(1. Shanghai Geological Survey and Research Institute, Shanghai 200072; 2. Tongji University school of economics and management, Shanghai 200072)

How to correctly evaluate the economic loss of land subsidence disaster is not only an important topic for land subsidence research in Shanghai, but also the need of disaster prevention and mitigation decision-making. Based on the analysis of the mechanism and harm of land subsidence in Shanghai, this paper applies relevant theories such as geology, hydrology, disaster science, economics and statistics. The economic loss evaluation system of land subsidence in Shanghai was initially established, and the evaluation principles and methods were established. On this basis, the economic losses caused by land subsidence disasters in Shanghai and the economic benefits of controlling land subsidence are comprehensively evaluated for the first time, and the risk losses of land subsidence disasters in Shanghai from 200/kloc-0 to 2020 are predicted.

Keywords: land subsidence; Evaluation principle; Evaluation method; Economic loss; Risk loss; Disaster reduction benefit

1 preface

Shanghai is one of the earliest cities in China where land subsidence was discovered and investigated. As early as the early 1920s, land subsidence was discovered in Shanghai and then further developed. 1965 before the control measures were taken, the accumulated average settlement in the central urban area was 65438+2.63m, the average annual settlement was 37.93mm, and the annual maximum settlement was 1 1965. After the settlement control measures were taken in the mid-1960s, the average annual settlement dropped sharply to 6. 19mm, and the settlement control effect reached 84%, which kept the land subsidence in the controlled micro-settlement period. Therefore, Shanghai has always been in the forefront of the world in the research of land subsidence mechanism, settlement control measures and settlement control effects, and has made remarkable achievements in settlement control and disaster reduction, which has provided a strong guarantee for Shanghai's urban construction and sustainable development.

While studying land subsidence, the relevant institutions have also conducted extensive investigations on various disaster phenomena and accumulated some disaster loss data. However, due to the limitation of historical conditions, there are some problems in the previous research on economic losses of land subsidence, such as incomplete loss classification, insufficient estimation basis and improper evaluation principles and methods, which lead to a serious low estimation result. Therefore, how to correctly evaluate the economic loss of land subsidence disaster is not only an important topic of land subsidence research in Shanghai, but also the need of disaster prevention and mitigation decision-making. Therefore, in the new round of land and resources survey project "Rational development of groundwater resources in the Yangtze River Delta and investigation and evaluation of geological disasters in Shanghai (1999 ~ 2002)", "Economic loss evaluation of land subsidence in Shanghai" is a sub-project of this project, and it was included in the project funded by Shanghai Science and Technology Development Fund by Shanghai Science and Technology Commission in 20001year. The research of the subject mainly focuses on four aspects: (1) Establishing the economic loss evaluation system of land subsidence: namely, studying the mechanism and harm of land subsidence, establishing the classification system of economic loss indicators, clearly evaluating the space, time and time, and formulating the principles and methods of economic loss evaluation of land subsidence; (2) Estimate the economic losses caused by land subsidence disasters in Shanghai 192 1 2000; (3) Evaluate the economic benefits of controlling land subsidence; (4) Forecast the economic loss of land subsidence disaster risk in Shanghai from 200/KLOC-0 to 2020.

2 Disaster mechanism and harm of land subsidence in Shanghai

Most parts of Shanghai are covered by loose overburden with a thickness of more than 300 meters, which is rich in groundwater resources. When a large amount of groundwater is pumped, the effective pressure in the soil layer increases, and the compressive deformation of loose soil layer will lead to the gradual decrease of ground elevation and land subsidence. Land subsidence in Shanghai is closely related to the quantity, time, area and horizontal distribution of groundwater exploitation, so groundwater exploitation is the main disaster-causing factor of land subsidence in Shanghai. Since 1990s, engineering construction has become an important disaster-causing factor that cannot be ignored. According to research, the land subsidence caused by engineering construction in this period accounts for about 32% of the total subsidence.

Because the object of land subsidence is the whole urban system, from the perspective of disaster science, the disaster-bearing bodies of land subsidence include all aspects of the city, such as industry, energy, architecture, transportation, disaster reduction engineering facilities, production and living service facilities and all kinds of wealth accumulated by people. Shanghai covers an area of 1‰ and a population of 1%, providing about 5% of the country's GDP and more than 10% of its fiscal revenue. Once attacked by natural disasters, its economic losses will be extremely huge.

Land subsidence will directly lead to the loss of safety elevation. On the one hand, elevation loss will bring many direct hazards, such as destroying infrastructure and buildings such as roads, bridges, ports and docks, underground pipelines and deep wells. On the other hand, due to the waterfront, the average elevation of Wusong in Shanghai is only 3 ~ 3.5m, which is easily affected by typhoons, rainstorms and tides. Such geographical conditions are extremely sensitive to land subsidence. The same ground elevation loss may not cause obvious harm to high-altitude inland cities, but for Shanghai, it may induce a series of secondary disasters, thus endangering urban safety. Tidal floods and floods induced or aggravated by land subsidence have become a major concern in Shanghai's disaster reduction and prevention work. Although the government has invested a lot of money in building and heightening flood control walls along the Yangtze River for many times over the years, and the urban drainage system has been completely transformed, the flood threat faced by Shanghai has not been fundamentally eliminated so far. The important reason is that the standard of flood control and drainage facilities has been seriously reduced after the ground elevation has been lowered.

The serious land subsidence in the history of Shanghai has gradually developed into the most important geological disaster in Shanghai, which has adversely affected the sustainable development of urban social economy. The disaster mechanism can be shown in figure 1.

Figure 1 Schematic Diagram of Disaster Mechanism of Land Subsidence

Classification system of economic loss of land subsidence in Shanghai

According to whether the land subsidence disaster directly caused the damage loss of the affected body, the economic loss of land subsidence can be divided into two categories: direct economic loss and indirect economic loss. See Figure 2 for the economic loss classification system of land subsidence in Shanghai.

Shanghai land subsidence economic loss evaluation and classification system.

Economic loss assessment of land subsidence in Shanghai

4. 1 Shanghai land subsidence economic loss evaluation principle

4. 1. 1 dynamic principle

The damage of land subsidence disaster to the affected body is a slow and continuous cumulative dynamic process, and the economic loss caused by it is a long process of continuous accumulation with the development and change of land subsidence disaster. Therefore, the economic loss assessment of land subsidence must follow the principle of dynamics.

4. 1.2 testability principle

The economic loss of land subsidence referred to in this paper refers to the economic loss that can be measured by money, but there are also quite a few losses, especially indirect losses, which are difficult to be measured by money at present, such as the loss of underground water-bearing structure and the loss of sustainable development ability caused by land subsidence, which will not be included in the scope of economic loss estimation, that is, the economic loss evaluation follows the principle of measurability.

4. 1.3 comprehensive principle

Because the disaster scope of land subsidence disaster is large, involving many types of affected bodies, and the disaster mechanism is complex, all kinds of losses should be comprehensively grasped and comprehensively considered when evaluating the economic losses of land subsidence, and different evaluation methods should be comprehensively considered when evaluating the economic losses of land subsidence, so as to improve the accuracy of the evaluation results.

4. 1.4 Robustness principle

The damage losses caused by land subsidence disasters are continuous and huge, and even some losses are not known at present. Especially due to statistical work and understanding, most of the injuries and losses of many victims in the past have not been clearly recorded. Therefore, the economic loss of land subsidence should be evaluated as accurately as possible according to the principle of robustness.

4. 1.5 separability principle

Land subsidence usually causes damage to the affected organism through other carriers. For example, land subsidence leads to the rise of relative sea level (river water level), which induces or aggravates tidal disasters and floods. Therefore, according to the disaster-causing mechanism of land subsidence, the interaction between land subsidence and other factors must be carefully analyzed, and the weight of land subsidence in the economic losses of the affected bodies must be decomposed.

4.2 Shanghai land subsidence economic loss assessment method

4.2. 1 final value method

Because of the time value of money, the losses of disaster-stricken bodies in different years cannot be the same value, and the economic losses of land subsidence in Shanghai are not the sum of static algebra of various losses in various years during the evaluation period. When estimating, we will use the relevant discount rate of each year in the evaluation period to compound all kinds of economic losses in the corresponding years until the end of 2000, and then add them together to get the total economic losses of land subsidence in Shanghai at the end of 2000.

4.2.2 Shadow Engineering Method

Shadow engineering method is a kind of engineering substitution method, that is, in order to estimate a loss project that cannot be directly obtained, it is assumed that a project with similar actual effect is adopted, and the economic loss of the project to be evaluated is replaced by the construction cost of the project. This report uses this method to estimate the loss of safety elevation when the settlement is not controlled.

4.2.3 Statistical inference method

On the basis of investigation and statistics, it is a method to infer the number of lost years without quantitative data according to some internal relationship or trend between disaster data. For the waterlogging losses in Shanghai over the years, there are not many quantitative loss data collected by various documents, but the disaster descriptions in most years are basically complete, and there are some disaster claims data in the 1980s and 1990s. For the year with insurance claim data, the loss data of other years can be estimated according to the proportional relationship between insurance claim and disaster loss data.

replacement cost approach

When estimating the losses caused by the ground subsidence of municipal engineering victims in previous years, the replacement cost of municipal engineering victims at the estimated time can be regarded as their economic losses. This method can be used to estimate the bridge loss.

4.2.5 Construction cost method or engineering cost method

That is to say, the economic loss caused by land subsidence is estimated according to the damage degree or repair cost of the affected body in building engineering or municipal engineering and the construction cost of disaster prevention investment. For example, this method can be used in estimating port terminals, underground deep wells, underground pipelines, flood control walls and drainage engineering facilities.

Disaster comparison method

It is mainly used to estimate the losses of tidal disasters and waterlogging disasters. When estimating the losses of tidal disasters and waterlogging disasters, because quite a few historical tidal disasters and waterlogging disasters only have disaster descriptions and no loss statistics, we can only use the disaster comparison method to calculate the economic losses of similar disasters according to the economic losses of known disasters by adjusting the correction coefficient.

4.2.7 Proportional method of indirect loss and direct loss

Because there are many indirect losses caused by tidal disasters and waterlogging disasters, and lack of historical statistical data, it is difficult to estimate them. Therefore, according to the analysis and inference of tidal disasters and waterlogging disasters in typical years, this report draws the ratio of indirect losses to direct losses in tidal disasters and waterlogging disasters by using the existing research results. For example, the indirect loss of tidal disasters is 3.8 times of the direct loss, and the indirect economic loss is estimated by the direct economic loss of tidal disasters or floods.

4.2.8 weight decomposition method

It is mainly used to estimate the losses of tidal disasters, waterlogging disasters, flood control projects and drainage projects. Because land subsidence is not the only factor that causes tidal disasters and waterlogging disasters, the weight of land subsidence must be decomposed when estimating the losses caused by land subsidence in tidal disasters.

4.3 Shanghai land subsidence economic loss assessment

The economic loss assessment of land subsidence in Shanghai covers the whole Shanghai area, but it is mainly located in the central city (land subsidence disaster area). The appraisal time is at the end of 2000, and the appraisal time range is 192 1 ~ 2000.

According to the evaluation principles and methods determined in this paper, the indexes in the classification system are evaluated respectively. The evaluation results show that during the 80 years from 192 1 to 2000, the economic loss caused by land subsidence in Shanghai was about 289.822 billion yuan, with an average annual loss of about 3.623 billion yuan. If the average land subsidence 1.892 mm in the central city is calculated, the economic loss caused by the average land subsidence 1 mm in the central city is 1.53 billion yuan. The economic losses caused by land subsidence in Shanghai are mainly indirect economic losses, accounting for 95% of the economic losses caused by land subsidence.

5 Economic benefit evaluation of controlling land subsidence disaster in Shanghai

5. 1 Shanghai land subsidence disaster control measures and effect analysis

Shanghai began to implement large-scale settlement control measures in the mid-1960s. Settlement control measures mainly include engineering measures to directly control land subsidence, relevant policy measures and scientific research activities, including artificial recharge of groundwater, restriction of groundwater exploitation, adjustment of groundwater exploitation level, formulation of annual groundwater exploitation and irrigation plan, dynamic monitoring and research of land subsidence, etc.

According to the grey evaluation of the effect of land subsidence control in Shanghai, after taking the land subsidence control measures, the land subsidence in the downtown area of Shanghai decreased by about 1 147.35mm from 1965 to 2000, with an average effect of 84%. See table 1.

Table 1 Effect of Controlling Land Subsidence Disaster in Shanghai

5.2 Economic Benefit Evaluation of Controlling Land Subsidence Disaster in Shanghai

5.2. 1 Loss estimation of land subsidence disaster under uncontrolled subsidence conditions

For the convenience of estimation, the following assumptions are made when estimating the economic loss of land subsidence without controlling the subsidence.

It is assumed that 1: after the flood control wall is heightened and strengthened, the tidal disaster loss remains unchanged.

Hypothesis 2: After the completion of new drainage facilities, the loss of drainage flow caused by the increase of settlement caused by uncontrolled settlement remains unchanged.

Hypothesis 3: There is no investment in scientific research and groundwater recharge.

Under the above assumptions, it is estimated that the total economic loss caused by land subsidence disasters in Shanghai 192 1 2000 is 31066 billion yuan without controlling land subsidence.

5.2.2 Economic Benefit Evaluation of Controlling Land Subsidence

From the mid-1960s to 2000, Shanghai actively took various measures to control land subsidence, which not only achieved remarkable results, but also achieved great economic benefits. The economic benefits of controlling land subsidence in Shanghai are shown in Table 2.

Table 2 Benefits of Controlling Land Subsidence Disaster in Shanghai

6 Shanghai land subsidence economic loss risk assessment

The risk assessment of land subsidence in economic loss is based on the prediction and analysis of land subsidence in a certain period in the future, and the total economic loss that may be caused by land subsidence in this period is evaluated by estimating the expected loss of each evaluation factor. The time period of this risk assessment is 200 1 ~ 2020.

6. 1 Assumption on risk assessment of economic loss of land subsidence in Shanghai.

Assuming 1:2006 54 38+0 ~ 2020, the original settlement control measures will still be taken.

Hypothesis 2: From 20065438+0 to 2020, no tidal sluice will be built at the mouth of Huangpu River, but the flood control wall in the urban area will continue to be heightened and strengthened.

Hypothesis 3: 2001~ urban drainage facilities will be built according to municipal planning within 2020.

Assumption 4: Limited settlement from 20065438+0 to 2020 will not cause great damage to municipal infrastructure.

6.2 Shanghai land subsidence economic loss risk assessment model

According to the economic loss classification system of land subsidence in Shanghai, the risk economic loss still mainly consists of eight items: loss of safety elevation, loss of municipal infrastructure, loss of buildings and structures, flood disaster aggravated by land subsidence and flood disaster. Assuming that the risk economic loss of land subsidence disaster in Shanghai is EX and EXi is the first-class risk economic loss, the risk assessment model of land subsidence economic loss in Shanghai is as follows:

Compilation of geological survey results in East China: 1999~2005

Where: the calculation formula of EXi can be expressed as:

Compilation of geological survey results in East China: 1999~2005

Where: xij (j = 1, 2 ..., ni): indicates the possible value of class I economic loss;

Pij (j = 1, 2……, ni): indicates the probability of taking xij as the value of Class I economic loss;

Ni (I = 1, 2 ..., 8): the number of possible values representing class I economic losses;

Then:

6.3 economical loss estimation results of land subsidence in Shanghai.

According to the above hypothesis and evaluation model, taking 65438+February 3, 20001as the estimation time point, it is estimated that the total economic loss of land subsidence disaster risk in Shanghai from 2006 to 2020 is about 3565438+54 million yuan.

7 conclusion

(1) Based on the full collection of land subsidence disasters in Shanghai, the disaster-causing mechanism and harm of land subsidence in Shanghai are analyzed and discussed, and the economic loss evaluation system of land subsidence in Shanghai is initially established, and the principles and methods of economic loss evaluation of land subsidence in Shanghai are established. It has certain reference value for the evaluation of economic losses of land subsidence in other similar areas.

(2) The economic losses caused by land subsidence are enormous. During the 80 years from 192 1 to 2000 * *, the economic loss caused by land subsidence in Shanghai was as high as 289.822 billion yuan, with an average annual economic loss of about 3.623 billion yuan, and the average economic loss caused by land subsidence 1mm was153 million yuan. Indirect economic loss is the main factor in the economic loss of land subsidence, which accounts for 95% of the economic loss of land subsidence.

(3) Shanghai has achieved good economic benefits in controlling land subsidence. The economic benefit of controlling land subsidence in Shanghai is as high as 20.838 billion yuan, and the benefit-cost ratio of controlling land subsidence is 12.4 times, with an average annual economic benefit of 579 million yuan.

(4) Due to the serious land subsidence in history, the adverse effects after losing the safety elevation still exist, and Shanghai will still face the risk of land subsidence loss in the future. Taking 65438+February 3, 20001as the estimated time point, the risk economic loss of land subsidence disaster in Shanghai from 200 1 to 2020 is about 3.51.54 billion yuan. In order to reduce the risk of loss, Shanghai should further strengthen the control and governance of land subsidence disasters and increase investment in disaster reduction and prevention, so as to achieve greater land subsidence control and disaster reduction benefits.

Economical loss Assessment of Land Subsidence in Shanghai

Zeng Zhengqiang 1, Chen Huawen 1, Zhang Weiran 2, Duan Zhengliang 2, Yan Xuexin 1, Gong Shiliang 1

(1. Shanghai Geological Survey, Shanghai 200072; 2. Tongji University School of Economics and Management, Shanghai 200092)

Abstract: How to correctly evaluate the economic loss of land subsidence is not only an important topic in Shanghai land subsidence research, but also the need of disaster prevention and reduction. Based on the mechanism and harm of land subsidence in Shanghai, this paper applies geology, hydrology, disaster science, economics and statistics to establish the evaluation system, principles and methods of land subsidence economical loss in Shanghai. On this basis, this paper first comprehensively evaluates the economic losses caused by land subsidence disasters in Shanghai and the economic benefits of controlling land subsidence, and predicts the risk losses of land subsidence disasters in Shanghai in 200 1-2020.

Keywords: land subsidence; Evaluation principle; Evaluation method; Economic loss; Risk loss; Benefits of reducing danger