The spatial extent and coverage of tornado sirens in San Marcos, Texas

Abstract The tornado siren has become the standard method of notifying resident populations of dangerous weather conditions. In March, 2012, the city of San Marcos, Texas purchased 14 Tempest-121 rotating sirens creating a coverage network. Because San Marcos has experienced two tornadoes during the previous twelve years, two research questions were constructed, 1) what is the spatial coverage of the tornado siren network in San Marcos, and 2) what is the approximate number of residents located outside the siren's network coverage area? The hypothesis stated that the siren network left more than 10 percent of the population outside the coverage area. Each tornado siren was individually located and associated GPS data allowed for construction of the siren network in a GIS. The analysis identified approximately 26 percent (22 km2) of San Marcos located outside the network's coverage area. Furthermore, analysis of census block data and the extent of siren coverage resulted in 5.14 percent of residents not included in siren coverage, approximately half compared to what was hypothesized. As San Marcos continues to expand, both in size and in population, the question of whether there is enough coverage for the entire city for the foreseeable future remains unclear.