Study On The Spatio-temporal Evolution And Prediction Of Drought Characteristics In The Western Plain Of Jilin

Drought has a great impact on human society,especially in the agricultural field.The losses and impacts caused by it are inevitable and severely restrict local agriculture and economic development.The western plain of Jilin belongs to a temperate continental monsoon climate,with evaporation greater than precipitation.It is a typical agro-pastoral ecotone and a fragile ecological environment.The difficulty of drought research lies in its complexity,randomness and unpredictability.The research on drought characteristics analysis and prediction is urgent.This paper analyzes the rainfall characteristics of each year and each growing season based on the monthly rainfall data in the western plain of Jilin from 1958 to 2017,calculates the Z index,discusses the spatial and temporal distribution characteristics and changing trends of drought in the region,and assigns weights based on game theory Prediction of drought conditions at unknown sites and error analysis from the spatial scale provide a scientific basis for drought prevention and strengthening of drought management.The main research results are as follows:(1)The spatial distribution of the annual average rainfall in the western plain of Jilin is basically the same as the average rainfall in the growing season,showing a decreasing trend from the southeast to the northwest.The inter-annual rainfall in the east showed an upward trend,and the west showed a downward trend.The decline in the rainfall in the growing season was larger than the inter-annual scale.Only parts of the southeast of Changchun City,the northwest of Songyuan City,and the west of Baicheng City showed an upward trend.All regions showed a downward trend.The maximum annual rainfall in the plains of Jilin Province shows a decreasing trend from the southeast to the northwest.The high values are mainly concentrated in Siping City and the southeast of Changchun City,which are greater than 800mm;the low values are mainly Baicheng City and the west of Songyuan City and are less than 600mm;the average rainfall is distributed in the junction area of Songyuan City and Changchun City.(2)In the past 60 years,the degree of drought in the western plain of Jilin Province has shown a slight increase.On the interannual scale,there have been 18 years of drought with a frequency of 30.00%;on the growing season scale,there have been 17 years of drought with a frequency of 28.33%.Generally speaking,most droughts occurred from 1995 to 2011,with an average of one drought every 1.5 years.Analysis on an interannual scale shows that mild droughts mainly occur in the southwestern plains;moderate droughts mainly occur in Qian’an,Nong’an and Shuangliao;severe droughts mainly occur in Tongyu and Qianguoerluosi Mongolian Autonomous Counties(formerly Guo).Analyzed on the growing season scale,mild droughts mainly occurred in the western plains;moderate droughts mainly occurred in Nong’an and Shuangliao;severe droughts occurred more frequently in Baicheng,Tongyu,Qianguo,Shuangliao and Siping..The trend rate of the inter-annual Z value in the western plain of Jilin Province is-0.13～-0.06mm/10a,with an average of-0.08mm/10a.In the eastern part of the plain area,the inter-annual Zvalue trend rate showed an upward trend.Among them,the southeastern part of Changchun City,the north of Songyuan City and the east of Baicheng City increased rapidly;the west showed a downward trend,of which the southwestern part of Songyuan City and the south part of Siping City declined.Faster.(3)On the inter-annual scale,the western plain of Jilin has periodic fluctuations of rainfall in the main annual seasons of 5-10 years and 17-40 years,with five and two alternating droughts and floods,respectively.The growing season scale and the interannual scale have similar characteristics.There are two obvious periodic fluctuations of rainfall in the growing season in 5-15 years and 20-35 years in the plain area,with five and two alternating droughts and floods,respectively.Three oscillation periods are detected in the wavelet variance graph,which are 3.7 years,9.8 years and 27.8 years.The analysis shows that 27.8 years is the cycle of possible droughts and floods in this area.On the whole,the solid line in the wavelet analysis is not closed,indicating that there is a greater possibility of flooding in the future growing season,and flood prevention is the main task for some time in the future.(4)The drought spatial prediction based on the least squares method is better than the single kriging or inverse distance weighted interpolation method.After weighting,the absolute error is 0.19 and the relative error is 0.60.Compared with the results obtained by single kriging or inverse distance,its accuracy and confidence are better.