Study On The Drought Climate Change In Chengdu Plain In The Past 60 Years

In order to research the on drought climate changes in the Chengdu Plain in the past 60 years,we used linear tendency rate method,M-K mutation test,Penman-Monteith model,and standardized precipitation evapotranspiration index(SPEI)to analyze the past 60 years(1960-2019)daily-scale climate data in the four places,including Dujiangyan,Wenjiang,Ya'an and Leshan on the Chengdu Plain.The main conclusions are as following:1.Characteristics of climate elements change in Chengdu Plain in the past 60 years.(1)The characteristics changes of annual and seasonal:In the past 60 years,annual and seasonal average temperature of the four places firstly decreased and then increased,the overall tendency was increased.The linear trend rate of average annual temperature were Dujiangyan(0.23 ? /10a)>Leshan(0.19 ? /10a)>Ya'an(0.14 ? /10a)=Wenjiang(0.14?/10a);The rate of change in the four places were the largest in spring,followed by autumn and winter,and the smallest occurred in summer.The annual precipitation of the four places has all oscillated and decreased,and the order were Dujiangyan(-92.88mm/10a),Leshan(-74.93mm/10a),Ya'an(-37.24mm/10a),Wenjiang(-21.86mm/10a)in the past 60 years;The seasonal precipitation as a whole oscillates down(except for wenjiang in spring and winter,and Ya'an in spring showed an upward trend),with the largest changes in autumn,slightly larger in summer and spring,and the smallest in winter.The annual and seasonal average relative humidity in the four places have fluctuated and declined in the past 60 years,especially since the 21 st century.The linear trend rate of the annual average relative humidity in four places ranked as wenjiang(-1.06%/10a),Dujiangyan(-0.88%/10a),Leshan(-0.76%/10a),Ya'an(-0.25%/10a);The rate of change in four places were the highest in spring,followed by summer and winter,and the most stable in autumn.(2)Test of mutation climate elements change: The annual precipitation and annual relative humidity of the four places in the Chengdu Plain had no obvious the mutation,while the obvious the mutation in temperature.Based on the main mutation temperature changes in four places,the climate mutation change point is comprehensively determined to be 2000 in this area.(3)The characteristics of climate elements changes before and after the mutation:Average annual temperature of the four places increased after mutation,and the rate of change increased slightly after the mutation.Average annual precipitation of the four regions decreased after the mutation,and the rate of change decreased as a whole before and after the mutation(except for the increased of Wenjiang after the mutation).Average annual average relative humidity of the four places decreased after the mutation,and the rate of change increased slightly before and after the mutation(except Leshan was the obvious declined after the mutation).2.Characteristics of potential evapotranspiration changes in Chengdu Plain in the past 60 years.(1)Annual and seasonal change characteristics: The annual and four-season potential evapotranspiration change trends of the four places in this area were different in the past 60 years.Annual potential evapotranspiration in Ya'an and Dujiangyan oscillates down,and the rate of change were-11.49mm/10 a and-3.31mm/10 a.The data tendency of Wenjiang and Leshan decrease at first and then rise again in later years,and the overall evapotranspiration rises slightly.The rate of change were 8.98mm/10 a and1.27mm/10 a.Changes in potential evapotranspiration in four seasons: In spring,Dujiangyan,Wenjiang and Leshan were declining trend at first,then grow up,but Ya'an oscillation falls;In summer,Ya'an,Dujiangyan and Leshan oscillations fall,but Wenjiang decrease at first and then rise again in later years;In autumn and winter,Ya'an and Dujiangyan oscillations fall,but Wenjiang and Leshan rose slightly.(2)Characteristics of potential evapotranspiration changes before and after the mutation: The annual potential evapotranspiration changes in four places were complex before and after the mutation.The average annual potential evapotranspiration of Dujiangyan,Wenjiang and Leshan Enlarged after the mutation,but the average annual potential evapotranspiration decreased after the mutation in Ya'an.Four places from before to after the mutation,The tendency changes from increase to drop(except for Ya'an before and after the mutation,it was all down).3.Characteristics of drought changes in the Chengdu Plain in the past 60 years.(1)Annual and seasonal variation characteristics: In the past 60 years,annual drought index of the four places have oscillated and declined,and the tendency changes were Dujiangyan(-0.32/10a),Leshan(-0.28/10a),Wenjiang(-0.14/10a),Ya'an(-0.09/10a);Four seasons of drought index change trends are obviously different:In spring and winter,Dujiangyan,Leshan and Wenjiang oscillates declining,but Ya'an rises slightly.In summer and autumn,all four places fluctuate and decline.In the past 60 years,the frequency of annual droughts of four places in the region have increased,and the order of changes were Dujiangyan(10.92%/10a)> Leshan(9.39%/10a)> Wenjiang(2.84%/10a)> Ya'an(2.11%/10a),Since the 21 st century,droughts have become more frequent and extreme droughts have increased;There were little difference in the frequency of drought in the four seasons,with the largest in autumn.In the past 60 years,the annual drought intensity of the four places has increased,and the order of changes were Dujiangyan(1.83/10a)> Leshan(1.66/10a)> Wenjiang(0.64/10a)> Ya'an(0.27/10a).The drought intensity since the 21 st century increase were obvious;The change of drought intensity in four seasons were different in the four places: In spring and summer,Ya'an oscillation decreased,but the other three fluctuated up,and the four droughts fluctuated up in autumn and winter.(2)characteristics of Drought change before and after the mutation: The mean value of the annual drought index of four places in this area became smaller after the mutation.And the rate of change were decreased as a whole before and after the mutation(except the Wenjiang was increasing after the mutation).The average drought frequency of the four places in this area increased after mutation,and there was no extreme drought before the mutation in the four places,but the extreme drought occurred after the mutation,indicating that extreme droughts increased after the mutation.The average drought intensity of four places in the area increased after mutation,and the rate of change increased slightly before and after the mutation(except for decline after the mutation in Wenjiang).