physical geog - earths life support systems

evaporation

the process by which liquid water is transformed into water vapour, which is a gas. large amount of energy is required - usually provided by heat or by the movement of air

sublimation

when ice ssheets, glaciers and snow fields release water by the direct change of state from a solid to a gas without passing through the liquid stage

transpiration

the process by which water is lost from a plant through the stomata (very small pores) in its leaves

evapotranspiration

the total amount of moisture removed by evaporation and transpiration from a vegetated land surface

condensation

process of droplets of water or ice are formed when water vapour is cooled to dew point

ablation

the melting of the ice, mainly during summer months, usually at the snout end of the glacier

precipitation

water in any form which falls from the atmosphere to the surface of the earth

interception

process by which raindrops are prevented from falling directly on to the soil surface by the presence of a layer of vegetation, water is intercepted by plant leaves, stems and branches. during periods of heavy rain, the capacity of the plant surfaces may exceed and water will drip off the leaves and branches (throughfall) and will run along branches and down the trunk (stemflow)

overland flow

when the outcome of rainfall intensity on a slope is greater than the rate at which the water can infiltrate into the soil a thin layer of water forms on the surface and it begins to move downslope under gravity

infiltration

the passage of water into the soil. water is drawn into the soil by gravity and capillary action. this process takes place at a higher rate at the start of a rainstorm but as the soil becomes more saturated then the infiltration rate falls steadily

throughflow

the transfer of water from the sil storage zone to the channel at a much slower rate than overland flow

percolation

the downward vertical movement of water within a soil. the water enters the grundwater store. the rate depends on the size of the pores through which water travels

groundwater

water that collects underground in the pore spaces in the soil and rock

groundwater flow

when it fills all the pore spaces available, the rock or soil is said to be saturated. the water can then be transferred slowly through rock and into the bed of the river

channel precipitation

rain water that falls directly into the river channel

soil moisture

water held in the unsaturated soil above the water table