Controls on ecosystem groundwater use efficiency: insights from forest ecosystems in the northern hemisphere

This is the authors' abstract. We don't add key points for this paper.

Groundwater is essential for vegetation productivity and terrestrial carbon dynamics. Despite forests being the largest global carbon sink, studies on vegetation-groundwater relationships are scarce, especially at a hemispheric scale. Here, we evaluate groundwater use efficiency (GWUE) in northern hemisphere forests using remote sensing-derived gross primary productivity (GPP) and groundwater storage (GWS) data. In this study, GWUE is treated as a modeled diagnostic index derived from GPP and GWS, rather than a direct measure of plant groundwater uptake. Three main results were obtained: (1) From 2000 to 2024, GWUE generally increased, averaging 1.20 gC·m−2·mm−1, with higher values in humid tropical and subtropical forests and lower values in dry temperate and cold boreal forests; (2) Evergreen broad-leaved forests exhibited the highest GWUE at the biome level, while deciduous needle-leaved forests had the lowest; (3) Machine-learning interpretation highlighted leaf area index, evapotranspiration, and vapor pressure deficit as the leading predictors associated with GWUE variation across climatic regions and forest types. These results help identify where forest carbon–groundwater coupling is strongest across Northern Hemisphere forests and provide a screening-level basis for spatially targeted assessments of drought vulnerability and groundwater sensitivity.