Water and Climate

Global climate projections, predicting regional climate impacts and providing weather forecasts all depend on understanding the central and dominant role of water in the climate system.

Water is essential to life on Earth. Water in its liquid, gaseous, and frozen phases ties together major pieces 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 feature of extreme events such as drought and floods, and its abundance and timely delivery are critical for meeting societal and ecological demands. NOAA's mission to serve society's needs for water and climate information will be achieved through its investments in improved monitoring, research, and prediction capabilities needed to explain and forecast the state of the climate system.

What is the Role of Water in the Climate System?

Water on Earth is present in three phases. In its liquid form, precipitation meets basic water demands by humans, animals, and plants. Its runoff into streams sustains ecosytstems and, along with percolation into aquifers, ensures long term storage and supply for human uses. The oceans are the world's primary source of water vapor that feeds precipitation. Atmospheric water vapor is a greenhouse gas which, together with carbon dioxide, is responsible for Earth's surface temperature being well above freezing. In water's frozen form, sea ice and snow cover tend to cool the planet by reflecting the Sun's incoming solar radiation. Glaciers, especially those at mid-latitudes, provide water storage and summer supply for both agriculture and metropolitan areas around the world.

Why is Water Important in the Climate System?

"Water is life." - Wallace Stegner

Clean water is an essential resource for human life and health, economic growth, and ecosystem vitality. The need for water supplies adequate for human use including drinking water, industrial application, irrigated agriculture, hydropower, waste disposal, and the protection of human and ecosystem health are critical. Water supplies are stressed by population growth, pollution, and development. These stresses are intensified by climate variations and changes that alter the hydrologic cycle

What do we know about the role of water in the climate system?

Water acts together with other external forcings that affect the climate system, such as increases in atmospheric carbon dioxide (CO₂) or changes in solar radiation. For example, models and observations show that water vapor increases as the climate warms, which in turn tends to further warm the atmosphere. It is also known that liquid water, in the form of clouds, reflects sunlight but also retains heat near the Earth's surface like a greenhouse gas. Quantifying this interaction between water vapor, clouds, and heat exchange near the Earth's surface is key to understanding climate sensitivity and the factors governing climate change. A warming climate is known to increase surface evaporation, which, barring an increase in precipitation, reduces soil moisture, ground water storage, and stream flow.

What don't we know about the role of water in the climate system?

The intensity of the effect of water on climate is not accurately known, because the current water vapor-cloud-climate feedbacks are incompletely understood. Uncertainties related to such feedbacks are a key source of the differences among various climate models that project human-induced climate change. Limited observations of the hydrologic state of the Earth System further restrict understanding. For example, soil moisture and ground water are not well monitored globally, confounding efforts to understand interactions between land surface changes and the water cycle, and hindering efforts to explain the local hydrologic response to precipitation and temperature variations. We do not understand well how warming in the Arctic and ensuing melting of permafrost will affect the release of methane and nitrous oxide, greenhouse gases that also contribute to planetary warming.

What will we need to know in the future?

Advances in prediction capability require enlarging the range of observations and improving models to deliver accurate regional-scale predictions. The models especially can improve on how they represent the physical processes associated with all phases of water. Predicting what will happen with water in the future depends heavily on a better understanding of where the water is now (e.g., snowpacks, soil moisture) through enhanced observations. The degree of skill with which water variables can be predicted will depend on location and season.

While NOAA has produced streamflow and flood forecasts for several decades, there is economic value of an expanded suite of products focused on the role of water in the climate system to support flood mitigation and to manage water availability and quality for agriculture, potable use, hydropower, power plant cooling, ecosystem health, navigation, and contaminant loading.

What is NOAA's role?

NOAA is responsible for collecting and ensuring uniform standards for national scale data, including precipitation, temperature, humidity, and sea level. The interpretation of such data to explain evolving water-climate conditions is a fundamental component of NOAA climate services.

NOAA must increasingly focus on providing integrated information on the role of water in the climate system. NOAA must continue to deliver the data, products, and services needed for risk management planning, operations, and research. NOAA will continue to integrate its research and operational assets to deliver water resource predictions and information.

How does society benefit from this knowledge?

Decision makers in water management, agriculture, urban planning, disaster management, energy, and transportation rely on NOAA to deliver climate information built on fundamental understanding of the role of water in the climate system. Improved understanding of the influence of water on climate variability and trends at regional and watershed scales will be of significant benefit to decision makers dealing with climate-sensitive issues. Whether the role of water in the climate system is changing as a result of human activities or natural, low- frequency variation, society will have to adapt, and focused scientific information must be provided to support choices. The growing economic and social costs of extreme events indicate that there is need for improved response to these disruptions, whether or not their frequency and intensity are changing.