The article substantiates the assertion that for radio communication design areas in the territory close to the hydrospheric objects (rivers, lakes, sea areas) it is necessary to use calculation methods taking into account the difference in the level of signal attenuation due to seasonality. This is especially true for the Astrakhan region characterized by hot summers (to which it is advisable to add the last month of spring - May - and the first month of autumn - September, also characterized by high air temperatures). Seasonal features of radio wave propagation are determined by the continuous superrefraction above the water part of the radio line, which is formed due to the temperature inversion during the whole period of hot weather in the Astrakhan region. This is a fairly long period of time (at least 5 months a year) that must be taken into account in design systems to obtain an accurate picture of the signal level distribution in the ultra-high frequency range for such systems as television and radio broadcasting systems, cellular communication systems. Upon the results of the research and field tests it has been inferred that the effect of ultra-long-range propagation of radio waves in a tropospheric waveguide does not depend on the frequency range of the radiating system. A new method for calculating the attenuation of radio signals over the water surface in the near-water tropospheric waveguide has been developed.