The regions contaminated by local fallout depend critically on local weather conditions, particularly wind, and cannot be accurately predicted, but the total areas are roughly proportional to the size (kilotonnage) of the fission part of the bomb.
Source: wiktionary
In addition, the intense study of the nuclear winter phenomenon now going on in both the United States and the Soviet Union may push the arms competition further into lighter, low-kilotonnage weapons.
Source: wiktionary
Nuclear tests were nationally televised, and data on systems, kilotonnages, and weapons were published by major American newspapers.
Source: wiktionary