Research On Spatiotemporal Evolution Law Of Meteorological Drought In Jilin Province

Nowadays,in the context of global warming,coupled with the increase of global population and rapid economic development,the impact of drought is not only limited to the regional water crisis,but also began to seriously affect agricultural production and socioeconomic development.Drought,as one of the most important meteorological disasters in Jilin Province,has a great impact on the economy of Jilin Province,especially in crop production.Drought usually causes a lot of problems,such as serious shortage of local water resources,grassland degradation,land desertification and large area reduction of crops and so on in Jilin Province.In view of this,the temporal and spatial evolution of drought in Jilin Province was analyzed to clearly understand the reasonable assessment of its trend and provide the theoretical basis of flood-drought disaster monitoring and management in Jilin Province.It also provided a theoretical basis for drought prevention,disaster reduction and relief in Jilin Province,as well as the basic decision-making establishment of disasters.Based on the daily meteorological data average temperature(T_mm),diurnal temperature ranges(T_delta),relative humidity?RH?,solar radiation?Rs?,wind speed?U₂?,geothermal flux?G?,and precipitation?P?of 28 meteorological stations from 1958 to 2017 in Jilin Province,the spatial variation characteristics were analyzed.Then,Z,SPI,SPEI._T and SPEI._PM drought indexes were selected for comparative analysis,in order to determine the suitable drought index in Jilin Province,and to analyze the frequency,range,intensity,length,starting and ending time of drought,as well as the spatial distribution,trend and evolution characteristics of drought in different time scales?year,season and month?.After that,the Morlet wavelet function was selected to study the periodic variation of drought in Jilin Province.In addition,the drought duration and drought accumulation intensity were used to establish a two-dimensional copula joint distribution to analyze the characteristics of drought recurrence period.Finally,using the global sensitivity analysis EFAST method,the sensitivity analysis of the relevant meteorological parameters of SPEI._PM index was carried out to explore the response degree,spatial distribution and sensitivity ranking of these meteorological factors to SPEI._PM.Among them,the main results of the above studies were as follows:?1?Study on the suitability of drought Index?1?The Z and SPI indexes were used to compare the drought conditions respectively on the annual,monthly and seasonal scales in Jilin Province.The SPI index was more suitable than Z index for drought monitoring and evaluation when there was only precipitation data in Jilin Province.From the point of space and time,by comparing the four indexes of Z,SPI,SPEI._T and SPEI._PM,the actual drought situation was verified by drought disaster area,non-harvest area and “Disaster Code” of Jilin Province,which suggested that SPEI._PM index was the most suitable drought index for drought assessment in Jilin Province.?2?In Jilin Province,the trend of drought in different of yearly,seasonal and monthly scales was different,and the droughts in spring and winter showed the upward trend,while most of the droughts in summer and autumn showed the downward trend.From the spatial frequency of drought,it was concluded that spring drought was mainly distributed in the south-central,southeast and northeast of Jilin Province.Summer drought was mainly distributed in the western,central and southeastern parts of Jilin Province.Autumn drought was mainly distributed in the western,central and eastern regions of Jilin Province.Winter drought was mainly distributed in the western and southcentral regions of Jilin Province.From the point of view of time,the sequence of drought frequency in different grades of yearly,seasonal and monthly scales mainly reflected the following characteristics: light drought > medium drought > severe drought > special drought;the frequency on annual scale that was close to that of monthly scale,seasonal scale,the frequency of light drought was winter drought > autumn drought > spring drought > summer drought;the frequency of medium drought was summer drought > autumn drought > winter drought > spring drought;the frequency of severe drought was winter drought > spring drought > summer and autumn drought;the frequency of special drought was spring drought > summer drought > autumn drought > winter drought.?3?Based on the study of drought stations proportion,it was concluded that there were significant differences in drought stations proportion in different years and seasons.On the whole,provincial drought = local drought = inconspicuous drought > regional drought.?4?From a spatial point of view,there was a difference in the distribution of the maximum and minimum values of the start and end time based on the SPEI.MP index,but the trend distribution of the start and end time was basically the same.The length of drought in most areas showed a non-significant downward trend,and in the western region showed upward trend of Jilin Province,The length in the western region would increase in the future.The drought intensity of the whole province showed a downward trend,and the accumulation of drought intensity in the western part of Jilin Province was greatly affected by the drought intensity.From the time point of view,the beginning time,the end time,the duration of drought and the intensity of drought showed an upward trend,while the cumulative intensity of drought showed a decreasing trend.There was a high probability of spring drought,summer drought and spring-summer continuous drought in Jilin Province.?2?Analysis of drought cycle and recurrence period based on SPEI._PM index?1?Since 2017,the real parts of wavelet coefficients had shown a negative trend,and there was a tendency for drought in the future in Jilin Province.The localization characteristics of drought cycle variation were obvious.The first,second and third main periods of annual drought were 24 a,2.5a and 3.5a respectively.The period is not very different between the monthly and the annual scale.In spring,the first main cycle of more than half of the areas was 10²0a.Most of the summer drought was characterized by small period?2¹0a?,and the fluctuation more frequent.More than half of the areas in autumn showed a provincial drought event every 10-20 years.In most areas of winter,it had a provincial winter drought event every 2.5-5 years in Jilin Province.?2?According to the analysis of the characteristics of drought probabilistic and return period based on the Copula joint distribution,the optimal copula types for drought duration and cumulative intensity in Jilin Province were Gumbel copula,BB8 copula and Clayton copula?180 degrees?.With the continuous increase of drought duration and cumulative intensity,the joint probability decreased gradually,while the combined recurrence period of drought showed an increasing trend.Among them,the frequency of severe drought events in the west of Jilin Province was higher than that in the middle and east of Jilin Province.The drought recurrence period shows the following sequence: the western region < the southern region < the central region < the southeast region < the northeast region.Among them,the joint return period increased slowly at first and then steeply with the increase of drought duration and drought accumulation intensity.?3?Global sensitivity analysis based on SPEI._PMThe sensitivity of the SPEI differs in time scales,throughout the area of Jilin province,the sensitivity of different meteorological variables to the SPEI._PM from high to low was precipitation,temperature,relative humidity and average wind speed.While solar radiation and geothermal flux had no significant influence on it.Meanwhile,the sensitivity of different meteorological variables to the SPEI._PM varied across time scales.The sensitivity of the SPEI differs in time scales: P > T_mean > RH > U₂ > Rs > G > T_delta?1-to 6-month time scale?,P > U₂ > RH ?T_mean > G > Rs > T_delta?7-to 18-month time scale?,and P > U₂ > G > Tmean > RH > Rs > T_delta?more than 24-month time scale?,respectively.Hence,in the context of global warming,drought analysis and monitoring were not only affected by precipitation,but also by average temperature,relative humidity and average wind speed.The results have the potential to provide a reference for agricultural production and management in Jilin Province.In conclusion,SPEI._PM was the most suitable index for Jilin Province.The frequency of light drought was relatively high,and it has a tendency of drying in the future.It was relatively dry in the western region of Jilin province,and the sequence of drought range was overall Global drought = local drought = no significant drought > regional drought.The local characteristics of drought cycle change were obvious,and the spatial distribution of main periods in different seasons was significantly different.With the increase of drought length and cumulative intensity,the joint probability decreased gradually,and the joint recurrence period tended to increase.The occurrence sequence of recurrence period of drought events was in the western region < southern region < central region < southeast region < northeast region.The sensitivity of meteorological factors to SPEI was also different in different time scales,the first four sensitivity factors are P,T_mean,RH and U₂.