Answer to Question 1
Regional floods occur due to heavy rains or rapid snowmelt that causes streams to overtop their banks because the water cannot infiltrate or discharge as fast as the precipitation. Flash floods occur because of surface conditions that limit or prevent infiltration, heavy rainfall, and topography. They occur with little warning, and unlike regional floods, they cause the water level to rise very rapidly and have very high flow velocities.
Answer to Question 2
About 30 percent of all Earth's freshwater is groundwater. However, when glacial ice is excluded, 96 percent of freshwater occurs as groundwater.