Difference in simulations between the dynamic root model and the previous model with static roots for gross primary productivity (GPP; upper left), total ecosystem carbon (upper right), evapotranspiration (lower left) and nitrogen uptake (lower right). Vegetation simulated in land models has historically been under-resilient because plants adapt to extremes like moderate drought by deepening their roots. This figure shows increased transpiration and GPP in regions that experience occasional moisture stress and have adaptable plant species. In more arid regions, the plant resilience strategy is to trigger senescence (indicated by negative values in these quantities) until rains return. Credit: Drewniak [2018], Figure 9
Source: Journal of Advances in Modeling Earth Systems (JAMES)

The land surface models used in weather and climate models have always made the simplifying assumption that the roots of different categories of plants are static in time and space, penetrating to a fixed depth regardless of conditions. This has long been known to be a poor assumption, but realistically simulating the way roots adapt to changing water and nutrient availability has proved very challenging. Drewniak [2019] has achieved a significant step in improving the simulation of root dynamics, with implications for improved simulation of ecosystem responses to extremes like drought, and better projections of climate change sensitivity.

By building on previous work simulating crop rooting behavior, Drewniak has generalized the approach to plant systems from the tropics to arctic regions, applied in the Department of Energy Exascale Earth System Model (E3SM). The new algorithm results in improved rooting depth and plant productivity simulations in all regions except the seasonally dry monsoon areas, where unique plant adaptation strategies remain a challenge to model. Her work also points the way forward for the next round of improvements in ecosystem root modeling.

Citation: Drewniak, B. A. [2019]. Simulating dynamic roots in the energy Exascale Earth system land model. Journal of Advances in Modeling Earth Systems, 11. https://doi.org/10.1029/2018MS001334

—Paul A. Dirmeyer, Editor, JAMES

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