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DWD RADKLIM / RADOLAN — introduction#

The earthlens.radklim backend fetches DWD's gauge-adjusted radar precipitation over Germany from DWD Open Data over anonymous HTTPS. It covers two streams:

  • RADKLIM — the reprocessed, climatologically consistent radar climatology (1 km grid, 2001–present), in an hourly product (RW) and a 5-min product (YW). This is the dataset to use for statistics.
  • RADOLAN — the operational, near-real-time stream (same grid and products), served on a rolling ~2-day retention window. Use it for near-real-time monitoring, not for return periods.

It is a raster backend: download() returns the list[Path] of the raw granules it fetched. Reading them (NetCDF / HDF5) is done downstream by pyramids — earthlens never imports wradlib / xarray / netCDF4.

RADKLIM vs RADOLAN — which to use#

RADKLIM (radklim-rw / radklim-yw) RADOLAN (radolan-rw / radolan-yw)
Purpose climatology / statistics near-real-time monitoring
Homogeneity reprocessed, consistent operational, inhomogeneous
Coverage full archive, 2001– rolling ~2 days only
Served as one yearly .tar.gz NetCDF archive per year per-timestamp .hdf5 / .bz2 granules
Return periods reasonable (but ~25-yr record — see caveat) no

RADKLIM-YW (5-min, 1 km) is the single most useful dataset for German sub-hourly extreme rainfall and pluvial-flood work. Caveat: the record is only ~25 years, which is excellent for studying event structure but short for fitting long return periods.

What earthlens fetches (and what it does not)#

  • reproc products enumerate the yearly archives covering the requested window and download each — e.g. YW2017.002_2024_netcdf.tar.gz (~13.5 GB/yr for YW, ~836 MB/yr for RW). The reprocessing has no finer addressable unit on the NetCDF tree, so a [start, end] window maps to whole years.
  • operational products read the stream's directory listing and download the per-timestamp granules whose scan time falls in the window (behind a retention guard — a window older than ~2 days returns nothing, with a warning pointing you at the RADKLIM archive).

Formats and the decode boundary#

  • RADKLIM NetCDF (inside the yearly .tar.gz) and operational HDF5 are read directly by pyramids — the recommended, default formats.
  • The operational .bz2 RADOLAN binary (data_format="bin") is an opt-in format that needs a wradlib/pyramids decoder; earthlens only fetches it.

Grid, licence, authentication#

  • Grid — the fixed DWD RADOLAN polar-stereographic grid over Germany (1 km cells). earthlens ships the native-grid granule; it does not reproject or subset. A request whose bbox cannot overlap Germany is rejected.
  • Licence — CC-BY-4.0 / GeoNutzV (DWD open geodata). Attribution is required — credit Deutscher Wetterdienst (DWD).
  • Authentication — none. The source is anonymous HTTPS.