Land model sensitivity to leaf area index in CESM2 and E3SM
James Lende1, Xubin Zeng1, and Michael Brunke1
1Department of Hydrology and Atmospheric Sciences
The University of Arizona, Tucson, AZ
Leaf Area Index (LAI) is a key vegetation parameter that directly affects the land-atmosphere energy, water, and carbon exchanges for weather, climate, and hydrometeorological studies. In nature, surface fluxes are expected to be similar when LAI becomes very small (e.g., close to zero versus zero) or when LAI becomes very large (e.g., 7 versus 20). To test if the land model can maintain this convergence, we conducted sensitivity tests using the CESM2 atmosphere-land coupled single column model over the Southern Great Plains by multiplying the observational LAI by a factor from 0.01 to 100.0. We found that increasing LAI affects surface and atmospheric processes; e.g., increasing evapotranspiration (ET) and decreasing planetary boundary layer height (PBLH). These results are overall consistent with our expectations. To check if the results are similar over different regions, we first run the Community Earth System Model (CESM2) Community Land Model (CLM) offline globally (before we run the land-atmosphere coupled global model in the future). We found that results are dependent upon vegetation. For instance, for Broadleaf Deciduous Tropical Trees, variables such as ground temperature, albedo, and canopy evapotranspiration do not converge for large LAI values. To test the robustness of these results, we will run the Energy Exascale Earth Systems Model (E3SM) Land Model (ELM) offline globally. In our presentation, we will discuss and understand these sensitivity test results, and attempt to reduce land model deficiencies identified in these tests.