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  • In the future, water may be our most valuable commodity. Understanding the water cycle – the continuous movement of water through the Earth's upper crust, surface and atmosphere – is crucial.

    The water cycle involves events that happened millions of years to milliseconds ago. Find out more about these unpredictable forces in this timeline.

    20,000,000 BC – Polar ice sheets growing

    It is estimated that the ice sheets at the poles start growing, trapping the Earth’s atmospheric gases in the ice at that point in time.

    18,000 BC – Kapua peat bog begins accumulating

    The Kapua peat bog in the Waikato begins accumulating and will be about 14 metres thick with plant material in 2009.

    140 years – Groundwater intake of Lake Rotorua

    Water that is infiltrating the ground around Lake Rotorua will take approximately 140 years before it enters Lake Rotorua through the Hamurana Stream at about 3 m3/s.

    100 years – Lake water storage

    Water can be stored in lakes from a matter of a day or two to maybe 100 years in the deepest lakes.

    100 years – 100-year flood event

    The term ‘100-year flood’ is used in an attempt to simplify the definition of a flood that, statistically, has a 1% chance of occurring in any given year. It doesn’t mean that there can’t be two 100-year flood events in 1 year.

    75 years – Rivers in the sea

    Ocean currents are like huge rivers that move large amounts of water around the Earth. The Earth’s circumference is 24,000 kilometres, so if you were travelling on a boat at 1 km an hour it would take you 75 years to go around the Earth at that speed.

    10 days – Water in the atmosphere

    If all the water that is stored in the atmosphere rained out and fell to the surface, we would have about 27 millimetres of water on the surface and it would rain for approximately 9–10 days.

    Days–seconds – Weather scales

    Weather scales range from the synoptic scale (hundreds to a few thousand kilometres in distance over a few days), to the mesoscale (individual storms), the microscale (hydrological processes over only a few hours) and the misoscale (wind gusts that change minute by minute or even quicker).

    Related content

    Discover more about the water cycle, this article includes the interactive Dynamic and complex: the global water cycle. It describes the exchange of water in every form between the Earth’s systems and is part of what makes the Earth so unique.

    Activity ideas

    These activities can help students model aspects of the water cycle.

      Published 15 April 2009 Referencing Hub articles
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