PNNL

Abstract

The foliage clumping index (CI) quantifies the leaf spatial distribution within a vegetation canopy, which regulates the radiative transfer processes and land surface energy flux partitioning. Substantial seasonal variations of CI have been revealed in multiple studies, however, the impacts of seasonal variations in CI on global land surface heat fluxes remain unclear. Here, we, for the first time, deployed the satellite-derived temporally varied and spatially resolved CI information in the radiative transfer scheme of the Community Land Model version 5 (CLM5) to evaluate the impacts of foliage clumping on global surface heat fluxes considering CI seasonal variations. After including CI, we found that the mean sensible heat dissipated from ground increased by 3.9 W/m2 globally and up to 15 W/m2 regionally, while the mean sensible heat from vegetation decreased by 4.9 W/m2, globally, leading to the total sensible heat decreased by 1.0 W/m2 (~3%). The global mean latent heat for evapotranspiration increased by 0.9 W/m2 (~2%) mainly due to increased latent heat for evaporation and transpiration in tropical areas. The impacts of CI showed substantial seasonal differences especially for sensible heat fluxes dissipated from ground and vegetation over ENF and DNF. Over ENF and DNF, considering CI but ignoring its seasonal variation significantly biased the sensible heat from vegetation and ground in boreal summer, leading to mean ground temperature biased up to 0.5 k. We highlight the need to include foliage clumping and consider its seasonal variations in modeling land surface heat fluxes.