Improving representation of deforestation effects on evapotranspiration in the global E3SM land model

Monday, December 10, 2018 - 16:45
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Evapotranspiration (ET) plays an important role in the land-atmosphere coupling of energy, water, and carbon cycles. Following deforestation, ET is typically observed to decrease significantly accompanying the dramatic changes in land surface characteristics, and may interact with large-scale atmospheric dynamics. However, the default Energy Exascale Earth System Model (E3SM) Land Model (ELM) predicts an increase in ET after deforestation, likely leading to incorrect estimates of the effects of deforestation on land-atmosphere coupling. We used observations from a recent synthesis of 29 pairs of adjacent intact and deforested FLUXNET sites to calibrate two stomatal resistance parameters, two photosynthesis parameters, and three soil water parameters in the model. The resulting plant parameters are consistent with recent observational syntheses. The calibrated model accurately represented the FLUXNET observed deforestation effects on ET. On applying this improved model parameterization to the globe, we found the predicted effects of deforestation on ET were changed from an up to 136.5 mm yr-1increase to an up to 266.7 mm yr-1decrease for the tropical rainforest regions during 1960-2010, which experienced the most dramatic deforestation. Future model development to improve ET simulation should focus on stomatal resistance and soil water related parameterizations. Finally, our predicted differences in seasonal ET changes from deforestation are large enough to substantially affect land-atmosphere coupling and should be considered in such studies.

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