Use of a multiscalar GRACE-based standardized terrestrial water storage index for assessing global hydrological droughts

A multiscalar standardized terrestrial water storage index (STI) is proposed to assess global hydrological droughts in this study. STI is defined as the standardized statistical deviation of terrestrial water storage (TWS) measured by CSR GRACE to the climatology at multiple time scales. STI follows the definition of water deficit in multiscale standardized drought indices such as SPI and SPEI, and the accumulative TWS is ftted by the cumulative normal distribution in the calculation procedure.