| Shaanxi province is located in the northwest of China.The climate and geographic and geomorphic conditions in Shaanxi are diversity and heterogeneous.Due to the fragile ecosystem,Shaanxi province is recognized as a typical ecologically vulnerable area.Under the intensifying global warming in recent decades,extreme climate events occurred frequently,posing greater threat on sustain reginal development and human wellbeing.Thus,it is urgent to have a clear understanding of regional climate change and natural disaster risk in order to better plan for a sustainable future.This paper analyzed the multi-spatiotemporal characters of temperature,precipitation,drought,flood in Shaanxi province based on meteorological data,SPEI(Standardized Precipitation-Evapotranspiration Index)of drought and flood.This work also investigated the statistical regularity of the drought/flood events,and explored the possibility trend of disaster recurrence by using commensurability symmetry method.Besides,it also analyzed the correlation between drought/flood events and macroscale driving factors(e.g.,ENSO events and sunspots),and assessed and mapped the drought/flood risk maps.This research aims to provide spatially explicit assessment of drought/flood risk and further provide scientific reference for the stakeholders,thereby help reduce regional disaster losses.The main conclusions are as follows:(1)The annual temperature in Shaanxi province increased at the rate of 0.020?/a(P<0.01)from 1960 to 2015.The amplitude of temperature increase in northern Shaanxi and Guanzhong basin was more significant than that in southern Shaanxi.Besides,all seasons showed an increasing trend,among which the increasing rate of winter was the highest,followed by spring and autumn.The annual precipitation in Shaanxi province decreased with fluctuation from 1960 to 2015.The decreasing rate of annual precipitation in Guanzhong basin was higher than the other two sub-regions,and the annual precipitation in southern Shaanxi inversely showed a slight increasing trend.The change of seasonal precipitation was not significant.Besides,the precipitation in northern Shaanxi tended to be more dispersive,while the precipitation in Guanzhong basin and southern Shaanxi became more concentrated in recent 56 years.(2)The spatiotemporal characters of drought/flood:The climate in Shaanxi province turned from wet to dry as a whole from 1960 to 2015.The rank of drying rate(DR)is Guanzhong basin>northern Shaanxi>southern Shaanxi.Besides,the total frequency of drought was more than that of flood in Shaanxi province.Most of the slight drought occurred in Guanzhong basin and southern Shaanxi,and moderate drought mostly occurred in southern Shaanxi,while severe drought events distributed in the north of northern Shaanxi and the south of Guanzhong basin.Overall,severe drought and flood were more likely to occur in Guanzhong basin compared with northern Shaanxi(also called Shaanxi loess plateau).(3)According to the commensurable formula,butterfly structure and commensurability structure analysis,it inferred that drought will attack Shaanxi in 2023 and flood will occur in 2017.At the climate zone scale,it is very likely that drought attack northern Shaanxi in 2024,and flood attack northern Shaanxi in 2019;in Guanzhong basin,the occurrence possibility of drought and flood are high in 2019 and 2018 separately;and in southern Shaanxi,the occurrence possibility of drought and flood are high in 2018 and 2017 separately.The results based on both gridded metrological data and metrological station data revealed that there will be drought occurring in Guanzhong basin in the next five years.As for the seasonal drought/flood,it inferred that spring,summer,autumn and winter drought will attack Shaanxi in 2021,2027,2017 and 2022 respectively.Besides,spring,summer,autumn and winter flood will attack Shaanxi in 2017,2017,2017 and 2022 respectively.(4)The drought/flood tendency in gridded data indicated that few spring drought will occur in Shaanxi,and the summer drought will mostly distribute in northern and southern Shaanxi.The winter drought in the future may mainly distribute in the middle of Shaanxi loess plateau,and the border of Guanzhong basin and southern Shaanxi.In addition,spring flood may occur in the middle of Shaanxi loess plateau in the next two years,and summer flood likely attack the south of Shaanxi loess plateau and the west of Guanzhong basin;the autumn flood may occur in the south of Guanzhong basin.(5)It revealed negative correlation between PCD(precipitation-concentration degree)and SPEI during 1960 s,while positive correlation between PCD and SPEI since 1970 s.For the spatial pattern of their relation,significant positive correlation existed in the north of Guanzhong basin and the south of Shaanxi loess plateau.Besides,this paper found that flood more likely occurred when sunspots number curves reached the valley,while there was no evident relation between sunspots number with drought events.It also revealed that significant negative correlation between ENSO events and SPEI:drought events usually occur in El Nino years,while flood events usually occur in La Nina years.(6)The drought risk in the middle and south of Shaanxi loess plateau is high,while the drought risk in Guanzhong basin is moderate,and the low drought risk region is located in the southern Shaanxi.Besides,the flood risk in the northwest of Shaanxi loess plateau and middle of southern Shaanxi is high,while the low flood risk region is located in the north of Shaanxi loess plateau.This work analyzed the multi-spatiotemporal characters of drought/flood events in Shaanxi province,based on which revealed the occurrence regularity and future tendency of drought/flood events at different time scales and spatial scales.Furthermore,this research built a drought/flood risk assessment model based on multi-source spatial data(both physical and socio-economic data),making it possible to map and visualize drought/flood risk at fine spatial scale.The methods and results may benefit for future research on natural disasters at bigger spatial scales,and this work also has the potential to provide theoretical framework and scientific guidance for Shaanxi government to mitigate the loss cased by natural disaster. |
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