Ecosystem Disturbances: Wildland Fire
The method of LandCarbon disturbance modeling and emission estimation produces spatially-explicit forecasts of fire patterns, and the resulting greenhouse gas emissions for U.S biomes. At the heart of the approach is a series of statistical and process-based models, coded in C++, that simulate processes of fire ignition, spread, and emissions. Patterns of historic ignitions are characterized using logistic regressions that relate ignition location to daily fuel moisture conditions, as well as, vegetation type and urban extent. These ignition models are used to determine when and where ignitions are located under stable or changing climate scenarios. Once ignitions are located, the area burned is determined by allowing each ignition to spread using the minimum travel time algorithm. After fire spread is complete, emissions are calculated using the FOFEM and CONSUME models.
Vegetation, fuels, daily weather, and fuel moisture data are critical to the LandCarbon disturbance simulations. Vegetation and fuels data are provided by the LANDFIRE project. The daily weather data we use have 12 km spatial resolution and span from 1950 to 2010. For future climate-change scenarios, we randomly resample annual sequences of historic daily weather and rescale them to match the monthly means provided by downscaled climate-change forecasts. Fuel moistures and fire behavior indices are calculated for both historic and forecast daily weather using the National Fire Danger Rating System and then used as predictor variables for ignition locations, fire spread, and fire emissions.
The disturbance method also has a component to simulate the placement of fuel treatments in landscapes. Historic treatment frequencies and size distributions are summarized by management units (e.g., Yosemite National Park) from the National Fire Plan Operations and Reporting System (NFPORS) database. During simulations, these frequencies and size distributions are used in a stochastic fashion to determine the number and extent of individual treatments to place within each management unit. Modifiers can be applied to the frequency and area of individual treatment types to allow comparison of different management scenarios. For example, modifiers could be used to compare the potential fire emissions between an increased prescribed fire scenario and an increased mechanical fuel treatment scenario.
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