Study On The Construction And Applicability Of Standardized Crop Water Deficit Index In Dry Farming Area Of Northern China

Due to the economic impact caused by climate change,regional conflicts and the COVID-19 pandemic,the international food security problem is becoming increasingly serious.Under the background of global change,droughts occur frequently in the northern China,which affects the yield of spring maize.Therefore,it is particularly important to efficiently monitor and assess drought levels,in order to provide a scientific basis for preventing the loss of spring maize caused by drought disasters and the sustainable development of agriculture in this region.In this paper,based on the Crop Water Deficit Index（CWDI）,the Standardized Crop Water Deficit Index(SCWDI_sm)was constructed from the perspective of water supply and demand by using meteorological data,spring maize growth period data,soil moisture data,historical disaster data,yield data,etc.At the same time,in order to ensure the reliability and validity of the index,the goodness-of-fit test and applicability evaluation of SCWDI_smare carried out from many aspects.By analyzing the annual variation of SCWDI_sm,the ratio of drought stations and drought frequency,the temporal and spatial variation characteristics of spring maize drought in this area were studied.The main work and research conclusions of this paper are as follows:（1）There is a high correlation between precipitation in the growing stages and the fluctuation of soil moisture in ECMWF,which indicates that soil moisture in ECMWF responds to precipitation events in time,and can be used as a direct supply of spring corn moisture,which is suitable for the construction of agricultural drought index.（2）In the goodness-of-fit test of the index,the probability density and distribution curves of the three-parameter log-Logistic are in high agreement with the empirical curves,which means that the three-parameter log-Logistic distribution can be used to represent the time series of cumulative crop water deficit in different fertility periods of spring maize.And standardizing it can better reflect the characteristics of the data for more effective analysis.（3）Compared with common drought indexes such as Pa,SMAPI,MI and CWDI,SCWDI_sm shows stronger correlation and higher consistency in both regional and station scales,which shows that SCWDI_sm is more effective and has more obvious advantages in drought monitoring,and can be used to study spring maize drought in dry areas in northern China.（4）During 1981-2018,SCWDI_sm increased significantly at the rate of 0.31·10a^-1（P<0.01）,and the inter-annual drought showed an expanding trend.The increase of ENSO events in recent 10 years was the influencing factor for the increasing drought events.Spatially,the drought frequency of spring maize in the whole growth period can basically reach more than once in 3 years in most areas,and it is mainly light drought and moderate drought.The Loess Plateau is mainly threatened by light drought and moderate drought,and the frequency of moderate drought in the south of Inner Mongolia and along the Great Wall is relatively high,while the frequency of severe drought and extreme severe drought in the north of Songnen Plain and Zhangcheng district of Hebei Province are relatively high.（5）The ratio of drought stations in five growth stages showed a significant upward trend,and the drought range was the largest at jointing-tasseling stage.2001 was the year with the widest range and the heaviest degree of drought in the seedling-jointing stage.In space,except the sowing-emergence stage,the drought frequency in the other four growth stages showed a spatial pattern of high in the west and low in the east.Most of the northern spring maize areas were dominated by light drought,and the frequency of light drought in the loess plateau reached more than once in 3 years during the seedling-jointing stage;The frequency of drought in Inner Mongolia and the middle part of the area along the Great Wall reached once in 3 years during jointing-tasseling stage.The frequency of severe drought in the middle part of the Northeast Plain reached more than once in 4 years during the tasseling-milking stage,and the severe drought threatened the tasseling-milking stage.