| In the context of climate change,China’s drought problem has become increasingly prominent,causing serious losses to industrial and agricultural production.The meteorological drought formed by precipitation shortage is the driving factor of agricultural drought.Studying the response of agricultural drought to meteorological drought has important guiding significance for agricultural drought prevention and drought management and mitigation of drought loss.Existing studies have focused on the analysis of the correlation between the agricultural drought index and the meteorological drought index,and there are few studies on the relationship between the drought characteristics(such as drought duration and drought intensity)reflected by the two types of drought,making it difficult to guide drought prevention.In this paper,Gansu Province is taken as the research area.The standardized precipitation evapotranspiration index(SPEI)and Vegetation Condition index(VCI)are used to characterize the meteorological drought and agricultural drought respectively.The time variation characteristics of meteorological and agricultural drought in Gansu Province are analyzed by means of univariate linear regression,m-k test and wavelet analysis.The meteorological and agricultural drought in Gansu Province are analyzed by statistical method and Arc GIS interpolation technology Based on the spatial distribution of drought,the response relationship between SPEI index and VCI index in different time scales was analyzed by using the maximum correlation coefficient method.Based on the run theory,the accumulated values of drought duration and drought grade reflected by two types of drought are identified,and the statistical models of the accumulated values of meteorological drought duration and agricultural drought duration are established.The main conclusions are as follows:(1)Under the annual scale,the meteorological drought in the whole province and each region shows a linear increasing trend.In different seasons,except for winter and autumn Longnan area,the drought increased linearly in the whole province and other areas.According to the 5-year moving average analysis,the increasing trend of meteorological drought in the annual and seasonal scales is mainly concentrated in the middle and late 1990 s and 2000 s.The frequency of drought in different years is annual scale,and the frequency of meteorological drought in Gansu Province is the highest in 1990 s.In different seasons,the frequency of drought was the highest in the 1990 s except in summer.According to wavelet analysis,there are many main periods at the annual and seasonal scales.The longer main period is 32 years,and the shorter main period is 5-7 years.(2)The spatial distribution trend of meteorological drought is that in spring,the drought in Hexi area shows a significant decreasing trend,while in other areas,the drought shows a significant increasing trend.In summer,except for Longdong area,other areas of Gansu showed a significant increase trend of drought.In autumn,the drought in Longdong area showed a decrease trend,but the increase and decrease trend of drought were not significant.In winter,except for the drought in Longnan area,it did not increase significantly,but in most areas of Gansu,it did not decrease significantly.The spatial distribution trend of meteorological drought is that the high frequency area of drought in spring is Longdong area and Hexi area in summer.The spatial pattern of autumn drought reflected by spei in different time scales is quite different,but generally,the regions with higher drought frequency are mainly in Hexi and Longdong,while the drought frequency in Gannan is lower.In winter,the frequency of drought is the highest in Longdong area.(3)The annual VCI sequence showed a significant increase trend which meat the agricultural drought was significantly reduced.The period of serious agricultural drought was 1982-1985 in the 1980 s,1992-1995 in the 1990 s,2003-2005 in the 2000 s,in which the drought of cultivated land was serious throughout the 1990 s.In spring,summer,autumn and the whole growth section,VCI sequence showed a significant increase trend.The trend of annual drought area proportion is significantly reduced,especially after 2005.According to the mutation test,the mutation point of VCI sequence was 2008.In summer,the VCI sequence change point of the whole province is 2011,and that of forest land,grassland and cultivated land is 2014.In autumn,the mutation point of abrupt VCI sequence was 2006,and in winter,the mutation point of different land use types was between 2007 and 2011.(4)The areas with high frequency of agricultural drought in the year were distributed in the middle and east of Jiuquan,the east of Longzhong and the northwest of Longdong.In spring,the drought prone areas are mainly concentrated in the eastern part of Gansu,the central part of Hexi and some parts of Eastern Gansu.In summer,the frequency of drought in Hexi area,Longdong area,especially in Qingyang increased significantly.In autumn,the spatial distribution of drought frequency is basically consistent with that in summer.In the whole growing season,Hexi area,central Longzhong and Eastern Longdong are the areas with high drought incidence.Based on the slope analysis,the agricultural drought in the whole province was significantly reduced.The proportion of area was 89.6%,the proportion of area passing 0.01 significance test and 0.05 significance test was 53.3% and 13.0%,respectively.In spring,summer,autumn and growing season,the overall trend of drought reduction is that the proportion of agricultural drought reduction area is more than 85%,and the proportion of agricultural drought reduction area passing 0.01 significance test and 0.05 significance test is more than 45% and 13%,respectively.Among them,autumn is the season with the lowest decreasing area of drought trend and the lowest proportion of significance.The average value of growth season reflected that the area of drought trend slowdown was the highest,and the proportion of significance was the highest.(5)The SPEI time scales with the largest number of grids corresponding to the VCI index are SPEI-6 in spring,SPEI-12 in summer,SPEI-3 in autumn,and SPEI-3 in growing season.VCI index has the best correlation with SPEI-3,which is the most sensitive to SPEI-3 response.(6)In meteorological drought and agricultural drought,short-term drought lasting for one month accounts for the largest proportion,and the response of short-term agricultural drought to short-term meteorological drought is consistent.In the longest meteorological drought duration and agricultural drought calendar,there are more cases of continuous drought in winter and spring or in autumn and winter.The statistical relationship model between the cumulative drought level of the VCI index and the cumulative drought level of SPEI-3 was established.The linear model of Huanxian Station has a good fitting effect,R2 = 0.318,RMSE = 0.907;although the Yuzhong Station polynomial model R2 is small,the RMSE = 0.051,the verification effect is good;the Maqu station log model fits well,R2 = 0.347,RMSE = 1.340.The three models had the worst fitting effect on Zhangye Station.Zhangye is located in an agricultural irrigation area where vegetation growth depends on irrigation water,so it is not very sensitive to meteorological drought.The above research results can provide scientific basis for the management of agricultural drought prevention and drought relief in Gansu Province. |
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