Drought Monitoring in Heilongjiang Province Based on NDVI-Ts Space

Combining the spectral vegetation index with thermal infrared information, the triangular space of NDVI Ts based on satellite remote sensing data provides an effective method for monitoring surface dryness at large spatial scales. Vegetation Temperature Condition Index (VTCI) based on the triangular space of MODIS NDVI Ts is applied to monitoring summer drought in Heilongjiang Province in 2007. The VTCI is based on satellite derived information only, and therefore the index is potential for operational application. The Terra MODIS NDVI(MOD13A2) V005, LST(MOD11A2) V005 and the land cover product(MOD12Q1) V004 products, at 1 kilometer spatial resolution, are used as the indicators for the monitoring and analysis. The monitoring period is from 10 June to 12 August 2007. It's found that the space of NDVI Ts for the whole study area is typically triangular because the monitored area is large enough to make the value of NDVI and soil moisture vary in a very large scope. Then, a linear regression analysis is conducted to get the equations of the dry and wet line from the triangular space for the whole area, and the VTCI for the Heilongjiang Province is extracted. Combined with MODIS land cover product IGBP and frequency distribution of the VTCI, the spatial pattern and temporal evolution of the drought are also analyzed. At last, the ground measured precipitation data at the same periods are used to validate the drought monitoring measurements. The result shows that the drought widely distributed in spatial scale and is very serious. It is more serious in main crop producing areas, especially in the western Songnen Plain and the west of eastern Sanjiang Plain. From 10 June to 25 June the drought is heavier than the other 3 monitoring periods. Some fluctuations occur in July, then the drought weakens in most areas in August, except the Daxinganling Mountains in northwest where the drought enhances to some extent. The correlation analysis between VTCI and ground based measured precipitation indicates that there is a significant linear correlation between VTCI and total monthly precipitation. The VTCI and cumulative total monthly precipitation are also linearly correlated from the monitoring month to the previous months. Obvious correlation is also found between VTCI and the percentage of departure from normal monthly precipitation in the monitoring month, and between VTCI and the cumulative percentage of departure from normal monthly precipitation from the monitoring month to the previous months. The result suggests that VTCI is not only correlated with recent rainfall but also correlated with past cumulative rainfall. So it is a reasonable simplification of the NDVI Ts space and can monitor drought instantly, which is proved adaptive in Heilongjiang Province.