Macroscopic evaluation of scPDSI and SPEI links to vegetation water stress factors

The self-calibrating Palmer Severity Drought Index (scPDSI) and the multi-time-scale Standardized Precipitation Evapotranspiration Index (SPEI) are commonly employed to explore the impact of water availability on vegetation. However, their usage lacks clearly defined boundaries. This study presents a global-scale macroscopic assessment of the relationship between scPDSI and SPEI with vegetation water stress factors. Our findings reveal that, in comparison to meteorological conditions, scPDSI exhibits a stronger correlation with root-zone soil moisture (RSM). Among SPEI on various scales, SPEI at the 9-month scale (SPEI09) effectively captures RSM dynamics, while SPEI at the 1-month scale (SPEI01) is more responsive to variations in vapor pressure deficit. Moreover, the sensitivity analysis of vegetation activity response to scPDSI and multi-scale SPEI indicates higher sensitivity in drylands to scPDSI and SPEI09, while that in boreal regions of the Northern Hemisphere exhibit the highest sensitivity to SPEI01. This study will provide scientific reference for selecting scPDSI and different SPEI time scales as indicators of water availability conditions.