Spatial Evacuation Analysis Project

Thomas J. Cova and Richard L. Church
National Center for Geographic Information Analysis (NCGIA)
Department of Geography
University of California, Santa Barbara (UCSB)

The spatial evacuation analysis project is concerned with developing a systematic geographic approach to mapping neighborhood evacuation egress. This issue is particulary relevant in residential neighborhoods subject to fast-onset hazards of uncertain spatial impact (e.g. firestorms and toxic spills on highways). The project was originally motivated by the fatalities that occurred during the disastrous evacuation of the Oakland/Berkeley Hills Fire of 1991 (image at right shows the thermal footprint of the firestorm). The underlying theme in this research is that neighborhood egress varies spatially across an urban landscape. This variation can be revealed by adopting a spatial perspective on regional evacuation using a geographic information systems (GIS) approach.

Keywords: GIS, evacuation, egress, hazard, vulnerability, risk

Project Background

The traffic congestion that residents experienced while attempting to evacuate the Oakland Hills Fire of 1991 underscores the point that a neighborhood's geographic characteristics may significantly impede the evacuation process. The narrow streets, irregular intersections, and residential density of this area resulted in a neighborhood configuration that was unable to serve the intense demands of an urgent evacuation. As one of the last evacuees to safely leave the fire zone put it, "This is not a place designed to get out of (SFC, 1991)."

This raises a number of interesting questions. What might be a valuable definition of a neighborhood in this context? What is a neighborhood that is "designed to get out of?" Are there neighborhoods that may have poor egress from an evacuation standpoint, and can we develop a method for finding them? The initial focus of this project was concerned with formalizing definitions for these concepts. The result was a methodological framework to support the mapping of regional evacuation vulnerability that we call spatial evacuation analysis (Cova and Church, 1995; Cova and Church, 1997).

Example Case Study: Santa Barbara, California

The city of Santa Barbara has experienced its share of spatially unpredictable hazards, which include, most notably, firestorms and toxic material spills. The purpose of this study was to demonstrate how spatial evacuation analysis can be used to reveal neighborhoods that might be difficult to evacuate under hazardous conditions.

The map below shows a classification of a portion of Santa Barbara regarding evacuation egress. The thematic map unit is the number of people per exiting lane in a neighborhood's worst-case evacuation. Yellow areas have 100 people per lane in a worst-case evacuation scenario. Red areas would have an average of 500 people per lane in a worst case evacuation. For this reason, red neighborhoods represent evacuation "hot spots" and should be examined closer. In other words, they represent areas for further geographic inquiry. How many vehicles are there in this neighborhood? How many registered drivers? Does the neighborhood have an evacuation plan?

Figure 1. Evacuation vulnerability map for the Santa Barbara vicinity.

Below is a map that shows a close-up of the red neighborhood in the lower right corner of the map above. Because this neighborhood is adjacent to a six-lane freeway, it has lost all its connecting streets along its northeast side. Compounding the problem is its relatively high residential density. Overall, the ratio of residents to exiting lanes in this neighborhood is abnormally high (500+). As the adjacent corridor (Hwy. 101) is frequently utilized for shipping hazardous materials, an evacuation of this neighborhood is not unlikely. This type of information can aid emergency managers in tactical evacuation and response planning (Cova, 1998).

Figure 2. Evacuation vulnerability map for downtown Santa Barbara.

References

Cova, T.J. (1998) GIS in emergency management. In: Geographical Information Systems: Principles and Applications , Maguire, D.J., Goodchild, M.F., Rhind, D.W., and Longley, P. (eds.), forthcoming.

Cova, T.J., and Church, R.L. (1997) Modeling community evacuation vulnerability using GIS. International Journal of Geographical Information Science , 11(8), pp. 763-784.

Cova, T.J., and Church, R.L. (1995) A spatial search for neighborhoods that may be difficult to evacuate.
Proceedings GIS/LIS '95, ASPRS/ACSM, Nashville, TN, vol. I, pp. 203-212.

(SFC) San Francisco Chronicle (1991) Charing cross bottleneck was big killer. Sunday, November 2, pg. A14.

Last updated: 4/97