The Wildland–Urban Interface (WUI): From Simple Models to Mitigating Fire Risk

The Wildland–Urban Interface (WUI): From Simple Models to Mitigating Fire Risk

Michael GhilEcole Normale Supérieure, Paris, and University of California, Los AngelesV. Spyratos, ENS & ENGREF; P. Bourgeron, INSTAAR, CU, Boulder; and

C. Lampin & M. Jappiot, CEMAGREF, Aix-en-Provence

Please see these sites for further details:http://www.environnement.ens.fr/ , http://e2c2.ipsl.jussieu.fr/

http://www.atmos.ucla.edu/tcd/, http://www.aix.cemagref.fr/htmlpub/divisions/afax/emax.htm

MotivationMotivation• The WUI occupies about 10% of the surface and contains

about 40% of the houses in the conterminous U.S. • Fires have caused huge damages in the WUI in the Western

U.S., as well as Southern Europe this past summer and fall.• Further spreading of construction into (semi-)pristine vegetated

areas. • Global change seems to increase dryness in the areas of

interest.• Actual joint, interactive modeling of housing and vegetation

seems to be novel and interesting.• Simple, “toy” models can provide useful ideas.• The hierarchical modeling approach allows one to go

back-and-forth between “toy” (conceptual) and detailed (“realistic”) models, and between models and data.

• The WUI occupies about 10% of the surface and contains about 40% of the houses in the conterminous U.S.

• Fires have caused huge damages in the WUI in the Western U.S., as well as Southern Europe this past summer and fall.

• Further spreading of construction into (semi-)pristine vegetated areas.

• Global change seems to increase dryness in the areas of interest.

• Actual joint, interactive modeling of housing and vegetation seems to be novel and interesting.

• Simple, “toy” models can provide useful ideas.• The hierarchical modeling approach allows one to go

back-and-forth between “toy” (conceptual) and detailed (“realistic”) models, and between models and data.

Some spectacular WUI firesSome spectacular WUI fires

A house is threatened by a wall of flames from a wild fire west of the Missionary Ridge fire, north of Durango, Colorado (AP/Charlie Riedel).

As Colorado burns in the summer

of 2002, flames from a new fire loom

menacingly behind a mountain home

near Durango (Barry Gutierrez)

A toy model of the WUIA toy model of the WUI

Panels (a, b, c) – thecentral cell is ignited:(a) it’s a tree stand;(b) it’s a flammable

house; or(c) It’s a fireproofed

house.

Panels (a, b, c) – thecentral cell is ignited:(a) it’s a tree stand;(b) it’s a flammable

house; or(c) It’s a fireproofed

house.

A lattice model with nearest-neighbor interactions, already

used in forest-fire modeling: novelty is including the houses.

Panels (d, e) – example

of fire spreading over

the landscape: red cells

are on fire, black cells

are burnt; green and yellow cells are unburnt trees and houses.

Fire-spread probabilityFire-spread probability

Mean fire size S as a function of p, the vegetation’s

probability of fire spread, for different house densities

d: d0 indicates fireproofed houses only, d1 flammable

houses only.

Mean fire size S as a function of p, the vegetation’s

probability of fire spread, for different house densities

d: d0 indicates fireproofed houses only, d1 flammable

houses only.

Fire proofing vs. Fuel treatmentFire proofing vs. Fuel treatment

Regime diagram of mean fire size S as a function of p and d (d0

or d1): (a) note narrow transition zone between widespread and

limited fire size; and (b) higher efficiency of fireproofing of houses.

Application to Mediterranean landscapesApplication to Mediterranean landscapes

Fire distribution over 2 days in Europe: GIS tool

Contexte (6/8)

Urbanization in a forested area, in the South of France

Motivations are similar to Western U.S.

Methodology : Combine 2 criteriaMethodology : Combine 2 criteria

Clustered

Isolated

Diffuse

Structure of habitat Structure of vegetation

Continuous, dense

Discontinuous, sparse

Absent, other

Density of fire outbreaks per 1000 ha over the period 1997–2006

Density of fire outbreaks per 1000 ha over the period 1997–2006