| China has a vast territory,complex geographical environment,frequently changing climate and serious natural disasters.Among the meteorological disasters in China,the frequency of droughts is high,the scope of impact is wide,and the duration is long,resulting in serious agricultural losses.Chongqing has a undulating terrain and belongs to the subtropical monsoon humid climate zone and drought-prone area.The drought have a large impact on agriculture in Chongqing.In addition,Chongqing's agricultural infrastructure is not perfect,production investment is less,and the ability to cope with drought is weak.If a severe drought occurs,it will threaten Chongqing's food security.Therefore,carrying out study on the spatial and temporal distribution of drought intensity and its impact on crop yield in Chongqing has important practical guiding significance for scientific disaster prevention and reduction,rational distribution of agricultural production,and ensuring food security and social and economic stability in Chongqing.Based on the daily precipitation data of 34 national meteorological stations in Chongqing from1961 to 2016,this paper defines the seasonal drought intensity index and the annual drought intensity composite index based on the Chongqing drought standard,and uses the method of ArcGIS spatial interpolation,M-K test,Hurst index and Morlet wavelet analysis to study the spatial and temporal distribution of drought intensity in Chongqing from 1961 to 2016.The drought years of major crops were determined based on the annual drought intensity composite index and drought intensity index of crop growth period.Using HP filter method to fit trend yield per hectare of main crops in Chongqing from 1978 to 2015,and calculating its climatic yield per hectare and relative climatic yield per hectare in dry years.Using grey correlation analysis to study the fluctuation of climatic yield per hectare of main crops in Chongqing and its response to drought.Using panel data model to quantitatively analyze the impact of drought intensity on yield per hectare of main crops in Chongqing counties.The main findings are as follows:(1)Temporal and spatial distribution of drought intensity in Chongqing.(1)The Chongqing drought standard is scientific and reasonable,but the standard can only qualitatively determine the drought intensity level and lacks quantitative calculation methods.It can only determine the seasonal drought type and its intensity level,and cannot reflect the composite situation of drought throughout the year.Based on the Chongqing drought standard,this paper proposes the definition and quantitative calculation formula of drought intensity in Chongqing,including seasonal drought intensity index and annual drought intensity composite index.(2)The drought intensity in Chongqing varies greatly.The intensity of spring drought has a decreasing distribution from the western Chongqing to the northeastern Chongqing and southeastern Chongqing.The intensity of summer drought has a decreasing distribution from the western Chongqing and the northeastern Chongqing to the central Chongqing and southeastern Chongqing.The midsummer drought intensity is the strongest among the five seasonal droughts in Chongqing,and the midsummer drought intensity has a tendency to decrease outward from the central part of Chongqing.The autumn drought intensity has a decreasing distribution from the northeastern Chongqing and western Chongqing to the central Chongqing and southeastern Chongqing.The winter drought intensity has a decreasing distribution from the northeastern Chongqing to the western Chongqing and southeastern Chongqing.The annual drought intensity in the western Chongqing is the largest,followed by the central Chongqing and the northeastern Chongqing,and the annual drought intensity in the southeastern Chongqing is the smallest.The extreme value of summer drought,midsummer drought,autumn drought and winter drought intensity index in northeastern Chongqing,the extreme value of midsummer drought and autumn drought intensity index in southeastern Chongqing,the extreme value of summer drought and midsummer drought intensity index in western Chongqing,and the extreme value of midsummer drought intensity index in central Chongqing can all meet the standard of special severe drought.The annual drought intensity has a decreasing distribution from the western Chongqing to the southeast Chongqing.(3)The temporal change trend of drought intensity in Chongqing are different,the intensity index of spring drought and winter drought show a decreasing trend,the intensity index of autumn drought showed an increasing trend,and the summer drought intensity index,the midsummer drought intensity index and annual drought intensity composite index varied greatly.(4)The time change of the annual drought intensity composite index in Chongqing has stages and periodic changes of 3 a,5 a and 18 a.In the past 55 years,Chongqing experienced a light drought period from 1961 to 1968,a severe drought period from 1969 to 1978,a lightest drought period from1979 to 1989,and the most severe drought period from 1990 to 2015.The Hurst index predicts that the annual drought intensity composite index will increase in the short term.(2)The fluctuation of climatic yield per hectare of main crops in Chongqing and its response to drought(1)The HP filter method fitted the best trend yield per hectare of major crops in Chongqing from1978 to 2015,followed by the 21-year linear sliding average method,and the logistic curve was the worst.In most dry years,the climatic yields per hectare and relative climatic yields per hectare of grain,rice,wheat,sweet potato,rape,hemp and sugarcane in Chongqing are negative due to drought.(2)Grey correlation analysis was used to analyze the gray correlation degree between climate yield per hectare and relative climate yield per hectare of major crops and seasonal drought intensity in Chongqing.The gray correlation degree between seasonal drought,grain climatic yield per hectare and relative climatic yield per hectare from strong to weak are the composite intensity index of midsummer drought,autumn drought,spring drought,summer drought and winter drought.Among the food crops,the gray correlation degree between seasonal drought,rice climatic yield per hectare and relative climatic yield per hectare from strong to weak are the composite intensity index of midsummer drought,summer drought,autumn drought and spring drought.The gray correlation degree between seasonal drought,wheat climatic yield per hectare and relative climatic yield per hectare from strong to weak are the composite intensity index of spring drought,autumn drought and winter drought.The gray correlation degree between seasonal drought,sweet potato climatic yield per hectare and relative climatic yield per hectare from strong to weak are the composite intensity index of midsummer drought,summer drought and autumn drought.Among the economic crops,the gray correlation degree between seasonal drought,rape climatic yield per hectare and relative climatic yield per hectare from strong to weak are the composite intensity index of spring drought,autumn drought and winter drought.The gray correlation degree between seasonal drought,hemp climatic yield per hectare and relative climatic yield per hectare from strong to weak are the composite intensity index of midsummer drought,autumn drought,spring drought and summer drought.The gray correlation degree between seasonal drought,sugarcane climatic yield per hectare and relative climatic yield per hectare from strong to weak are the composite intensity index of summer drought,midsummer drought,autumn drought and spring drought.(3)The impact of drought intensity on the yield per hectare of main crops in Chongqing counties.The panel data model analysis shows that the composite index of drought intensity in Chongqing counties has a negative impact on the yield per hectare of grain,rice,peanut,soy and sorghum,resulting in the reduction of the above crops.For every 1 increase in the annual drought intensity composite index of the county,the grain yield per hectare will decrease by 20.88 kg/hm~2.The yield per hectare of grain in Yongchuan County will be the strongest in the event of drought,and Chengkou County will be the weakest.For every 1 increase in the drought intensity composite index in the rice growing period of the county,the rice yield per hectare will decrease by 35.61 kg/hm~2.The yield per hectare of rice in Dazu County will be the strongest in the event of drought,and Youyang County will be the weakest.For every 1 increase in the drought intensity composite index in the peanut growing period of the county,the peanut yield per hectare will decrease by 6.67 kg/hm~2.The yield per hectare of peanut in Jiangjin County will be the strongest in the event of drought,and Yunyang County will be the weakest.For every 1 increase in the drought intensity composite index in the soybean growing period of the county,the soy yield per hectare will decrease by 3.95 kg/hm~2.The yield per hectare of soy in Dazu County will be the strongest in the event of drought,and Yunyang County will be the weakest.For every 1 increase in the drought intensity composite index in the sorghum growing period of the county,the sorghum yield per hectare will decrease by 9.55kg/hm~2.The yield per hectare of sorghum in Yongchuan County will be the strongest in the event of drought,and Qianjiang County will be the weakest.In summary,based on the Chongqing drought standard,this paper proposes the definition and calculation formula of seasonal drought intensity index and annual drought intensity composite index in Chongqing,reveals the temporal and spatial distribution of drought intensity in Chongqing,obtain the gray correlation between climate yield per hectare and relative climate yield per hectare of major crops and seasonal drought intensity,and quantitatively analyze the impact of drought intensity on the yield per hectare of main crops in Chongqing counties.This study can provide some reference for Chongqing's agricultural production to cope with drought threats. |
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