The KNMI manages 33 automatic weather stations on land. These weather stations measure meteorological parameters such as temperature, precipitation, wind, air pressure and global radiation. All hourly observations and measurements received in real time are checked daily for accuracy and completeness. The validated data is archived in the KNMI's Climatological Information System (KIS). Daily data are compiled from the hourly data and the reference crop evaporation is calculated once every 24 hours according to the Makkink method. After processing and archiving the data in KIS, it can no longer be changed. This ensures data integrity.
