We propose a large interdisciplinary study to better quantify and understand how the interactions between climate change, ecosystems, and human population change the fire regime in southern California and subsequent impacts on air quality. The largest and most destructive fires in Southern California occur during intense Santa Ana wind events. Over the past decade, these fires have incurred billions of dollars in costs associated with fire fighting, damages to property from both fire and erosion, and impacts on human health. Predicting how these fires and subsequent impacts are likely to change in the future requires a multi-disciplinary approach that accounts for climate change effects on regional winds and ecosystems, ecosystem response to fires, and changing patterns of land use. We plan to address six science questions:

1. How much carbon and aerosols are released during Santa Ana fires?
2. What are the direct impacts of fires on air quality and aerosol transport?
3. What are long-term impacts of fires on ecosystem recovery processes and trajectories?
4. What are the patterns of winds across Southern California during Santa Ana events and how do they affect fires?
5. How do vegetation, fire weather, and land use control contemporary fires?
6. How are fires and their impacts going to change in the future?

We will develop an integrated approach that combines field measurements, airborne and space-borne observations, and models. We will develop remote sensing algorithms to derive combustion completeness (CC) and tree/shrub mortality, analyze the relative importance of ecosystem composition and fire weather in regulating CC, and estimate fire emissions during large Santa Ana fires. We plan to use WRF-Chem to estimate the spatial distribution of surface particulate matter (PM) and ozone concentration and to build a climatology of PM violations during the summer and fall fire season for the past 3 decades. We will assess the vulnerability of local communities to respiratory disease risk from fires using population and demographic data. We plan to collect field data across gradients of fire severity and frequency. We will use chronosequence approaches to quantify the fire impacts on the ecosystem recovery and construct empirical trajectories of vegetation recovery. We will investigate if the rate and direction of post- fire recovery is changing using Landsat TM/ETM+ data back to 1980s. We will perform a multi- decade reconstruction of climate at 6 km resolution using the Weather Research and Forecasting Model (WRF) and examine how local topography controls the spatial variability of winds during Santa Ana events. Empirical models for fire frequency and burned area will be constructed as functions of biophysical, hydroclimate and human activities. We plan to use the MAPSS biogeography model to simulate species composition and biomass under SRES A1B scenarios of future climate change, and assess how the changes in ecosystem response will affect future fire occurrence using our empirical fire model. In parallel, we will investigate how climate change will affect the frequency and intensity of Santa Ana events and the subsequent impacts on burned area. Finally we will investigate the combined effects of changing ecosystems and winds for future distribution and severity of fires and estimate the subsequent impacts on air quality and human health. Our interdisciplinary study will improve our capability to mitigate the damages caused by these devastating wildfires.