| In recent years,with the occurrence of global warming and extreme climate events,climate change research is imminent.Previous studies have focused more on the climate evolution of the millennium scale,and the climate situation in the past century has been more closely linked with human production and life.In this paper,utilized the tree rings,historical documents and instrumental meteorological data,aiming to reveal the changes in precipitation in the Qinling Mountains in the past 160 years and their relationship with droughts and floods.Based on the tree-ring width index of Larix Chinensis,and the multi-year meteorological station data of Baoji in Mei County,the multi-regression model was used to reconstruct the precipitation from November to June of the year during the past 160 years.The precipitation series was used to study the climate change characteristics and trends in the Taibai Mountains,which is the main peak of the Qinling Mountains.At the same time,based on measured temperature and precipitation data from 32 meteorological stations in the Qinling Mountains from 1959 to 2015,the SPEI of the Qinling Mountains for was calculated.And revealed the characteristics of spatio-temporal changes in dryness and humidity in the Qinling region under the background of climate warming.Through the combination of historical document data and instrumental meteorological data,the occurrence and change cycle and law of drought and flood events in the historical period of the Qinling Mountains were reproduced.The result showed:(1)The tree-ring data was used to simulate and reconstruct the accumulated precipitation series in Taibai Mountain of the Qinling Mountains from November to June in the past 160 years,which made up for the insufficiency of the instrumental precipitation data.The results of wavelet cycle analysis show that there were four oscillation periods in the precipitation in the study area.The variance interpretation of the reconstruction equation was 39.6%(R2adj = 0.370,F=15.109,P<0.001).The significance test was performed.The reliability of the reconstruction sequence was supported and verified by the meteorological disaster history records and the surrounding reconstruction results.The reconstructed precipitation series showed obvious wet and dry changes and periodic fluctuations.In the past 160 years,the humid periods were mainly from 1875 to 1885,1908 to 1923 and 1983 to 2002;the periods of drought included 1857~1867,1886~1907,1923~1935and 1954~1965.Cycle analysis results show that there are four types of cycles in the study area in the past 160 years,such as 47~54 years,17~22 years,quasi-13 years,and 3~7 years.And showed the weakening of the small cycle,the increasing trend of the large cycle.Climate change in the study area is also affected by larger-scale hydrological and climatic changes.(2)The radial growth of Larix Chinensis in Taibai Mountain was significantly affected by cumulative precipitation from November to June,showing a significant negative correlation with clear physiology of trees.In addition to July and October of current year,the response of tree-ring and precipitation in the other months was inversely correlated with the response of temperature,that is,when the chronology was positively correlated with the temperature,the precipitation in the corresponding month was negatively correlated with the chronology,vice versa.The correlation coefficient between the cumulative annual precipitation of the STD chronology showed the scale from November to June was the highest(r=-0.539,P<0.001,n=55).There was a positive correlation between the average monthly temperature and the chronology from February to July,and there was a significant positive correlation between the average temperature in March and June.For the monthly average temperature combinations,it was found that the cumulative temperature correlation between March and June of the year reached 0.405(P<0.01,n=55).(3)Based on historical data,statistics show that there were 83 droughts and floods in Qinling Mountains during 1850 to 1959.There was a continuous distribution of droughts and floods,and the occurrence of droughts and floods events were alternated.From 1850 to 1959,drought and flood disasters occurred in the Qinling region 35 times and 48 times,accounting for 42.17% and 57.83% of the total number of droughts and floods respectively.In the ranks of droughts and floods,there was a continuous distribution of droughts and floods,showing that the occurrence of droughts and floods alternates.Drought and flood disasters mainly occured in a single season.At the same time,there were occurrences of droughts and floods in double seasons,three seasons,and even four seasons.Drought and flood disasters generally had 4 oscillation periods of 7 years,11 years,21 years and 31 years on the time scale,which correspond to the ENSO activity cycle and are basically consistent with the global climate change process.(4)From 1960 to 2015,there was a trend of aridity in the Qinling Mountains,and the aridity trend of the northern slope was greater than the southern slope.The annual average standard potential evapotranspiration index in the Qinling Mountains fell at a rate of 0.10/10 a,and the drought trend increased significantly.In the past 56 years,the overall trend of the drought and flood grades on the southern slope and the northern slope of the Qinling Mountains was relatively consistent,showing that the drought increased while the flood disasters decreased,while the frequency of droughts and floods and the level of disasters were different between the north and the south.The annual average standard potential evapotranspiration index on the northern and southern slopes of the Qinling Mountains decreased by 0.075/10 a and 0.128/10 a respectively,indicating that the aridity trend of the northern slope is greater than the southern slope.The results of wavelet analysis showed that the changes in the 5-7 and 9-11 year cycles of the SPEI index coincided with the cycles of ENSO and sunspots,suggesting that the climate change in the Qinling Mountains may be affected by climate changes at larger scales.(5)There is a common oscillation period between the precipitation sequence and the historical records and standard potential evapotranspiration index series calculated from instrumental data.In the past 160 years,the dry-wet changes in the Qinling Mountains have been affected to some climatic factor in the space-time scale,such as some wider range of hydrological climate change effects.The tree-ring reconstruction sequence,historical literature sequence,and standard potential evapotranspiration index sequence are consistent with the ENSO change cycle.In the past 160 years,dry-wet changes in the Qinling Mountains have been affected by a wider range of hydrological and climatic changes on the temporal and spatial scales.There are common intervals of 5~7a and 11~13a for the three alternative indicator sequences.The reconstructed precipitation and observed values were consistent in the period from 1960 to 2012.The reconstruction sequence can basically reflect the characteristics of precipitation changes.The trend of the drought and flood index reconstructed by the tree-ring reconstructed precipitation and historical literature shows a certain degree of convergence.In some periods,the changes in the low and high values of the two sequences are relatively synchronous.Among the drought events in the Qinling Mountains from 1960 to 2015,they mostly occurred in the ENSO warm event year,or in the year before and after the warm event year,and they mostly occurred in the mid-and strong-level warm event years.The ENSO event has a significant impact on the changes of dryness and humidity in the Qinling Mountains,and the greater the intensity of the warm event,the more that a serious drought event will occur. |
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