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

Aihong Cui, Jianfeng LI*, Qiming ZHOU, Ruoxin Zhu, Huizeng Liu, Guofeng Wu, Qingquan Li

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

23 Citations (Scopus)


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 GRACE to the climatology at multiple time scales. Because of the statistical nature of its definition, the proposed index is comparable to other standardized drought indices in different time scales, e.g., standardized precipitation index (SPI), standardized precipitation evapotranspiration index (SPEI) across different regions at multiple time scales. Our comparisons of STI with multiscalar drought indices (i.e. SPI and SPEI) and uni-scalar indices (i.e. self-calibrating palmer drought severity index [scPDSI], standardized soil moisture index [SM-Z], standardized runoff index [R-Z], and GRACE-based drought severity index [DSI]) show that STI can capture drought events with less noise than other indicators in persistent drought events. As a hydrological drought index based on TWS (which includes groundwater, soil moisture, etc.), STI at short-term time scales (e.g. 3 and 6 months) have higher correlations (mostly > 0.7) with SPI/SPEI at long-term scales (e.g. 18 and 24 months). Since the TWS measured by GRACE incorporates the impacts of the accumulated changes in meteorological variables, hydrological processes, and human activities as well as the advantage of multiscale, STI better represents vegetation growth reflected by Normalized Difference Vegetation Index (NDVI) than uni-scalar drought indices including the GRACE-based DSI, suggesting STI is a robust indicator for hydrological droughts and vegetation changes.
Original languageEnglish
Article number126871
JournalJournal of Hydrology
Issue numberPart A
Early online date1 Sept 2021
Publication statusPublished - Dec 2021

User-Defined Keywords

  • Hydrological droughts
  • Terrestrial water storage
  • Meteorological droughts
  • Drought indices


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