Tier 1 High Hazard Zones (HHZ)

This layer, in combination with Tier 2 High Hazard Zones, was used to generate the final Combined High Hazard Zones dataset. Tier 1 High Hazard Zones were last updated in 2020. Tier 1 High Hazard Zones are where tree mortality directly coincides with critical infrastructure. They pose a threat to life and property. CAL FIRE mapped Tier 1 High Hazard Zones by identifying assets to be protected as: communities, powerlines, roads, communication structures, and recreation facilities as well as miscellaneous other critical infrastructure. These assets to be protected were then buffered; communities were buffered by 1,000 feet and all other assets were buffered by 200 feet. Tree Mortality data was provided by the USDA Forest Service Forest Health Protection staff Aerial Detection Surveys from 2012-2015. Field review and revision was needed to refine and finalize HHZ areas. These zones were periodically updated to reflect new mortality or infrastructure assets at risk. ------- Emergency Declaration: On October 30, 2015 Governor Brown issued an emergency declaration requiring public agencies to identify areas of tree mortality that hold the greatest potential to result in wildfire and/or falling trees and threaten people and property in these areas. Once identified, these areas will be prioritized for removal of dead and dying trees that present a threat to public safety. https://www.caloes.ca.gov/wp-content/uploads/Legal-Affairs/Documents/Proclamations/20151030-Tree_Mortality_State_of_Emergency.pdf本图层与二级高风险区域（Tier 2 High Hazard Zones）相结合，用于生成最终的综合高风险区域数据集。一级高风险区域（Tier 1 High Hazard Zones）最后一次更新于2020年。一级高风险区域是指林木死亡直接与关键基础设施重合的区域，此类区域会对生命和财产构成威胁。加州消防局（CAL FIRE）通过将需保护的资产界定为社区、电力线路、道路、通信设施、娱乐设施及其他各类关键基础设施，完成了一级高风险区域的绘图工作。随后对上述需保护资产开展缓冲区划定工作：社区的缓冲区范围为1000英尺，其余资产的缓冲区范围为200英尺。2012至2015年间，美国农业部森林服务局森林健康保护部门的航空探测调查团队提供了林木死亡数据。需开展实地复核与修订工作，以细化并最终确定高风险区域范围。此类区域将定期更新，以纳入新增林木死亡情况及受威胁的基础设施资产。 ------- 紧急声明：2015年10月30日，布朗州长发布紧急行政令，要求公共机构识别出最有可能引发野火和/或树木倒伏、威胁该区域内人员与财产安全的林木死亡区域。一经识别，此类区域将被优先开展枯死、濒死林木的移除作业，以保障公共安全。 https://www.caloes.ca.gov/wp-content/uploads/Legal-Affairs/Documents/Proclamations/20151030-Tree_Mortality_State_of_Emergency.pdf