Oceans and Coasts

Water Cycle

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The basic water cycle is relatively simple and is taught as early as elementary school. However, the water cycle is one of NOAA’s Grand Science Challenges.

Water Cycle
Water moves through Earth's systems in a cyclic fashion taking many forms as it travels. This process is known as the Hydrologic or Water Cycle. Source: National Weather Service Jetstream project.

Like the accompanying diagram, the water cycle is often shown and taught as a simple circular cycle. Although this can be a useful model, students should understand that the reality is very different.

The paths and influences of water through Earth’s ecosystems are extremely complex and are not completely understood. In fact, the water cycle is one of 6 Grand Science Challenges identified in NOAA’s 20 year plan. As part of this plan NOAA is striving to "Improve understanding of the water cycle at global to local scales to improve our ability to forecast weather, climate, water resources and ecosystem health".

Water is essential to life on Earth. In its three phases (liquid, gaseous, and frozen) water ties together the major parts of the Earth/climate system - air, clouds, ocean, lakes, vegetation, snowpack, and glaciers. It influences the intensity of climate variability and change. It is the key part of extreme events such as drought and floods. Its abundance and timely delivery are critical for meeting the needs of society and ecosystems.

Human uses of Earth's water include drinking water, industrial application, irrigated agriculture, hydropower, waste disposal, and recreation. It is important that water sources for these uses, and for ecosystem health, are protected. In many areas water supplies are being stressed because of population growth, pollution, and development. These stresses have been made worse by climate variations and changes that affect the hydrologic cycle.

"Climate change is affecting where, when, and how much water is available. Extreme weather events such as droughts and heavy precipitation, which are expected to increase as climate changes, can significantly impact water resources. A lack of adequate water supplies, an overabundance of water, or degraded water quality has a substantial influence on civilization—now and throughout history—affecting the economy, energy production and use, human health, transportation, agriculture, national security, natural ecosystems, and recreation." (Source: http://www.ncdc.noaa.gov/oa/userengagement/water.pdf)

Education Connection
More than just a diagram to be memorized, the water cycle significantly impacts our daily lives, the local and global ecosystems and even economic systems. The resources in this Collection can help teachers guide students beyond the simple diagram. The water cycle provides the opportunity to explore the Nature of Science including; the use of models and empirical evidence based explanations as described in the Next Generation Science Standards. This Collection provides real-time and historic data sources that track and measure the water in different parts of the water cycle; satellite images show water vapor in the atmosphere, interactive maps can be searched to show precipitation, soil moisture, droughts, snow depths, river flows, glaciers and evaporation rates. Included are also lesson plans, games and hands on activities that model the complexity of the cycle.

Adapted from material provided by ESRL and NCDC
Last updated: 10/5/2015


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