| Over the past century,global warming has caused changes in regional hydrological and meteorological elements.Extreme precipitation and drought events occur more frequently than in the past.Thus,the spatial and temporal distribution pattern of precipitation is also evolving.In the northwest arid areas in China,the precipitation is an important source of surface water and groundwater,the change of precipitation to runoff and water resources in the region has an important influence.It plays an important role in revealing the regional precipitation change characteristics of climate change should be under the risk of water resources allocation and management,and can provide regional empirical reference for the global precipitation evolution.This thesis takes the Wei River Basin as the research object,and mainly studies from the following aspects: 1)Based on the daily rainfall at 5 meteorological stations of Wei River Basin in nearly 60 years,using the method of Maximal Information Coefficient(MIC)to simplify the indexes which selected from numerous Precipitation Index with high attention.Combined with the actual precipitation situation in the research area,there were 20 precipitation indexes retained to reflect the regional precipitation characteristics roundly,named SFCPI(Structural and Functional Coupling Precipitation Index,SFCPI).The aim was to systematically and comprehensively reflect regional precipitation characteristics and potential impacts.2)The Mann-Kendall statistical test method was used to test the variation trend of each precipitation index in SFCPI,and the spatial and temporal distribution pattern of the precipitation index was judged through the analysis of the variation results.3)The range of Concentration Index(CI)in the research area was obtained by analyzing the groups data of CI - Proportion of maximum precipitation in 25% of the rainiest days in the total annual precipitation.4)Explores the effect of atmospheric circulation indexes,including El Nino-Southern Oscillation(ENSO)index,the Western Pacific Subtropical High index,the Arctic Oscillation index,the index of the North Atlantic Oscillation and Southern Oscillation index,on precipitation indexes.Analyzing the time and space distribution changes of environmental elements,including: the normalized difference vegetation index(NDVI),drought and flooding events,and studying their relationships with precipitation indexes.5)Analyzing the change trend of atmospheric circulation indicators,predicting their trends in the future.The results show that:(1)Structural and Functional Coupling Precipitation Index was constructed.the Maximal Information Coefficient was used to simplify the 36 precipitation indexes that are highly concerned at home and abroad.Under the condition that the correlation coefficient is greater than 0.35,the precipitation indexes that are highly correlated with other indexes were retained.Thus,20 indexes were selected to form the structural and functional precipitation index,SFCPI.The simplified index system can still comprehensively evaluate the changes of the precipitation mean characteristics,the extreme precipitation intensity,grade and duration,the precipitation duration and the annual precipitation distribution.(2)The trend and spatial distribution characteristics of precipitation indexes at different scales in Wei River Basin were investigated.The trend test and analysis of SFCPI were carried out,and the spatio-temporal evolution characteristics of precipitation indexes in the study area were obtained.The results show that in the past 60 years,the whole Wei River Basin is in a trend of drought,and it decreases from north to south.The downstream area has been in a continuous drought,and there will be an increasing trend in the future.From the perspective of spatial distribution,the spring precipitation decreased significantly.Although the related indexes were different,it had a great impact on the spring drought and was easy to induce disasters.From the vertical belt(Loess Plateau-Guanzhong Plain-Qinling Mountains),the precipitation intensity has an increasing trend,and the further north,the more significant the increase.(3)The ranges of CI levels are determined in Wei river basin.Based on the statistical analysis of a large number of data,this study found that when the CI value of an area was over 0.55,approximately 70% of the precipitation was contributed by 25% of the rainiest days in this region;when the CI value of an area was over 0.58,approximately 75% of the precipitation was contributed by 25% of the rainiest days in this region;when the CI value of an area was over 0.62,approximately 80% of the precipitation was contributed by 25% of the rainiest days in this region;when the CI value of an area was over 0.67 approximately 85% of the precipitation was contributed by 25% of the rainiest days in this region;(4)The relationship between atmospheric circulation factors and precipitation indicators was discussed.The spatial distribution pattern of precipitation indicators was compared with the environmental factors to find the precipitation indicators that have the closest impact on the surface environment.The results show that the atmospheric circulation factors have a significant influence on the precipitation structure in the study area,and the change of precipitation also has a great influence on the ecological environment in the area.ENSO and the Arctic Oscillation mainly affect the indexes that measure the overall precipitation level of the region,resulting in a precipitation distribution pattern decreasing from southeast to northwest.Under such a distribution pattern,vegetation flourishes in regions with sufficient precipitation and vegetation coverage is low in regions with insufficient precipitation.The changes of the North Atlantic Oscillation mainly affected the degree of drought in the study area.However,the abnormal fluctuation of the Southern Oscillation index has a great influence on the extreme precipitation index in this region.(5)The potential changes and impacts of precipitation in climate change are estimated.Trend analysis was carried out on the changes of atmospheric circulation factors,and the possible influence of precipitation was estimated.It found that based on the stable changes in the Arctic Oscillation and the North Atlantic Oscillation,spring drought in the region is still likely to occur in the future.According to the variation of the Southern Oscillation,it will see a new round of growth in 2020,which means that the possibility of extreme precipitation and continuous rainstorm in the flood season in the study area will increase,and the corresponding work should be done in advance. |
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