A method for evaluating vegetation restoration of historical earthquake monomer landslide

Abstract

The application discloses a historical earthquake monomer landslide vegetation recovery evaluation method, which can calculate the vegetation recovery rate of a historical earthquake induced ancient landslide and quantifies the activity of the landslide. First, the evaluation period of the historical earthquake monomer landslide vegetation recovery is set, and the average value of the vegetation coverage of the landslide year by year in the evaluation period is calculated. Then, the cumulative vegetation coverage curve of the monomer landslide in the evaluation period is drawn, and the reference period and the evaluation period of the historical earthquake monomer landslide vegetation recovery are determined according to the curve shape and the data inflection point. Then, the vegetation coverage of the reference period and the evaluation period is calculated, and the historical earthquake monomer landslide vegetation recovery evaluation model is established. Finally, the VRR of the evaluation period is calculated, the vegetation recovery grade and the landslide activity type are divided according to the VRR value. The application can be used for evaluating and analyzing the vegetation recovery condition of the monomer ancient landslide area induced by the historical earthquake in recent decades, revealing the long-time evolution characteristic law, and accurately evaluating the vegetation recovery condition of the historical earthquake monomer landslide.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ecological restoration evaluation in disaster areas, and particularly relates to a historical earthquake single landslide vegetation restoration evaluation method. BACKGROUND

[0002] Earthquakes in mountainous areas are prone to induce a large number of landslides, change the topography and geomorphology of the area, and have a long-term impact on vegetation. Since the occurrence time of ancient landslides induced by historical earthquakes is long ago, the vegetation coverage of the area before the landslide and a period after the landslide cannot be obtained, so the existing landslide area vegetation restoration evaluation model cannot be used to carry out related evaluation analysis. At present, the method for evaluating the vegetation restoration of the landslide area at home and abroad is to calculate the vegetation restoration rate VRR through the following evaluation model:

[0003]

[0004] Among them, NDVI0 is the NDVI value before the earthquake, NDVI1 is the NDVI value after the earthquake, NDVI2 is the NDVI value of a year after the earthquake, and NDVI is the normalized difference vegetation index.

[0005] The vegetation restoration after the earthquake is crucial for the repair of the landslide area, and can also reflect the activity of the landslide, so it is necessary to track the dynamic changes of the vegetation in the landslide area for a long time. So far, there have been many events of historical landslide revival in the world, causing regional casualties and economic losses. Evaluating the vegetation restoration of the landslide area after m years and quantifying the activity of the landslide can help avoid the harm caused by the revival of historical landslides, and timely measures can be taken to repair and further improve the landslide disaster prevention and reduction capacity.

[0006] Due to the frequent occurrence of historical landslide revival events, which are affected by many factors and closely related to vegetation coverage, the evaluation of the vegetation restoration rate of the landslide area based on NDVI and FVC (vegetation coverage) data is still the main method. Based on this, the application provides a scientific, reasonable and reliable historical earthquake single landslide vegetation restoration evaluation method for calculating the vegetation restoration rate of the historical earthquake single landslide, quantifying the activity of the landslide, preventing the revival of the landslide, and further repairing the landslide area with a low vegetation restoration rate. SUMMARY

[0007] In view of the problem in the above background art that the existing landslide area vegetation restoration evaluation method cannot evaluate the vegetation restoration of historical earthquake single landslides, the purpose of the application is to provide a historical earthquake single landslide vegetation restoration evaluation method, which calculates the vegetation restoration rate of historical earthquake single landslides to quantitatively evaluate the activity of the landslide and avoid the revival of historical earthquake landslides causing large casualties and property losses.

[0008] In order to achieve the above purpose, the application adopts the following technical solutions:

[0009] A historical earthquake monomer landslide vegetation restoration evaluation method, comprising the following steps:

[0010] Step S1, selecting a historical earthquake monomer landslide body, setting an evaluation period of historical earthquake monomer landslide vegetation restoration;

[0011] Step S2, in the evaluation period of m years, calculating the average value of vegetation coverage FVC of each year of the landslide in the evaluation period i (i=1,2,……m):

[0012]

[0013] Wherein, NDVI soil is the value of NDVI of the full bare area, NDVI veg is the value of NDVI of the full coverage area, NDVI veg NDVI max is the maximum value of NDVI in the landslide area instead of NDVI soil NDVI min is the minimum value of NDVI in the landslide area instead of NDVI

[0014] Step S3, according to the average value of vegetation coverage, drawing a cumulative vegetation coverage curve of monomer landslide in the evaluation period, and determining the reference period and evaluation period of evaluating the vegetation restoration of historical earthquake monomer landslide according to the curve shape and data inflection point;

[0015] Step S4, calculating the vegetation coverage FVC B of the reference period and the vegetation coverage FVC T of the evaluation period respectively;

[0016] Step S5, establishing a historical earthquake monomer landslide vegetation restoration evaluation model according to FVC B and FVC T

[0017]

[0018] The vegetation restoration rate VRR of the evaluation period of the historical earthquake monomer landslide is calculated; according to the VRR value, the vegetation restoration grade and the landslide activity type are divided.

[0019] Further, in step S3, the determination method of the reference period and the evaluation period is:

[0020] Case 1: when the shape of the cumulative vegetation coverage curve of the monomer landslide in the evaluation period fluctuates greatly and has obvious inflection points, determine n inflection points, select each inflection point G j ​(j = 1, 2, ……n, n≤m-2) are the division points, and the entire evaluation period is divided into k periods (k≤1, 2, ……n+1); the first period is the reference period of the evaluation, and any period after the reference period is the evaluation period;

[0021] Case 2: When the shape of the cumulative vegetation coverage curve of the monomer landslide in the evaluation period is relatively smooth and has no obvious inflection point, the intervals are autonomously divided according to the evaluation period and the research characteristics; the first period in the evaluation period is the reference period, and any period after the reference period is the evaluation period.

[0022] Further, for the above two cases, the vegetation coverage FVC B of the reference period and the vegetation coverage FVC T of the evaluation period are calculated as follows.

[0023] For case 1: the vegetation coverages of the reference period and the evaluation period are obtained by the calculation formula of FVC k .

[0024] or

[0025] wherein, FVC l is the value corresponding to the previous inflection point in the k period on the cumulative vegetation coverage curve, FVC l+1 is the value corresponding to the next inflection point in the k period on the cumulative vegetation coverage curve, P is the number of years in the period; FVC x is the average vegetation coverage in the x year in the k period.

[0026] For case 2: the vegetation coverages of the reference period and the evaluation period are calculated by selecting the average value in the interval.

[0027] Further, in step S5, the vegetation recovery level and the landslide activity type are divided as follows.

[0028]

[0029] Compared with the disadvantages and deficiencies of the prior art, the present application has the following beneficial effects:

[0030] The present application can calculate the vegetation recovery rate after m years of the historical landslide, and overcomes the problem that the VRR cannot be calculated due to the lack of vegetation data in a period before and after the historical earthquake landslide. The present application calculates the vegetation recovery rate in the evaluation period by combining the data of the reference period and the evaluation period, and the obtained result is close to the actual vegetation recovery situation, can accurately reflect the vegetation recovery situation after m years of the historical landslide, and can further quantify the activity of the landslide. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1is a schematic diagram of a historical earthquake monomer landslide body selected by an embodiment of the present application;

[0032] Figure 2 is a cumulative vegetation coverage curve of a monomer landslide in 2000-2020 years provided by embodiment 1 of the present application;

[0033] Figure 3 is a cumulative vegetation coverage curve of a monomer landslide in 2000-2020 years provided by embodiment 2 of the present application;

[0034] Figure 4 is a grid visual expression diagram of a monomer landslide vegetation coverage mean corresponding to a reference period provided by embodiment 2 of the present application;

[0035] Figure 5 is a grid visual expression diagram of a monomer landslide vegetation coverage mean corresponding to an evaluation period of 2006-2010 years provided by embodiment 2 of the present application;

[0036] Figure 6 is a VRR and landslide activity type in an evaluation period of 2006-2010 years provided by embodiment 2 of the present application. DETAILED DESCRIPTION

[0037] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application.

[0038] The present application provides a historical earthquake monomer landslide vegetation restoration evaluation method, which divides vegetation restoration grades by calculating a historical landslide vegetation restoration rate and quantifies landslide activity.

[0039] Embodiment 1

[0040] For case 1: the morphology of the cumulative vegetation coverage curve of a monomer landslide in an evaluation period fluctuates greatly and has a clear inflection point, the evaluation method is as follows:

[0041] Step S1, a historical earthquake monomer landslide body in Tianshui City, Gansu Province (refer to Figure 1 ), is selected, and the evaluation period of the historical earthquake monomer landslide vegetation restoration is set to 2000-2020 years;

[0042] Step S2, based on the selected monomer landslide body, the downloaded NDVI data corresponds to the result that the NDVI of the landslide area in Tianshui City shows an increasing trend from 2000 to 2020, and the change is very small, which cannot meet the assumption of condition 1, so the number of RAND function in Excel represents the average value of vegetation coverage FVC from 2000 to 2020; Calculate the average value of vegetation coverage FVC (i.e. the value given by ST100) of each year of the landslide from 2000 to 2020;

[0043] Step S3, according to the average value of vegetation coverage, draw the cumulative vegetation coverage curve of monomer landslide from 2000 to 2020, as shown in Figure 2 The curve fluctuates greatly and has obvious inflection points, a total of j = 3 inflection points are determined, and each inflection point G j is selected as a segmentation point, and 2000-2020 is divided into k = 4 periods; The first period is j = 1 from 2000 to 2005, that is, the reference period from 2000 to 2005 is determined; Then the evaluation period k = 2, 3, 4 corresponds to 2005-2009, 2010-2016, 2017-2020 respectively;

[0044] Step S4, the calculation formula of FVC k is used to calculate the vegetation coverage FVC B of the reference period and the vegetation coverage FVC T of the evaluation period respectively;

[0045] The vegetation coverages of the reference period and the evaluation period are represented by FVC k , and the calculation formula is:

[0046] Or

[0047] Where, FVC l is the value corresponding to the previous inflection point in the k period on the cumulative vegetation coverage curve, FVC l+1 is the value corresponding to the next inflection point in the k period on the cumulative vegetation coverage curve, and P is the number of years in the period; FVC x is the average value of vegetation coverage in the x year in the k period.

[0048] Then FVC B = 0.67 from 2000 to 2020; k = 2, FVC T(2006-2009) = 0.07; k = 3, FVC T(2010-2016) = 0.65; k = 4, FVC T(2017-2020) = 0.25;

[0049] Step S5, establish a historical earthquake monomer landslide vegetation recovery evaluation model:

[0050]

[0051] The vegetation restoration rates VRR of the evaluation periods 2005-2009, 2010-2016 and 2017-2020 are calculated as follows: k = 2, VRR (2006-2009) = -90.07%; k = 3, VRR (2010-2016) = -3.02%; k = 4, VRR (2017-2020) = -62.66%; the vegetation restoration grades and landslide activity types are divided according to the VRR values, as shown in Table 1:

[0052] Table 1 The FVC average values, FVC average value cumulative frequencies, FVC B , FVC T , VRR and vegetation restoration grades and landslide activity types corresponding to case 1 in 2000-2020

[0053]

[0054] As can be seen from Table 1, the vegetation restoration of 2005-2009 is extremely poor, which is an active landslide; the vegetation restoration of 2010-2016 is extremely good, which is a non-active landslide; the vegetation restoration of 2017-2020 is extremely poor, which is an active landslide.

[0055] Example 2

[0056] For case 2: the shape of the cumulative vegetation coverage curve of the single landslide in the evaluation period is relatively smooth and straight without obvious inflection point, and the evaluation method is as follows:

[0057] Step S1, a historical earthquake single landslide in Qinzhou District of Tianshui City, Gansu Province (refer to Figure 1 ) is selected, and the evaluation period of the vegetation restoration of the historical earthquake single landslide is set as 2000-2020;

[0058] Step S2, based on the selected single landslide, the corresponding NDVI data is obtained by the Land Use and Global Change Remote Sensing Team of the Institute of Geographical Sciences and Resources of the Chinese Academy of Sciences (https: / / doi.org / 10.12199 / nesdc.ecodb.rs.2021.012), the spatial resolution is 30m, and it belongs to annual maximum NDVI data. The NDVI of 2000-2020 almost shows a growth trend with little change, which meets the assumption of case 2; the average vegetation coverage FVC of the landslide in each year of 2000-2020 is calculated:

[0059]

[0060] Wherein, NDVI soilNDVI is the value of the full-naked area NDVI, NDVI veg NDVI is the value of the full-coverage area NDVI;

[0061] The calculation formula of NDVI is:

[0062] Wherein, NIR is the reflectivity of near-infrared band radiation; RED is the reflectivity of visible infrared band radiation;

[0063] NDVI is calculated by the "raster calculator" of ArcGIS veg The maximum value of NDVI in the landslide area NDVI max is used instead of NDVI soil The minimum value of NDVI in the landslide area NDVI min is used instead; the maximum and minimum values of NDVI are obtained by checking the statistical values of landslide raster image; the average value of vegetation coverage of single landslide per year is obtained by checking FVC statistical values again;

[0064] Step S3, according to the average value of vegetation coverage, the cumulative vegetation coverage curve of single landslide in 2000-2020 is drawn, as shown in Figure 3 There is no obvious inflection point in the curve, according to the evaluation period of 20 years, 5 years are selected as a period, so that 2000-2005 can be determined as the benchmark period for evaluating the vegetation recovery of single landslide in historical earthquake; 2006-2010, 2011-2015 and 2016-2020 are determined as the evaluation period for evaluating the vegetation recovery of single landslide in historical earthquake;

[0065] Step S4, the vegetation coverage FVC B of the benchmark period and the vegetation coverage FVC T of the evaluation period are calculated respectively; wherein, FVC B and FVC T are represented by the mean value of FVC in the interval (retaining two significant digits), FVC B = 0.51, and the raster mean value is shown in Figure 4 FVC T(2006-2010) = 0.48, and the raster mean value is shown in Figure 5 FVC T(2011-2015) = 0.55; FVC T(2016-2020) = 0.48;

[0066] Step S5, the historical earthquake single landslide vegetation recovery evaluation model is established according to FVC B and FVC T :

[0067]

[0068] The vegetation restoration rate (VRR) for individual landslides during the historical earthquake assessment periods of 2006-2010, 2011-2015, and 2016-2020 is calculated as follows: VRR (2006-2010) = -5.24%; VRR (2011-2015) =7.85%; VRR (2016-2020) = -8.97%; Based on the VRR value, the vegetation restoration level and landslide activity type are classified as shown in Table 2:

[0069] Table 2 shows the average FVC, cumulative frequency of average FVC, and FVC value from 2000 to 2020 for scenario 2. B FVC T VRR, vegetation restoration level, and landslide activity type

[0070]

[0071] Table 2 shows that vegetation restoration was extremely poor during the landslide period from 2006 to 2010, indicating it was an active landslide. Figure 6 As shown, the landslide vegetation recovery was poor from 2011 to 2015, indicating an active landslide; the landslide vegetation recovery was extremely poor from 2016 to 2020, indicating an active landslide.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for assessing vegetation restoration in a single landslide caused by a historical earthquake, characterized in that, Includes the following steps: Step S1: Select a historical earthquake landslide site and set the assessment period for vegetation restoration of the historical earthquake landslide site. Step S2, during the set evaluation period m In the middle of the year, the average vegetation cover of the landslide was calculated for each year within the assessment period. FVC i ( i=1,2,……m ): ； in, NDVI soil The value of NDVI for the naked region. NDVI veg The NDVI value for the full coverage area. NDVI veg Use the maximum value of NDVI within the landslide area NDVI max replace, NDVI soil Use the minimum NDVI value within the landslide area NDVI min replace; Step S3: Plot the cumulative vegetation coverage curve of a single landslide during the assessment period based on the average vegetation coverage. Determine the baseline period and assessment period for assessing the vegetation restoration of a single landslide from a historical earthquake based on the curve shape and data inflection points. Step S4: Calculate the vegetation cover for the baseline period. FVC B and vegetation cover during the assessment period FVC T ; Step S5, according to FVC B and FVC T Establish a vegetation restoration assessment model for individual landslides caused by historical earthquakes: ； The vegetation restoration rate during the assessment period of individual landslides in historical earthquakes was calculated. VRR ;according to VRR The values ​​are used to classify vegetation restoration levels and landslide activity types.

2. The method for assessing vegetation restoration in historical earthquake-affected landslides as described in claim 1, characterized in that, In step S3, the method for determining the benchmark period and the evaluation period is as follows: Scenario 1: When the morphological fluctuation of the cumulative vegetation cover curve of a single landslide within the assessment period shows a clear inflection point, the total... n Each inflection point is selected. G j ( j = 1, 2, ..., n, n ≤ m-2 Using ) as the dividing point, the entire evaluation period is divided into 100 parts. k Expect( k≤ 1,2,……n+1 The first period is the baseline period for this assessment, and any subsequent period is the assessment period. Scenario 2: When the cumulative vegetation coverage curve of a single landslide is relatively smooth and straight without obvious inflection points during the assessment period, the intervals are divided independently according to the assessment period and research characteristics. The first period within the assessment period is the baseline period, and any subsequent period is the assessment period.

3. The method for assessing vegetation restoration in historical earthquake-affected landslides as described in claim 2, characterized in that, Vegetation cover during the baseline period FVC B and vegetation cover during the assessment period FVC T The calculation method is as follows: For scenario 1: The calculation is done in phases, with vegetation cover for the baseline and evaluation periods determined by... FVC k The calculation formula is as follows: or ; in, FVC l The first on the cumulative vegetation cover curve k The value corresponding to the previous inflection point during the period, FVC l+1 The first on the cumulative vegetation cover curve k The value corresponding to the next inflection point within the period, P This refers to the year number in that period; FVC x For the first k During the period x Average vegetation cover over the years; For scenario 2: For autonomous zoning calculation, the vegetation cover of the baseline period and the evaluation period is calculated using the average value within the interval.

4. The method for assessing vegetation restoration in historical earthquake-affected landslides as described in claim 1, characterized in that, In step S5, the vegetation restoration level and landslide activity type are classified as follows: 。

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