2023 USDA Plant Hardiness Zone Map Mean Annual Extreme Low Temperature Rasters

These rasters provide the local mean annual extreme low temperature from 1991 to 2020 in an 800m x 800m grid covering the USA (including Puerto Rico) based on interpolation of data from more than a thousand weather stations. Each location's Plant Hardiness Zone is calculated based on classifying that temperature into 5 degree bands.The classified rasters are then used to create print and interactive maps.Temperature station data for the 2023 edition of the USDA Plant Hardiness Zone Map (PHZM) came from many different sources. In the eastern and central United States, Puerto Rico, and Hawaii, data came primarily from weather stations of the National Weather Service and several state networks. In the western United States and Alaska, data from stations maintained by USDA Natural Resources Conservation Service, USDA Forest Service, U.S. Department of the Interior (DOI) Bureau of Reclamation, and DOI Bureau of Land Management also helped to better define hardiness zones in mountainous areas. Environment Canada provided data from Canadian stations, and data from Mexican stations came from the Mexico National Weather Service and the Global Historical Climate Network. The USDA PHZM was produced with PRISM, a highly sophisticated climate mapping technology developed at Oregon State University. The map was produced from a digital computer grid, with each cell measuring about a half mile on a side. PRISM estimated the mean annual extreme minimum temperature for each grid cell (or pixel on the map) by examining data from nearby stations; determining how the temperature changed with elevation; and accounting for possible coastal effects, temperature inversions, and the type of topography (ridge top, hill slope, or valley bottom). Information on PRISM can be obtained from the PRISM Climate Group website https://prism.oregonstate.edu. Once a draft of the map was completed, it was reviewed by a team of climatologists, agricultural meteorologists, and horticultural experts. If the zone for an area appeared anomalous to these expert reviewers, experts doublechecked the draft maps for errors or biases. A detailed explanation of the mapmaking process and a discussion of the horticultural applications of the 2012 PHZM (similar to 2023) are available from the articles listed below. Daly, C., M.P. Widrlechner, M.D. Halbleib, J.I. Smith, and W.P. Gibson. 2012. Development of a new USDA Plant Hardiness Zone Map for the United States. Journal of Applied Meteorology and Climatology, 51: 242-264.Widrlechner, M.P., C. Daly, M. Keller, and K. Kaplan. 2012. Horticultural Applications of a Newly Revised USDA Plant Hardiness Zone Map. HortTechnology, 22: 6-19.

本批栅格数据（raster）基于千余个气象站点的观测数据插值生成，覆盖包含波多黎各在内的美国全域，空间分辨率为800米×800米，展示了1991至2020年的局地年平均极端最低气温。各点位的植物抗寒区（Plant Hardiness Zone）通过将对应气温划分为5华氏度区间计算得出。经分类后的栅格数据可用于制作印刷版与交互式地图。

2023版美国农业部（USDA）植物抗寒区地图（Plant Hardiness Zone Map, PHZM）所用的气象站点数据来源于多个渠道：在美国东部、中部、波多黎各及夏威夷地区，数据主要来自美国国家气象局（National Weather Service）的站点以及多个州级气象观测网；在美国西部与阿拉斯加地区，美国农业部自然资源保护局、美国农业部林务局、美国内政部（DOI）垦务局以及美国内政部土地管理局维护的气象站点数据，也助力更精准地划定山区的植物抗寒区。加拿大环境部（Environment Canada）提供了加拿大境内站点的观测数据，墨西哥站点的数据则来源于墨西哥国家气象局以及全球历史气候学网络（Global Historical Climate Network）。

美国农业部PHZM基于PRISM技术生成，该技术是俄勒冈州立大学研发的高精度气候制图技术。本次制图基于数字计算机网格，每个网格单元边长约为0.5英里。PRISM技术通过以下步骤估算每个网格单元（即地图上的像素）的年平均极端最低气温：调取邻近站点的观测数据、分析气温随海拔的变化规律、并考虑沿岸效应、气温逆温现象以及地形类型（山脊、山坡或山谷底部）的影响。有关PRISM技术的详细信息可通过PRISM气候小组官网https://prism.oregonstate.edu查询获取。

地图草稿完成后，由气候学家、农业气象学家与园艺学专家组成的团队进行审核。若专家团队认为某区域的抗寒区划结果存在异常，则会对地图草稿进行双重核查，排查误差或偏差。

有关制图流程的详细说明以及2012版（与2023版内容相近）PHZM的园艺应用探讨，可通过以下所列文献获取：
1. 戴利（C. Daly）、韦德切纳（M.P. Widrlechner）、哈尔布莱布（M.D. Halbleib）、史密斯（J.I. Smith）与吉布森（W.P. Gibson），2012年。《美国新版农业部植物抗寒区地图的研发》，《应用气象学与气候学期刊》，51卷：242-264页。
2. 韦德切纳（M.P. Widrlechner）、戴利（C. Daly）、凯勒（M. Keller）与卡普兰（K. Kaplan），2012年。《新版修订农业部植物抗寒区地图的园艺应用》，《园艺技术》，22卷：6-19页。