Floods occur when water overflows or submerges land that is normally dry. This can happen in several ways:

• Overflow from water bodies: Flooding occurs when rivers, lakes, seas, or oceans overflow their normal boundaries due to excessive water. This can happen when water overtops or breaks levees or barriers.

• Heavy or prolonged rainfall: When rainfall intensity is more than the soil and drainage systems can absorb, excess water accumulates on the surface causing floods, especially in urban areas with paved surfaces that prevent absorption.

• Snowmelt: Rapid melting of snow and ice can add large volumes of water to rivers and streams, causing them to overflow.

• Storm surges and ocean waves: Strong winds and low-pressure systems during tropical storms or cyclones can push seawater onto coastal land, resulting in coastal flooding.

• Dam or levee failures: Structural failures in dams or levees can release large amounts of water suddenly, causing flooding downstream.

• Flash floods: Sudden and intense rainfall, often from thunderstorms, can cause rapid flooding with little warning. This is common in dry or urban areas where water runoff is quick and soil absorption is low.

Floods are influenced by geographic factors such as proximity to rivers, coastal areas, topography, and human activities like deforestation, urbanization, and wetland drainage, which can increase flood risk.

In summary, floods occur when water from rain, melting snow, or ocean waves exceeds the land's capacity to absorb or contain it, leading to overflow and inundation of normally dry areas.