Climatic Yield Of Maize Response To Drought Evolution Characteristics Of Different Growth Periods In Shaanxi Province

Drought disaster is an important factor affecting national food security and social stability.It is of great theoretical and practical value to study the adverse effects of drought on agricultural production under climate change.Taking Shaanxi Province as the study area,based on the daily measured meteorological data of 32 meteorological stations from 1971 to 2020 and the actual yield data of maize per unit area from 1990 to 2020,this paper analyzed the temporal and spatial evolution characteristics of meteorological factors and drought in different growth periods of maize by using the methods of rotation orthogonal empirical function,cross wavelet analysis,trend analysis and crop yield separation.The maize yield separation method suitable for various regions in Shaanxi Province was discussed,and the effect of drought on climatic yield of maize in key growth period was quantified.The main conclusions are as follows:(1)Variation characteristics of meteorological factors in maize growth periodIn Shaanxi Province from 1971 to 2020,the precipitation of maize planting period,flowering period and maturity period changed with the climatic tendency rate of-0.004,-0.18 and 1.82 mm/10 a,respectively,and the trend was not significant.The spatial variability of precipitation in seeding period was the highest,followed by flowering period and maturity period.In terms of spatial variation,precipitation in Guanzhong and southern Shaanxi showed a decreasing trend during sowing period,increased trend along the Great Wall of Northern Shaanxi,western Guanzhong and areas around Shangnan and Ningqiang in southern Shaanxi during Huaisao period,and continued to increase trend in most areas of Shaanxi during maturity period.Potential evapotranspiration did not decrease significantly at sowing stage,flowering stage and whole growth stage,but decreased significantly at maturity stage.The variation degree of potential evapotranspiration was the largest and the risk was also the largest in sowing period,followed by filamentum stage and maturity stage.From the perspective of spatial variation,the potential evapotranspiration of sowing period,flowering period,maturity period and the whole growth period showed a trend of increasing gradually from south to north,and the spatial variability was small.Most of the potential evapotranspiration increased during sowing period,while the potential evapotranspiration increased during filaments period,mainly distributed in northern Shaanxi,western Guanzhong and central and western parts of southern Shaanxi,and decreased in most areas during maturity period.(2)Drought variation characteristics in maize growth periodsIn Shaanxi Province from 1971 to 2020,the SPEI index changed with-0.096/10 a,0.027/10 a and 0.042/10 a,respectively,during the sowing period,flowering period and maturity period.The spatial distribution characteristics of drought in different maize growth stages showed more in the north and less in the south,and the trend of drought was concentrated in Yulin,Yan ’an,central and western Guanzhong,while the rest regions showed alternating changes of drought and humidity.Drought frequency of maize from sowing to ripening stage in Shaanxi Province was 44.63%,46.25% and 41.31%.The drought frequency was higher in the central and southern parts of Shaanxi during the sowing period,and the drought space in the flower silk period showed a distribution pattern of high north-south and low in the middle.The drought frequency in the mature period of Shaanxi province gradually increased from Yulin to the southwest.Droughts were most frequent during maize growth in the 1970 s,1990s and 2000 s.The ratio of dry stations in sowing period,flowering period and mature period was 44.6%,46.3% and 41.3%,respectively.The ratio of drought station to drought station showed an increasing trend in sowing period and whole growth period,while the ratio of other growth periods showed a decreasing trend,and the decreasing rate was the highest in maturity period.In Shaanxi Province from 1971 to 2020,there were obvious interannual cycle changes in the scale of10～17a for maize sowing date,maturity stage and total growth period,which experienced multiple dry-wet cycle processes.At the same time,there were 5a small-scale signals in the cycle changes of different growth periods,and the scale was unstable around 1975,1995 and 2010.The average frequency of light drought,medium drought,severe drought and extra drought were 20%,12%,8% and 2% respectively.The spatial distribution of drought frequency of different grades was different.(3)Response of maize yield to drought index SPEI The climatic yield of maize in northern Shaanxi and Guanzhong region separated by HP filter method is more reasonable,which can better reflect the influence of interannual variation of meteorological factors on maize yield.The characteristics of simultaneous increase or decrease of maize climatic yield in southern Shaanxi were more obvious when fitting by quadratic exponential smoothing method.The climatic yield of maize in Tongchuan,Baoji,Xianyang and Weinan was closely related to the dry and wet conditions of the flowering stage,while that of maize in Yulin,Yan ’an,Ankang,Hanzhong and Shangluo was more closely related to the dry and wet conditions of the whole growth stage.In northern Shaanxi and Guanzhong,there were both small scale and large scale signals of significant positive correlation between maize yield and the resonance relationship between dry and wet conditions,that is,with the increase of SPEI,maize climatic yield showed an increasing trend.The nine regions in Shaanxi province had significant positive correlation resonance period from 1994 to 2000.The average yield increase threshold of the three typical regions in Shaanxi province is ranked as southern Shaanxi > Northern Shaanxi >Guanzhong.The average yield reduction threshold is ranked as northern Shaanxi <Southern Shaanxi < Guanzhong.