CHAPTER 3 THREATS AND HAZARDS RISK ASSESSMENT This chapter been prepared to identify the hazards believed to pose the greatest risk to the residents of Brown County; to profile the extent and severity of past county hazards; and to assess the vulnerability of the county to the risk of future hazard events. Through the risk assessment process, emergency management personnel will be able to more effectively evaluate potential hazard mitigation measures and develop useful strategies to address the risks associated with the identified hazards. HAZARD IDENTIFICATION Although Brown County could potentially be at risk from several distinct hazards, this plan narrows the scope of the hazards to those that pose the greatest risk to residents and facilities of the county. Identification of the hazards was based on a priority ranking of the many different natural and man-made/technological hazards previously identified in the 2012 Brown County All Hazards Mitigation Plan. The natural and man- made/technological hazards included in this list were first identified in the Resource Guide to All Hazards Mitigation Planning in Wisconsin that was prepared by the Association of Wisconsin Regional Planning Commissions through funding provided by the State of Wisconsin Department of Military Affairs, Wisconsin Emergency Management, and the Federal Emergency Management Agency. The following is a list of the hazards considered by the Steering Committee. Natural Hazards •Lightning Storm/Thunderstorm •Heavy Snow Storm •Ice Storm •Tornadoes/High Winds Flooding Tornados •Blizzards •Stormwater Flooding •Flooding (Flash, Ravine, Lake) •Extreme Cold •Extreme Heat •Fog •Hail Storms •Dam Faiure Flooding Winter Storms Wild Fires •Forest Fires •Wildland Fires •Coastal Hazards •Agriculture •Drought •Earthquake •Landslide •Subsidence Thunderstorms Drought Brown County 55 2020 All Hazards Mitigation Plan HAZARDS RISK ASSESSMENT SURVEY Members of Brown County’s previous 2007 and 2012 All Hazards Mitigation Plan Steering Committee created a Natural Hazard Identification and Risk Assessment Matrix. Each Steering Committee member was asked to assign a risk rating (1 = low, 2 = moderate, and 3 = high) to the various risk assessment criteria for each natural hazard. The total number of points for each of the identified natural hazards was then calculated. Members of the 2019 Committee reviewed the results for updates but did not propose significant changes. The Steering Committee members Table 3.1: Risk Assessment Ranking for Natural Hazards, Brown County, Wisconsin combined the following natural hazards: Risk Rank Natural Hazard Assessment Lightning Storms and Ranking Total Thunderstorms as “Lightning 1 Blizzards 32 Storms/Thunderstorms” (exclusive 2 Heavy Snow Storms 31 occurrence was deemed to be rare 2 Stormwater Flooding 31 in Brown County); 4 Ice Storms 30 Tornado and High Winds as 5 Tornadoes/High Winds 28 Flooding (Flash, Riverine, “Tornado/High Winds” (deemed that 5 28 and Lake) their assessment and mitigation 7 Extreme Cold 26 actions would be the same in Brown Lightning 8 23 County); Storms/Thunderstorms 9 Extreme Heat 22 Flash Flooding, Riverine Flooding, and Lake Flooding as “Flooding 10 Dam Failure Flooding 20 (Flash, Riverine, and Lake)” 11 Agricultural 18 (deemed that their assessment and 12 Coastal Hazards 17 mitigation actions would be the 13 Drought 16 same in Brown County). 13 Forest Fires 16 13 Wildland Fires 16 13 Fog 16 17 Subsidence 15 18 Hail Storms 14 18 Landslide 14 20 Earthquake 13 Source: Brown County Hazards Mitigation Plan Steering Committee, 2019, Brown County 56 2020 All Hazards Mitigation Plan NATURAL HAZARDS - HISTORICAL SUMMARY Past hazards statistics assisted the Steering Committee in determining the natural hazards to be evaluated in the plan. The National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC) publishes National Weather Service (NWS) data describing past weather events and the resulting deaths, injuries and damages associated with each hazard event. This data is available at the county level. While the data is advertised as being available beginning in January, 1950, a considerable portion of the data for several of the hazard events is only available as early as the 1990’s. This plan only utilized the data from January 1, 1990 through September of 2018. Descriptions of individual natural hazard events are located in the risk and vulnerability assessment in the portion of this chapter. Frequency TABLE 3.2: NATURAL HAZARD OCCURRENCES The data from the NCDC shows that of 1990‐JUNE 2019, BROWN COUNTY, WISCONSIN the 388 discernible events recorded NATURAL HAZARD Total from January 1, 1990 through September of 2019, thunderstorms and BLIZZARD 7 associated high winds are the most COLD/WIND CHILL 14 frequently occurring natural hazard DENSE FOG 12 event with 103 events recorded. This DROUGHT 4 was followed by hail (73 events), winter DUST DEVIL 2 storms (36 events), heavy snow (23 EXCESSIVE HEAT 6 events), and strong winds (19 events) EXTREME COLD/WIND CHILL 4 1 to round out the top five . Table 3.2 FLASH FLOOD 14 shows the frequency of all reported FLOOD 10 natural hazards occurring in Brown FUNNEL CLOUD 6 County between January 1, 1990 and September of 2018. HAIL 73 HEAT 10 Deaths HEAVY RAIN 28 From January, 1990 through June of HEAVY SNOW 22 2019, deaths caused by natural hazard HIGH WIND 9 events occurred mostly from cold ICE STORM 2 weather events. There were 5 deaths LIGHTNING 14 associated with cold/wind chill events STRONG WIND 21 occurring on one occasion in 1996, 2009, 2013, 2016, and 20182. THUNDERSTORM WIND 104 TORNADO 13 WINTER STORM 38 WINTER WEATHER 12 TOTAL 425 Source: NOAA National Climatic Data Center, 2019. 1 NOAA: http://tinyurl.com/y38yykxg 2 NOAA: http://tinyurl.com/y38yykxg Brown County 57 2020 All Hazards Mitigation Plan Injuries Six injuries occurred in Brown County from January, 1990 through September, 2018. Three injuries were the result of a heat wave in 2006 while one injury occurred from each of the following events: an ice storm in 1996, winds associated with a thunderstorm in 1996, and a strong wind event in 2008. Property Damage The most damaging event during this same time frame, in terms of property damage, was a tornado in 2013 that resulted in approximately two million dollars in damage. Other event categories that have caused significant property damage in Brown County have been floods, flash floods, high winds, and thunderstorms. Lightning storms and winter storms have also resulted in more significant property damages. Crop Damage The most damaging event from January 1, 1990 through June of 2019, in terms of crop damage, was associated with thunderstorm winds. Other events like floods and tornados have undoubtedly caused crop damage/loss, however, no reported losses were documented with NOAA. NATURAL HAZARDS PRIORITIZATION The purpose of rating the potential risks associated with each natural hazard and reviewing past hazard event data is to address those natural hazards posing the greatest threat to residents and to property. Based on the assessment of past data, the Steering Committee identified the following updated natural hazards to be the focus of the plan assessment, goals, objectives and strategies: Brown County 58 2020 All Hazards Mitigation Plan Winter Storms • including heavy snow, ice, and blizzards involving high winds Lightning Storms & Thunderstorms Tornadoes & High Winds Flooding • including flash, ravine, and lake Extreme Cold Extreme Heat Fog Hail Dam Failure Flooding Fires • includes Forest and Wildfires Stormwater Flooding Coastal Hazards Drought Brown County 59 2020 All Hazards Mitigation Plan OTHER NATURAL HAZARDS POSING NO SIGNIFICANT RISK The following natural hazards were determined by the Steering Committee to have a minimal chance of occurring, to pose minimal risk to the safety of residents or property, or to offer very limited mitigation options. These natural hazards are excluded from the full assessment, but they are briefly discussed here to meet the comprehensive requirements for developing a hazards mitigation plan under Federal law. Earthquakes According to the U.S. Geological Survey (USGS), there have been five documented and recognized earthquake events in Wisconsin. The closest of these to Brown County occurred in Clintonville in March 20, 2012, being a magnitude of 1.5 on the on the Richter Scale. The other events appear to have occurred near Iola and were documented between July and September of 2018. The four events that occurred near Iola were small ranging from 1.3 to 1.5 magnitude.3 The nearest active earthquake fault outside of Wisconsin is the New Madrid Fault, which stretches from northeast Arkansas to southern Illinois. Brown County falls within the lowest earthquake hazard shaking area. This represents the levels of horizontal shaking which have a 1‐in‐ 50 chance of being exceeded in a 50‐year period. Similarly, Brown County falls within a 0%g‐force to 1%g‐force peak ground acceleration (PGA) zone as shown on the USGS PGA values map with a 10 percent chance of being exceeded over 50 years. Therefore, Brown County is considered unlikely to be substantially affected by earthquakes in the long‐term future. The threat to Brown County from an earthquake is considered very low. 3 USGS interactive Earthquake map: http://tinyurl.com/yxwtpv9j Brown County 60 2020 All Hazards Mitigation Plan If a tremor or earthquake was to occur anywhere in the county, damage to structures and infrastructure could be substantial due to the fact that construction design standards in the immediate geographic area do not require buildings to be designed and constructed to meet standards consistent with an area prone to earthquake activity. Obviously, the more urbanized and densely populated areas within Brown County would experience much greater loses, injuries, and possibly deaths if an earthquake were to occur. According to the Wisconsin Department of Revenue, the 2018 Equalized Value of Brown County is $21,829,376,900, up from $18,157,652,100 in 2011.