Impacts of vegetation structural dynamics on land hydrologic cycle: A modeling analysis with explicit representation of vegetation structural dynamics in the NASA GISS Global Climate Model

Abstract:

Vegetation is a key component of the Earth system. It defines the land surface boundary conditions for the exchange of energy, momentum, and water vapor between land and atmosphere, regulates long-term atmospheric CO2 concentration, and thus deeply shapes Earth’s climate systems. Dynamic global vegetation models (DGVMs) have been used in Earth system models to simulate plant physiological activities, vegetation dynamics, ecosystem biogeochemical cycles, and land surface characteristics for atmospheric components. However, DGVMs are unable to predict transient vegetation compositional and transient changes at decadal scales because of underrepresentation of functional diversity, lack of detailed demographic processes, among many other land, vegetation and climate uncertainties. To understand the importance of vegetation compositional and structural dynamics, we have developed a simplified vegetation demographic model and coupled it with the NASA Goddard Institute of Space Studies global climate model (ModelE), which includes a vegetation model (Ent) and land surface model (TerraE). The simplified model is able to explicitly simulate demographic processes, individual-based competition for light and soil water, and predict transient vegetation structural dynamics and their interactions with atmosphere. With this coupled model, we simulated the dynamics of global potential vegetation in the coming century with different shared socioeconomic pathway (SSP) scenarios. We analyzed the temporal patterns of global forest structure and their effects on land water cycle (precipitation, evapotranspiration, runoff, and soil water dynamics) and found the worldwide mortality of large trees could enhance drought extremes initially. These simulations highlight the importance of correctly predicting vegetation compositional and structural dynamics with climate change in Earth system models.