The Hydrological Cycle

• Precipitation is any water that falls to the surface of the earth from the atmosphere, including rain, snow and hail. It is an input.
• Convectional rainfall is caused by the heating of the sun. Warm air rises, condenses at higher altitudes and falls as rain.
• Relief rainfall is when warm air is forced upon a barrier such as mountains, causing it to condense at higher altitudes and fall as rain.
• Frontal rainfall is when warm air rises over cool air when two bodies of air at different temperatures meet, because the warm air is less dense and therefore lighter. It condenses at higher altitudes and falls as rain.
• Evaporation occurs when water is heated by the sun, causing it become a gas and rise into the atmosphere. It is an output.
• Transpiration occurs in plants, when they respire through their leaves, releasing water they absorb through their roots, which then evaporates due to heating by the sun. It is an output.
• Evapotranspiration is the combination of evaporation and transpiration.
• Infiltration is the process of water moving above ground into the soil vertically.
• The infiltration capacity refers to how quickly infiltration occurs.
• Percolation is when water moves from the ground or soil into porous rock or rock fractures.
• The percolation rate is dependent on the fractures that may be present in the rock and the permeability of the rock.
• Throughflow is water that moves through the soil and into streams or rivers downhill. The more vegetated the area is, the faster throughflow is.
• Surface Runoff is water that flows above the ground/impermeable surfaces.
• Groundwater flow is water moving through the rocks horizontally towards the river.
• Streamflow is water that moves through established channels.
• Stemflow is the flow of water that has been intercepted by plants or trees, down a stem, leaf, branch or other part of the plant.
• Soil Water Storage is water stored in the soil which is utilised by plants.
• Groundwater storage is water that is stored in the pore spaces of rock.
• Interception storage is water intercepted by plants on their branches or leaves before reaching the ground.
• Surface storage is the part of precipitation retained at the ground's surface.
• Precipitation = Total Runoff + Evapotranspiration + Storage
• Discharge = Cross Sectional Area x Velocity