Abstract. A phenological data set collected by citizen scientists from 1970 to 2018 in Latvia is presented, comprising almost 47 000 individual observations of eight taxonomical groups, in addition to agrarian activities and abiotic parameters, covering in total 159 different phenological phases. These original data published offline in annual issues of the Nature and History Calendar (in Latvian, Dabas un vēstures kalendārs) have been digitized, harmonized, and geo-referenced. Overall, the possible use of such data is extensive, as phenological data are excellent bioindicators for characterizing climate change and can be used for the elaboration of adaptation strategies in agriculture, forestry, and environmental monitoring. The data can also be used in cultural–historical research; for example, the database includes data on sugar beet and maize, the cultivation of which was imposed on collective farms during the Soviet period. Thus, such data are not only important in the Earth sciences but can also be applied to the social sciences. The data significantly complement current knowledge on European phenology, especially regarding northern regions and the temporal biome. The data here cover two climate reference periods (1971–2000; 1981–2010), in addition to more recent years, and are particularly important in monitoring the effects of climate change. The database can be considered the largest open phenological data set in the Baltics. The data are freely available to all interested at https://doi.org/10.5281/zenodo.3982086 (Kalvāne et al., 2020).

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Abstract. A phenological data set collected by citizen-scientists from 1970 to 2018 in Latvia is presented, comprising almost 47,000 individual observations of eight taxonomical groups, in addition to agrarian activities and abiotic parameters, covering in total 159 different phenological phases. These original data published offline in annual issues of the Nature and History Calendar (in Latvian, Dabas un vēstures kalendārs) have been digitized, harmonized and geo-referenced. Overall, the possible use of such data is extensive, as phenological data are excellent bioindicators for characterising climate change and can be used for the elaboration of adaptation strategies in agriculture, forestry, and environmental monitoring. The data also can be used in cultural–historical research; for example, the database includes data on sugar beet and maize, the cultivation of which was imposed on collective farms during the Soviet period. Thus, such data are not only important in the Earth sciences but can also be applied to the social sciences. The data significantly complement current knowledge on European phenology, especially regarding northern regions and the temporal biome. The data here cover two climate reference periods (1971–2000; 1981–2010), in addition to more recent years, and are particularly important in monitoring the effects of climate change. The database can be considered the largest open phenological data set in the Baltics. The data are freely available to all interested at https://zenodo.org/ https://doi.org/10.5281/zenodo.3982086 (Kalvāne et al., 2020).