Skip to main content
U.S. flag

An official website of the United States government

Are drought indices and climate data good indicators of ecologically relevant soil moisture dynamics in drylands?

November 16, 2021

Droughts are disproportionately impacting global dryland regions where ecosystem health and function are tightly coupled to moisture availability. Drought severity is commonly estimated using algorithms such as the standardized precipitation-evapotranspiration index (SPEI), which can estimate climatic water balance impacts at various hydrologic scales by varying computational length. However, the performance of these metrics as indicators of soil moisture dynamics at ecologically relevant scales, across soil depths, and in consideration of broader scale ecohydrological processes, requires more attention. In this study, we tested components of climatic water balance, including SPEI and SPEI computation lengths, to recreate multi-decadal and periodic soil-moisture patterns across soil profiles at 866 sites in the western United States. Modeling results show that SPEI calculated over the prior 12-months was the most predictive computation length and could recreate changes in moisture availability within the soil profile over longer periods of time and for annual recharge of deeper soil moisture stores. SPEI was slightly less successful with recreating spring surface-soil moisture availability, which is key to dryland ecosystems dominated by winter precipitation. Meteorological drought indices like SPEI are intended to be convenient and generalized indicators of meteorological water deficit. However, the inconsistent ability of SPEI to recreate ecologically relevant patterns of soil moisture at regional scales suggests that process-based models, and the larger data requirements they involve, remain an important tool for dryland ecohydrology

    Publication Year 2021
    Title Are drought indices and climate data good indicators of ecologically relevant soil moisture dynamics in drylands?
    DOI 10.1016/j.ecolind.2021.108379
    Authors David Barnard, Matthew Germino, John B. Bradford, Rory O'Connor, Caitlin M. Andrews, Robert K Shriver
    Publication Type Article
    Publication Subtype Journal Article
    Series Title Ecological Indicators
    Index ID 70238819
    Record Source USGS Publications Warehouse
    USGS Organization Forest and Rangeland Ecosystem Science Center; Southwest Biological Science Center