Thursday, August 30, 2012

Identifying a Cost-Effective Aviation Fleet for the U.S. Forest Service

This brief provides an overview of a RAND study to support the U.S. Forest Service in determining the composition of a fleet of airtankers, scoopers, and helicopters that would minimize the total social costs of wildfires.

The Rand research team developed two separate but complementary models to estimate the optimal cost-minimizing portfolio of initial attack aircraft—that is, aircraft that support on-the-ground firefighters in containing potentially costly fires while they are still small.

The National Model compares different prospective portfolios of aircraft against simulated fire seasons comprising historical wildfires in the United States between 1999 and 2008, showing how outcomes might have differed with more or fewer available aircraft. One important limitation of the National Model is that it assumes that a uniform level of local firefighting resources, such as ground crews, bulldozers, and fire engines, is available to fight every fire.

The baseline National Model simulation suggests that a fleet of five 3,000-gallon airtankers and 43 1,600-gallon scoopers would minimize total social costs, using the assumption that water is half as effective as retardant.

Because the model approaches aircraft allocation on a national level and the number of airtankers is small (five), it exaggerates the capabilities of airtankers to quickly deploy anywhere in the United States. To counter this shortcoming, the research team created a restricted variant of the model with zones correlating to Forest Service Geographic Area Coordinating Centers, making the airtanker’s assumed 45-minute average mission time more realistic. In this restricted variant, the optimal fleet is composed of eight 3,000-gallon airtankers and 48 1,600-gallon scoopers. An additional shortcoming of the National Model is that it does not permit three-way comparisons of airtankers, scoopers, and helicopters, so the model’s results exclude helicopters. The RAND Local Resources Model addresses this limitation.
The Local Resources Model uses realistic estimates of the local firefighting capabilities available to fight each fire when estimating the appropriate aircraft fleet size and mix. Specifically, it uses data on the fire season and ground resources, and it relies on estimates of containment outcomes generated by the Fire Program Analysis (FPA) system, a Forest Service system designed to facilitate resource allocation decisions. The Local Resources Model also allows the costs of large fires to vary by location and fire condition (e.g., large fires near urban areas are more costly).

The Local Resources Model suggests an optimal initial attack fleet composed of one 3,000-gallon airtanker, two 2,700-gallon helicopters, and 15 1,600-gallon scoopers.

An important limitation of the FPA system and, hence, the Local Resources Model is that it attributes as much efficacy to a gallon of water dropped from a scooper as to a gallon of retardant dropped from an airtanker. However, the National Model suggests that even when the efficacy of water relative to retardant is degraded to just 20 percent—or even 5 percent—the optimal fleet mix remains dominated by scoopers. Thus, the FPA system’s assumption that water and retardant are equivalent does not explain the models’ consensus that the optimal Forest Service fleet is scooper-dominated.
by Edward G. Keating, Andrew R. Morral, Carter C. Price, Dulani Woods, Daniel M. Norton, Christina Panis, Evan Saltzman, and Ricardo Sanchez, 
MG-1234-USDAFS, 2012, 140 pp. $29.95, ISBN: 978-0-8330-7677-9 (available at
The Rand Corporation RAND Homeland Security and Defense Center

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