Historical records have been used to reconstruct climates dating back several thousands of years. Historical data can be grouped into three major categories. First, there are observations of weather phenomena per se, for example the frequency and timing of frosts, or the occurrence of snowfall. Secondly, there are records of weather-dependent environmental phenomena, termed parameteorological phenomena, such as droughts and floods. Finally, there are phenological records of weather-dependent biological phenomena, such as the flowering of trees, or the migration of birds. Major sources of historical palaeoclimate information include: ancient inscriptions; annals and chronicles; government records; estate records; maritime and commercial records; diaries and correspondence; scientific or quasi-scientific writings; and fragmented early instrumental records of temperature and rainfall.