Security Assessment Using SPA-VFS and Obstacle 1 Factors Diagnosis of Water-Energy-Food Nexus 2 Based on A PSR Framework 3

In the context of population growth and increasingly scarce resources, the sustainability of water-energy- 8 food nexus (WEFN) has been considered as a major global challenge. This study presented the evaluation 9 index system of WEFN security based on the pressure-state-response (PSR) model. The set pair analysis 10 and variable fuzzy sets (SPA-VFS) were supplied to evaluate WEFN security, which analyzed the 11 situation and obstacles of WEFN security in Northwest China from 2008 to 2017. The results showed 12 that, (1) In the WEFN, the pressure-subsystem in Shaanxi and Inner Mongolia was in a critical safe level; 13 in the state-subsystem, the security level of Shaanxi was the best and the response-subsystem in Inner 14 Mongolia and Gansu is in an unsafe level; (2) Over the years, the safety level of WEFN in the five 15 provinces of Northwest China had obvious spatio-temporal characteristics, which was always between 16 critical safety and unsafety, but the overall trend was positive. (3) The results of obstacle degree of three 17 subsystems were compared as follows: pressure-subsystem  state-subsystem  response-subsystem. And, 18 their obstacle factors were almost all related to water. The key to improving WEFN security in Northwest 19 China in the future is to deal with the serious mismatch between water resources and energy resources.

4 forefront of China. The reserves of coal are as high as 200 billion tons, accounting for about 40% of the oil reserves. Energy is the biggest advantage of economic development in Northwest China, and its 120 economic development depends on a large amount of energy consumption. Furthermore. the Northwest 121 with a vast territory, accounts for more than one third of China's land area; it has 9.6% of the national 122 population, but the per capita land area is 2.2 times of the national average. The per capita cultivated land 123 area is 2.1 mu, which is 1.66 times higher than that of the whole country, but the food output is only 11% 124 of the national average.
Inverse indicators: Where, and ′ represent the original and normalized values of the j-th indicator in i-th year, 146 and represent the maximum and minimum indicators, respectively.

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The entropy weight method was utilized to calculate the weight of indicators. m assessment objects were constructed, each assessment object had n indicators, and the judgment matrix of evaluation indicators was () ij m n X  . The entropy value of each index was determined.

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Step 2: SPA is used to construct the single index relation degree ijkg u . The core idea of SPA is to Step 4: The comprehensive connection degree of subsystems is calculated by synthetic weighted 206 method.
Step 5: Normalized relative membership of single index and subsystem are shown in Eq. (12) and
likely to cause distortion. In order to enhance the precision of the assessment results and avoid the 211 occurrence of distortion, hierarchical eigenvalue ij h is used to quantify the evaluation results.
Then, the confidence criterion is used to evaluate the assessment level of the subsystem ij L .

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The deviation degree of index ij T represents the difference between a certain index and the target 223 value of WEFN.
Factor contribution degree ij P indicates the degree of influence of an evaluation index on the 225 overall goal.
Obstacle degree ij A and ij B indicate the influence degree of single index and classification index 227 on WEFN security, respectively.
3 Results and Discussion 229

The Result of Security Assesment 230
In Northwest China, the Eigenvalue h and safety level of pressure, state and response subsystems 231 of WEFN were calculated, from 2008 to 2017, respectively (Table 2).
In Table 2 III  III  IV  IV  IV  IV  III  IV  IV  IV  IV  IV  III  IV III  III  IV  IV  IV  IV  III  IV  IV  III  IV  IV  III  IV IV  III  IV  III  IV  IV  III  IV  IV  IV  IV  IV  III  IV III  III  IV  IV  IV  IV  III  IV  IV  IV  IV  III  III  IV III  III  III  III  IV  IV  IV  IV  III  IV  IV  III  III  IV IV  III  III  III  IV  III  III  IV  III  IV  IV  IV  III  IV IV  III  III  III  IV  IV  III  IV  III  III  IV  III  III  IV IV  III  III  III  IV  IV  III  IV  III  IV  IV  III  III  IV III  III  III  III  III  IV  III  IV  III  IV  III  III  III  IV III  III  IV  III  III  IV  III  IV  IV  IV  IV  III  III  III  III As sketched in Fig.3

Obstacle Factors Diagnosis 285
The ODM was applied to diagnose the obstacle factors affecting WEFN security in Northwest China 286 from 2008 to 2017. The order was made according to the degree of obstacle, and the frequency of obstacle 287 factors was counted. This study took the first three obstacle factors (Table 3).

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In the pressure-subsystem, obstacle factors are C8, C11 and C1, and their frequencies were 23, 21 289 and 18, respectively. This indicated that with the economic growth, Northwest China is highly dependent 290 on energy, and a large amount of chemical fertilizers and other substances are applied to nourish the 291 crops, which not only brings benefits, but also causes water pollution and increases the pressure on 292 resources and environment of WEFN. In recent years, the industrial development of Ningxia and Inner 293 Mongolia has been rapid, and the proportion of industrial water has been also increasing year by year, 294 whose obstacle degree was about 20%.

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In the state-subsystem, obstacle factors were C14, C17 and C20, and the frequency was 24, 23and 14 indicators are all related to water resources. Their frequency was very high, which further verified that 298 the lack of water resource is the central cause for the low safety level of WEFN in Northwest China. In the response-subsystem, obstacle factors were C29, C30 and C34, and the frequency was 23, 23 304 and 14, respectively. And, they appeared more frequently in Ningxia and Inner Mongolia. It could be 305 seen from the data that the investment in water conservancy in Northwest China was relatively small.

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Although the investment has increased in recent years, it is far behind the proportion of investment in 307 energy projects. Moreover, Gansu, Ningxia and Inner Mongolia have much room for improvement in 308 energy processing and conversion efficiency.

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From the perspective of the average obstacle degree of the whole Northwest China (Fig. 6), the 310 pressure-subsystem has the greatest impact on WEFN security. The obstacle degree of the three 311 subsystems were compared as follows: pressure-subsystem  state-subsystem  response-subsystem.

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The

Regulatory Countermeasures 325
The regulation of WEFN security involves multi-region, multi-level and multi-department "state" and the positive effect process of "response", improve the safety level of WEFN, so as to ensure

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(1) Improving the pattern of agricultural development. It is essential to reduce the irrigation area of 335 crops and adjust the planting structure. While ensuring the self-sufficiency rate of food, provinces should 336 reduce food output and increase food import. These measures can effectively reduce water demand.

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Moreover, Agricultural departments can combine the characteristics of developed grazing and breeding 338 industry to mobilize farmers to use animal manure as organic fertilizer. Finally, irrigation methods must 339 be improved. Water saving methods suitable for the characteristics of the irrigation area can be selected, 340 such as mulching irrigation, border irrigation, etc.

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(2) Exploring and saving water. The main factor affecting WEFN security is the lack of water 342 resource, and the key measure to improve the per capita water resources is to explore and save water.

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Firstly, it is necessary to further optimize the industrial layout and to reduce water consumption in all 344 aspects of energy exploitation from the aspects of technology and management. Secondly, the 345 government can invest in the construction of rainwater harvesting and water storage projects aiming to 346 fully utilize precipitation resources. Third, it is necessary to enhance public awareness of water-saving 347 and carry out water resource utility education and sensitization. Furthermore, "reclaimed water" can be 348 utilized. For example, washing vegetables and rice can be used to flush toilets. It is also important to overhaul public water supply facilities on time to prevent water leakage.

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The WEFN is a large and complex system. The research done in this study was only the evaluation 377 and obstacle factors diagnosis of WEFN security in Northwest China at the present stage, but did not 378 predict the future security state of WEFN. The next research plan is to study the evolution rule of WEFN 379 security under different circumstances, so as to clearly put forward a mode that is more consistent with 380 the coordinated development of resources in the WEFN in Northwest China.