Drought Characteristics Of The North-south Transitional Zone In China Based On TVDI Index

Frequent and persistent drought disasters not only cause crop failure and reduced yield,but also exacerbate water scarcity.As a geographic transition zone in China,the North-South transitional zone in China is facing severe drought due to the changes in global climate in recent decades,the drought in the region is severe and has reduced agricultural production.To carry out drought monitoring in this region and analyze the spatio-temporal variation of drought in this region,so as to provide scientific basis for the protection of water resources,regional agricultural production and sustainable development of regional economy.In this paper,temperature vegetation drought index(TVDI)was computed using MOD11A2 and MOD13A2 products from MODIS data of moderate resolution Imaging Spectroradiometer based on LST—EVI to invert the soil moisture of vegetation growing season from 2010 to 2018 in the study area.Accumulation anomaly method,trend test method,coefficient of variation method and barycenter transfer method were used to investigate the temporal and spatial distribution of drought,the intensity and trend of change,the track and barycenter of gravity transfer of drought in the study area.The correlation between each factor and drought was characterized using precipitation,temperature,potential evapotranspiration and elevation data obtained by interpolation of meteorological stations,and then the major and minor factors of drought were fitted by regression analysis,and the main conclusions were as follows:(1)The Enhanced Vegetation Index(EVI)is more sensitive to high vegetation coverage and has a wider monitoring range compared to the Normalized Difference Vegetation Index(NDVI).It has a higher accuracy in model construction when it replaces NDVI.The fitting effect of the dry-wet edge of each month during the vegetation growing season is better,and the fitting coefficient R~2 is almost above 0.6.The results of drought inversion in the TVDI model from May to August 2012 were significantly negatively correlated with the measured soil volume water content during the same period.The fitting effect was good and can be used to explore and analyze the specific characteristics of drought in the study area.(2)Over the nine-year period of the study area,the overall drought level was classified as semi-arid,and the overall drought situation was roughly divided into two stages:from 2010to 2014,the study area gradually became more humid,while from 2014 to 2018,it became drier.The semi-arid type has the largest area,and during the 2010～2014,areas such as Gansu Province,the northwest of Sichuan Province,and Baoji City in Shaanxi Province were relatively humid,while the western part of Henan Province,the northern part of Sichuan Province and Chongqing City,and the western part of Hubei Province were severely affected by drought.During the 2014-2018,the area of arid and semiarid regions further expanded,and areas such as the Guanzhong Plain and western Sichuan became drier.Drought conditions further aggravated.(3)Among all types of changes,the area with no significant increase in aridity type is the largest.At the interannual scale,the central region mainly experiences an increase in aridity,while the situation in the eastern and western regions is complex and varied.At the monthly scale,drought is most severe in June,July,and August,and the severity of drought increases more rapidly during these months.The magnitude of changes is higher in the western region compared to the eastern region.,and the most unstable areas are concentrated in Aba Tibetan and Qiang Autonomous Prefecture of Sichuan Province and Gannan Tibetan Autonomous Prefecture of Gansu Province.The center of drought occurrence is mainly located in Hanbin District of Ankang City and Hanyin County,with the center of drought shifting eastward from2010 to 2013 and gradually returning to Hanyin County in the west from 2013 to 2018.The degree of variation in aridity from northwest to southeast is greater than that from northeast to southwest.\(4)During the study period,the total annual precipitation gradually decreased,with a spatial distribution characteristic of more precipitation in the north than in the south and more in the east and west than in the central region.The average annual temperature declined slightly over the study period,with temperatures generally lower in the western and northern parts of the study area than in the eastern and southern parts,which is extremely similar to the overall distribution pattern of TVDI,with more than half of the area with no significant positive correlation types.The potential evapotranspiration rate increased slightly but decreased in a stepwise manner from east to west,showing no significant positive correlation with TVDI.Precipitation,temperature,potential evapotranspiration,and altitude all had an extremely significant impact on drought.Altitude and precipitation had a negative impact on drought,while temperature had a positive impact.The degree of impact of each factor on drought was ranked as follows:temperature(0.585)>altitude(0.43)>evapotranspiration(0.08)>precipitation(0.062).