The Growth Mode Of Built-up Land In Floodplains And Its Impacts On Flood Vulnerability

Built-up land in floodplains(BLF)is a vital indicator of the socio-hydrological system,and its dynamics are key to understanding and managing flood risk.However,previous studies have neglected the impacts of BLF growth modes(e.g.,patch sizes and expansion types)on flood vulnerability.This paper fills this gap by assessing the BLF’s growth modes and revealing their divergent impacts on flood vulnerability using a case study in the Yangtze River Economic Belt(YREB)and the world.In this paper,the global once-in-a-century inundation scenario data set,GHS-BUILT dataset,historical flood range data and flood frequency data,total flood death data and total flood loss data published by CIMA are used.This paper uses ArcGIS spatial analysis tools,landscape expansion index,Pearson correlation analysis and other methods to quantitatively analyze the growth characteristics of the BLF spatiotemporal patterns,patch size changes,and expansion types from the regional level to the global level in1990–2014.The relationship between the above BLF growth characteristics and floods was revealed.The following are the main conclusions of this study:1.This research investigated the spatial and temporal pattern of built-up land in floodplains.First,the Yangtze River Economic Belt experienced rapid and substantial BLF growth from 1990 to 2014.In 24 years,the BLF area of the Yangtze River Economic Belt increased by 8.53×10~3 km~2,an increase of 97.58%;by 2014,the BLF area of the Yangtze River Economic Belt reached 17.28×10~3 km~2,accounting for 50.04%of the total construction land in the Yangtze River Economic Belt.Secondly,most of the BLF growth(72.67%)in the Yangtze River Economic Belt is concentrated in the downstream areas,with an increase area of 6.20×10~3 km~2 and a growth rate of 125.20%.The midstream and upstream regions increased at a rate of 64.99%and 54.26%,with an increase of 1.67×10~3 km~2 and 0.67×10~3 km~2,respectively.In addition,the growth of construction land in the floodplain of the Yangtze River Economic Belt also shows an accelerating trend.The average annual growth rate of BLF increased from 2.76%in1990s to 2.96%in 2000s.From a global perspective,the BLF has obvious spatial uneven distribution characteristics.In 2014,the BLF was mainly distributed in Asia and Europe.The total area of BLF in these two areas was 31.76×10~3 km~2,accounting for 69.15%of the global total area of BLF.From 1990 to 2014,the world experienced rapid and substantial BLF growth.BLF increased by 16.45×10~3 km~2,an increase of 55.79%.Among them,Asia’s BLF expansion area is the largest,increasing by 9.81×10~3 km~2,accounting for 59.67%of the global BLF expansion area,an increase of 83.38%,which is 1.49 times the global average increase.2.This research analyzes the patch size changes of built-up land in floodplains.At the level of the Yangtze River Economic Belt,small patches(size≤1 km~2)dominated the growth of BLF from 1990 to 2014.The number of plaques and area of BLF for small patches increased by 53.54%(23403)and 64.54%(3.04×10~3 km~2)in 1990–2014,respectively;while the number of patches for large patches(size>1km~2)And area increased by 99.88%(855)and 138.15%(5.54×10~3 km~2).The number and area of small patches in the downstream area increased the most,increasing by 12765,1.76×10~3 km~2,and the number and area of large patches increased by 627,4.45×10~3 km~2,respectively.From a global perspective,the growth of small patch BLF is larger than other sizes of BLF patches at global and regional scales.The number and area of small patch BLF in the world increased by 62849 and 9×10~3 km~2 respectively,accounting for 96.08%and 38.71%of the total number and area of new BLF patches,respectively.3.This research quantified the expansion types of the built-up land in floodplains.The edge-expansion type dominated the BLF growth in the YREB during 1990–2014.It covered an area of 5.05×10~3 km~2,accounting for 57.52%of the total expanding patch area.The leapfrog and infilling-type extended BLF are 33.49%(2.94×10~3 km~2)and8.99%(0.79×10~3 km~2),respectively.The edge-expanding type dominated the BLF growth in the global during 1990–2014.The patch number of this expansion model was 51560,with an area of 29.17×10~3km~2,accounting for 49.18%of the total patch and area of BLF expansion.36.04%.The leapfrog dominated the patch number of BLF in the world.The proportion of patch and area expanded by this model to the total number and area of BLF expansions is 60.90%(87134)and 15.65%(9.28×10~3 km~2).In contrast,the infilling-type of BLF expansion was relatively weak in global,but its average patch area is as high as 4.77 km~2,which is 44.79 times and 8.43 times that of leapfrog and edge-expansion.4.This research reveals the impact of built-up land growth characteristics on flood vulnerability in floodplains.Based on the historical flood range data of the Yangtze River Economic Belt from 1990 to 2014,the relationship between BLF growth characteristics and frequency of floods was revealed based on Pearson correlation analysis.It was found that there was a significant correlation between the increase of BLF and the frequency of floods,especially the correlation of BLF growth of small patches was stronger(R=0.31,p<0.01).The leapfrog BLF(R=0.34,p<0.01)and edge-expanding BLF(R=0.16,p<0)are significantly related to the frequency of floods,while infilling-type BLF is related to the frequency of floods Not obvious.And the impact of BLF patch size and expansion type on flood risk is greater than the total increase of BLF(R=0.19,p<0.1).Using the global flood data from 1990 to 2014,based on Pearson correlation analysis to reveal the relationship between global BLF growth characteristics and floods.The study found that the global BLF growth characteristics are significantly correlated with the frequency of floods,the total number of flood deaths,and the total flood losses.The correlation between the increase of BLF in small patches and floods is higher than that of BLF in large patches.In terms of expansion types,the correlation between global leapfrog expansion BLF and flood disasters is higher than the correlation between edge-expanding and infilling-type BLF and flood disasters.The correlation between BLF growth characteristics and floods in countries with different levels of development has some differences.This paper first quantitatively analyzes the spatio-temporal pattern of construction land expansion in floodplain from the regional level to the global level and quantitatively reveals the patch size change and expansion model.On this basis,the possible impact of BLF growth characteristics on flood vulnerability is quantitatively explored.The patch size and expansion type can thus influence the vulnerability of BLF patches,which is also supported by real-world cases.These findings enrich a general understanding of BLF growth and its impacts on flood vulnerability.The scientific community and policymakers should pay attention to not only the quantity of BLF growth,but also its spatial arrangement.