"Development of Modeling Tools For Predicting Smoke Dispersion From Low Intensity Fires"

Warren E. Heilman, Sharon Zhong, Joseph J. Charney, John Hom, Kenneth Clark, Gil Bohrer, Nicholas Skowronski, Xindi Bian, Michael T. Kiefer, and Ryan Shadbolt

Poster presented for the Joint Fire Science Program Ten-Year Symposium in Savannah, GA., December 2009.

Prescribed burning can be a viable tool for managing forest ecosystems. However, smoke from prescribed fires, which often occur in the wildland-urban interface (WUI), can linger in an area for relatively long periods of time and have an adverse effect on human health. Smoke from low-intensity prescribed fires can also reduce visibility over roads and highways in the vicinity of these fires, producing hazardous conditions for transportation. Improved tools that quantitatively predict the potential impacts of smoke are necessary in order to maximize the benefits of prescribed fires and balance the conflicting needs of ecological fire use and effective smoke management.

This three-year (2009-2012) study, funded by the Joint Fire Science Program and the National Fire Plan, is focused on the evaluation and potential adaptation of three state-of-the-art fine-scale atmospheric dispersion modeling systems for predicting short-range, near-source smoke transport and diffusion from low intensity fires within and above forest vegetation layers. These modeling systems include the Weather Research and Forecasting (WRF) - FLEXPART system, the Regional Atmospheric Modeling System (RAMS) - Forest Large Eddy Simulation (RAFLES) system, and the Atmosphere to Computational Fluid Dynamics (A2C) system. Smoke concentration, meteorological, and fuel measurements via surface and tower-based instrumentation within and in the vicinity of prescribed burn units in the New Jersey Pine Barrens will be used to validate the modeling systems. Through this study, we seek to (1) improve our understanding of the effects of different forest canopies on particulate matter and water vapor transport and diffusion within and above those canopies, (2) examine how those effects could be included in operational smoke prediction systems, (3) determine the uncertainties and limitations of current models in predicting smoke dispersion from low intensity fires, and (4) develop new observational data sets for effective validation of smoke dispersion models.

"The Climate Variability of the Haines Index over the United States"

Sharon Zhong, Wei Lu, Joseph J. Charney, Xindi Bian, and Warren E. Heilman

Presentation for the Eighth Symposium on Fire and Forest Meteorology in Kalispell, MT., October 2009.

The Haines Index, also known as the Lower Atmosphere Severity Index, is employed operationally as a tool to indicate the potential for large or erratic fire growth by considering the dryness and stability of air over a specific area. In this study, we have derived a 28-year (1980-2007) Haines Index (HI) climatology for North America using the North American Regional Reanalysis (NARR). NARR is a long-term (from 1979 to present) and dynamically consistent meteorology and hydrology gridded dataset with a grid spacing of 32 km and a 3-hour time interval.

Using the climatology, we have examined the spatial distribution of warm season (May through October) mean lapse rates, dewpoint depressions, factor As, and factor Bs for each of the low-, mid-, and high-elevation variants of the HI. The factor As and factor Bs are then used to compute the HI for each variant, and the mean and standard deviation of the resultant HI are investigated to establish the seasonal and inter-annual variations of the HI for various regions in the United States. The climatology illustrates the insensitivity of the index in particular regions, while highlighting the impact of mesoscale meteorological features such as the dryline, sea/lake breezes, and orographic flows.

To investigate how HI behavior responses to the climate change, the United States is further divided into 6 climatic regions wherein yearly trends in the HI are analyzed. The yearly trends demonstrate different patterns of high risk frequency across the United States. The climatological trends indicate that the frequency of high HI values in the Pacific Northwest and Pacific Southwest is almost constant during this time period, while the Midwest, Rocky Mountains, Northeast and Southeast all exhibit increases in the occurrence of high HI values.

"A Numerical Study of Smoke Transport and Dispersion Associated with the October 2007 Southern California Wildfires."

Wei Lu, Sharon Zhong, Xindi Bian , Joseph J. Charney, and Warren E. Heilman

Presentation for the Eighth Symposium on Fire and Forest Meteorology in Kalispell, MT., October 2009.

In October 2007, severe wildfires broke out across southern California, resulting in the substantial emission of trace gases and particles to the atmosphere. To address the regional impacts of smoke from these fires, we performed numerical simulations of the meteorological conditions, using the Weather Research and Forecasting (WRF) model, and the smoke transport and dispersion, using a Lagrangian particle dispersion model called FLEXPART. The transport and diffusion of atmospheric constituents over the western U.S. is often constrained by the mountainous terrain, which has a profound effect on regional meteorology particularly in the lower troposphere where fire emissions are released and most of the transport and diffusion occurs.

The meteorological fields simulated by the WRF model were evaluated by comparing them with observed weather data from a network of surface weather stations and six upper air rawinsonde stations in California and Nevada. The simulated smoke distribution was compared with MODIS Hazard Mapping System (HMS) satellite imagery. A series of sensitivity experiments wherein the depth over which particles in the FLEXPART model are released was used to explore the sensitivity of the resultant particle distribution to different injection heights. These sensitivity experiments highlight the importance of including accurate information about plume rise and equilibrium height in numerical simulations of smoke dispersion, as well as their importance to anticipating the regional impact of smoke from wildland fires in the southwestern United States.

"The Climatology of the Haines Index as Viewed from the North American Regional Reanalysis"

Wei Lu, Joseph J. Charney, Xindi Bian, Warren Heilman, and Sharon Zhong

Poster presented for The '88 Fires: Yellowstone and Beyond Conference in Jackson Hole, WY., September 2008.

The Haines Index (HI) is a widely used index that is designed to detect the potential for dry, unstable air to impact a plume-dominated fire such that the fire becomes large or exhibits erratic fire behavior. Conceptually, the HI represents an empirical relationship between a dry, unstable atmosphere and extreme and erratic fire behavior in large wildfires. Since its development, the HI has becomes widely used and accepted by fire managers as an indicator of the potential for an existing wildfire to become large and/or erratic in behavior. While fire weather forecasters and fire managers most often employ the HI locally to aide in making decisions regarding daily fire activities, a climatological analysis of the index provides a starting point from which researchers and operational users can attempt to determine whether they should adjust their methods of calculating and interpreting the HI. The first comprehensive long-term climatology of the HI using continuous, gridded meteorological fields employed 40 years of 2.5 x 2.5 degree latitude/longitude global reanalysis from the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) to analyze the broad spatial and temporal trends in the HI. This study addresses the need for more spatially detailed climatological information by employing the 32-km North American Regional Reanalysis (NARR) to calculate the HI for the 28-year period from 1980 to 2007.