Spatialtemporal Variation Of Meteorological Drought And Its Impacts On Grain Yield In Loess Plateau Based On The Traditional Arid-Wet Index

Under the background of climate warming,drought becomes one of the major natural disasters in China and the world.The ecological environment of the Loess Plateau is fragile and sensitive to climate change.The drought event will seriously restrict the development of social economy.Therefore,it is of great significance to further study the evolution characteristics of drought in Loess Plateau and analyze the impact of drought change on dryland crop yield,so as to enhance the ability of disaster prevention and mitigation in agricultural production,adjust the corresponding ecological environment policies,and promote the sustainable development of regional economy.In previous study,aridity index was defined as the ratio of traditional potential evapotranspiration?ET₀?to precipitation?P?and served as the meteorological drought index.Based on the daily meteorological data of 55 selected weather stations in the Loess Plateau?LP?during 1960—2017,this traditional meteorological drought index was re-defined by ET₀calculated from FAO56-Penman-Monteith equation in this study.Then analyzed the spatiotemporal variation of meteorological drought was analyzed.Finally,the relationship between drought frequency and grain yield per unit area was detected.The results are as follows.Firstly,the average annual P and ET₀in the LP from 1960 to 2017 were 426.5mm and999.7mm,respectively.The spatial distribution of precipitation and potential evapotranspiration in different seasons has its own characteristics.The climate boundary values between the humid,semi-humid,semi-arid,arid and dry,redefined by the FAO56-PM equation,were 0.58,1.17,1.77,2.36 and 4.74,respectively.The average annual aridity index of whole LP is ranged from1.22 to 8.84,and it decreased gradually from northwest to south.The spatial distribution variation of inter-decadal of the arid-wet climate boundary line 1.79 and 2.36 was obvious;but its variation in line 4.67 was not obvious.The annual aridity index of 63.3%of meteorological stations was increased.The annual aridity index decreased in arid areas and increased in arid,semi-arid and sub-humid areas.Secondly,in the past 58 years,the total drought frequency of the LP was 73.7%.The drought frequency corresponding to different climatic regions decreased successively from north to south.Spring and winter were prone to severe drought,summer and autumn were prone to moderate drought and slight drought.On the whole,the LP experienced frequent drought and the drought frequency tended to increase slightly in past decades.The drought frequency in spring and autumn tended to increase,but it was in summer and winter tended to decrease.The frequency of moderate and slight drought tended to increase,but the frequency of major drought tended to decrease.Thirdly,the average annual drought frequency was the largest in northwest ana smallest in south and small.The frequency of drought decreased from northwest to south,and then increased from west to east.The frequency of moderate drought and great drought were the smallest in the northwest and the largest in the southeast.The drought in each season was frequent in dry area of the LP.Drought frequency in spring and winter were high.There are 10 stations that have drought free years.The number of drought free years was maximum in spring,followed by summer and the least in autumn.Fourth,the weather stations that correlations between grain yield and aridity index and annual P that reached significant level?p<0.05?were 16 in LP mainly rained area from1996 to 2017,respectively.These stations are mainly distributed in northern and central eastern gansu,shanxi,northern shaanxi and other regions,about three-quarters of the number of rained area stations,each station per unit area yield of grain with aridity index,annual P respectively shown closely negative correlation and positive correlation.There was a significant negative correlation between the grain yield per unit area and the aridity index in north shaanxi,which was dominated by dry farming.The lower the aridity index was,the more the yield per unit area was.The grain yield per unit area was closely positively correlated with annual P,spring,summer,autumn,that summer and autumn P had a significant impact on grain yield,which passed the significance test of 0.05,indicating that the greater the P,the greater the yield per unit area.Fifth,perennial average drought frequency may have a certain influence on the grain yield in the central and northwestern arid areas of the LP.The spatial distribution of the areas affected by the frequency of drought in each season was different,and the lower the drought frequency was,the more the grain yield was.Dry region different level drought frequency also have different degrees of influence on the grain yield.The correlation of grain yield with frequency of slight drought and middle drought was negatively but didn't pass significant test.Stations that affected by the heavy drought frequency was Wuqi,Tongwei,Hengshan,Jingtai nearby what have a closely negative correlation,and passed the significance test of 0.05.