What conditions lead to a flood occurring?

A flood occurs when a stream or river exceeds its channel capacity, leading to overflow and inundation of the surrounding areas. This situation typically arises due to a combination of heavy rainfall, rapid snowmelt, or prolonged periods of precipitation that saturate the ground. As the volume of water increases beyond what the riverbanks can contain, it spills over, causing flooding.

In contrast, consistently low water levels do not contribute to flooding; instead, they indicate dry conditions. Periods of drought are characterized by a lack of water, which would not result in flooding but rather a scarcity of water resources. Similarly, while increased evaporation rates might affect water levels and contribute to dry conditions, they do not lead to flooding. Thus, the correct answer highlights the essential relationship between a stream's capacity and the occurrence of flooding.