Twister

Tornado Alley spreads beyond the Plains, reaching as far south as Florida and as far west as Colorado. Near the top of its span sits Polk County, Iowa.The Des Moines suburb sees only about one twister touch down each year, but the state as a whole ranks sixth in the nation for total number of tornadoes and fourth in annual tornadoes per 10,000 square miles. The National Weather Service estimates tornadoes kill about 42 people each year around the country.Polk County residents know the dangers of a twister are quite real.During the spring and summer tornado season, the county's Emergency Management Agency warns residents of possible tornadoes, or when funnel clouds have been sighted, using outdoor sirens. But the agency had no way to know if the sirens were heard by all residents, especially because the county's population has been growing.So instead of waiting for a tornado touchdown to see if the sirens are audible at new houses and businesses, the agency adopted a geographic information system to plot the sirens' coverage and make adjustments accordingly.A.J. Mumm, emergency management specialist for Iowa's Emergency Management Division, used to work in Polk County's Emergency Management Agency and made the siren maps.Mumm used ArcView GIS 3.2 from Environmental Systems Research Institute of Redlands, Calif., to plot the areas, known as footprints, where the sirens were audible.'That was a starting point for us to evaluate the coverage,' he said.Once Mumm plotted the footprints, county workers could adjust the sirens for maximum coverage. The county agency found that there were many overlaps in the downtown area, but other populated zones lacked coverage.'We wanted to make sure we had the most effective coverage with limited resources,' Mumm said. 'We had to see if we were missing populated areas or duplicating areas too much with the sirens.'Mumm used a Compaq Computer Corp. notebook PC with a 400-MHz Intel Pentium II processor and 32M of RAM running ArcView GIS under Microsoft Windows 98.Mumm said he liked the fact that the system ran on a notebook because it made the data portable for workers who had to move around in an emergency.'We could do other modeling on the scene and feed a system to make reverse 911 calls to residents,' he added.GISes have been used to predict the effects of weather on communities for almost a decade, and this application is as innovative as it is logical, said Bill Gentes, executive director of the Urban and Regional Information Systems Association.'This type of technology typically was used after the event happened, so applying GIS in this manner is almost real-time modeling,' Gentes said. 'The whole technology is going through a massive change as more and more municipalities are collecting data. They are going from being reactive to predictive.'Before using ArcView GIS, Mumm said, the office used software developed by the Environmental Protection Agency and National Oceanic and Atmospheric Administration for computer-aided management of emergency operations. The software had limited capability and county workers had to lay out the warning system by hand using cutouts to represent the sirens on a table map.The manual process made it difficult to plot coverage areas accurately and update the records, Mumm said. The system kept siren data in a table format, making it hard to understand and sometimes incomplete, he added.Mumm also used the ESRI GIS to plot where to put new sirens to expand the coverage area. Three cities and a local school district reviewed their coverage and identified 12 locations where more sirens were needed.'We placed the sirens and saw the minimum number needed to reach the maximum number of people,' Mumm said. 'At $15,000 [per siren system], we were able to limit the spending.'Polk County encouraged residents to visit its Web site and make sure their homes were covered by the siren system. The Internet map runs on a GeoMedia Web server from Intergraph Corp. of Huntsville, Ala.The county also used ArcView to map the locations of all the schools, day care centers, nursing homes, hospitals and other vulnerable populations in the community and plot their proximity to hazardous chemical facilities. If a poisonous spill occurs or a twister is spotted, Mumm said, the Emergency Management Agency will know the hazard area that must be evacuated.The system also plots critical facilities such as electrical substations and water treatment plants.'This was a way for us to more efficiently manage our information because it is based on the geographic information,' Mumm said. 'The cost was minimal because we had most of the information already so it was just a matter of plugging it into the software.'