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Project 3: Analyzing Spatial Data in a GIS
Jim Kompanek
Introduction:
In Lesson 2 (Kompanek 2006), the destruction and damage of property, as well as monetary loss, of the May 3, 1999 tornadoes that ripped through Oklahoma were mapped on a county, as well as a census tract level. The tornadoes that stuck that day were the largest outbreak in Oklahoma's history, with over 40 people killed and 675 injured as a result (NOAA 1999a). The following figures display potential candidate relief sites based on the areas with potentially the greatest need. The potential for need was identified based on population density, at a county, as well as census tract levels, and tornado strength. All data was obtained from King (2006a and 2006b).
For the purpose of this project, the following thematic maps were created with ESRI ArcMap 9.1:
Relief priority zones of each tornado based on population density and tornado strength at the county level, including possible relief staging area sites (schools, churches, and hospitals);
Relief priority zones of each tornado based on population density and tornado strength at the county level, including possible relief staging area sites (schools, churches, and hospitals), as well as tornado paths and magnitude;
Relief priority zones of each tornado based on population density and tornado strength at the census tract level, including possible relief staging area sites (schools, churches, and hospitals);
Relief priority zones of each tornado based on population density and tornado strength at the census tract level, including possible relief staging area sites (schools, churches, and hospitals), as well as tornado paths and magnitude.
The following table is also provided:
Potential relief staging areas, including schools, churches, and hospitals (site names are displayed in Figure 2).
Figure 1. Tornadoes as observed from a NOAA weather satellite on May 3, 1999. Image courtesy of NOAA. Used here for educational purposes only (NOAA 2006b).
Potential Relief Zones and Relief Staging Areas:
Figure 2. Relief priority zones of each tornado based on population density and tornado strength at the county level, including possible relief staging area sites (schools, churches, and hospitals). Figure created using ESRI ArcMap 9.1. Please click on image for full size graphic.
As reported in Lesson 2, the damage caused by a tornado (as defined by the total number of damaged and destroyed housing units, as well as the monetary value of the losses) was not entirely linked by the strength of a tornado. Instead, it was a culmination of factors, including tornado strength and overall density of the area, both in housing units and population. The same is true with the identification of areas in most need of relief, as well as potential relief staging areas. As can be observed in Figure 2, both Oklahoma and Cleveland Counties were located within the highest relief priority zones.
Oklahoma County is the location of Oklahoma City, the largest city in Oklahoma (Wikipedia 2006a), with its metropolitan area extending into neighboring Cleveland County (Wikipedia 2006b), and to a lesser extent, Canadian County (Wikipedia 2006c). It is not surprising that these counties would require the most attention for relief crews. Even if other counties suffered more powerful tornado strikes (see Additional Figures, Figures 4 and 5), the potential for injuries or loss of life would be significantly lower due to their lower population densities. With their higher overall populations, there were more potential relief staging areas, including schools, churches, and hospitals (Table 1) in the Oklahoma City metro-area.
Table 1. Potential relief staging areas, including schools, churches, and hospitals.
Potential Relief Zones and Relief Staging Areas by Census Tract:
Figure 3. Relief priority zones of each tornado based on population density and tornado strength at the census tract level, including possible relief staging area sites (schools, churches, and hospitals). Figure created using ESRI ArcMap 9.1. Please click on image for full size graphic.
The above figure (Figure 3) indicates the same information as Figure 2 but instead indicates relief priority zones as determined by population statistics at the census tract level. A downside of the county population statistics, is that most counties do not have homogenous or uniform population densities. For example, if a theoretical tornado landed in Central Park in New York City, the predicted loss of property and life would appear significantly worse than reality, if models were based on population and housing density for all of Manhattan.
When comparing Figures 2 and 3, the high priority relief areas are significantly smaller when population data is based on the tract level. This difference would be significant if equivalent models were employed for the organization of search and rescue teams. If all models were based on county-wide statistics, time could be wasted as rescue teams were sent to prairie fields, when nearby urban neighborhoods were in ruins.
Conclusion:
As observed in Figure 2, the tornadoes that struck Oklahoma City, in both Oklahoma and Cleveland Counties, would potentially be the areas greatest impacted and in need of relief. This was determined by their overall population density at the census tract level and by the magnitude of the respective tornadoes. It is based on the assumption that areas with higher population density and higher tornado strength, would be in greater need of relief.
Thirty-three potential relief staging sites were identified as a result of this exercise (see Table 1). Overall, the areas identified with potentially the greatest need of relief, would also have the most potential relief sites within close proximity (i.e., Oklahoma City-metro). One problem identified is that not all of the areas impacted by the tornadoes were within close proximity to any relief site. A potential solution might involve extending the buffer for relief sites (currently set at one mile for this exercise) until each area was within a reasonable proximity to a relief area.
Although this exercise provided a framework for the identification of potential areas in need of relief, as well as relief sites, there are certain limitations for real-world emergency planning. The biggest limitation being the assumption that population density is uniform across a census tract. A rural census tract may have several pockets of higher-density residential housing and under the model presented above, and the potential need for relief would be the same whether a tornado hit a cornfield or a trailer park. A more accurate representation may include the use of population statistics at the block level. Another limitation is the assumption that the destruction-corridor is uniform along the path of a tornado. According to The Tornado Project (1999), there isn't necessarily a correlation between the intensity and size of a tornado, as weaker tornadoes can be larger than stronger ones. The path of destruction may also expand and contract along a tornado's path. The assumption of a one-mile buffer may result in the exclusion of potential relief sites which are undamaged, or the inclusion of destroyed or heavily damaged relief sites.
Additional data, as well as overlays would increase the effectiveness of relief-models. Updated aerial photos from immediately after a tornado could be used to accurately plot its path, to help include undamaged and exclude damaged relief sites. A more detailed survey of potential relief sites, such as National Guard/Reserve armories, police and fire stations, as well as doctor offices and clinics, could be used to further aid in any relief operations--Especially in rural areas with no other relief sites in close proximity. Features that may result in higher damage, even in lower population density areas, such as industrial, chemical, or nuclear disposal sites, would also be useful when factored in. Fire insurance maps, or their equivalents, could be used for this purpose. The identification of areas within a tornadoes path which may increase relief priority, such as nursing homes, schools in session, or trailer parks, would also be useful for determining relief need.
Additional Figures:
Figure 4. Relief priority zones of each tornado based on population density and tornado strength at the county level, including possible relief staging area sites (schools, churches, and hospitals), as well as tornado strength. Figure created using ESRI ArcMap 9.1. Please click on image for full size graphic.
Figure 5. Relief priority zones of each tornado based on population density and tornado strength at the census tract level, including possible relief staging area sites (schools, churches, and hospitals), as well as tornado strength. Figure created using ESRI ArcMap 9.1. Please click on image for full size graphic.
References Cited:
King, Beth
