A Study On The Comprehensive Population Exposure To Global Earthquakes And Floods Based On Multiple Indicators And Multiple Scale

Flood and seismicity are the two types of natural disasters that have the most serious impact on human society.The study of comprehensive population exposure under the spatial cross-overlapping effect is beneficial to the understanding of the formation mechanism of multi-hazard comprehensive risks and comprehensive disaster prevention and mitigation.However,previous studies focused on the population exposed to a single type of disaster in flood or seismicity,and there is still a lack of comprehensive exposure research cases.In order to fill this research gap,this paper attempted to take the most serious seismicity and flood disaster as an example,Using the global seismicity peak acceleration data,the once-in-a-century river flood inundation dataset,combined with World Pop population distribution data and population prediction data of the different scenario,etc.,A comprehensive analysis of the distribution and changes in global seismicity and flood population exposure from2000–2020 using multiple indicators,and analyzed the trend of population change in the future.This research content and main results include:(1)The study result of global distribution of the hazardous areas of seismicity(HA seismicity)and flood(HA flood)was concluded.The global disaster risk area was2.21×10~7 km~2,accounting for 14.83%of the total area of the study area.Among them,the HA seismicity and HA flood were 1.52×10~7 km~2 and 7.41×10~6 km~2,respectively.The area of 5.54×10~5 km~2 was located in the hazardous area of multiple(HA multiple).Asia had the largest HA seismicity,reaching 9.29×10~6 km~2;the HA seismicity in Latin America took the second place,reaching 3.50×10~6 km~2.There were also many the HA seismicity in Europe(1.27×10~6 km~2)and North America(0.91×10~6 km~2);There were relatively few HA seismicity in Oceania and Africa.Compared with the HA seismicity,the HA flood were more evenly distributed in all continents,among which the areas of Asia and Latin America were 1.98×10~6 km~2 and 1.53×10~6 km~2 respectively,and the HA flood in Africa,North America,Europe and Oceania are 1.22×10~6 km~2,1.18×10~6 km~2,1.14×10~6 km~2 and 3.58×10~5 km~2,respectively.The total area of the global HA multiple was 5.54×10~5 km~2.It was concentrated in Asia,with an area of 3.74×10~5 km~2;followed by Latin America(1.08×10~5 km~2),and less distributed in Europe,North America,Africa and Oceania.There were 68 countries exposed to HA multiple in the world,accounting for 35.03%of the total number of countries/regions in the world.(2)The global HA seismicity and HA flood exposed population distribution pattern in 2020 was analyzed.A disproportionate amount of the global population lived in HA seismicity(Pop S)or HA flood(Pop S).In 2020,a total of 2.476 billion worldwide lived in the HA seismicity or HA flood,accounting for 32.26%of the world’s total population,which was about twice the proportion of global disaster risk area.The Pop S was 1.53billion,and the population density was 101 people/km~2,which was 1.72 times the global average population density.Among them,Asia had the largest Pop S,accounting for 75.87%of the total.It was worth noting that the population density of the HA seismicity in Africa had reached 157 people/km~2,which was about 1.55 times the average level of the HA seismicity in the world.The Pop F was 1.096 billion,with a population density of 148 people/km~2,which was 2.53 times the global average population density.As high as 77.92%of the Pop S was distributed in Asia,which was8.54×10~8.At the same time,the population density of Asia was as high as 430people/km~2,which was about three times the global average.The Pop M was 152million,accounting for only 1.94%of the total population,but its population density reached 275 people/km~2,which was 4.71 times the global average population density.Compared with the Pop S and Pop F,the Pop M was further concentrated in Asia,accounting for more than 90%of the total exposed population,with a population density of 369 persons/km~2.At the same time,low income and lower–middle income countries had more exposed population,concentrating 48.94%(7.50×10~8),56.82%(6.23×10~8)and 68.78%of the global Pop S,Pop F,and Pop M.Such as India,Bangladesh,Pakistan and other countries.(3)The changes in the global Pop S,Pop F and Pop M from 2000 to 2020 were studied.From 2000 to 2020,the population exposed to global disaster risk area in the world experienced rapid growth.The global exposed population increased from18.92×10~8 in 2000 to 24.75×10~8 in 2020,an increase of 30.81%,faster than the global population growth rate in the same period.The Pop M increased from 1.16×10~8 in 2000to 1.52×10~8 in 2020,an increase of 31.55%.Asia concentrated 90.69%of the population increase.The population growth rate of Oceania was 24.05%,which was 2.09 times and 17.30 times that of the HA seismicity and HA flood,respectively.Europe’s exposed population showed a downward trend,from 2.63×10~6 to 2.49×10~6,with a growth rate of–5.25%.In addition,larger population in low income and lower–middle income countries grow faster.Low income and lower–middle income countries accounted for59.43%and 66.48%of the increase in the HA seismicity and HA flood,respectively.Meanwhile,80.54%of the increase in the HA multiple occurred in low income and lower–middle income countries.This further suggested that low income and lower–middle income countries were at greater risk from hazards,especially in the HA multiple.(4)The Changes in the global Pop S,Pop F and Pop M were explored.The exposed population in the global disaster risk area from 2020 to 2100 will show a trend of first increasing and then significantly decreasing.The time to reach the peak is slightly different under the three future scenarios,the population growth is the fastest in the SSP3 scenario,followed by the SSP2 scenario,and the SSP5 scenario has a relatively slow growth.The future population in the global disaster risk area of low income countries will show a significant upward trend.Under the significance level of 0.05,the population of global disaster risk area of low income countries in the future shows a significant upward trend under the three scenarios.10 years and a rate of 10.38×10~4person/10 years.Exposure population in lower–middle income countries show a significant increase under the SSP3 scenario and a significant decrease under the SSP5scenario.The population of upper–middle income countries increase significantly under the SSP3 scenario,but decreases significantly under the SSP2 and SSP5 scenarios.High income countries show a significant upward trend under the SSP5 scenario,while continuing to decline under the SSP2 and SSP3 scenarios.In addition,all the above Hurst exponents are greater than 0.5,which indicates that the future trend of the population time series in multi-hazard areas is consistent with the past.Therefore,this paper analyzed the temporal and spatial patterns and future trends of the Pop S,Pop F and Pop M at multiple scales,including global,continental,and national.The results showed that the population of the global disaster risk area was changing rapidly and the population was concentrated.Low income and lower–middle income countries faced higher population exposure than high and upper–middle income countries.These findings can promote the understanding of the temporal and spatial changes and future trends of seismicity and flood exposure,and provide a certain scientific basis for understanding global seismicity and flood risks and their changes.Global disaster risk management decisions need to focus not only on single-hazard population exposure but also seismicity and flood population exposure,especially in low and lower–middle income regions.