Research On The Temporal And Spatial Characteristics Of Drought Based On Standardized Infrared Index

Drought is one of the frequent natural disasters in China.It has a wide range of influences and long duration,which poses a serious threat to food production and human life.Shaanxi Province is located in the hinterland of northwestern China,and is located in the fragile environment of the eastern part of the northwestern region,natural disasters occur frequently.Frequent drought is not conducive to the growth of food crops,especially the key growth period of winter wheat and summer maize in spring and summer,which poses a major threat to food production security in the region.Therefore,drought monitoring research on drought occurrence in Shaanxi Province,accurate grasp of drought development status,timely analysis of drought spatial and temporal characteristics is of great significance to agricultural production and economic development in the region.Drought remote sensing monitoring technology is widely used in drought monitoring research because of its many advantages such as real-time,dynamic and high efficiency.This study using correlation analysis,Theil-Sen Median trend analysis,Mann-Kendall test,Hurst index and other methods combined with vegetation index,measured soil relative humidity,precipitation,and agricultural drought area analyzed the Standardized Vegetation Index(SVI),Standardized Precipitation Index(SPI)and the Standardized Infrared Index(SII)in Shaanxi Province and the temporal variation characteristics,spatial variation characteristics and the evolution trend of drought in 15 years.The main conclusions are as follows:(1)The drought monitoring results in Shaanxi Province using three indexes SVI,SPI and SII have a certain correlation with soil relative humidity,precipitation data and drought area,but the SII index indicates that the drought occurrence is consistent with the actual drought.It shows that the use of SII for drought monitoring has certain effectiveness and feasibility.(2)The annual average SII values of Shaanxi province,northern Shaanxi,Guanzhong area and southern Shaanxi have increased year by year,with increasing rates of 0.0826,0.0683,0.0565 and 0.0739 respectively.The drought change in southern Shaanxi is the biggest,the drought change in Guanzhong area is the smallest,and the drought change in northern Shaanxi is stronger than Guanzhong area and weaker than southern Shaanxi.The M-K mutation detection method combined with the SII anomaly curve is used to determine the year when the SII value of the four regions is abrupt:Shaanxi Province was in 2002,2008 and 2011,the northern Shaanxi region was in 2003 and 2008,the Guanzhong region was in 2010 and 2014,and the southern Shaanxi region was in 2006,2008 and 2012.According to the "National Drought Disaster Statistics for the Past 50 Years",there are abrupt years above,both droughts have eased or aggravated years compared to the past few years.(3)Through the recent 15 years,the changes of arid area coverage in the five time scales of Shaanxi province,northern Shaanxi,Guanzhong area and southern Shaanxi are obtained different regions and different time scales have drought occurred,but the drought was the most serious in spring,followed by summer and autumn.In terms of interannual variation,the arid area coverage rate in each region decreased at different rates.The drought was the most serious in 2001?2005,since 2010 the drought has eased.(4)Based on the SII drought grading standard,the average SII values of Shaanxi province,northern Shaanxi,Guanzhong area and southern Shaanxi were classified into drought grades and the spatial distribution characteristics of each drought type were obtained:the main arid and extremely arid regions in northern Shaanxi located in the north and northwestern regions;the arid and extremely arid regions in the Guanzhong area are mainly located in the central and eastern regions,showing a general intermediate drought and surrounding humidness;southern Shaanxi is the region with the most rainfall in Shaanxi Province,only the north and the border areas of the Guanzhong area are in an arid area and the whole is relatively humid.At the same time,according to the frequency of occurrence of various drought types,the frequency of drought in 15a from northern Shaanxi to Guanzhong and to southern Shaanxi showed a decreasing trend,but the frequency of drought and extreme drought in northern Shaanxi was the highest,and drought occurred in southern Shaanxi has the lowest frequency.(5)According to the coupling information of the trend and persistence of SII value,the area of increasing drought in Shaanxi Province accounts for 14.23%,mainly located in Hanzhong,Ankang and Shangluo City in southern Shaanxi,there are also small areas in the southwestern part of Baoji City in Guanzhong area and in the southeastern part of Yan'an City in northern Shaanxi.The drought-promoting region accounts for 55.74%,mainly located in Yan'an city in northern Shaanxi,Xianyang and Tongchuan in Guanzhong area;The 11.89%areas with aridening trend,it is mainly located in Yulin city in the north of Shaanxi Province and Xi'an in Guanzhong area,in Weinan City,Hanzhong and Shangluo cities in southern Shaanxi also have a small amount of distribution,and another 18.14%of the region's future trends are uncertain.This study analyzes the suitability of SII index for drought monitoring from the perspective of index construction,and analyzes the temporal and spatial variation characteristics of drought in different time scales,different seasons and different grades in Shaanxi province,northern Shaanxi,Guanzhong area and southern Shaanxi,combined with Mann-Kendall test,the Hurst index and other methods have obtained the evolution trend of drought in various regions.The results of this study can be of guiding significance for Shaanxi Province to take active and effective drought prevention and drought resistance.