Water cycle

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.

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."

A large gap between treeline and the water level in California's Shasta Lake on August 25, 2014, is one sign of the state's devastating drought. Shasta Reservoir is at 30 percent of its total capacity and 47 percent of its historical average capacity.
Groundwater: California's big unknown
In the end, to manage water effectively, we need to know all the components of the water budget.

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 glaciersoffsite link. 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.

Predicted changes in the annual number of days of extreme rainfall (defined as rainfall totals in excess of the historic 98th percentile) across the United States by 2041-2070 as compared to 1971-2000 if greenhouse gases continue to increase at a high rate (A2 scenario).
Heavy downpours more intense, frequent in a warmer world
According to the 2009 National Climate Assessment, heavy downpours have increased in frequency and intensity during the last 50 years...

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.

Researcher Janet Intrieri, of NOAA/ESRL's Physical Sciences Division, boards the NOAA G-IV at McClellan Airfield for a science flight.
Experiment studying major West Coast winter storms – Atmospheric Rivers
Improving our understanding of atmospheric rivers will help us produce better forecasts of where they will hit and when, and how much rain and snow they will deliver.


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.offsite link 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 NOAA's Earth Science Research Lab and National Centers for Environmental Prediction
Last updated: 10/5/2015