9-second gridded continental Australia change in effective area of similar ecological environments (cleared natural areas) for Reptiles 1990:2050 MIROC5 RCP 8.5 (CMIP5) (GDM: REP_r3_v2)

Proportional change in effective area of similar ecological environments for Reptiles as a function of land clearing and change in long term (30 year average) climates between the present (1990 centred) and projected future (2050 centred) under the MIROC5 model (RCP 8.5) based on Generalised Dissimilarity Modelling (GDM) of compositional turnover. This metric describes the combined effects of climate change and land clearing on the area of similar environments to each grid cell as a proportion. Each cell is compared with a sample of 60,000 points in both the present uncleared landscape and an alternative scenario (either present with clearing, or future with clearing), and the pairwise similarities summed (e.g. a completely similar cell will contribute 1, a dissimilar cell 0, with a range of values in between). Only cells which are flagged as uncleared contribute. For each time point, this describes the area of similar environments, which will be low for rare environments and high for widely distributed environments. By dividing the test area by the current area, we are able to quantify the reduction in area as a function of land use/climate change. Values less than one indicate a reduction, values of 1 no change, and values greater than 1 (rare cases in the north) show an increase in similar environments. This metric was developed along with others for use in an assessment of the efficacy of the protected area system for biodiversity under climate change at continental and global scales, presented at the IUCN World Parks Congress 2014. It is described in the AdaptNRM Guide “Implications of Climate Change for Biodiversity: a community-level modelling approach”, available online at: www.adaptnrm.org. Data are provided in two forms: 1. Zipped ESRI float grids: Binary float grids (*.flt) with associated ESRI header files (*.hdr) and projection files (*.prj). After extracting from the zip archive, these files can be imported into most GIS software packages, and can be used as other binary file formats by substituting the appropriate header file. 2. ArcGIS layer package (*.lpk): These packages contain can be unpacked by ArcGIS as a raster with associated legend. Additionally a short methods summary is provided in the file 9sMethodsSummary.pdf for further information. Layers in this 9s series use a consistent naming convention: BIOLOGICAL GROUP _ FROM BASE_ TO SCENARIO_ ANALYSIS e.g. A_90_CAN85_S or R_90_MIR85_L where BIOLOGICAL GROUP is A: Mammals, M: mammals, R: reptiles and V: vascular plants

基于物种组成更替的广义相异性模型（Generalised Dissimilarity Modelling, GDM），本数据集呈现了MIROC5模型（典型浓度路径RCP 8.5）下，以1990年为基准的当前时段与以2050年为基准的未来时段之间，土地清理与长期（30年平均）气候变化对爬行类相似生态环境有效面积的比例变化。

该指标量化了气候变化与土地清理对每个网格单元对应相似生态环境面积的综合影响比例。研究将每个网格单元分别与当前未开垦景观、两种替代情景（当前已开垦或未来已开垦）中的60000个采样点进行比对，对两两相似性进行求和（例如，完全相似的网格单元得分为1，完全不相似的得分为0，其余情况得分介于0到1之间）。仅标记为未开垦的网格单元参与计算。在每个时间节点下，该指标反映相似生态环境的面积：稀有生境对应数值较低，广布生境对应数值较高。通过将测试时段面积除以当前基准面积，可量化土地利用/气候变化导致的面积缩减幅度。当指标值小于1时表示面积缩减，等于1时表示无变化，大于1时（北半球少数案例）则表示相似生态环境面积有所增加。

该指标与其他指标一同开发，用于评估大陆及全球尺度下气候变化对生物多样性保护区系统的有效性，相关成果发表于2014年世界自然保护联盟（IUCN）世界公园大会。其详细说明见于AdaptNRM指南《气候变化对生物多样性的影响：群落级建模方法》，可通过网址www.adaptnrm.org在线获取。

数据集提供两种存储格式：
1. 压缩的ESRI浮点栅格：包含二进制浮点栅格文件（*.flt）、配套的ESRI头文件（*.hdr）与投影文件（*.prj）。从压缩包解压后，这些文件可导入绝大多数地理信息系统（Geographic Information System, GIS）软件，通过替换对应头文件的方式，也可作为其他二进制格式文件使用。
2. ArcGIS图层包（*.lpk）：该类文件可通过ArcGIS软件解压为带配套图例的栅格图层。
此外，文件9sMethodsSummary.pdf中提供了简短的方法概述以供参考。本9s系列图层采用统一命名规则：生物类群_基准时段_情景_分析类型，例如A_90_CAN85_S或R_90_MIR85_L，其中生物类群对应关系为：A：哺乳类，M：哺乳类，R：爬行类，V：维管植物。