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Music

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Water is the fundamental ingredient for life on Earth.

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Looking at our Earth from space,

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with its vast and deep ocean, it appears as though

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there is an abundance of water for our use.  However,

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only a small portion of Earth's water is accessible for our needs.

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How much fresh water exists and where it is stored

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affects us all.   Nearly two-thirds of this fresh water

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is stored in the polar ice caps, snow packs, and glaciers,

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making it inaccessible for long periods of time.

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The water cycle is dynamic -

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it describes the continuous movement

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of water on, above and below the surface of the Earth

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and the transitions from one state to another.

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Sea surface temperature, surface winds, and air temperature

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influence the rate of evaporation at the ocean surface.

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In the tropics, warm ocean surface temperatures

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support high rates of evaporation.

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Wind also increases evaporation.

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When the air's temperature is warmer, it can hold more water.

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While the atmosphere does not store a large quantity of water

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compared to the ocean, rivers and lakes,

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it can transport water quickly from one place to another.

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Low-lying regions of the atmosphere with high moisture and strong winds,

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can form "atmospheric rivers" to transport water horizontally.

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Clouds are formed as water vapor cools and condenses

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into droplets and ice crystals.

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Clouds and water vapor act as insulators in the atmosphere.

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Clouds help shield the Earth from the Sun and trap heat from below.

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Sound of thunder

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When cloud particles grow large enough, they may fall out as rain or snow.

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Under the right conditions, areas of precipitation can grow

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into large storms.   As storms grow,

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they transfer heat vertically into the upper atmosphere.

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The migration of storms helps to distribute heat between the equator

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and poles - shaping wind patterns globally.

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How storms grow and intensify

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depends upon atmospheric moisture, surface temperatures and

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wind patterns.  Precipitation is concentrated in some

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parts of the world and scarce in others.  It can vary substantially

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from season-to-season and from year-to-year.

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Water that falls on the land surface as precipitation

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is stored within snow packs, lakes, reservoirs,

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soils and underground aquifers.

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Water availability varies from place-to-place

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and over time.  The availability of water

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affects the type and abundance of vegetation.

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the primary source of food for animals and people.

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Extreme water cycle variability,

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unusually dry or wet conditions,

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impacts humans worldwide.

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Each year, hazards such as floods exact a costly

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economic and human toll.

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Most of the water that falls on to land remains stored there for weeks or more.

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Snowfall is stored as snow pack or ice.

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Melt water and rainfall

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are stored in lakes and soils.  Some of the water is absorbed

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by plant roots or drains into the water table.

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Eventually, the water

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will evaporate to the atmosphere or return to the ocean

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in streams and rivers, providing a source of nutrient rich

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water that supports ocean life.

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Sensors on a suite of NASA satellites observe and measure

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water on land, in the ocean and in the atmosphere.

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These measurements are important to understanding the availability

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and distribution of Earth's water, which is both

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vital to life and vulnerable to the impacts of climate change