A number of sites in the Fukushima contaminated area were surveyed for long-term changes in dose equivalent rate above the soil surface during 2015–2017 using D-shuttle dosimeters. D-shuttle readings in most cases decreased faster than if due to radioactive decay only. More rapid decrease can be explained by natural attenuation processes, such as erosion of the topsoil, the vertical migration of radionuclides in the soil and the deposition of cleaner sediments transported by surface runoff.