| In the context of global warming,precipitation events are generally extreme.The upper reaches of the Minjiang River is one of the most serious areas of soil erosion in Jiangxi Province.Extreme precipitation is an important factor affecting the change of water and sediment in the region.The relationship between river water and sediment is the result of the combined effects of natural factors and human activities,and its changing process is affected by many factors.Human activities,especially soil and water conservation measures,and the construction of water conservancy projects,will have a major impact on water and sediment changes in the basin.Therefore,this paper analyzes the temporal and spatial variation characteristics of precipitation and extreme precipitation in the basin from 1957 to 2015,and analyzes the dynamic changes of water and sediment in the basin.The extreme precipitation index and the magnitude of the effects of extreme precipitation changes and human activities on water and sediment changes in the Meichuan River Basin.The specific conclusions are as follows:(1)Based on the daily precipitation data from 1957 to 2015 in the Meichuan River Basin,the temporal and spatial variation of precipitation in the basin was analyzed.The average annual precipitation in the basin is 1692.95mm.During the year,the precipitation is mostly concentrated in the flood season.The precipitation in the flood season accounts for68%of the annual precipitation.The annual precipitation does not increase significantly.The annual trend rate is 23.07mm/10a,and the trend of precipitation during the flood season is The annual precipitation is about the same,and the precipitation in the four seasons shows no significant increase.The interannual tendency rates are 10.28mm/10a,19.57mm/10a,3.41mm/10a,9.69mm/10a respectively.The mutation test indicates the annual,flood season and autumn precipitation.In 1972,there were few to many mutations.In the summer and winter,precipitation occurred in 2002 and 1998 respectively.The annual precipitation in the Meichuan River Basin is 26~30a,7~11a,3~6a.Three types of time scales change periodically.The main periods of precipitation in the four seasons are different;the spatial distribution of precipitation in the basin is gradually increasing from southwest to northeast of the basin.(2)Selecting 10 extreme precipitation indicators(R25,R50,Rx1day,Rx5day,R95p,R99p,PRCPTOT,SDII,CDD,CWD)commonly used at home and abroad,and analyzing the temporal and spatial variation characteristics of extreme precipitation in the Meichuan River Basin.On the interannual changes,R25,Rx1day,Rx5day,R95p,R99p,PRCPTOT and SDII showed no significant increase trend,CDD and CWD showed no significant decrease trend.In particular,R50 showed a significant increase trend;in interdecadal change,R25,R50,Rx1day,Rx5day,R95p,R99p,PRCPTOT,SDII all showed less before the 1990s,and increased significantly in the 1990s and 2000~2015;there is a close relationship between the extreme precipitation indexes,Pearson The significance test showed that except for CDD,the correlations among the other extreme precipitation indicators were positively correlated;in spatial distribution,the overall trends of R25,R50,Rx1day,R95p,R99p,PRCPTOT and SDII were all represented by the southwest of the basin.It gradually increased to the northeast.In particular,Rx5day and CWD increased stepwise from the west to the east of the basin,and the CDD gradually increased from the northwest to the southeast of the basin.(3)Based on the runoff data from 1957 to 2015 in the Meichuan River Basin and the sediment transport data from 1958 to 2015,the process and trend of water and sediment change in the basin are studied.The annual average runoff of the basin is 60.15×10~8m~3,and the runoff performance shows an increasing trend in the past 59 years,but it is not significant.In the interdecadal change,the runoff experienced a process of increase?decrease?increase?decrease.M-K mutation test,cumulative anomaly curve and sliding t-test showed that the total annual runoff occurred in 2002 with more or less mutations.The change of runoff has a period of change around 6a,11a and 28a.Among them,the period of 28a is the strongest,which is the first main period of runoff change,and the time scales of 11a and6a correspond to the second and third mains of runoff.The annual average sediment transport volume in the basin is 104.12×10~4t.The annual distribution of sediment transport is mainly concentrated in the flood season.It has the characteristics of“large water and large sand”.The sediment transport volume decreased from 1958 to 2015,and declined after the mid-1990s.Obviously,the mutation test showed that the amount of sediment transport was more or less mutated in 1999.The change of sediment transport in the Meichuan River Basin has a cycle of change of 5a,17a and 28a.Among them,the cycle of 28a is the strongest,which is the first main cycle of sediment transport change,followed by 17a and 5a;The correlation between the water and sediment data in the flood season and the extreme precipitation indices shows that both the runoff and sediment transport have the best linear correlation with PPRCPTOT,followed by R25 and R95p.Therefore,when fitting the linear relationship between water sand and extreme precipitation,three extreme precipitation indexes of PRCPTOT,R25 and R95p can be selected,among which PRCPTOT is the best index.(4)The extreme precipitation factors of PRCPTOT,R25 and R95p were selected as natural representative to evaluate the effects of extreme precipitation changes and human activities on water and sediment changes in the Meichuan River Basin.The results show that the main reason for the change of runoff from 2003 to 2015 comes from the change of precipitation(extreme precipitation).The human activities have relatively little interference to the annual runoff variation in the Meichuan River Basin.The contribution rate of human activities to the change of sediment transport from 2000 to 2015 Larger,with PRCPTOT,R25 and R95p as extreme precipitation factors,the contribution rates are 114.7%,118.8%,and 123.9%,respectively.The results of the three extreme precipitation indices are basically the same.The main reason for the change of sediment transport in the Meichuan River Basin comes from for human activities.Human activities,especially soil and water conservation measures,and the construction of water conservancy projects,will have a major impact on water and sediment changes in the basin.It is calculated that human activities reduce the sediment transport in the basin by 3.17×10~4t per year.The extreme precipitation changes result in an increase of 0.51×10~4t per year.The impact of extreme precipitation changes on the sediment transport in the Meichuan River Basin is relatively small. |
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