Land use and land cover change modeling
The Land-use and Carbon Scenario Simulator (LUCAS)
There are large uncertainties in how land and climate systems will evolve and interact to shape future ecosystem carbon dynamics. To address this uncertainty, we developed the Land-Use and Carbon Scenario Simulator (LUCAS) to track changes in land use, land cover, land management, and disturbance, and their impact on ecosystem carbon storage and flux. The LUCAS model combines a state-and-transition simulation model (STSM) for modeling land-change with a stock and flow model for modeling carbon dynamics, within a scenario-based framework. These two models were developed in conjunction within the ST-SIM modeling environment to provide a complete package for testing a range of future scenarios of land-use change and their impacts on carbon dynamics. Land-use change scenarios developed from the Intergovernmental Panel on Climate Change's (IPCC) Special Report on Emission Scenarios (SRES), and Representative Concentration Pathways (RCPs), as well as scenarios developed from historical land-use change datasets that include a range of mitigation and adaptation policies can be applied in the model.
State-and-Transition Simulation Model
State-and-transition simulation models (STSMs) simulate changes in state classes (i.e. transitions between LULC classes), and track state class totals and transitions, in both spatial and non-spatial modeling environments, for defined strata (ecological regions, administrative units) using a stochastic Monte Carlo modeling approach. A STSM was developed, in the ST-SIM environment, to model a range of LULC change scenarios for ecological regions of the conterminous United States. This required establishing basic model parameters, including defining possible land-cover states, and possible transition pathways between land-use states, as well as defining the initial land-cover conditions. A range of land-use scenarios are then applied to determine transition amounts through time. Spatial multipliers and spread constraints help to control where change may occur on the landscape.
Stock and Flow Model
A carbon stock and flow model was developed in conjunction with the STSM, to model carbon change over the landscape. The Integrated Biosphere Simulator (IBIS) ecosystem model and MC2 model were used to derive input parameters for the carbon stock and flow model. IBIS supplied annual estimates of carbon stocks, fluxes, NPP, and NBP, along with regional-scale evapotranspiration and surface run-off. The MC2 model provided raster-based projections of ecosystem carbon stocks and fluxes, changes in vegetation due to climate, and projections of wildfire frequency. These attributes will be used in ST-SIM to evaluate the effects of alternative development pathways (i.e. mitigation and adaptation policies and actions) on regional-scale carbon dynamics.