Study of observed changes in the first harmonic amplitude of the daily precipitation amount series in the territory of Russia

Using the data from weather observation stations, an assessment of the statistical significance of the first harmonic amplitude of the average long-term daily precipitation amount series in Russia in 1961–2020 and their changes in 1991–2020 compared to 1961–1990 is made. It is shown that at most stations the first harmonic has a reliable value different from the noise, except for eleven stations in the southern regions of the European Part of Russia. It is revealed that, on average, there is a significant decrease in the first harmonic amplitudes of the daily precipitation series across Russia. An analysis of the spatial distribution of the studied quantities is performed and the presence of large areas with their homogeneous character is demonstrated.