Answer:
A. Rapid snow melt in regions upstream
Explanation:
"Rapid snow melt" in the upstream regions is most likely the cause of spring time flooding in a river valley. The effects of rapid snow melt are different for different areas. But in the upstream region it is a concern. In the spring time the rapid snow melting has become a cause of concern for many people around the world. But besides flooding snow melting can cause "landslides and debris flows" too. In the "alpine regions" like "Switzerland", snowmelt is a major cause for the runoff. Snow melting in such regions with the combination of rain can cause disastrous floods.
