Agricultural Drought Evolution Characteristics And Risk Zoning Of Winter Wheat Different Growth Stages In Northern China From 1960 To 2015

China is a big agricultural country,agriculture is the lifeblood of the national economy,and the drought disaster is one of the most serious factors affecting agricultural production.Although the Solar-thermal resources are abundant in the northern part of our country,the precipitation is limited and unevenly distributed,the seasonal changes of precipitation is large.The northern region of our country is a frequent area of agricultural meteorological disasters,especially in the north side of Qinling Mountains-Huaihe River Line,drought occurs frequently.If the drought occurs during winter wheat growing season,especially the critical period of winter wheat,it will directly affect the harvest,which will adversely affect the sustainable development of society and economy.Therefore,it is urgent to study the rule of the occurrence of winter wheat drought in northern winter wheat area.In this study,136 meteorological stations in 1960-2015 years of meteorological data were selected in Chinese northern winter wheat region,the spatial and temporal variations and distribution characteristics of winter wheat in different growth stages in northern China in recent 56 years were analyzed by using the national standard agricultural drought assessment index-the crop water deficit anomal index(CWDIa).At last,according to the principle of natural disaster risk,with drought frequency as the index of drought risk,combined with the sensitivity of the disaster environment and the classification standard of drought,to determine the drought risk zoning of winter wheat.The results showed that:(1)The multi-year linear trend of the CWDIa in recent 56 years at whole growth stage indicated that: the south and north regions showed a wet trend and the middle region showed a drought trend,spatial distribution of the drought intensity showed that the central region of the study area has a high value,and arid space sites with rising trends are located in high value areas.The results of wavelet analysis shows that the variation of drought index in the South,middle and north regions have the main period of 3.9a,2.5a and 2.6a,that is,there was a 2-6a oscillation period for the dry and wet changes at whole growth stage.(2)Before winter,the South and middle section showed a trend of drought,while the north area showed a wet trend,the high value area of drought intensity during sowing-seedling stage was located at the junction of Henan,Shanxi and Hebei,and the southern edge of Shandong.The range of high value of drought intensity at the tillering stage was larger than sowing-seedling stage.Besides those above,there is a high value distribution in Longdong of Gansu and Anhui.The results of wavelet analysis showed that the changes of drought index in South,middle and North regions before winter were the first main period of 2.6a,2.3a and 2.3a,and there was a oscillation period of 2-6a in dry and wet changes.(3)After winter,the multi-year linear trend of drought index showed the characteristics of "wetting and drying" in southern section,while the middle and northern regions were opposite.The high value area of drought intensity during reviving-jointing stage was located in the northern of Shanxi,Beijing,Tianjin,Hebei,Henan and Shandong.The high value area of the drought intensity in booting and heading stage was moved westward,and the high value area is mainly distributed in the Shanxi and Gansu region.The high value area of drought intensity during milky-mature stage extends eastward to the south.The drought intensity of the western and central regions of the whole study area is large,and the sites of rising trend of drought is increasing with the growth period.he wavelet analysis shows that the changes of the drought index in the south,middle and north regions after winter have the first main period of 2.3a,3.1a and 5.7a,and there is a oscillation period of 2-8a in dry and wet changes.(4)The drought frequency in the whole breeding period is mainly light drought.The high frequency area of drought is located in Beijing,Tianjin,Hebei,and the northern part of Henan and Shandong.Before winter,the frequency of drought was low,mainly is light drought.The high frequency area during sowing-seedling stage is mainly distributed in northern Henan,east of Shanxi,northern Hebei,and southeast of Shandong.compared with sowing-seedling stage,the frequency of drought increased and the range of high frequency increased during tillering stage.After winter,the frequency of drought increased with the growth period.The north central part is the high frequency area of the drought during reviving-jointing stage,and the frequency of drought over half of the total area exceeds 33.3%.The frequency of drought in the booting and heading stage increased,and a high grade drought occurred in the whole study area.The frequency of severe and extreme drought increased at milky-mature stage,and the increasing area was concentrated in the central part of the study area.(5)The drought risk of winter wheat generally shows high in north,east and low in south,west during whole growth period.Before winter,the risk of drought is small.The drought risk sowing-seedling stage is increasing from south to north.There is a opposite features during tillering stage.After winter,the risk of drought was higher than before.The high risk area during reviving-jointing stage is distributed in Beijing,Tianjin and Hebei,which is high in the north and low in the south.The high risk areas in the booting and heading stage most widely distributed,and the distribution pattern was high in the north and low in the south.The drought range of milky-mature stage is smaller than booting and heading stage,and the drought risk area increased from west to east,and increased from south to north and then decreased.However,during the whole life of winter wheat,Longnan of Gansu and southern Shanxi are low risk areas.In addition to the tillering period,Anhui and south central Jiangsu also belong to the low risk area,while the high risk areas are mostly distributed in south of Hebei and north of Henan,and in Shanxi and Shandong,the different drought risk varies with the growth period.