Analysis Of Spatio-Temporal Variations Of Maize Drought In Liaoning Province Based On Crop Water Deficit Index

Using the daily meteorological data of 52 meteorological stations in Liaoning Province and the observation data of maize growth period from 1961 to 2015,the whole process of maize growth in Liaoning Province was divided into five stages.Calculate the accumulative crop water deficit index(CWDI)of each station in every growth period,then test the drought index,the result of which is that the CWDI is a real reflection of the maize drought situation of in Liaoning province.Based on the calculated crop water deficit index,the rotated empirical orthogonal function decomposition method was used to analyze the drought index matrix of Liaoning maize drought during every growth period.The main modes were extracted and the corresponding spatial loads and time coefficients were analyzed.Then the spatial and temporal variation characteristics of each grade of maize drought in every growth stage during the last 55 years in Liaoning province were obtained.The main conclusions are as follows:(1)In general,the frequency and degree of maize water deficit increased simultaneously in Liaoning Province after twenty-first Century.The average of crop water deficit index in sowing-seedling stage was the largest,which was the growth stage with the most frequently of maize drought.It of seedling-jointing comes second,and it of tasseling-milky is the smallest.In space,the distribution of water deficit index of crop is mainly featured by west with high values while east with low ones,and North-South with high values while midlands with low ones.The area with high average of crop water deficit index is mainly located in the large part of western and southren of Liaoning Province.(2)From 1961 to 2015,in the early maize growth stage(sowing-Jointing)the average value of the ratio of maize drought occurring stations was higher in Liaoning province,but the fluctuation was smaller.In the middle stage of the maize growth(jointing-milky)and late stage(milky-maturing),the average value of the ratio of maize drought occurring stations was smaller,but the interannual fluctuation was more volatile.Drought has the greatest impact during the early maize growth stage,and especially the mild drought is most widespread.The frequency distribution of every grade of drought in each growth stage is mainly characterized by that west-high-and-east-low in the whole province.And the high incidence area of maize drought is mainly distributed in the hilly region of western Liaoning,the corridor of the west of Liaoning and the Liaodong peninsula.The highest frequency of maize drought was in the early stage of growth,the late growth stage comes second,and the middle growth stage has the lowest frequency.The frequency of mild drought was the highest in every growth period.In this century,the maize drought affected area and its frequency of each grade in every growth stage increased synchronously.(3)The REOF decomposition of maize drought index in Liaoning in the 1961-2015 years was carried out.The cumulative variance contribution rate of the first three main modes reached over 70%,which could reflect the spatial distribution of drought well in Liaoning.The characteristic vectors of the first three modes of the five maize growth stages are positive or negative simultaneously,which indicates that the maize drought in Liaoning showed a strong spatial consistency in the whole region.In general,the northwest of Liaoning,the northern and Liaodong Peninsula are drought high sensitive areas of maize.The time coefficients of the two maize growth periods – sowing-seedling and seeding-jointing show that the years with maize drought were relatively more.The time coefficient of jointing-tasseling,tasseling-milky and milky-maturing periods showed a relative decrease in the maize drought year.This indicates that the sensitivity of maize drought during the early growth stage is higher in Liaoning area,while the sensitivity of drought in the middle and late stages of growth reduced.During the early maize growth stage,the typical years of maize drought in Liaoning province were 1972,1981,2003,2007 and 2011.After 2000,the maize drought frequency increased significantly.During the middle stage of maize growth,the typical drought years were 1980,1999 and 2000.The typical drought years in the late miaze growth stage of maize are 1981,1979 and 2014.In addition,maize is prone to spring and summer continuous drought(1961,1972)and summer and autumn continuous drought(1989,2014)in Liaoning Province.