| Drought is one of the natural disasters with the widest distribution,the highest frequency and the largest economic loss in the world,which poses a serious threat to agricultural production,social and economic development and people ’s life.At present,drought has become the primary climatic factor affecting agricultural production in Guanzhong area of Shaanxi Province.In this paper,the Guanzhong area was taken as the research object.Based on the 8d surface temperature composite product of MOD11A2 and the 16 d vegetation index composite product of MOD13A1,the NDVI-LST feature space was constructed to obtain the TVDI of the 20-year time series in Guanzhong area from 2001 to 2020,and the spatial and temporal distribution pattern and evolution characteristics of drought in Guanzhong area were analyzed.The Theil-Sen median trend analysis,Mann-Kendall test and Hurst index analysis were used to explore the drought change trend in the study area,and the correlation between TVDI distribution and altitude,slope,precipitation and temperature was analyzed,which provided scientific basis for coping with climate change strategies and guiding agricultural production in Guanzhong area.Research showed that :(1)The spatial and temporal differentiation and dynamic changes of vegetation coverage and surface temperature in Guanzhong area were obvious.In the past 20 years,the vegetation NDVI in Guanzhong area showed a slow upward trend,with an increase of about 0.01 / a,and the overall trend was relatively stable.The spatial distribution pattern of NDVI was gradually increasing from southwest to northeast.The high vegetation coverage area was mainly distributed in the southwest Qinling Mountains,and the low value area was distributed in the middle of Guanzhong area,corresponding to the urban distribution area centered on Xi ’an.The spatial distribution of NDVI showed significant seasonal differences,and its variation characteristics were consistent with the periodic characteristics of vegetation growth.January and July were the continuous growth period,and August and December were the decline period.The average LST of 2001-2020 had a certain range of fluctuation changes,and the overall trend was decreasing.From January to December,the foothills in the southwest obviously divided the Guanzhong area into Guanzhong Plain and mountainous area,and the surface temperature difference between the two sides was obvious.The temperature of Taibai Mountain,the main peak of Qinling Mountains,was the lowest in 12 months,and the surface temperature of Guanzhong Plain was higher than that of other areas.For different land use types,the mean LST of cultivated land,forest land,grassland,urban and rural industrial and mining residential land and unused land increased first,and then continued to decline at different rates after rising in June,showing obvious seasonal regularity.(2)The average annual TVDI was between 0.493 and 0.634.Among them,the drought in2013 was the most serious,and the area of the arid area accounted for the largest proportion.In 2011,the drought was the slightest,and the wet area accounted for the largest proportion.The location of the drought center was relatively fixed.The drought degree in the main urban area of Xi ’an and Lishan was lower than that in other areas of the Guanzhong Plain.Most of the northern Guanzhong Plain was in a normal and humid state except 2013,while the Taibai Mountain area in the northern Qinling Mountains was the wettest.However,the spatial location and proportion of the internal drought center and drought area were quite different between months.In 2020,the monthly average TVDI changed corresponding to different land use types in Guanzhong area and did not show strong seasonal regularity.According to the TVDI value from high to low,the corresponding land use types were urban and rural industrial and mining residential land,cultivated land,grassland,unused land and forest land.(3)The spatial and temporal changes and future trends of drought in Guanzhong area from 2001 to 2020 showed that in the past 20 years,48.30 % of the regional TVDI values in Guanzhong area have shown an increasing trend.Combined with the results of M-K test,the drought situation in Guanzhong area from 2001 to 2020 was in a relatively stable range,and the drought phenomenon was not becoming more and more serious.From the perspective of future trends,the average Hurst index was 0.44,and the change characteristics of TVDI were opposite to the trend of TVDI in Guanzhong area in the past two decades,that is,TVDI in this area will show a decreasing trend in the future,and drought conditions may be alleviated.TVDI in Guanzhong area was negatively correlated with precipitation and positively correlated with temperature.Topographic factors such as altitude and slope also had a certain impact on TVDI. |
