CHclim25 - aridity index (AI)

Aridity index is calculated as in the CGIAR/CSI dataset  from CHclim25 sum of precipitation (Prec) and CHclim25 potential evapotranspiration (etp). Yearly individual years, current average (1981-2010) and future average (2020-2049, 2045-2074, and 2070-2099) 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).