteorological data of observed farmland; The observed farmland is divided into research stages in combination with the characteristics of the observed farmland ecosystem, and the high temperature days and high temperature events in each research stage are identified according to the meteorological data and the high temperature thresholds determined in different research stages, and a corresponding high temperature database is constructed; Determine the cases corresponding to each high temperature day and each high temperature event, and calculate the NEE average of all cases corresponding to each high temperature day and each high temperature event based on the obtained daily NEE values; The average NEE value of all cases in the same period of each high temperature day and the average NEE value of all cases in the same period of each high temperature event are taken as the final NEE value of the high temperature day and the cases in the same period of the high temperature event, respectively; The NEE values ​​of high temperature days and high temperature events were compared with the final NEE values ​​of the corresponding cases in the same period, and the representation forms of high temperature in farmland at different research stages were determined based on the comparison results; According to the representation form of high temperature in farmland, a regression model was established to estimate the change of NEE caused by high temperature at different research stages; Among them, the representation forms of high temperature in farmland include high temperature days and high temperature events.

[0006] In combination with the first aspect, optionally, the meteorological data includes: daily maximum temperature, daily rainfall, daily net radiation, daily sunshine hours and daily soil relative humidity.

[0007] In combination with the first aspect, optionally, the high temperature database includes a high temperature day database and a high temperature event database; The step of constructing a high temperature database comprises: The days with the highest temperature higher than the high temperature threshold of the corresponding research stage are identified as high temperature days, and a high temperature day data set is constructed based on the identified high temperature days to generate a high temperature day database; Consecutive high temperature days in the same research phase are identified as a high temperature event. A high temperature event data set is constructed based on the identified high temperature events to generate a high temperature event database.

[0008] In combination with the first aspect, optionally, the high temperature day database includes: the occurrence date of the high temperature day, the NEE value of the farmland, the daily maximum temperature, the rainfall, the net radiation, the sunshine hours and the relative humidity of the soil; The high temperature event database includes: the start and end dates of each high temperature event and the corresponding daily farmland NEE value, daily maximum temperature, daily rainfall, daily net radiation, daily sunshine hours and daily soil relative humidity.

[0009] In combination with the first aspect, further, determining the concurrent cases corresponding to each high temperature day and each high temperature event includes: Determine the occurrence date of high temperature days and the start and end dates of high temperature events; The phases without high temperature occurrence in the allowed deviation dates in other selected years are taken as candidate concurrent cases of the high temperature day or high temperature event; Eliminate candidate concurrent cases with abnormal NEE values, and use the remaining candidate concurrent cases as the final concurrent cases.

[0010] In combination with the first aspect, further, determining the representation form of high temperature in farmland at different research stages according to the comparison results includes: Paired sample t-test was used to analyze the differences between the NEE values ​​of high temperature days and the NEE values ​​of high temperature events and their final NEE values ​​of the same period cases; If there is a difference between the high temperature day and the high temperature event that reaches the significance level, then the one with the significant difference is selected as the representation form of high temperature in the farmland during the research stage; If the differences in high temperature days and high temperature events both reach a significant level, the one with a smaller p-value in the t-test will be selected as the representation form of high temperature in farmland during this research period; If the differences in high temperature days and high temperature events do not reach the significance level, the high temperature threshold of the corresponding research stage will be re-determined until at least one of the differences in the re-identified high temperature days and re-identified high temperature events in this research stage reaches the significance level, thereby determining the characterization form of high temperature in farmland in this research stage.

[0011] In combination with the first aspect, further, the regression model for calculating the NEE change caused by high temperature at different research stages is established according to the representation form of high temperature in farmland, including: If the representation form of high temperature in farmland is represented by high temperature days, the NEE change between the NEE value of high temperature days and the final NEE value of the corresponding cases in the same period is calculated, and a regression model of the change of NEE at different research stages with the change of the daily maximum temperature of high temperature days is constructed; If the representation form of high temperature in farmland is high temperature events, the NEE change between the NEE value of the high temperature event and the final NEE value of the corresponding case in the same period is calculated, and a regression model is constructed to show the change of NEE at different research stages with the change of the daily maximum temperature of the high temperature event.

[0012] In combination with the first aspect, further, after determining the representation form of high temperature in farmland at different research stages according to the comparison results, the method further includes: Determine the dry and wet conditions when high temperatures occur based on the rainfall data in the meteorological data; High temperature days and high temperature events are further classified according to dry and wet conditions.

[0013] In combination with the first aspect, optionally, the observed farmland includes a wheat-corn rotation farmland ecosystem.

[0014] In a second aspect, the present invention provides a model construction system for measuring the change in NEE of farmland caused by high temperature, comprising: Acquisition module: used to obtain daily NEE values ​​and meteorological data of observed farmland; Database construction module: used to divide the observed farmland into research stages in combination with the characteristics of the observed farmland ecosystem, and to identify high temperature days and high temperature events in each research stage according to the meteorological data and the high temperature thresholds determined in different research stages, and to construct a corresponding high temperature database; Calculation module: used to determine the cases corresponding to each high temperature day and each high temperature event, and calculate the NEE average of all cases corresponding to each high temperature day and the NEE average of all cases corresponding to each high temperature event according to the obtained daily NEE values; NEE final value determination module: used to take the NEE average value of all cases in the same period of each high temperature day and the NEE average value of all cases in the same period of each high temperature event as the NEE final value of the high temperature day and the high temperature event respectively; Representation form determination module: used to compare the NEE values ​​of high temperature days and high temperature events with the final NEE values ​​of the corresponding cases in the same period, and determine the representation forms of high temperature in farmland at different research stages according to the comparison results; Establishment module: used to establish a regression model for calculating the change of NEE caused by high temperature at different research stages according to the representation form of high temperature in farmland; Among them, the representation forms of high temperature in farmland include high temperature days and high temperature events.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention can integrate various information by acquiring daily NEE values ​​and meteorological data of observed farmland, laying a foundation for subsequent accurate analysis of the impact of high temperature on the NEE change of farmland; divide the observed farmland into research stages, and accurately identify high temperature days and high temperature events in different research stages to construct a high temperature database, which is helpful to focus on high temperature, a key influencing factor, and conduct targeted analysis on it; compare the NEE values ​​of high temperature days and high temperature events with the final NEE values ​​of cases in the same period, so as to determine whether the high temperature of farmland in different research stages is characterized in the form of high temperature days or high temperature events, so that the impact of high temperature on the NEE of farmland can be presented in an intuitive and clear manner, which is convenient for further in-depth understanding of the relationship between high temperature and NEE change; according to the determined representation form of high temperature in farmland, a regression model for calculating the NEE change caused by high temperature in different research stages is established, and the model can accurately reflect the quantitative relationship between high temperature factors and the NEE change of farmland based on the previous fine processing of data and the accurate characterization of the high temperature impact, and can be used to calculate the change of farmland NEE under different high temperature conditions, realize the quantitative estimation of the change of farmland carbon source sink caused by high temperature event process, and help understand the impact of climate change on farmland carbon sequestration and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flow chart of a model construction method for calculating the change of NEE of farmland caused by high temperature provided by an embodiment of the present invention; Figure 2 is a schematic diagram of the observation farmland division research phase provided by an embodiment of the present invention; Figure 3 It is the NEE value of all farmland with high temperature events and the NEE value of the cases in the same period in the first stage of the embodiment of the present invention; Figure 4 It is the NEE value of all farmland with high temperature days and the NEE value of the cases in the same period in the second stage of the embodiment of the present invention; Figure 5 It is the NEE value of all farmland with high temperature events and the NEE value of the cases in the same period in the third stage of the embodiment of the present invention; Figure 6 is a linear regression model of the change in NEE with the daily maximum temperature of the high temperature event in the first stage of the embodiment of the present invention; Figure 7 is a linear regression model of the change in NEE with the maximum temperature of the high temperature day in the second stage of the embodiment of the present invention; Figure 8 It is a linear regression model of the change of NEE in the third stage according to the embodiment of the present invention as the daily maximum temperature of the high temperature event changes. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present application and the specific features in the embodiments are detailed descriptions of the technical solution of the present application, rather than limitations on the technical solution of the present application. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments can be combined with each other.

[0018] The term "and / or" in this article is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0019] In the description of the present invention, if “first” or “second” is described, it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0020] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0021] Embodiment 1

[0022] like Figure 1 As shown, this embodiment provides a model construction method for measuring the change in NEE of farmland caused by high temperature, including: Step 1: Obtain daily NEE values ​​and meteorological data of the observed farmland; In some embodiments, meteorological data may include: daily maximum temperature, daily rainfall, daily net radiation, daily sunshine hours and daily soil relative humidity, where soil relative humidity is data at a soil depth of 0-10 cm. Daily NEE values ​​and meteorological data can be obtained from the National Meteorological Information Center; Step 2: Divide the observed farmland into research stages based on the characteristics of the observed farmland ecosystem, identify the high temperature days and high temperature events in each research stage based on the meteorological data and the high temperature thresholds determined in different research stages, and build a corresponding high temperature database; Different observation farmlands generally have different characteristics. By dividing the observation farmlands into research stages and accurately identifying high temperature days and high temperature events in different research stages to build a high temperature database, it helps to focus on high temperature, a key influencing factor, and conduct targeted analysis on it.

[0023] The following is a further detailed explanation of the division of research stages using the wheat-maize rotation farmland ecosystem as an example: The stage when high temperature may occur in the wheat-corn rotation farmland ecosystem is clarified, and further stage division is made according to the surface crop conditions at that stage. This is because the response of farmland ecosystem to high temperature stress varies when the surface vegetation conditions are different, and different thresholds should be used to identify high temperature. Therefore, combined with the characteristics of the wheat-corn rotation farmland ecosystem, the research period can be divided into three stages, namely: the first stage dominated by winter wheat photosynthesis, the second stage dominated by soil respiration, and the third stage dominated by summer corn photosynthesis.

[0024] Specifically, the high temperature thresholds for each research stage can be determined by consulting literature and historical data.

[0025] The meteorological data obtained through step 1 can determine the daily maximum temperature. Therefore, the dates when the maximum temperature of the day is higher than the high temperature threshold can be identified as high temperature days, and a high temperature day database can be constructed based on the high temperature day data set; consecutive high temperature days are identified as a high temperature event, and accordingly, a high temperature event database can be constructed based on the high temperature event data set.

[0026] As an embodiment, the information contained in the high temperature day database may include: the date of occurrence of the high temperature day, the farmland NEE value, the daily maximum temperature, rainfall, net radiation, sunshine hours and soil relative humidity. The information contained in the high temperature event database may include: the start and end dates of each high temperature event and the corresponding daily farmland NEE value, daily maximum temperature, daily rainfall, daily net radiation, daily sunshine hours and daily soil relative humidity.

[0027] Step 3: Determine the cases corresponding to each high temperature day and each high temperature event, and calculate the NEE average of all cases corresponding to each high temperature day and each high temperature event according to the obtained daily NEE values; the NEE average of all cases corresponding to each high temperature day and the NEE average of all cases corresponding to each high temperature event are used as the final NEE values ​​of the high temperature day and the cases corresponding to the high temperature event respectively; Due to the different development processes of crops on different dates, there are large differences in the NEE values ​​of farmland on different dates. Therefore, the difference between the NEE values ​​of high temperature days and high temperature events and the NEE values ​​of the cases in the same period reflects the changes in NEE values ​​caused by high temperature, which can eliminate the impact of crop development process.

[0028] When determining the concurrent cases, the occurrence date of the high temperature day and the start and end dates of the high temperature event should be determined first; the stage without high temperature occurrence in the allowed deviation date in other selected years is used as the candidate concurrent cases of the high temperature day or high temperature event. In this embodiment, for the high temperature day, the allowed deviation date can be determined as a date within three days of the occurrence date in other selected years. For the high temperature event, the allowed deviation date can be determined as a date within three days of the start date of the high temperature event in other selected years.

[0029] In order to eliminate the impact of other factors besides high temperature on NEE values, candidate cases with abnormal NEE values ​​can be eliminated, and the remaining candidate cases can be used as the final cases. Optionally, the NEE anomalies caused by factors such as rainfall, net radiation, sunshine hours and soil relative humidity can be eliminated, so that the difference between the NEE values ​​of high temperature days and high temperature events and their NEE values ​​of the cases at the same time is mainly caused by high temperature, rather than other factors.

[0030] Step 4: Compare the NEE values ​​of high temperature days and high temperature events with the final NEE values ​​of the corresponding cases in the same period, and determine the representation forms of high temperature in farmland at different research stages according to the comparison results; the representation forms of high temperature in farmland include representation by high temperature days and representation by high temperature events; In some embodiments, step 4 specifically includes: The paired sample t-test method was used to analyze whether the difference between the NEE values ​​of high temperature days and high temperature events and the final NEE values ​​of the cases in the same period reached a significant level; in this embodiment, if the p-value of the t-test is less than 0.05, it indicates that it has reached a significant level.

[0031] If there is a difference between the high temperature day and the high temperature event that reaches the significance level, then the one with the significant difference is selected as the representation form of high temperature in the farmland during the research stage; If the differences in high temperature days and high temperature events reach the significance level, it means that there are significant differences in the two forms of high temperature, which indicates that the two forms of high temperature have a significant impact on farmland NEE. Then the one with the smaller p value of the t-test is selected as the form of high temperature in farmland during the research stage. If the differences in high temperature days and high temperature events do not reach the significance level, that is, the p values ​​are greater than 0.05, it means that the differences in the two forms of high temperature are not significant, which indicates that the two forms of high temperature have no significant effect on farmland NEE. In this case, the high temperature threshold for the corresponding research stage will be re-determined until at least one of the differences in the re-identified high temperature days and re-identified high temperature events in this research stage reaches the significance level, thereby determining the representation form of high temperature in farmland in this research stage.

[0032] It should be understood that if the high temperature threshold for the corresponding research stage is re-determined, the identification of the corresponding high temperature days and high temperature events, the construction of the high temperature database, the cases of the same period, and the final NEE values ​​of the cases of the same period also need to be re-determined.

[0033] Step 5: Establish a regression model for estimating the change in NEE caused by high temperature at different research stages based on the representation form of high temperature in farmland; Continuing with the wheat-corn rotation farmland ecosystem as an example, the regression models include: a regression model in which the change in NEE in the first stage dominated by winter wheat photosynthesis changes with the daily maximum temperature of high temperature days or high temperature events (determined by the determined representation form); a regression model in which the change in NEE in the second stage dominated by soil respiration changes with the daily maximum temperature of high temperature days or high temperature events (determined by the determined representation form); and a regression model in which the change in NEE in the third stage dominated by summer corn photosynthesis changes with the daily maximum temperature of high temperature days or high temperature events (determined by the determined representation form).

[0034] In some embodiments, after determining the characterization forms of high temperature in farmland at different research stages, the method further includes: Determine the dryness and wetness status when high temperature occurs based on rainfall data; Further classification of high temperature days and events based on dryness and wetness; Further classification of high temperature days and high temperature events according to dryness and wetness can be used to study whether there are differences in the impact of high temperature on farmland NEE under different dryness and wetness conditions.

[0035] The method provided by the embodiment of the present invention is further described below in conjunction with an application example, and the technical effect produced by the method provided by the embodiment of the present invention is further verified: Taking a certain county as an example, a model construction method for calculating the NEE change of farmland caused by high temperature is provided, in which the observation farmland is selected as a wheat-corn rotation farmland, and the specific steps include: Obtain daily NEE values ​​and meteorological data of observed farmland: In this application example, the daily farmland NEE values, daily maximum temperature, daily rainfall, daily net radiation, daily sunshine hours and daily soil relative humidity data at a soil depth of 0-10 cm in the county from 2007 to 2018 were specifically collected.

[0036] Identify the stage when high temperature may occur in the wheat-corn rotation farmland ecosystem: The high temperature in the area of ​​the county mainly occurs in the summer half of the year, so the summer half of the year is taken as the research stage. Due to the different responses of farmland ecosystems to high temperature stress under different surface vegetation conditions, different thresholds should be used to identify high temperature. Therefore, Figure 2 As shown, combined with the characteristics of the wheat-corn rotation farmland ecosystem in the county, the research period can be further divided into three stages: March 22 to May 27 was the first stage dominated by winter wheat photosynthesis, June 3 to June 30 was the second stage dominated by soil respiration, and July 15 to September 20 was the third stage dominated by summer corn photosynthesis.

[0037] By consulting literature and historical data, it was determined that the high temperature thresholds of the county in the three stages were 30℃, 35℃ and 35℃ respectively; accordingly, from 2007 to 2018, a total of 93 high temperature days and 13 high temperature events were identified in the first stage; a total of 77 high temperature days and 12 high temperature events were identified in the second stage; a total of 51 high temperature days and 13 high temperature events were identified in the third stage.

[0038] The corresponding cases in the same period of each high temperature day and each high temperature event were extracted, and the average value of NEE of all the corresponding cases in the same period of each high temperature day and each high temperature event was obtained as the final value of NEE of the corresponding cases in the same period of the high temperature day and the high temperature event.

[0039] The NEE values ​​of high temperature days and high temperature events were compared with the final NEE values ​​of the respective cases in the same period to determine whether the high temperature of farmland in different study stages was characterized in the form of high temperature days or high temperature events: In the first stage, the results of the paired sample t-test showed that only the NEE value of farmland during the high temperature event was significantly different from the NEE value of the case during the same period, with t=6.78, p<0.001, satisfying p<0.05, while there was no significant difference in the representation form of high temperature days, indicating that high temperature should be represented in the form of high temperature events in this stage to study its impact on farmland NEE.

[0040] like Figure 3 As shown in the figure, the NEE values ​​of farmland in high temperature events are greater than those in the same period, with average values ​​of -5.64gC / m² / d and -7.64gC / m² / d, respectively. That is, high temperature caused a significant increase in the NEE value of farmland, which may be attributed to the fact that high temperature has inhibited the photosynthesis of winter wheat to a certain extent. In addition, the impact of high temperature on the NEE value of farmland varies under different dry and wet conditions: under drought conditions, the average NEE value of farmland in high temperature events is -5.34gC / m² / d, while under wet conditions, the average NEE value of farmland in high temperature events is -7.31gC / m² / d. That is, high temperature inhibits photosynthesis more strongly under drought conditions.

[0041] In the second stage, the results of the paired sample t-test showed that only the NEE value of farmland on high temperature days was significantly different from the NEE value of cases in the same period, with t=3.46, p<0.001, satisfying p<0.05, while there was no significant difference in the form of high temperature events, indicating that high temperature should be characterized in the form of high temperature days in this stage to study its impact on farmland NEE.

[0042] like Figure 4 As shown in the figure, the NEE values ​​of farmland on most high-temperature days are greater than those of the cases in the same period, with average values ​​of 3.41gC / m² / d and 2.78gC / m² / d, respectively. That is, high temperature caused a significant increase in the NEE value of farmland, which may be attributed to the fact that high temperature promoted soil respiration to a certain extent. In addition, the impact of high temperature on the NEE value of farmland varies under different dry and wet conditions: the average values ​​of the NEE values ​​of farmland on high-temperature days under drought, normal and wet conditions are 3.09gC / m² / d, 3.48gC / m² / d and 3.8gC / m² / d, respectively.

[0043] In the third stage, the results of the paired sample t-test showed that only the NEE value of farmland during the high temperature event was significantly different from the NEE value of the cases during the same period, with t=7.41, p<0.001, satisfying p<0.05, while there was no significant difference in the form of high temperature days, indicating that high temperature should be characterized in the form of high temperature events in this stage to study its impact on farmland NEE.

[0044] like Figure 5As shown in the figure, the NEE of farmland in high temperature events is greater than that of the cases in the same period, with average values ​​of -7.15gC / m² / d and -8.87gC / m² / d, respectively. That is, high temperature caused a significant increase in the NEE value of farmland, which may be attributed to the fact that high temperature has a certain degree of inhibition on the photosynthesis of summer corn. In addition, the impact of high temperature on the NEE value of farmland in this stage is not significantly different under different dry and wet conditions. Under dry and wet conditions, the average NEE values ​​of farmland in high temperature events are -7.11gC / m² / d and -7.18gC / m² / d, respectively.

[0045] According to the representation form of high temperature in farmland, a regression model for calculating the change of NEE caused by high temperature in different research stages is established, including calculating the change of NEE of high temperature day or high temperature event and the NEE of the case in the same period, and constructing a regression model of the change of NEE in different research stages with the change of the daily maximum temperature of high temperature day or high temperature event: In the first stage, if Figure 6 As shown in Figure 2, the linear regression equation of the farmland NEE change y caused by the high temperature event and the maximum temperature x on the event day is y=0.5372x-15.42, where R 2 =0.2921. During a high temperature event, the higher the daily maximum temperature, the greater the change in NEE. For every 1°C increase in temperature, NEE increases by 0.5372 gC / m² / d.

[0046] In addition, the variation of NEE with the daily maximum temperature of high temperature events varies under different dry and wet conditions: under drought conditions, the equation for the variation of NEE with the daily maximum temperature is y=0.5779x-16.47, where R 2 =0.5224, reaching the 0.05 significance level, and the average change was 2.25gC / m² / d. The average change of NEE under humid conditions was 0.59gC / m² / d.

[0047] In the second stage, if Figure 7 As shown in Figure 2, the linear regression equation of the farmland NEE change y caused by the high temperature day and the daily maximum temperature x of the high temperature day is y=-0.1160x-4.93, where R 2 =0.0147. As can be seen from the figure, the increase in daily maximum temperature has no significant effect on the change in NEE.

[0048] In addition, the change of NEE with the change of the maximum daily temperature on hot days has certain differences under different dry and wet conditions: the average values ​​of NEE change under drought, normal and wet conditions are 0.29gC / m² / d, 0.73gC / m² / d and 0.91gC / m² / d, respectively.

[0049] In the third stage, if Figure 8As shown in the figure, the linear regression equation of the farmland NEE change y caused by the high temperature event and the maximum temperature x on the event day is y=0.8317x-28.4, where p<0.05, R 2 =0.384. During the high temperature event, the higher the daily maximum temperature, the greater the change in NEE. For every 1°C increase, NEE increases by 0.8317 gC / m² / d.

[0050] In addition, the change in NEE with the change in the maximum daily temperature of high temperature events varies under different dry and wet conditions: the average value of NEE change under drought conditions is 2.16gC / m² / d, while the average value of NEE change under wet conditions is 1.44gC / m² / d.

[0051] By integrating the linear regression equations of the three research stages, a regression model of the change in farmland NEE caused by high temperature was obtained.

[0052] In summary, the changes in NEE of the wheat-corn rotation farmland ecosystem in the county from 2007 to 2018 were calculated based on historical cases of the same period, which provides a model construction method for measuring the changes in NEE of farmland caused by high temperature. The model for measuring the changes in NEE of farmland caused by high temperature can realize the quantitative estimation of the changes in carbon sources and sinks of farmland caused by high temperature, and help understand the impact of climate change on carbon sequestration and emission reduction in farmland.

[0053] Embodiment 2

[0054] This embodiment provides a model construction system for measuring the change in NEE of farmland caused by high temperature, including: Acquisition module: used to obtain daily NEE values ​​and meteorological data of observed farmland; Database construction module: used to divide the observed farmland into research stages in combination with the characteristics of the observed farmland ecosystem, and to identify high temperature days and high temperature events in each research stage according to the meteorological data and the high temperature thresholds determined in different research stages, and to construct a corresponding high temperature database; Calculation module: used to determine the cases corresponding to each high temperature day and each high temperature event, and calculate the NEE average of all cases corresponding to each high temperature day and the NEE average of all cases corresponding to each high temperature event according to the obtained daily NEE values; NEE final value determination module: used to take the NEE average value of all cases in the same period of each high temperature day and the NEE average value of all cases in the same period of each high temperature event as the NEE final value of the high temperature day and the high temperature event respectively; Representation form determination module: used to compare the NEE values ​​of high temperature days and high temperature events with the final NEE values ​​of the corresponding cases in the same period, and determine the representation forms of high temperature in farmland at different research stages according to the comparison results; Establishment module: used to establish a regression model for calculating the change of NEE caused by high temperature at different research stages according to the representation form of high temperature in farmland; Among them, the representation forms of high temperature in farmland include high temperature days and high temperature events.

[0055] The model building system for calculating the NEE change of farmland caused by high temperature provided in the embodiment of the present invention can realize the model building method for calculating the NEE change of farmland caused by high temperature provided in the first embodiment of the present invention, and has the functional modules and beneficial effects corresponding to the execution method.

[0056] Embodiment 3

[0057] The embodiment of the present invention further provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the steps of the method in the first embodiment are first implemented.

[0058] The computer-readable storage medium includes: a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and other media that can store program codes.

[0059] Those skilled in the art will appreciate that the embodiments of the present application may provide methods, systems or computer program products. Therefore, the present application may take the form of a complete hardware embodiment, a complete software embodiment or an embodiment combining software and hardware. Moreover, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0060] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0061] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0062] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0063] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A model construction method for measuring the change in NEE of farmland caused by high temperature, characterized in that: The method comprises: Obtain daily NEE values ​​and meteorological data of observed farmland; The observed farmland is divided into research stages in combination with the characteristics of the observed farmland ecosystem, and the high temperature days and high temperature events in each research stage are identified according to the meteorological data and the high temperature thresholds determined in different research stages, and a corresponding high temperature database is constructed; Determine the cases corresponding to each high temperature day and each high temperature event, and calculate the NEE average of all cases corresponding to each high temperature day and each high temperature event based on the obtained daily NEE values; The average NEE value of all cases in the same period of each high temperature day and the average NEE value of all cases in the same period of each high temperature event are taken as the final NEE value of the high temperature day and the cases in the same period of the high temperature event, respectively; The NEE values ​​of high temperature days and high temperature events were compared with the final NEE values ​​of the corresponding cases in the same period, and the representation forms of high temperature in farmland at different research stages were determined based on the comparison results; According to the representation form of high temperature in farmland, a regression model was established to estimate the change of NEE caused by high temperature at different research stages; Among them, the representation forms of high temperature in farmland include high temperature days and high temperature events.

2. The model construction method for calculating the change in NEE of farmland caused by high temperature according to claim 1, characterized in that: The meteorological data include: daily maximum temperature, daily rainfall, daily net radiation, daily sunshine hours and daily soil relative humidity.

3. The model construction method for calculating the change in NEE of farmland caused by high temperature according to claim 1, characterized in that: The high temperature database includes a high temperature day database and a high temperature event database; The step of constructing a high temperature database comprises: The days with the highest temperature higher than the high temperature threshold of the corresponding research stage are identified as high temperature days, and a high temperature day data set is constructed based on the identified high temperature days to generate a high temperature day database; Consecutive high temperature days in the same research phase are identified as a high temperature event. A high temperature event data set is constructed based on the identified high temperature events to generate a high temperature event database.

4. The model construction method for calculating the change of NEE of farmland caused by high temperature according to claim 3, characterized in that: The high temperature day database includes: the occurrence date of the high temperature day, the NEE value of the farmland, the daily maximum temperature, the rainfall, the net radiation, the sunshine hours and the relative humidity of the soil; The high temperature event database includes: the start and end dates of each high temperature event and the corresponding daily farmland NEE value, daily maximum temperature, daily rainfall, daily net radiation, daily sunshine hours and daily soil relative humidity.

5. The model construction method for calculating the change of NEE of farmland caused by high temperature according to claim 1, characterized in that: The determination of the cases corresponding to each high temperature day and each high temperature event includes: Determine the occurrence date of high temperature days and the start and end dates of high temperature events; The phases without high temperature occurrence in the allowed deviation dates in other selected years are taken as candidate concurrent cases of the high temperature day or high temperature event; Eliminate candidate concurrent cases with abnormal NEE values, and use the remaining candidate concurrent cases as the final concurrent cases.

6. The model construction method for calculating the change in NEE of farmland caused by high temperature according to claim 1, characterized in that: The characterization forms of high temperature in farmland at different research stages are determined according to the comparison results, including: Paired sample t-test was used to analyze the differences between the NEE values ​​of high temperature days and the NEE values ​​of high temperature events and their final NEE values ​​of the same period cases; If there is a difference between the high temperature day and the high temperature event that reaches the significance level, then the one with the significant difference is selected as the representation form of high temperature in the farmland during the research stage; If the differences in high temperature days and high temperature events both reach a significant level, the one with a smaller p-value in the t-test will be selected as the representation form of high temperature in farmland during this research period; If the differences in high temperature days and high temperature events do not reach the significance level, the high temperature threshold of the corresponding research stage will be re-determined until at least one of the differences in the re-identified high temperature days and re-identified high temperature events in this research stage reaches the significance level, thereby determining the characterization form of high temperature in farmland in this research stage.

7. The model construction method for calculating the change of NEE of farmland caused by high temperature according to claim 1, characterized in that: The regression model for calculating the change of NEE caused by high temperature at different research stages is established according to the representation form of high temperature in farmland, including: If the representation form of high temperature in farmland is high temperature day, the NEE change between the NEE value of high temperature day and the final NEE value of the corresponding case in the same period is calculated, and the NEE change at different research stages with high temperature day is constructed. Regression model of daily maximum temperature change; If the representation form of high temperature in farmland is high temperature events, the NEE change between the NEE value of the high temperature event and the final NEE value of the corresponding case in the same period is calculated, and a regression model is constructed to show the change of NEE at different research stages with the change of the daily maximum temperature of the high temperature event.

8. The model construction method for calculating the change in NEE of farmland caused by high temperature according to claim 1, characterized in that: After determining the representation forms of high temperature in farmland at different research stages according to the comparison results, the method further includes: Determine the dry and wet conditions when high temperatures occur based on the rainfall data in the meteorological data; High temperature days and high temperature events are further classified according to dry and wet conditions.

9. The model construction method for calculating the change of NEE of farmland caused by high temperature according to any one of claims 1 to 8, characterized in that: The observed farmland includes a wheat-corn rotation farmland ecosystem.

10. A model construction system for measuring the change in NEE of farmland caused by high temperature, characterized in that: include: Acquisition module: used to obtain daily NEE values ​​and meteorological data of observed farmland; Database construction module: used to divide the observed farmland into research stages in combination with the characteristics of the observed farmland ecosystem, and to identify high temperature days and high temperature events in each research stage according to the meteorological data and the high temperature thresholds determined in different research stages, and to construct a corresponding high temperature database; Calculation module: used to determine the cases corresponding to each high temperature day and each high temperature event, and calculate the NEE average of all cases corresponding to each high temperature day and the NEE average of all cases corresponding to each high temperature event according to the obtained daily NEE values; NEE final value determination module: used to take the NEE average value of all cases in the same period of each high temperature day and the NEE average value of all cases in the same period of each high temperature event as the NEE final value of the high temperature day and the high temperature event respectively; Representation form determination module: used to compare the NEE values ​​of high temperature days and high temperature events with the final NEE values ​​of the corresponding cases in the same period, and determine the representation forms of high temperature in farmland at different research stages according to the comparison results; Establishment module: used to establish a regression model for calculating the change of NEE caused by high temperature at different research stages according to the representation form of high temperature in farmland; Among them, the representation forms of high temperature in farmland include high temperature days and high temperature events.

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