A quantitative analysis method of the contribution of regional water quality influencing factors based on index decomposition

Abstract

The present invention discloses a method for quantitatively analyzing the contribution of regional water quality influencing factors based on index decomposition, and the method comprises the following steps: step 1, basic data acquisition; step 2, regional water quality evaluation index selection; step 3, single station water quality comprehensive index calculation; step 4, regional water quality comprehensive index calculation; step 5, regional water quality influencing factor decomposition model construction; step 6, regional water quality influencing factor change calculation by time period; step 7, regional water quality influencing factor contribution analysis. The method of the present invention is not limited by data sample size and data distribution, and can handle zero values ​​in data sequences. It has strong flexibility in identifying regional water quality influencing factors, helps to analyze the long-term water quality change law and driving mechanism on a regional scale, can be used as a basis for regional water resources protection and pollution prevention and control measures effectiveness evaluation and policy formulation, and can provide basic support for regional water quality change trend prediction, with a wide range of applications and strong scalability.

Description

Technical Field

[0001] The present invention belongs to the technical field of attribution analysis of surface water quality changes, and in particular relates to a quantitative analysis method for the contribution of regional water quality influencing factors based on exponential decomposition. Background Art

[0002] As an important link for transporting substances needed to maintain terrestrial and aquatic organisms, rivers provide important guarantees for human life, production and ecological water use. River pollution not only threatens its use as a source of drinking water for humans, but also leads to the degradation of river ecosystems. The direct factor affecting the water quality of regional rivers is pollutants, and the generation, migration and transformation of pollutants are affected by the combined effects of the natural environment and human activities, such as rainfall runoff, land use, water conservancy project construction, economic and social development, and local water resource protection policies. Identifying the influencing factors of regional river water quality changes is an important basis for conducting surface water quality simulation and prediction, and is of great significance for regional water resource protection and sustainable utilization.

[0003] The method combining the water quality model based on physical processes with parameter sensitivity analysis can more precisely identify the factors affecting water quality and their contribution, but the construction of the water quality model requires more basic data, and the research scale is usually small, such as a single basin or a relatively isolated single water body. For the analysis of water quality influencing factors at the administrative regional scale, it is more effective to use data analysis or mining methods. The commonly used methods currently include principal component analysis, correlation analysis, and multiple regression. Although the above methods can quantitatively reflect the degree of influence of each influencing factor on the change of the target variable, they cannot explain the degree of influence of each influencing factor on the change of the target variable in any period of time. In addition, the above methods are based on statistical tests, have strict mathematical assumptions, and have high requirements for sample size and sample data distribution. It is difficult for general water quality monitoring data to meet the requirements. Therefore, a flexible method for quantitative analysis of the contribution of regional water quality influencing factors is urgently needed to reveal the driving mechanism of regional long-term water quality changes and provide a reference for the dynamic formulation of regional water resources protection and pollution control policies. Summary of the invention

[0004] The purpose of the present invention is to provide a method for quantitatively analyzing the contribution of regional water quality influencing factors based on exponential decomposition to solve the above technical problems.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention discloses a method for quantitatively analyzing the contribution of regional water quality influencing factors based on exponential decomposition, the method comprising the following steps:

[0007] Step 1, basic data acquisition: obtain basic data of the study area, including river water quality data, water resources data and social and economic data of the administrative region; the river water quality data of the administrative region refers to the monthly water quality monitoring data of the long-term water quality monitoring indicators of the river water quality monitoring stations within the administrative region. The water quality monitoring indicators are the 24 basic items of surface water environmental quality standards specified in the "Surface Water Environmental Quality Standards", including water temperature, pH value, dissolved oxygen, permanganate index, chemical oxygen demand, five-day biochemical oxygen demand, ammonia nitrogen, total phosphorus, total nitrogen, copper, zinc, fluoride, selenium, arsenic, mercury, cadmium, chromium, lead, cyanide, volatile phenol, petroleum, anionic surfactants, sulfide, fecal coliform bacteria; the water resources data include the annual precipitation, water resources and water consumption statistics of the administrative region; the social and economic data include the annual industrial added value per 10,000 yuan, gross domestic product and total population statistics of the administrative region;

[0008] Step 2, selection of regional water quality evaluation indicators: According to the standard limits of basic items of surface water environmental quality standards stipulated in the "Surface Water Environmental Quality Standards", the monthly water quality monitoring data of single water quality monitoring indicators of each river water quality monitoring station within the administrative area are evaluated, and the frequency of exceeding the standard for each water quality monitoring indicator except the two water quality monitoring indicators of water temperature and pH value is counted, that is, the proportion of the number of times the concentration value of the water quality monitoring indicator exceeds the water quality category grade III standard limit corresponding to the indicator to the total number of historical monitoring times, and the water quality monitoring indicator with an exceeding frequency exceeding the set threshold is selected as the regional water quality evaluation indicator; the two water quality monitoring indicators of water temperature and pH value are directly included in the regional water quality evaluation indicators;

[0009] Step 3: Calculation of single-station water quality comprehensive index: Based on the selected regional water quality evaluation indicators, calculate the single-station water quality comprehensive index of each river water quality monitoring station within the administrative area. The calculation formula is:

[0010]

[0011] Where: WQI j is the comprehensive water quality index of the jth water quality monitoring station; n is the total number of regional water quality evaluation indicators; C i is the normalized value assigned to the i-th regional water quality evaluation index; P i is the weight coefficient of the i-th regional water quality evaluation index;

[0012] Among them, the normalized value C of the i-th regional water quality evaluation index is i The calculation is done using the following formula:

[0013]

[0014] Where: T i is the measured concentration value of the water quality evaluation index of the ith area; S i,1 , Si,2 , S i,3 , S i,4 , S i,5 They are the standard limits of water quality categories I, II, III, IV and V specified in the Surface Water Environmental Quality Standards corresponding to the regional water quality assessment index of the ith item;

[0015] Step 4: Calculation of regional water quality comprehensive index: Based on the single-station water quality comprehensive index of all river water quality monitoring stations within the administrative area, combined with the representative river length of the water quality monitoring station, the regional water quality comprehensive index WQI is obtained by weighted average. The calculation formula is:

[0016]

[0017] Where: WQI is the comprehensive index of regional water quality; L j is the representative river chief of the jth water quality monitoring station in the administrative area; p is the total number of water quality monitoring stations in the administrative area;

[0018] Step 5: Construction of a decomposition model of regional water quality influencing factors: Select precipitation, water resources, water consumption, industrial added value per 10,000 yuan, gross domestic product, and total population as regional water quality influencing factors, and establish a regional water quality influencing factor decomposition model with the regional water quality comprehensive index as the target variable. The formula is:

[0019]

[0020] Where: WQI is the regional water quality comprehensive index; R is the regional precipitation; W is the regional surface water resources; U is the regional water consumption; V is the regional industrial added value per 10,000 yuan; GDP is the regional gross domestic product; POP is the total population of the region; WQR represents the effect of unit precipitation on water quality; RW represents the rainfall-runoff relationship; WU represents the water supply and use structure; UV represents the water consumption per 10,000 yuan of industrial added value; VG represents the industrial structure; GP represents GDP per capita; P represents the population size;

[0021] Step 6: Calculate the change of regional water quality influencing factors by time period: Use the logarithmic mean Dirichlet index decomposition method LMDI to calculate the contribution of each regional water quality influencing factor to the target variable. Select the LMDI addition decomposition mode, and the change of the regional water quality comprehensive index from time t-1 to time t is decomposed into the change of l regional water quality influencing factors Δx k , k=1,…l, that is:

[0022]

[0023] Where: ΔWQI is the change in the regional water quality comprehensive index from time t-1 to time t; WQI t-1 and WQI tare the comprehensive regional water quality index at time t-1 and t respectively; Δx k is the change in the water quality influencing factors in the kth region;

[0024] Derived from the logarithmic mean weight function, Δx k The calculation formula is:

[0025]

[0026] in:

[0027]

[0028] Substitute the data of regional water quality comprehensive index, precipitation, water resources, water consumption, industrial added value per 10,000 yuan, gross domestic product, and total population for each time period to calculate the change of water quality influencing factors in each region for each time period;

[0029] Step 7. Analysis of the contribution of regional water quality influencing factors: Based on the calculation results of the changes in the water quality influencing factors in each region from time to time, the contribution value of the water quality influencing factors in each region is analyzed, with positive values ​​representing positive driving effects and negative values ​​representing negative driving effects.

[0030] Furthermore, the long series of monthly water quality monitoring data of water quality monitoring indicators in step 1 is monthly water quality monitoring data of water quality monitoring indicators for more than 10 years.

[0031] Furthermore, the water resources data in step 1 is sourced from the administrative region water resources bulletin; and the socio-economic data is sourced from the administrative region statistical yearbook.

[0032] Furthermore, the water quality monitoring index with a frequency exceeding a set threshold selected in step 2 as the set threshold in the regional water quality evaluation index is 25%; and total nitrogen does not participate in the water quality evaluation. If the selected regional water quality evaluation index includes total nitrogen, it will be excluded.

[0033] Furthermore, the weight coefficient of the regional water quality evaluation index in step 3 is determined according to the recommended value for aquatic biological protection, and is corrected in combination with the severity of pollution of the regional water quality evaluation index; the normalized value of the regional water quality evaluation index is assigned an interval value according to the standard limit values ​​corresponding to each water quality category level of the basic items of surface water environmental quality specified in the "Surface Water Environmental Quality Standard", wherein the two regional water quality evaluation indicators of water temperature and pH value adopt a one-vote veto scoring principle, that is, when 6≤pH≤9, C i =0, otherwise C i =100; when -6℃≤WT≤45℃, C i =0, otherwise C i =100.

[0034] Furthermore, the single-station water quality comprehensive index WQI in step 3 j The water quality evaluation results corresponding to different value ranges are: WQI j ≤20, the water quality is excellent; 21 <WQI j ≤40, the water quality is good; 41 <WQI j ≤60, the water quality is normal; 60 <WQI j ≤80, the water quality is poor; 81 <WQI j ≤100: the water quality is extremely poor and unsuitable for drinking.

[0035] Furthermore, the specific process of analyzing the contribution value of the water quality influencing factors of each region in step 7 is: cumulatively adding up the changes in the water quality influencing factors of each region in each time period. If the sum is greater than 0, it indicates that the water quality influencing factors of the region promote the increase of the regional water quality comprehensive index, that is, it inhibits the improvement of the overall water quality in the region; if the sum is less than 0, it indicates that the water quality influencing factors of the region inhibit the increase of the regional water quality comprehensive index, that is, it promotes the improvement of the overall water quality in the region; the larger the absolute value of the sum, the greater the contribution of the water quality influencing factors in the region.

[0036] The beneficial effects of the present invention are as follows: the method of the present invention is not limited by the data sample size and data distribution, and overcomes the problem that the existing water quality attribution analysis method has strict requirements on the data sample size and data distribution, and can handle zero values ​​in the data sequence, and has strong flexibility in identifying regional water quality influencing factors; the use of the logarithmic mean Dirichlet index decomposition method can effectively solve the residual problem in the decomposition of influencing factors and achieve residual-free decomposition; at the same time, it solves the problem that the existing water quality attribution analysis method cannot explain the contribution of each influencing factor to the change of the target variable in any period of time. The method of the present invention is helpful to analyze the long-term water quality change law and driving mechanism at the regional scale, and can be used as a basis for the effectiveness evaluation and policy formulation of regional water resources protection and pollution prevention and control measures, and can provide basic support for the prediction of regional water quality change trends, with a wide range of applications and strong scalability.

[0037] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the process of the method of the present invention;

[0039] Figure 2 This is a schematic diagram of the calculation results of the frequency of exceeding the standard for water quality monitoring indicators in Shanxi Province;

[0040] Figure 3This is a diagram showing the statistical results of the multi-year average (a) and standard deviation (b) of the comprehensive water quality index of each river water quality monitoring station in Shanxi Province from 2004 to 2016;

[0041] Figure 4 This is a schematic diagram of the calculation results of the comprehensive regional water quality index in Shanxi Province from 2004 to 2016;

[0042] Figure 5 This is a schematic diagram of the calculation results of the changes in the comprehensive index of regional water quality in Shanxi Province and the changes in the factors affecting regional water quality from 2004 to 2016. DETAILED DESCRIPTION

[0043] The present invention discloses a quantitative analysis method of the contribution of regional water quality influencing factors based on exponential decomposition, such as Figure 1 As shown, the method comprises the following steps:

[0044] Step 1. Obtain basic data: Obtain basic data of the study area, mainly including river water quality data, water resources data and socio-economic data in the administrative region. Among them, river water quality data in the administrative region refers to the monthly water quality monitoring data of the river water quality monitoring station with a long history (generally more than 10 years) within the administrative region. The water quality monitoring indicators are the 24 basic items of surface water environmental quality standards specified in the "Surface Water Environmental Quality Standard" (GB3838-2002), including water temperature (WT), pH value (pH), dissolved oxygen (DO), permanganate index (COD Mn ), chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD5), ammonia nitrogen (NH3-N), total phosphorus (TP), total nitrogen (TN), copper (Cu), zinc (Zn), fluoride (F - ), selenium (Se), arsenic (As), mercury (Hg), cadmium (Cd), chromium (Cr), lead (Pb), cyanide (CN), volatile phenol, petroleum, anionic surfactant, sulfide, fecal coliform; water resources data include annual precipitation, water resources, water consumption and other statistical data of the administrative area, and the data source is the water resources bulletin of the administrative area; social and economic data include annual industrial added value per 10,000 yuan, gross domestic product, total population and other statistical data of the administrative area, and the data source is the statistical yearbook of the administrative area.

[0045] Step 2, selection of regional water quality evaluation indicators: According to the standard limits of basic items of surface water environmental quality standards stipulated in the "Surface Water Environmental Quality Standard" (GB3838-2002), the monthly water quality monitoring data of single water quality monitoring indicators of each river water quality monitoring station within the administrative area are evaluated, and the frequency of exceeding the standard for each water quality monitoring indicator except the two water quality monitoring indicators of water temperature (WT) and pH value (pH) is counted, that is, the proportion of the number of times the concentration value of the water quality monitoring indicator exceeds the standard limit of Class III of the water quality category corresponding to the indicator to the total number of historical monitoring times, and the water quality monitoring indicator with an exceeding frequency of more than 25% is selected as the regional water quality evaluation indicator. In addition, for river water quality stations, total nitrogen does not participate in water quality evaluation, so if the selected regional water quality evaluation indicators include total nitrogen, it will be eliminated; water temperature (WT) and pH value (pH) are directly included in the regional water quality evaluation indicators.

[0046] Step 3: Calculation of single-station water quality comprehensive index: Based on the selected regional water quality evaluation indicators, calculate the single-station water quality comprehensive index (Water Quality Index, WQI) of each river water quality monitoring station within the administrative area. The calculation formula is:

[0047]

[0048] Where: WQI j is the comprehensive water quality index of the jth water quality monitoring station; n is the total number of regional water quality evaluation indicators; C i is the normalized value assigned to the i-th regional water quality evaluation index; P i is the weight coefficient of the i-th regional water quality evaluation index.

[0049] Among them, the normalized value C of the i-th regional water quality evaluation index is i The calculation is done using the following formula:

[0050]

[0051] Where: T i is the measured concentration value of the water quality evaluation index of the ith area; S i,1 , S i,2 , S i,3 , S i,4 , S i,5 They are the standard limits for water quality categories I, II, III, IV and V specified in the Surface Water Environmental Quality Standards corresponding to the i-th regional water quality assessment index.

[0052] The weight coefficients of each regional water quality evaluation index are determined according to the recommended values ​​for aquatic biological protection. For details, please refer to the literature "Pesce SF, Wunderlin DA. Use of water quality indices to verify the impact of Córdoba City (Argentina) on Suquía River [J]. Water Research, 2000, 34 (11): 2915-2926.", and appropriate corrections are made in combination with the severity of pollution of each regional water quality evaluation index. The normalized value is assigned an interval value according to the standard limit values ​​corresponding to each water quality category level of the basic items of surface water environmental quality specified in the "Surface Water Environmental Quality Standard" (GB3838-2002). In addition, since the two regional water quality evaluation indicators, water temperature (WT) and pH value (pH), are defined as appropriate ranges rather than standard limits in the "Surface Water Environmental Quality Standard" (GB3838-2002), the one-vote veto scoring principle is adopted, that is, when 6≤pH≤9, C i =0, otherwise C i =100; when -6℃≤WT≤45℃, C i =0, otherwise C i =100.

[0053] The larger the value of the single-station water quality comprehensive index calculated according to the above formula and parameter values, the worse the water quality. Definition of single-station water quality comprehensive index WQI j The water quality evaluation results corresponding to different value ranges are as follows: WQI j ≤20, the water quality is excellent; 21 <WQI j ≤40, the water quality is good; 41 <WQI j ≤60, the water quality is normal; 60 <WQI j ≤80, the water quality is poor; 81 <WQI j ≤100: the water quality is extremely poor and unsuitable for drinking.

[0054] Step 4: Calculation of regional water quality comprehensive index: Based on the single-station water quality comprehensive index of all river water quality monitoring stations within the administrative area, combined with the representative river length of the water quality monitoring station, the regional water quality comprehensive index WQI is obtained by weighted average. The calculation formula is:

[0055]

[0056] Where: WQI is the comprehensive index of regional water quality; L j is the representative river chief of the jth water quality monitoring station in the administrative area; p is the total number of water quality monitoring stations in the administrative area.

[0057] Step 5: Construction of a decomposition model of regional water quality influencing factors: Based on the fact that regional water quality is affected by the natural environment and human activities, factors such as precipitation, water resources, water consumption, industrial added value per 10,000 yuan, gross domestic product, and total population are selected as regional water quality influencing factors, and a regional water quality influencing factor decomposition model with the regional water quality comprehensive index as the target variable is established. The formula is:

[0058]

[0059] In the formula: WQI is the comprehensive index of regional water quality; R is the regional precipitation; W is the regional surface water resources; U is the regional water consumption; V is the regional industrial added value per 10,000 yuan; GDP is the regional gross domestic product; POP is the total population of the region; WQR represents the effect of unit precipitation on water quality; RW represents the rainfall-runoff relationship, reflecting the regional runoff relationship and also reflects the underlying surface conditions to a certain extent; WU represents the water supply and use structure; UV represents the water consumption per 10,000 yuan of industrial added value, reflecting the level of industrial water saving; VG represents the industrial structure; GP represents GDP per capita, reflecting the degree of regional social and economic development; P represents the population size.

[0060] Step 6: Calculate the change of regional water quality influencing factors by time period: Use the Logarithmic Mean Divisia Index (LMDI) decomposition method to calculate the contribution of each regional water quality influencing factor to the target variable. Select the LMDI addition decomposition mode, then the change of the regional water quality comprehensive index from t-1 to t can be decomposed into the change of l regional water quality influencing factors Δx k (k=1,…l), that is:

[0061]

[0062] Where: ΔWQI is the change in the regional water quality comprehensive index from time t-1 to time t; WQI t-1 and WQI t are the comprehensive regional water quality index at time t-1 and t respectively; Δx k is the change in the water quality influencing factors in the kth region.

[0063] Derived from the logarithmic mean weight function, Δx k The calculation formula is as follows:

[0064]

[0065] in:

[0066]

[0067] By substituting the data of regional water quality comprehensive index, precipitation, water resources, water consumption, industrial added value per 10,000 yuan, gross domestic product, and total population for each time period, the change of water quality influencing factors in each region at each time period can be calculated according to the above formula.

[0068] Step 7, Contribution analysis of regional water quality influencing factors: Based on the calculation results of the changes in the water quality influencing factors of each region from time to time, the contribution value of each regional water quality influencing factor is analyzed, with positive values ​​as positive driving effects and negative values ​​as negative driving effects. The changes in the water quality influencing factors of each region from time to time are cumulatively added up. If the sum is greater than 0, it indicates that the water quality influencing factors of the region have a promoting effect on the increase of the regional water quality comprehensive index, that is, they have an inhibitory effect on the improvement of the overall water quality of the region; on the contrary, if the sum is less than 0, it indicates that the water quality influencing factors of the region have an inhibitory effect on the increase of the regional water quality comprehensive index, that is, they have a promoting effect on the improvement of the overall water quality of the region; the larger the absolute value of the sum, the greater the contribution of the water quality influencing factors of the region. According to the quantitative analysis results of the contribution of regional water quality influencing factors, a reference can be provided for the dynamic formulation of regional water resources protection and pollution control policies.

[0069] Embodiment 1

[0070] This embodiment is a specific application example of the above method. In this embodiment, Shanxi Province is selected as the research area.

[0071] This embodiment discloses a method for quantitatively analyzing the contribution of regional water quality influencing factors based on exponential decomposition, comprising the following steps:

[0072] Step 1: Basic data acquisition: Obtain monthly water quality monitoring data of 19 river water quality monitoring stations in Shanxi Province from 2004 to 2016. The water quality monitoring indicators are 24 basic items of surface water environmental quality standards specified in the "Surface Water Environmental Quality Standard" (GB3838-2002), including water temperature (WT), pH value (pH), dissolved oxygen (DO), permanganate index (COD Mn ), chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD5), ammonia nitrogen (NH3-N), total phosphorus (TP), total nitrogen (TN), copper (Cu), zinc (Zn), fluoride (F -), selenium (Se), arsenic (As), mercury (Hg), cadmium (Cd), chromium (Cr), lead (Pb), cyanide (CN), volatile phenol, petroleum, anionic surfactant, sulfide, fecal coliform; obtain Shanxi Province water resources data, including Shanxi Province annual precipitation, water resources, water consumption statistics, the data source is the "Shanxi Water Resources Bulletin"; obtain Shanxi Province social and economic data, including Shanxi Province annual ten thousand yuan industrial added value, gross domestic product, total population statistics, the data source is the "Shanxi Statistical Yearbook".

[0073] Step 2: Selection of regional water quality evaluation indicators: According to the basic standard limits of surface water environmental quality standards stipulated in the Surface Water Environmental Quality Standard (GB3838-2002), the monthly water quality monitoring data of single water quality monitoring indicators of each river water quality monitoring station in Shanxi Province were evaluated, and the frequency of exceeding the standard for each water quality monitoring indicator except for the two water quality monitoring indicators of water temperature (WT) and pH value (pH) was counted, such as Figure 2 As shown in the figure, water quality monitoring indicators with a frequency of exceeding 25% are selected as water quality evaluation indicators for Shanxi Province. The water quality evaluation indicators for Shanxi Province are water temperature (WT), pH value (pH), dissolved oxygen (DO), chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD5), ammonia nitrogen (NH3-N), total phosphorus (TP), fluoride (F - ), volatile phenol, petroleum.

[0074] Step 3: Calculation of single-station water quality comprehensive index: Based on the selected Shanxi Province water quality evaluation indicators, calculate the single-station water quality comprehensive index (WQI) of each river water quality monitoring station in Shanxi Province. The calculation formula is:

[0075]

[0076] Where: WQI j is the comprehensive water quality index of the jth water quality monitoring station; n is the total number of regional water quality evaluation indicators; C i is the normalized value assigned to the i-th regional water quality evaluation index; P i is the weight coefficient of the i-th regional water quality evaluation index.

[0077] Among them, the normalized value C of the i-th regional water quality evaluation index is i The calculation is done using the following formula:

[0078]

[0079] Where: T i is the measured concentration value of the water quality evaluation index of the ith area; S i,1 , S i,2 , S i,3 , S i,4 , S i,s They are the standard limits for water quality categories I, II, III, IV and V specified in the Surface Water Environmental Quality Standards corresponding to the i-th regional water quality assessment index.

[0080] The weight coefficients of various regional water quality evaluation indicators are determined according to the recommended values ​​for aquatic biological protection, and are appropriately corrected in combination with the severity of pollution of various regional water quality evaluation indicators. The normalized values ​​are assigned intervals based on the standard limits corresponding to each water quality category level of the basic items of surface water environmental quality specified in the "Surface Water Environmental Quality Standard" (GB3838-2002). In addition, since the two regional water quality evaluation indicators WT and pH are defined as appropriate ranges rather than standard limits in the "Surface Water Environmental Quality Standard" (GB3838-2002), the one-vote veto scoring principle is adopted, that is, when 6≤pH≤9, C i =0, otherwise WT i =100; when -6℃≤WT≤45℃, C i =0, otherwise C i = 100. Based on this, the normalized values ​​and weight coefficients of regional water quality evaluation indicators in Shanxi Province are shown in Table 1.

[0081] Table 1 Normalized values ​​and weight coefficients of regional water quality evaluation indicators in Shanxi Province

[0082]

[0083]

[0084] The larger the value of the single-station water quality comprehensive index calculated according to the above formula and parameter values, the worse the water quality. Definition of single-station water quality comprehensive index WQI j The water quality evaluation results corresponding to different value ranges are as follows: WQI j ≤20, water quality is excellent; 21 <WQI j ≤40, the water quality is good; 41 <WQI j ≤60, the water quality is normal; 60 <WQI j ≤80, the water quality is poor; 81 <WQI j ≤100: the water quality is extremely poor and unsuitable for drinking.

[0085] According to the above single-station water quality comprehensive index evaluation system, the single-station water quality comprehensive index of each river water quality monitoring station in Shanxi Province from 2004 to 2016 was calculated. The statistical results of its multi-year average value and standard deviation are as follows: Figure 3 shown.

[0086] Step 4: Calculation of regional water quality comprehensive index: Based on the single-station water quality comprehensive index of all river water quality monitoring stations in Shanxi Province, the weighted average of the representative river length of the water quality monitoring station is used to obtain the regional water quality comprehensive index WQI. The calculation formula is:

[0087]

[0088] Where: WQI is the comprehensive index of regional water quality; L j is the representative river chief of the jth water quality monitoring station in the administrative area; p is the total number of water quality monitoring stations in the administrative area.

[0089] The calculation results of the comprehensive water quality index of Shanxi Province from 2004 to 2016 are as follows: Figure 4 It can be seen that during the period from 2004 to 2016, the overall water quality of rivers in Shanxi Province showed a trend of first getting worse and then getting better, with the turning point occurring in 2008.

[0090] Step 5: Construction of a decomposition model of regional water quality influencing factors: Select factors such as precipitation, water resources, water consumption, industrial added value per 10,000 yuan, gross domestic product, and total population as regional water quality influencing factors, and establish a regional water quality influencing factor decomposition model with the regional water quality comprehensive index as the target variable. The formula is:

[0091]

[0092] In the formula: WQI is the comprehensive index of regional water quality; R is the regional precipitation; W is the regional surface water resources; U is the regional water consumption; V is the regional industrial added value per 10,000 yuan; GDP is the regional gross domestic product; POP is the total population of the region; WQR represents the effect of unit precipitation on water quality; RW represents the rainfall-runoff relationship, reflecting the regional runoff relationship and also reflects the underlying surface conditions to a certain extent; WU represents the water supply and use structure; UV represents the water consumption per 10,000 yuan of industrial added value, reflecting the level of industrial water saving; VG represents the industrial structure; GP represents GDP per capita, reflecting the degree of regional social and economic development; P represents the population size.

[0093] Step 6: Calculate the change of regional water quality influencing factors by time period: Use the logarithmic mean Dirichlet index decomposition method (LMDI) to calculate the contribution of each regional water quality influencing factor to the target variable. Select the LMDI addition decomposition mode, then the change of the regional water quality comprehensive index from t-1 to t can be decomposed into the change of l regional water quality influencing factors Δx k(k=1,…l), that is:

[0094]

[0095] Where: ΔWQI is the change in the regional water quality comprehensive index from time t-1 to time t; WQI t-1 and WQI t are the comprehensive regional water quality index at time t-1 and t respectively; Δx k is the change in the water quality influencing factors in the kth region.

[0096] Derived from the logarithmic mean weight function, Δx k The calculation formula is as follows:

[0097]

[0098] in:

[0099]

[0100] By substituting the data of Shanxi Province's regional water quality comprehensive index, precipitation, water resources, water consumption, industrial added value per 10,000 yuan, gross domestic product, and total population for each period from 2004 to 2016, the above formula can be used to calculate the change in water quality influencing factors in each region from time to time.

[0101] The calculation results of the changes in the comprehensive water quality index of Shanxi Province from 2004 to 2016 and the changes in the water quality influencing factors of each region from time to time are shown in Table 2 and Figure 5 shown.

[0102] Table 2 Calculation results of the change of regional water quality comprehensive index and the change of water quality influencing factors in each region from 2004 to 2016

[0103]

[0104] Step 7, Contribution analysis of regional water quality influencing factors: Based on the calculation results of the changes in the water quality influencing factors of each region from time to time, the contribution value of the water quality influencing factors of each region is analyzed, with positive values ​​as positive driving effects and negative values ​​as negative driving effects. The changes in the water quality influencing factors of each region from time to time are cumulatively added up. If the sum is greater than 0, it indicates that the water quality influencing factors of the region have a promoting effect on the increase of the regional water quality comprehensive index, that is, they have an inhibitory effect on the improvement of the overall water quality of the region; on the contrary, if the sum is less than 0, it indicates that the water quality influencing factors of the region have an inhibitory effect on the increase of the regional water quality comprehensive index, that is, they have a promoting effect on the improvement of the overall water quality of the region; the larger the absolute value of the sum, the greater the contribution of the water quality influencing factors of the region.

[0105] According to the calculation results of the time-to-time changes in the comprehensive index of regional water quality in Shanxi Province and the time-to-time changes in the influencing factors of regional water quality from 2004 to 2016, the WQI in Shanxi Province has decreased by 5.04 from 2004 to 2016. Overall, among the influencing factors, WU, GP, and POP are the positive driving effect influencing factors of the target variable WQI, among which GP is the positive driving effect influencing factor with the largest contribution, with a cumulative contribution value of 98.72. WQR, RW, UV, and VG are the negative driving effect influencing factors of the target variable WQI, among which UV is the negative driving effect influencing factor with the largest contribution, with a cumulative contribution value of -49.98. In addition, the negative driving effects of VG and WQR are also relatively large, with cumulative contribution values ​​of -37.63 and -18.65 respectively. The contribution of other influencing factors is relatively small. It can be seen that for a highly industrialized region like Shanxi Province, compared with natural environmental factors such as rainfall and runoff, socioeconomic factors have a greater impact on regional water quality changes. On the other hand, the contribution of GP (reflecting the degree of regional socio-economic development) with the strongest positive driving effect to WQI was positive before 2013, but it showed a trend of gradual weakening, and even showed a negative driving effect after 2013. On the contrary, the contribution of UV (reflecting the level of industrial water conservation) with the strongest negative driving effect to WQI was negative before 2012, but became positive after 2012. This means that with the socio-economic development with GDP per capita as the main indicator, water quality has deteriorated, and when socio-economic development reaches a certain level, along with the government's strengthening of water quality protection and governance policies, water quality has improved. As for the level of industrial water conservation, the reduction of water consumption per 10,000 yuan of industrial added value and the improvement of industrial water use efficiency also have a positive effect on improving regional water quality. However, when it is reduced to a certain level, it may not play a positive role in improving regional water quality due to restrictions from other factors. The above quantitative analysis results of the contribution of regional water quality influencing factors can provide a reference for the dynamic formulation of regional water resources protection and pollution control policies.

[0106] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred arrangement scheme, a person skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A quantitative analysis method of the contribution of regional water quality influencing factors based on exponential decomposition, characterized in that: The method comprises the following steps: Step 1, basic data acquisition: obtain basic data of the study area, including river water quality data, water resources data and social and economic data of the administrative region; the river water quality data of the administrative region refers to the monthly water quality monitoring data of the long-term water quality monitoring indicators of the river water quality monitoring stations within the administrative region. The water quality monitoring indicators are the 24 basic items of surface water environmental quality standards specified in the "Surface Water Environmental Quality Standards", including water temperature, pH value, dissolved oxygen, permanganate index, chemical oxygen demand, five-day biochemical oxygen demand, ammonia nitrogen, total phosphorus, total nitrogen, copper, zinc, fluoride, selenium, arsenic, mercury, cadmium, chromium, lead, cyanide, volatile phenol, petroleum, anionic surfactants, sulfide, fecal coliform bacteria; the water resources data include the annual precipitation, water resources and water consumption statistics of the administrative region; the social and economic data include the annual industrial added value per 10,000 yuan, gross domestic product and total population statistics of the administrative region; Step 2, selection of regional water quality evaluation indicators: According to the standard limits of basic items of surface water environmental quality standards stipulated in the "Surface Water Environmental Quality Standards", the monthly water quality monitoring data of single water quality monitoring indicators of each river water quality monitoring station within the administrative area are evaluated, and the frequency of exceeding the standard for each water quality monitoring indicator except the two water quality monitoring indicators of water temperature and pH value is counted, that is, the proportion of the number of times the concentration value of the water quality monitoring indicator exceeds the water quality category grade III standard limit corresponding to the indicator to the total number of historical monitoring times, and the water quality monitoring indicator with an exceeding frequency exceeding the set threshold is selected as the regional water quality evaluation indicator; the two water quality monitoring indicators of water temperature and pH value are directly included in the regional water quality evaluation indicators; Step 3: Calculation of single-station water quality comprehensive index: Based on the selected regional water quality evaluation indicators, calculate the single-station water quality comprehensive index of each river water quality monitoring station within the administrative area. The calculation formula is: Where: WQI j is the comprehensive water quality index of the jth water quality monitoring station; n is the total number of regional water quality evaluation indicators; C i is the normalized value assigned to the i-th regional water quality evaluation index; P i is the weight coefficient of the i-th regional water quality evaluation index; Among them, the normalized value C of the i-th regional water quality evaluation index is i The calculation is done using the following formula: Where: T i is the measured concentration value of the water quality evaluation index of the ith area; S i,1 , S i,2 , S i,3 , S i,4 , S i,5 They are the standard limits of water quality categories I, II, III, IV and V specified in the Surface Water Environmental Quality Standards corresponding to the regional water quality assessment index of the ith item; The weight coefficient of the regional water quality evaluation index in step 3 is determined according to the recommended value for aquatic biological protection, and is corrected in combination with the severity of pollution of the regional water quality evaluation index; the normalized value of the regional water quality evaluation index is assigned an interval value according to the standard limit values ​​corresponding to each water quality category level of the basic items of surface water environmental quality specified in the "Surface Water Environmental Quality Standard", where the two regional water quality evaluation indicators of water temperature and pH value adopt a one-vote veto scoring principle, that is, when 6≤pH≤9, C i =0, otherwise C i =100; when -6℃≤WT≤45℃, C i =0, otherwise C i =100; Step 4: Calculation of regional water quality comprehensive index: Based on the single-station water quality comprehensive index of all river water quality monitoring stations within the administrative area, combined with the representative river length of the water quality monitoring station, the regional water quality comprehensive index WQI is obtained by weighted average. The calculation formula is: Where: WQI is the comprehensive index of regional water quality; L j is the representative river chief of the jth water quality monitoring station in the administrative area; p is the total number of water quality monitoring stations in the administrative area; Step 5: Construction of a decomposition model of regional water quality influencing factors: Select precipitation, water resources, water consumption, industrial added value per 10,000 yuan, gross domestic product, and total population as regional water quality influencing factors, and establish a regional water quality influencing factor decomposition model with the regional water quality comprehensive index as the target variable. The formula is: Where: WQI is the regional water quality comprehensive index; R is the regional precipitation; W is the regional surface water resources; U is the regional water consumption; V is the regional industrial added value per 10,000 yuan; GDP is the regional gross domestic product; POP is the total population of the region; WQR represents the effect of unit precipitation on water quality; RW represents the rainfall-runoff relationship; WU represents the water supply and use structure; UV represents the water consumption per 10,000 yuan of industrial added value; VG represents the industrial structure; GP represents GDP per capita; P represents the population size; Step 6: Calculate the change of regional water quality influencing factors by time period: Use the logarithmic mean Dirichlet index decomposition method LMDI to calculate the contribution of each regional water quality influencing factor to the target variable. Select the LMDI addition decomposition mode, and the change of the regional water quality comprehensive index from time t-1 to time t is decomposed into the change of l regional water quality influencing factors Δx k , k=1,…l, that is: Where: ΔWQI is the change in the regional water quality comprehensive index from time t-1 to time t; WQI t-1 and WQI t are the comprehensive regional water quality index at time t-1 and t respectively; Δx k is the change in the water quality influencing factors in the kth region; Derived from the logarithmic mean weight function, Δx k The calculation formula is: in: Substitute the data of regional water quality comprehensive index, precipitation, water resources, water consumption, industrial added value per 10,000 yuan, gross domestic product, and total population for each time period to calculate the change of water quality influencing factors in each region for each time period; Step 7. Analysis of the contribution of regional water quality influencing factors: Based on the calculation results of the changes in the water quality influencing factors in each region from time to time, the contribution value of the water quality influencing factors in each region is analyzed, with positive values ​​representing positive driving effects and negative values ​​representing negative driving effects.

2. The method for quantitative analysis of the contribution of regional water quality influencing factors based on exponential decomposition according to claim 1 is characterized in that: The long series of monthly water quality monitoring data of water quality monitoring indicators in step 1 is monthly water quality monitoring data of water quality monitoring indicators for more than 10 years.

3. The method for quantitative analysis of the contribution of regional water quality influencing factors based on exponential decomposition according to claim 1 is characterized in that: The water resources data in step 1 are sourced from the water resources bulletin of the administrative region; the social and economic data are sourced from the statistical yearbook of the administrative region.

4. The method for quantitative analysis of the contribution of regional water quality influencing factors based on exponential decomposition according to claim 1 is characterized in that: The water quality monitoring index with a frequency exceeding the set threshold selected in step 2 is set as the set threshold of 25% in the regional water quality evaluation index; and total nitrogen does not participate in the water quality evaluation. If the selected regional water quality evaluation index includes total nitrogen, it will be excluded.

5. The method for quantitative analysis of the contribution of regional water quality influencing factors based on exponential decomposition according to claim 1 is characterized in that: The single-station water quality comprehensive index WQI described in step 3 j The water quality evaluation results corresponding to different value ranges are: WQI j ≤20, the water quality is excellent; 21 <WQI j ≤40, the water quality is good; 41 <WQI j ≤60, the water quality is normal; 60 <WQI j ≤80, the water quality is poor; 81 <WQI j ≤100: the water quality is extremely poor and unsuitable for drinking.

6. The method for quantitative analysis of the contribution of regional water quality influencing factors based on exponential decomposition according to claim 1 is characterized in that: The specific process of analyzing the contribution value of the water quality influencing factors of each region described in step 7 is: cumulatively summing up the changes in the water quality influencing factors of each region in each time period. If the sum result is greater than 0, it indicates that the water quality influencing factors of this region promote the increase of the regional water quality comprehensive index, that is, it inhibits the improvement of the overall water quality of the region; if the sum result is less than 0, it indicates that the water quality influencing factors of this region inhibit the increase of the regional water quality comprehensive index, that is, it promotes the improvement of the overall water quality of the region; the larger the absolute value of the sum result, the greater the contribution of the water quality influencing factors of this region.

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