Chclim25 - bioclimatic variables (biovars)

Bioclimatic variables are calculated from CHclim25 minimum (Tmin) and maximum temperature (Tmax) and sum of precipitation (Prec) using function biovars in the R package dismo. Individual years, current average (1981-2010) and future average (2020-2049, 2045-2074, and 2070-2099)<strong> </strong>layers can be downloaded from separate zip files. Future layers are based on the transient daily time series of gridded climate scenarios of temperature at 0.02°D (~2.2 km) provided by the CH2018 initiative. We calculated future climatic layers for 4 GCMs (HADGEM, ECEARTH, MPIESM, and IPSL), 3 time slices (2020-2049, 2045-2074, and 2070-2099) and 3 representative concentration pathways (RCP 2.6, 4.5 and 8.5) The layer files are stored in compressed GeoTIFF format with the “deflate” algorithm with option “predictor2” from the GDAL. This format has a high compression ratio but allows direct import in most GIS softwares. All the maps are projected in the Swiss coordinate system CH 1903+ LV95 (epsg:2056) with a resolution of 25x25m using the extent of the digital height model DHM25 of the Swiss office for topography (swisstopo).生物气候变量（Bioclimatic variables）基于CHclim25数据集的最低气温（Tmin）、最高气温（Tmax）与降水总量（Prec），通过R包dismo中的biovars函数计算得到。单年份、当前气候平均态（1981-2010年）及未来气候平均态（2020-2049年、2045-2074年、2070-2099年）的图层均可通过独立压缩包文件下载。未来图层基于CH2018项目提供的0.02°（约2.2千米）分辨率网格化气温逐日瞬态时间序列气候情景数据。本数据集针对4种全球气候模式（GCMs：HADGEM、ECEARTH、MPIESM、IPSL）、3个时间切片（2020-2049年、2045-2074年、2070-2099年）以及3种典型浓度路径（RCP 2.6、4.5、8.5）计算生成了未来气候图层。图层文件采用GDAL库（Geospatial Data Abstraction Library）的"deflate"压缩算法并配置"predictor2"参数选项，以压缩GeoTIFF格式存储。该格式压缩比高，且可直接导入绝大多数地理信息系统（GIS）软件。所有地图均采用瑞士联邦地形局（swisstopo）数字高程模型DHM25的范围，以瑞士坐标系CH 1903+ LV95（epsg:2056）进行投影，分辨率为25×25米。