Constructing a global grassland drought index (GDI) product based on MODIS and ancillary data

Grassland, which has a great significance to human society, is susceptible to the drought. An efficient way to monitor the drought scale of grassland is imperative. In this paper, we proposed a new drought index named Grassland Drought Index (GDI) to monitor the drought conditions of the grassland ecosystem. The GDI was constructed by comprehensively integrating the soil moisture content, canopy water content (CWC) and precipitation together with different weights. The soil moisture with 1km spatial resolution was estimated by downscaling the AMSR-E soil moisture from 25km to 1km. The CWC was retrieved by the 1km MODIS products based on the PROSAIL model. And the precipitation was acquired by CRU data. Besides, the global distribution product of GDI in July 2010 was produced. By validation, the correlation coefficient R between the scaled GDI and the Standard Precipitation Index (SPI) was 0.6109, and the root-mean-square error (RMSE) was 0.7774.