Modeling global carbon and water fluxes and hyperspectral canopy
radiative transfer simultaneously using a next generation land surface
model---CliMA Land
Abstract
Recent progress in satellite observations has provided unprecedented
opportunities to monitor vegetation activity on the global scale.
However, a major challenge in fully utilizing remotely sensed data to
constrain land surface models (LSMs) lies in inconsistencies between
simulated and observed quantities. Transpiration and gross primary
productivity (GPP) that traditional LSMs simulate are not directly
measurable from space and they are inferred from spaceborne observations
using assumptions that are inconsistent with those of the LSMs, whereas
canopy reflectance and fluorescence spectra that satellites can detect
are not modeled by traditional LSMs. To bridge these quantities, we
present the land model developed within the Climate Modeling Alliance
(CliMA), which simulates global-scale GPP, transpiration, and
hyperspectral canopy radiative transfer (RT). Thus, CliMA Land can
predict any vegetation index or outgoing radiance, including
solar-induced chlorophyll fluorescence (SIF), normalized difference
vegetation index (NDVI), enhanced vegetation index (EVI), and near
infrared reflectance of vegetation (NIRv) for any given measurement
geometry. Even without parameter optimization, the modeled spatial
patterns of CliMA Land GPP, SIF, NDVI, EVI, and NIRv correlate
significantly with existing observational products. CliMA Land is also
very useful in its high temporal resolution, e.g., providing insights
into when GPP, SIF, and NIRv diverge. Based on comparisons between
models and observations, we propose ways to improve future land modeling
regarding data processing and model development.