09 September 2019

Improving Representation of Deforestation Effects on Evapotranspiration in the E3SM Land Model

Representation of deforestation effects on evapotranspiration in E3SM was improved through model optimization using observations in paired tower sites.

Science

Earth system models, including E3SM, have long standing problems representing deforestation effects on evapotranspiration, which is problematic when the models are used for forest and water resources management decisions. We optimized the E3SM Land Model (ELMv1) to match observations from a recent synthesis of 29 pairs of adjacent intact and deforested FLUXNET sites. The optimization significantly improved ELMv1’s parameterization of stomatal characteristics, photosynthesis, and soil water dynamics, allowing the model to reasonably represent the effects of deforestation on evapotranspiration.

Impact

Applying the improved ELMv1 to the globe scale reduced modeled annual ET bias by up to ~600 mm y-1, which will improve the modeling of land‐atmosphere coupling in E3SM. Our results also indicate that future model development should focus on stomatal resistance and soil water‐related parameterizations.

Summary

Deforestation changes Earth's surface characteristics and affects the water and carbon cycles and thereby climate. Although Earth system modeling is an important tool to understand the effects of deforestation, current models have large uncertainties. Here we used FLUXNET-based observations to identify biases in representing deforestation effects on evapotranspiration in the Energy Exascale Earth System Model (E3SM). Results showed these biases are mostly associated with the representation of trees and not with grasses, as had been previously thought. We used the observations to optimize model parameters and improved simulations of evapotranspiration and sensible heat fluxes following deforestation. Globally, these improvements led to a reduction in evapotranspiration bias of 600 mm y-1. The improved model leads to more accurate estimates of the effects of deforestation on the water cycle and climate and could benefit forest management and climate adaptation strategies.

Contact
William J. Riley
Lawrence Berkeley National Laboratory
Publications
Cai, X, W Riley, Q Zhu, J Tang, Z Zeng, G Bisht, and J Randerson.  2019.  "Improving Representation of Deforestation Effects on Evapotranspiration in the E3SM Land Model."  Journal of Advances in Modeling Earth Systems.  https://doi.org/10.1029/2018ms001551.