Keep in mind that even the most accurate maps will, over time, become dated because of changes in the environment and radioactive decay processes. Here is an example of how ground contamination can actually increase as trees drop leaves
Radiation invades cycle of life through fallen leaves
[excerpted] "As a result of the ongoing crisis at the tsunami-hit Fukushima No. 1 Nuclear Power Plant, radioactive substances have invaded the cycle of life through fallen leaves. The contamination of leaf soil used for gardening has become a major social problem, and high levels of radiation have been detected in areas where there are concentrations of fallen leaves, causing concern among local residents.
At the same time, some experts hope that if fallen leaves in which radioactive substances can easily accumulate are removed, it will help decontaminate forests efficiently..."
A favorite pursuit of children in the fall (at least in the US) is to appropriate parents' carefully raked leaf piles for fun and mock battle. Tragically, these leaves in Japan should not become the fodder of childhood play.