Drought Evolution Characteristics And Risk Zoning Of Maize Growth Period In The Loess Plateau From 1961 To 2015

Drought is a widely distributed natural disaster in the world,its impact on the agricultural system is most obvious and most direct.The Loess Plateau,which is in arid and semi-arid sensitive areas and fragile zones,is the main practice area for dry farming in China.Because of its special geographical location and unique climatic characteristics,so the study of agricultural drought in the region can not be ignored.In this study,85 meteorological data of the Loess Plateau region from 1961 to 2015 were selected.Crop water requirement at different growth stages of maize was added to the calculation of Standardized Precipitation Evapotranspiration Index(SPEI).Constructed a new agricultural drought assessment indicators Standardized Precipitation Requirement Index(SPRI).Based on the evaluation of the applicability of the new index,the temporal and spatial distribution of agricultural drought in the Loess Plateau region in recent 55 years was analyzed and its relationship with the large scale climatic factors was discussed.Finally,the drought risk zoning of maize in the Loess Plateau region was determined.The main conclusions are as follows:(1)The probability distribution goodness test of SPRI was performed using the K-S test,at the same time with the SPEI index comparison results show that,the SPRI has good goodness of fit at each time scale and the spatial range of the maize growth period.The evaluation of the applicability of agricultural drought in qualitative and quantitative aspects shows that the index can reflect the drought degree in the study area and can characterize the drought characteristics of the maize growth period in the region.The SPEI index has good applicability in drought monitoring of maize in the Loess Plateau.(2)The SPRI index of maize at different growth stages decreased in the Loess Plateau,and the drought trend was different in different growth stages.The trend of drought in the Ordos Plateau was the strongest in the three growth stages.The results of Hurst exponent based on R/S analysis show that there are obvious Hearst phenomena in the SPRI of the growth period since the last 55 years,that is,the trend of drought in the future growth period of maize may continue in the Loess Plateau.(3)Mutations in the SPRI of each growth period were examined using the Mann-Kendall method and the sliding t-test.The results showed that 1992 was the mutation of dry and wet change in the early stage of maize growth in the Loess Plateau.There was no significant mutation in booting and grouting period.The mutation of the entire crop growing season was 1986.The periodic results of wet and dry changes in the growth period of the Loess Plateau in recent 55 years showed that: there were two main periods in the early growth period,6.5a was the first main period,3.8a was the second main period.At the booting and grouting stage,3.1a is the first main period,4.7a is the second main period;the entire crop growing season is only one main period is 3.0a.(4)The crossed wavelet transform and coherent wavelet transform of SPRI and sunspot number,MEI,PDO and EASMI showed that SPRI index has a significant correlation with each climatic index.The results of the significance test are throughout the study,and the characteristics and resonance of SPRI and climatic factors can be clearly reflected in time and frequency domain..(5)The comprehensive risk of drought in the early stage of maize growth in the Loess Plateau increased from the southeast to the northwest.The comprehensive risk of drought in booting-grain-filling stage was increasing from east to west.The comprehensive risk of drought in the whole period was increasing from southeast to northwest.In addition,the Longzhong-Ningxia Loess Plateau and the Ordos Plateau are always drought-resistant and high-risk areas in the maize growth stages,and the southern of Shanxi Loess Plateau is the low comprehensive risk zone of drought.In other regions,the combined risk of drought in different growth stages is different,In the northern of Shanxi Loess Plateau,there is a great change in the comprehensive risk of drought at different growth stages.