Drought Monitoring Using the Modified Temperature/Vegetation Dryness Index

Based on the EVI/Ts feature space which was constructed by land surface temperature (Ts) and Enhanced Vegetation Index (EVI) extracted by MODIS data, the modified temperature/vegetation drought index (MTVDI) was calculated to monitor the drought status of Inner Mongolia Autonomous Region from 9 May to 11 July. The meteorological data and soil moisture data were collected to compare with MTVDI. The correlation analysis was carried out between MTVDI and the cumulative precipitation of the same period(cpsp), the early 16 days(cpe16), the early 30 days(cpe30) and the early 60 days(cpe60). The correlationship between MTVDI and the mean temperature was analyzed in the same way. It implied that the correlation between MTVDI and the cumulative precipitation of the same period became lower and lower, which demonstrated that rainfall has a lagging effect. It depended on the cumulative precipitation in the present period whether the correlation between MTVDI and the cumulative precipitation of the same period or of the previous was significant or no. There was no significant difference in the correlations between MTVDI and the mean temperature of the same period or the previous for two periods, which were from 9 May to 24 May and from 26 June to 11 July with light drought. In heavy drought periods from 25 May to 9 June and from 10 June to 25 June, the correlation coefficient between MTVDI and the mean temperature of the same period was much higher than the previous time, which proved that the drought status was aggravated by high temperature. Finally, the soil moisture data (0-10cm) measured by agro-meteorological stations was carried out linear correlation analysis with MTVDI. The result showed that MTVDI had a close relationship with surface soil moisture and it can be used as an indicator to monitor the drought status.