| Moderate resolution imaging spectroradiometer (MODIS) data are very suitable for vast extent, long term and dynamic drought monitoring for its high temporal resolution, high spectral resolution and moderate spatial resolution. The normalized difference vegetation index (NDVI) and land surface temperature (LST) obtained from MODIS data MOD13A3and M0D11A2were used to construct the NDVI-Ts feature space. The temperature vegetation drought index (TVDI) was calculated to evaluate drought in Ordos. The results show that:(1) NDVI-Ts character space obtained dry edge equations slope less than0,(-8.53～-18.20), the maximum value of land surface temperature was negatively correlated with the normalized difference vegetation index. NDVI-Ts character space obtained wet edge equations slope greater than0(0.68～43.13), the minimum value of land surface temperature and the normalized difference vegetation index were positively related to relationship.(2) The drought condition was inversed and verified with the soil moisture data from Ordos weather stations simultaneously in2010year. The results showed that there was a significant correlation between TVDI and soil moisture, which expressed the TVDI method can be used in drought monitoring and early warning of the areas with complex terrain.(3) The temperature vegetation drought index (TVDI) was calculated to evaluate drought in Ordos. It showed that the drought area was more than60%in Ordos, the drought area in Ordos was evidently increasing and continuously deteriorating from West to East, and it was heaviest drought in2008.(4) In recent10years, drought grade area ranked:drought area (42.21±13.15%)> light drought area (29.09±10.95%)> heavy drought area (17.96±11.74%)>normal area (9.39±7.5%)> wetted area (1.35d±0.85%). The different drought area showed:dry area were significantly higher than that of light drought area, light drought area were significantly higher than other drought area. Severe drought area were significantly higher than that of wet area, both of them had no significant difference with the normal area.(5) From2002to2011, it appeared the light drought degree (included light drought, drought, severe drought) in Ordos,. The drought was the comprehensive effect of precipitation and temperature results.2002～2004and2007, this4years belonged to light drought (0.4<TVDI<0.6), the other years belonged to drought (0.6<TVDI<0.8). (6) Annual different drought area anomaly had a certain fluctuation with time in Ordos. Server drought area, drought area had been enlarging trend; light drought area, normal area, wetted area had been narrowing trend. It was showed that the trend was increasing drought in Ordos. Such as severe drought area anomaly was fluctuated upward trend with time,2006,2008,2010～2011years of serious drought area>17.96%, in2008the severe drought area of47.86%, it was reached more than2.67times the annual average. |
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