The historical data we provide are reanalysis, but practitioners often refer to the latter as “observations” and use them for the same purposes as traditional observations from weather stations. In locations where observations are missing, 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 we use is the WFDEI dataset (http://www.eu-watch.org/data_availability) available at a 0.5° x 0.5° resolution (~ 50 km x 50 km) from 1979 to 2012 for temperature, maximum temperature, minimum temperature, rainfall, wind speed and solar radiation.