What is the term for a stream in an arid region that experiences flash floods?

The term for a stream in an arid region that experiences flash floods is "Arroyo." An arroyo is typically a dry creek or stream bed that only fills with water during significant rainfall events, leading to sudden and intense flash floods. This phenomenon is common in arid regions where the ground can become saturated very quickly, causing water to rush down these channels.

Wash refers to a similar concept, but it is more general and can refer to various types of dry stream beds, not necessarily limited to those that experience flash floods. Brook and creek generally describe smaller, flowing bodies of water that are usually not associated with the arid conditions or rapid flooding conditions that characterize arroyos. Therefore, the specific characteristics of an arroyo—particularly its behavior during heavy rain—make it the correct term for the situation described in the question.