4.3.2 Rain
Rain falling on the snowpack is inherently warmer than the pack and provides additional energy for melting, which accelerates the melt process.
No land mass is perfectly flat. Areas with just a slight slope are prone to flooding from excessive snowmelt.
If the land under the snow is frozen, it cannot absorb much water from the snowmelt. The water will travel downhill even if the slope is minimal and can lead to flooding.