A generalized relationship linking water balance and vegetation carbon
uptake across site-to-regional scales
Abstract
The linear relationship between gross primary productivity (GPP) and
evapotranspiration (ET), evidenced by site-scale observations, is well
recognized as an indicator of the close interactions between carbon and
hydrologic processes in terrestrial ecosystems. However, it is not clear
whether this relationship holds at the catchment scale, and if so, what
are the controlling factors of its slope and intercept. This study
proposes and examines a generalized GPP-ET relationship at 380
near-natural catchments across various climatic and landscape conditions
in the contiguous U.S., based on monthly remote sensing-based GPP data,
vegetation phenology, and several hydrometeorological variables. We
demonstrate the validity of this GPP-ET relationship at the catchment
scale, with Pearson’s r ≥ 0.6 for 97% of the 380 catchments.
Furthermore, we propose a regionalization strategy for estimating the
slope and intercept of the generalized GPP-ET relationship at the
catchment scale by linking the parameter values a priori with
hydrometeorological data. We validate the monthly GPP predicted from the
relationship and regionalized parameters against remote-sensing based
GPP product, yielding Kling-Gupta Efficient (KGE) values ≥ 0.5 for 92%
of the catchments. Finally, we verify the relationship and its parameter
regionalization at 35 AmeriFlux sites with KGE ≥ 0.5 for 25 sites,
demonstrating that the new relationship is transferable across the site,
catchment, and regional scales. The relationship will be valuable for
diagnosing coupled water–carbon simulations in land surface and Earth
system models and constraining remote-sensing based estimation of
monthly ET.