Spatial And Temporal Variation Of Precipitation Concentration In The Weihe River Basin And Its Impact On Droughts And Floods

This paper used the Weihe River basin as an object of study,used the precipitation concentration indexes at different time scales to characterize the intra-annual non-uniform distribution of precipitation,analyzed the spatial and temporal patterns of precipitation concentration,and explored the driving factors of its changes;quantitatively analyzed the likelihood of drought and flood events based on the conditional probability formula when different scenarios of abnormal precipitation concentration events occurred,so as to explore the impact of precipitation concentration changes on floods and droughts.The study also explored the impact of precipitation concentration on floods and droughts,revealed the mechanism of non-uniform distribution of precipitation in the Weihe River basin and its impact,and provided good guidance for climate change and flood and drought control.The main research,results were as follows:(1)The precipitation concentration indexes at different time scales were used to characterize the non-uniform distribution of precipitation,and the Mann-Kendall trend test was used to analyze the characteristics of the temporal distribution of precipitation concentration:the degree of precipitation concentration was higher at different time scales in the Weihe River basin.The daily precipitation concentration index(CID)and the decadal precipitation concentration index(PCD)in the Weihe River basin show insignificant trends,and there were no significant changes in the concentration of precipitation within days and decadal periods.The monthly precipitation concentration index(CIM)showed a significant upward trend at Shangzhou and Zhen'an stations,and more than half of the stations showed a slight increasing trend.The precipitation concentration period(PCP)showed a significant decreasing trend at Huajialing station,while other stations showed a slight decreasing trend,and the precipitation concentration period gradually advanced.(2)The spatial interpolation method was used to analyze the spatial trends of precipitation concentration:CID showed a decreasing trend from east to west,and the concentration of daily precipitation was large;CIM showed a decreasing trend from north to south,and the monthly distribution of precipitation was not uniform,and there was a certain seasonality.The PCP had a decreasing trend from north to southwest and southeast,and the annual average maximum precipitation in the basin occurred between mid-July and late July.(3)The correlation coefficient method and cross-wavelet transform method were used to explore the drivers of precipitation concentration changes by coupling local meteorological factors and anomalous atmospheric circulation factors:maximum temperature,mean water pressure and Pacific Decadal Oscillation(PDO)were the causal factors leading to opposite trends in precipitation concentration index;mean temperature,mean water pressure and El Nino-Southern Oscillation(ENSO)were the drivers leading to significant trends in precipitation concentration index;each factor promoted or inhibited each other,and together they led to changes in precipitation concentration.(4)A probability assessment model integrating precipitation concentration index and drought and flood indexes was constructed based on the conditional probability formula and Copula function to quantitatively investigate the effects of precipitation concentration on floods and droughts:under the same scenario,the precipitation concentration indexes had stronger effects on floods than on droughts,and CIM had the strongest effect on droughts,followed by CID,and finally PCD;PCD had the strongest effect on floods,followed by CID,and finally CIM.Under different scenarios,as the precipitation concentration indexes increased,the probability of drought events gradually decreased and the probability of flood events gradually increased.In terms of spatial distribution,there was a stronger risk of drought near the Foping station and a stronger risk of flooding near the Xiji station.