Temporal And Spatial Changes In Socio-economic Development Factors And Earthquake Hazard Exposure In China's Large Citie

In the context of rapid urbanization,China’s large cities(with a permanent population of more than 1 million in urban areas)are experiencing unprecedented population and wealth aggregation effects,carrying nearly 16%of China’s population and over 60%of its economic development.The booming socio-economic development of large cities has been accompanied by an increase in the population,assets and building facilities of large cities in seismic-prone and hazard zones,making the seismic hazard risk of large cities highly complex and uncertain,and the seismic prevention and mitigation of large cities facing new challenges.Therefore,assessing the exposure dynamics of large cities in high seismically hazardous areas driven by urbanization has become necessary for seismic hazard risk management in large cities and for promoting sustainable social development.Based on multi-temporal population,GDP and construction land grid data,this paper used spatial analysis,exposure index construction,future land use change simulation and other methods to analyze the spatiotemporal changes of socio-economic factors of 78 large cities in China and the spatiotemporal changes of exposures of large cities in high seismically hazardous areas from 1990 to 2050.We also explored the driving effects of urbanization in exposure change and the potential counter-effects of this exposure change pattern on the socio-economics of large cities,with the aim of providing a theoretical basis and methodology for seismic exposure assessment and catastrophe risk management in large cities.The main work and conclusions are as follows:(1)Historical and future spatiotemporal characteristics of population,GDP and building land in 78 large cities were statistically analyzed.Although the urban areas of large cities only account for 3.25%of China’s land area,but in 2015 their population,GDP and construction land area accounted for 25.33%,44.57%and 32.73%of the country respectively,with a concentration of socio-economic factors.The socio-economic factors of large cities grew rapidly during 1990-2015,with population,GDP and construction land increasing by 137.41 million(65.18%),28376.99 billion RMB(1305.95%)and 15015.19 km~2(71.64%)respectively in 2015 compared to 1990.In terms of spatial distribution,it shows a pattern of overall concentration in the central-east and a southward shift of the centre of gravity,with the population distribution showing a tendency to spread towards the central and southern regions;the directional and centripetal distribution of GDP gradually decreases,and then became stronger.The distribution of construction land shows a tendency to spread around the central-eastern provinces of Anhui and Henan.In 2030,the socio-economic factors of large cities are all higher than their historical levels in 2015,with population increasing by 1.54 times,GDP increasing by 2.69 times,and construction land increasing by 2.34 times.2030-2050,the population of urban areas of large cities shows a trend of growth followed by a rapid decrease,while GDP and construction land continue to grow at a relatively fast rate.(2)Based on the ground shaking parameter zoning map to extract areas of high seismic hazard,overlaying on the urban area of large cities,64 urban areas of large cities in high seismic hazard were extracted and their historical spatial and temporal changes in exposure elements were analyzed,and an exposure index was constructed using absolute exposure index and relative exposure index to comprehensively identify the exposure change characteristics of different types of large cities and to analyze the exposure growth characteristics of different seismic intensity zones.The area of high seismically hazardous large cities(167177.35 km2)covered 60.08%of the total area of these 64 large urban areas.During the process of rapid urbanization,their exposed population,GDP and construction land have experienced dramatic growth.from 1990to 2015,the population,GDP and construction land in high seismically hazardous large cities increased by 110.39 million people,19160.50 billion RMB and 106036.32 km2respectively.The spatial variation of exposure also had strong spatial heterogeneity,with the coefficient of variation of exposure elements showing the greatest overall variation in distribution in the eastern region and the least variation in the central region.The mega cities and super cities concentrated in the three major metropolitan clusters show a"double-high"pattern of absolute and relative exposure,while type II large cities,which are smaller and have slower socio-economic development,showed a"low-high"pattern of low absolute exposure growth but very high relative exposure.Therefore,it is necessary to plan and regulate the seismic hazard risk for different types of exposure changes.In terms of seismic intensity zones,exposure growth in large cities has been concentrated in the VII degree zone,with a higher rate of exposure growth in the VIII degree zone where the probability of highly destructive earthquakes is higher.(3)A qualitative and quantitative correlation between urbanization and exposure changes in large cities was performed,and the impact of exposure changes on potential risk in large cities was analyzed by constructing a potential loss index for socio-economic development factors.There is a high correlation between the rapid urbanization of large cities and changes in exposure to seismic hazards over the past 25years,both qualitatively and quantitatively,and the potential losses of socio-economic factors in large cities have increased during the urbanization process.(4)In this paper,two paths,the SSP2 moderate development path and the SSP5conventional development path,were selected to explore and compare the differences in the future trends of exposed population and GDP changes in large cities under the scenario of maintaining the current socio-economic development pattern and the extreme development scenario of rapid socio-economic development.The exposed population of large cities will decrease by 236.92 million under the SSP2 path and by a smaller amount of 736800 under the SSP5 path;the exposed GDP will increase by29135.45 billion RMB under the SSP2 path and by a larger amount of 56305.67 billion RMB under the SSP5 path;the exposed construction land will increase by 10224.50km2.The future growth pattern of exposed large cities will change from the historical phase of population-industry driven to an urban land expansion driven patternUnder rapid urbanization,it is inevitable that population,industry and infrastructure will continue to concentrate in large cities with higher seismic risks.It is necessary to achieve a paradigm shift from disaster response to seismic risk management and to strengthen seismic hazard risk awareness and analysis and assessment in large cities to make their development seismically resilient.