Intensive Versus Extensive Events?Insights from Cumulative Flood-Induced Mortality Over the Globe,1976–2016

More attention has been paid to the cost of intensive but sporadic floods than the cost of extensive but frequent events.To examine the impacts of intensive versus extensive events,we investigated the loss structure of global flood-induced mortality by using the cumulative loss ratio,marginal benefit chart,and cumulative loss plot.Drawing on the flood-induced mortality data for four decades(1976–2016)from the international disaster database EM-DAT,we defined the levels of flood loss according to the frequency of flood-induced deaths,and calculated the cumulative mortality and the marginal benefits of flood loss prevention practices at different levels.Our analysis showed that for the world’s leading 30 countries with large flood-induced mortality and different levels of development:(1)70%of them have the cumulative deaths from extensive floods exceeding half of those caused by intensive floods in the study’s four data decades;and(2)80%of them tend to gain less marginal benefit with increasing levels of flood prevention,with their marginal benefits peaking at loss prevention levels of 2-year or 5-year flood-induced mortality.These results indicate that,in the long run,the cumulative deaths of extensive floods are comparable to that of intensive events,and prevention of loss from extensive events can be an efficient way to reduce the total loss.For flood risk management under conditions of climate change,extensive loss events deserve more consideration.

Responses of flood peaks to land use and landscape patterns under extreme rainstorms in small catchments-A case study of the rainstorm of Typhoon Lekima in Shandong,China

Investigations of the formation mechanisms of flood peaks in small catchments facilitate flood prediction and disaster prevention under extreme rainstorms.However,there have been few studies on the re-sponses of flood peaks to land use landscape patterns using field surveys during extreme rainstorm events.Based on field data from 17 small catchments near the rainstorm center of Typhoon Lekima,7 landscape indices were chosen.The flood peak and its sensitivity to the land use landscape were investigated by combining remote sensing interpretation and related analysis.The conclusions are as follows:(1)The peak discharge of the small catchment was 2.36e56.50 m3/s,the peak modulus was 8.00 e48.89 m3/(s$km2),and the flood index K ranged from 3.61 to 4.55.(2)Under similar rainfall conditions,the flood peak modulus,K and the proportion of sloping cropland had significantly positive correlations(p<0.05).The flood peak modulus was significantly negatively correlated with the proportion of forest-grassland and terrace(p<0.05),and K and the proportion of forest-grassland and terraced land exhibited a negative correlation.(3)The flood peak modulus and K were positively correlated with the landscape fragmentation.(4)The sensitivities of small catchments to floods were evaluated to be moderate compared to K values from other studies.The ability of small catchments to cope with extreme rain-storms can be improved by increasing the areas of forest-grassland,and terraces and reducing landscape fragmentation.Our results could be applied to provide a basis for land use planning and support for the response against disasters caused by extreme floods.