Reanalysis data as observations

The historical data we provide are reanalysis, but practitioners often refer to them as “observations” and use them for the same purposes as observations from weather stations. In locations where observations are scarse, reanalysis are one of the solutions that provides past conditions over long time periods.

Reanalysis is a scientific method for developing a comprehensive record of how weather and climate are changing over time. In it, observations and a numerical model that simulates one or more aspects of the Earth system are combined objectively to generate a synthesized estimate of the state of the system. A reanalysis typically extends over several decades or longer, and covers the entire globe from the Earth’s surface to well above the stratosphere. Reanalysis products are used extensively in climate research and services, including for monitoring and comparing current climate conditions with those of the past, identifying the causes of climate variations and change, and preparing climate predictions. Information derived from reanalyses is also being used increasingly in commercial and business applications in sectors such as energy, agriculture, water resources, and insurance.


The reanalysis products we use are the ERA5 and the ERA5-Land datasets of the Copernicus Climate Change Service Climate Data Store available at a 0.25°x0.25° and 0.10°x0.10° resolution respectively (~ 25 km and 10 km) from 1981 to now for a larger number of weather variables.

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