1.College of Geomatics, Xi’an University of Science and Technology, Xi’an 710054, China; 2.School of Geology and Environment, Xi’an University of Science and Technology, Xi’an 710054, China;
Based on MODIS normalized difference vegetation index (NDVI) and land surface temperature (Ts) data, the authors constructed a bi-parabolic NDVI-Ts space which was verified by the filed measured soil moisture, and monitored the spatial and temporal distribution characteristics of drought conditions in Shaanxi Province from 2000 to 2016 based on the TVDI obtained from bi-parabolic NDVI-Ts space. The results show that the NDVI-Ts space was bi-parabolic and there was a significant negative correlation (P<0.05) between TVDI and 10 cm depth filed measured soil moisture. Spatially, the drought in Shaanxi Province during 2000—2016 were mainly distributed in the northwest, north of Shaanxi and the northeastern regions of Guanzhong plain; the drought area of Shaanxi Province accounted for 31.95% in 2000 and 27.65% in 2016, respectively. It is found that drought was significantly relieved in most northern part of Yulin City, the middle part of Yan’an City and the central part of Guanzhong Plain and some parts of southern Shaanxi, which accounted for 14.45 %. The drought conditions in 84.48 % of the province were changed, but the change failed to pass the significant test. 97.62% of the province had a small variation coefficient, which was between 0 and 0.8. It was mainly distributed in northern Shaanxi, south of Guanzhong Plain, and it showed that the drought conditions were stable in Shaanxi Province. There was a significant negative correlation between drought and annual precipitation, accounting for 23.74 % (P<0.1). With the increase of rainfall, TVDI decreased, and the drought was relieved. It was mainly distributed in most areas of Yulin City, central parts of Yan’an City, north and northwest of Hanzhong City, Ankang City, northern parts of Weinan City, eastern parts of Shangluo City and western and northern parts of Baoji City. It is found that the changes of drought in other areas were not significantly affected by precipitation. The annual temperature was not dominant factors that resulted in the change of drought in Shaanxi Province.
Fig.1 Scatter plots in NDVI-Ts space from 2000 to 2016
时间
R2
10 cm深度
20 cm深度
50 cm深度
20130509
0.555*
0.405
0.211
20130524
0.325*
0.273
0.099
20130914
0.318*
0.236
0.267
20130930
0.445*
0.433
0.217
Tab.1 Linear correlation R2 between TVDI and field-measured soil moisture
Fig.2 Drought distribution of Shaanxi Province during 2000—2016
Fig.3 Classification of TVDI slope and variation coefficient in Shaanxi Province
Fig.4 Correlation coefficient classification between TVDI and precipitation, annual temperature and temperature anomaly
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2019,
Vol. 31
