hydrology (W1)

• Reservoirs maintain a constant size when inflow water equals the outflow of water, even though water is constantly cycling through
• residence time is the average time any given quantity of water spends in a reservoir.
• there is about 1.4 billion cubic kms of water on Earth in total
• the hydrological cycle is driven by Earth's external heat engine (the sun), mainly through evaporation
• transpiration is the process of water entering the atmosphere through plants by evaporation from the leaves
• runoff may later seep into the group or evaporate but most eventually flows into the ocean
• sublimation is the process of water entering the atmosphere from the transformation of ice directly into water vapour
• relative humidity is the amount of water vapour in the air, expressed as a percentage of the total amount of water the air could hold at the same temperature if it were saturated.
• Air temperature effects the amount of water vapour in the air, warmer air can hold more than cooler air
• rain occurs when moisture condenses and the droplets grow too heavy to stay suspended by air currents.
• droughts are periods of months or years when precipitation is much lower than normal.
• A human can survive on around 2 litres of water per day
• Ground water accounts for around 99% of all usable fresh water
• only 1% of earth's water is usable
• ground water is stored in the cracks and pores between rocks and sand
• Aquifers are regions of soil capable of storing and transmitting water
• Aquitards are layers of the earth that can store water but do not transmit it easily
• land subsidise is the collapsing or sinking of the ground due to the loss of ground water beneath