Final answer:
True, volcanic ashfall can lead to famine by damaging agriculture, causing food shortages and impacting human populations. Historical instances like the Great Famine of 1315–1317 and the famine in China between 1959 and 1961 are evidence of this devastating effect.
Step-by-step explanation:
The statement that the prime risk of ashfall to human populations is famine is indeed true. Volcanic ash can have devastating effects on agriculture by covering crops and contaminating water supplies, leading to a decrease in food production. Historical evidence from events such as the Great Famine of 1315–1317 shows that natural disasters, including those influenced by climatic changes, can lead to massive food shortages and human suffering. The Great Famine led to the death of up to 10 percent of northern Europe's population. In more recent times, the requisitioning of grain in rural China combined with environmental disasters like floods and locust swarms resulted in famine, causing the deaths of millions. Famine can also be exacerbated by political or economic factors such as in Ethiopia, where a land tenure crisis and poverty played a significant role despite the country exporting food at the time.