In which situation can flood risk be higher?

Correct answer: Heavy rainfall and high runoff in a river valley

Direct answer: Option B is correct. Flood risk rises when a large amount of water reaches a river or low-lying area faster than the channel and soil can carry or absorb it. Heavy rainfall adds water, and high runoff quickly carries that water over the land into the river valley. If the river exceeds its bank capacity, it may overflow and flood nearby settlements and fields. Option A is wrong because low rainfall and strong sunshine generally reduce available water, though unusual local events are possible. Option C is wrong because permanently dry air does not normally supply the heavy water needed for a flood. Option D is wrong because zero rainfall gives no immediate rainfall runoff, although floods can sometimes come from upstream rainfall or dam releases; the statement itself is not the high-risk combination. The exact chain is: heavy rain → saturated soil → increased runoff → rising river discharge → possible overflow. Memory cue: flood danger depends on both water input and runoff speed, not rainfall alone.