Sustainability: Water - The Water Cycle

[Music] all the water on Earth today every drop is all the water there has ever been on the planet fresh water is actually millions of years old the same water flowing in a continuous loop falling as rain and snow from clouds to the Earth's surface running in rivers pooling in ponds flowing from faucets irrigating crops traveling through plants generating power eventually evaporating into the air and condensing into clouds again why is there life on Earth and the reason there's life on Earth is because Earth has this perfect water cycle the water cycle so simple even

small children understand the basics yet so complex the most advanced earth scientists hydrologist geologists and biogeochemist are studying every part and process the water cycle is fascinating it's something that's around us all the time and yet we don't really understand it how to summarize what is known about the water cycle with two words flows and stores the water cycle is a series of flows of water between various water stores or storages clouds in the atmosphere there's always a little bit of water in the atmosphere we talk about relative humidity it's a humid day it's a

dry day either way there's water sometimes a little sometimes a lot there's a lot of water in the ocean 70% of all the water on earth in the ice sheets and glaciers two-thirds of all the fresh water on earth in the snow packs atop mountains like the Sierra Nevada in the Great Lakes in rivers and streams in reservoirs and watersheds in wetlands in the soil in and on plants and trees rooted in the soil and beneath the soil in water tables and underground aquifers like the Ogallala High Plains runs underneath parts of eight states from

South Dakota to Texas all this storage is temporary water in all its forms is always in flux and always moving and there is a name for every kind of movement in the water cycle starting with precipitation precipitation is the process of water falling onto the surface of the earth you can have precipitation in many forms rain snow hail rain is falling water in liquid form snow ice hail and sleet are falling water in solid or frozen form fog and mist falling water in gas or vapor form precipitation that falls directly onto the oceans becomes part

of surface ocean and can be churned by wave and wind action into ocean currents rain and snow that falls directly on rivers and streams becomes one part of stream flow rain that falls on to land takes a different path to the river as does the snow and ice that falls and collects on mountaintops when temperatures warm when snow melts some of it runs through the snowpack and goes into small streams tributaries that feed into large rivers what about that precipitation that falls on and over land some is intercepted by vegetation plants and trees like you

might imagine someone in the game of football intercepting a pass these are raindrops trying to come to the ground and the Leafs on the tree intercept them before they hit the ground and the precipitation that does hit the ground it can run off if the ground is hardscape covered with asphalt or concrete or if the soil is too wet or saturated to absorb more water like an over soaked sponge otherwise precipitation infiltrates the soil surface percolates into the ground think of it as the water percolating through your coffee grounds in the morning gravity continues to

pull it down or so it will move through the topsoil into spaces between soil and rock particles down to bedrock and further into fractures into deep underground aquifers even groundwater here is moving sideways or laterally discharging toward a river lake or the sea generally the deeper the flow the slower the flow some of that fractured water might take a very long time thousands to millions of years to get out and how does water get back out into the atmosphere it evaporates is turn from a liquid into a gas or vapor by the heat of the

Sun if you put a bit of water into a bowl and you set it outside on a sunny day it's going to disappear it's still water it's just in the form of a gas rather in the form of liquid water evaporates from every wet surface even from wet air some rain and snow evaporates into the air while falling water evaporates through our respiration and perspiration and from plants through transpiration trans means through or across plant roots drop ground water and plant pull that water up through their stems into the reliefs and then release it back

up through evapotranspiration evapotranspiration a spelling bee worthy term for evaporation from soil and water services plus transpiration from plants evaporated water molecules are tiny enough to flow into the air mixed with smoke and dirt particles in the atmosphere cool condense into visible masses of water vapor clouds winds move clouds into colder air water droplets collide and merge grow bigger and heavier until they are so heavy they fall again as rain or snow sleet or hail precipitation collection runoff interception infiltration percolation discharge transpiration evaporation condensation the water cycle [Music] you [Music]