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100-year flood

A flood that statistically has a 1-percent chance of occurring in any given year.


Actionable Science

Information, products, and tools that are created to meet the planning and decision-making needs of a specific end-user, such as natural and cultural resource managers, policy professionals, community leaders, and other local decision makers |

Adaptation Plan

A plan to help a resource management agency or community adjust to the impacts of climate change, including actions that can be taken to reduce the negative impacts of climate change, increase climate resilience, and to take advantage of emerging opportunities. |

Adaptive Capacity

The ability of an organism or ecosystem to adjust to climate change to moderate potential damages, to take advantage of opportunities, or to cope with the consequences. This can include changes in behavior, movements including shifts in geographical range and distribution, and genetic evolution to adjust to environmental or ecological stressors. |

Adaptive Management

A decision process that promotes flexible decision making that can be adjusted in the face of uncertainties as outcomes from management actions and other events become better understood. Adaptive management recognizes the importance of natural variability in contributing to ecological resilience and productivity. It is not a ‘trial and error’ process, but rather emphasizes learning while doing. Adaptive management does not represent an end in itself, but rather a means to more effective decisions and enhanced benefits.
Drought ruined soybean crop in Sumter County, Georgia

Agricultural Drought

Water shortages from below-normal precipitation and/or above-normal temperatures or wind that evaporate moisture from soils and plants, having negative impacts on crops and livestock. |


Describes fish born in freshwater who spend most of their lives in saltwater and return to freshwater to spawn, such as salmon and some species of sturgeon. |

Aquatic flow 

Measurable characteristics of flowing water, including depth, flow rates, seasonality, temperature, nutrient loading, and water quality, and the resulting impacts on aquatic ecosystems. Sometimes referred to as "ecological flows."
Visualization of atmospheric river moving through the Pacific to the West Coast

Atmospheric River 

A relatively long, narrow region in the atmosphere – like rivers in the sky – that transport water vapor. These columns of vapor move with the weather, carrying an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River. When an atmospheric river makes landfall, it often releases this water vapor in the form of rain or snow. |
Avalanche debris by roadside


A large mass of snow, ice, earth, rock, or other material that slides swiftly down a mountain side. |



Refers to biological diversity, or the variety of life on Earth at all its levels, from genes to species to ecosystems. It can encompass the evolutionary and ecological processes that sustain life. |

Biological Carbon Sequestration 

Refers to the storage of atmospheric carbon in vegetation, soils, woody products, and aquatic environments.

Blue Carbon

Carbon is associated with oceans and seas.


Capacity Building

The process by which individuals or organizations obtain, improve, or retain the skills, knowledge, tools, equipment, or other resources to do their work well. |

Carbon Cycle 

The process in which carbon continually travels from the atmosphere to the Earth and then back into the atmosphere |
Image shows calcite and gypsum crystals on dolomite

Carbon Mineralization 

The process by which carbon dioxide becomes a solid mineral, thus preventing it from escaping back to the atmosphere.

Carbon Sequestration

The process of removing carbon dioxide gas (CO2) from the atmosphere and storing it somewhere stable, thus decreasing the amount of warming greenhouse gasses in the air and reducing the effects of climate change.

Carbon Sink 

A land or ocean mass that can absorb carbon, namely carbon dioxide, from the atmosphere and store it for long periods of time. Major carbon sinks include the ocean, old-growth forests, and oil deposits. |

Carbon Source 

Processes that release more carbon dioxide into the atmosphere than they absorb. For example, any process that uses fossil fuels—such as burning coal to make electricity—releases a lot of carbon into the atmosphere. |


A chemical element found in organic matter (i.e., plant and animal tissue) and in our atmosphere (i.e., gases such as carbon dioxide (CO2) and methane (CH4)). Carbon helps to regulate the Earth’s temperature and provides a major source of energy to fuel our global economy. |


Fish that spend most of their lives in freshwater and return to the sea to spawn. |

Citizen Science 

Also known as "community science", referring to scientific work undertaken by members of the general public who use their interests and talents in tackling a wide range of real-world problems, usually in collaboration with scientific institutions.

Climate Adaptation 

An intentional management strategy that helps preserve landscapes and communities under new climate conditions, for example building a sea wall to adapt to sea-level rise or planting drought-tolerant grasses to adapt to drier conditions.

Climate Change 

Climate change refers to long-term shifts in temperatures and weather patterns. These shifts may be natural, such as through variations in the solar cycle. But since the 1800s, human activities have been the main driver of climate change, primarily due to burning fossil fuels like coal, oil, and gas. |

Climate Forcing

Any influence on the climate that originates from outside the climate system itself. These can include changes in solar radiation or changes in the levels of greenhouse gases in the atmosphere. |

Climate Futures 

Descriptions of plausible future climate conditions for a specific place and time period. Usually developed using climate model projections to help users understand and prepare for the full range of possible future climate conditions and resource responses.

Climate Justice

A recognition of the disproportionate impacts of climate change on low-income communities and communities of color around the world, often the people and places least responsible for the problem. |

Climate Mitigation 

The process of decreasing the amount of greenhouse gasses being added to the atmosphere. This can be done by reducing greenhouse gas emissions or by directly removing carbon dioxide from the atmosphere through carbon sequestration.

Climate Model 

Computer programs and mathematical algorithms that simulate weather patterns over time. These climate models can estimate the Earth’s average weather patterns (the climate) under different conditions. |

Climate Projections 

Any description of the future climate and the pathway leading to it. More specifically, a climate projection describes model-derived estimates of future climate conditions. |

Climate Refugia

Areas that are relatively buffered from modern climate change, for example high mountains that still get snow or deep desert springs that survive droughts. Species that live in or move to these areas are better positioned to survive changing climate conditions or to have time to adapt to new conditions.

Climate Resilience

The ability of a natural or human system to withstand and respond to changes in climate.

Climate Stressor

A condition, event, or trend related to climate change that can exacerbate hazards such as sea level rise or drought. |


The average of the weather patterns in a location over a long period of time, usually 30 years or more. |


A process of scientific inquiry in which researchers, partners, and affected communities collaboratively design, implement, and apply research to solve on-the-ground problems.
Animation shows tides washing away brown mud from the shoreline and eroding green marshgrass. A graph follows the tide.

Coastal Erosion 

The process by which local sea level rise, strong wave action, storms, and coastal flooding wear down or carry away rocks, soils, and/or sands along the coast. |

Community Science

Also known as "citizen science," it is scientific work undertaken by members of the general public who use their interests and their talents in tackling a wide range of real-world problems, usually in collaboration with scientific institutions.


"All regions on and beneath the surface of the Earth and ocean where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers and ice sheets, and frozen ground (which includes permafrost)." |
Indigenous Fire Stewardship

Cultural Burn 

The intentional application of fire to land by Native American tribes, tribal organizations, and cultural fire practitioners to achieve cultural goals or objectives, including subsistence, ceremonial activities, biodiversity, or other benefits. |

Cultural Resources 

Physical remains of past human activity. These may include buildings; structures; prehistoric sites; historic or prehistoric objects or collection; rock inscription; earthworks, canals, or landscapes. |



A species or population of fish that migrate between salt water and fresh water. |


A method used to process and refine Global Climate Model outputs to produce outputs more suitable for use in climate studies, often by refining the models to be at smaller spatial scales. |


An extended lack of moisture within an area, caused by lack of precipitation (rainfall or snow) or reduced water levels in reseviors, aquifers, and other bodies of water. May result in adverse impacts to people, animals, or vegetation. See also Hydrological Drought, Meteorological Drought, Snow Drought, Ecological Drought, Agricultural Drought, and Socio-economic Drought. |


Image: California’s Hotter Drought and Tree Death

Ecological Drought 

Refers to the environmental consequences of drought, for example loss of plant growth and habitat or increases in fire and insect outbreaks.

Ecological Forecasting 

Predicting changes in ecosystems from external factors, such as climate change or pollution, and how those changes may affect people, economies, and communities. |

Ecosystem Services 

The benefits that people obtain from ecosystems. These include provisioning services such as food and water; regulating services such as regulation of floods, drought, land degradation, and disease; supporting services such as soil formation and nutrient cycling; and cultural services such as recreational, spiritual, religious, and other non-material benefits. |
Cheatgrass turning red in the fall in the Squirrel Creek burn area, Medicine Bow National Forest.

Ecosystem Transformation 

When an ecological system diverges, dramatically and irreversibly, from it's prior ecosystem structure and function. For example, if wildfires burn too hot or too frequently, they can prevent slow-growing trees from re-growing, causing forests to transform into grasslands.


All the organisms within a designated area and the physical environment with which they interact.

El Niño

The warm phase of a recurring climate pattern across the tropical Pacific. The pattern shifts back and forth between El Niño and La Niña irregularly every two to seven years, and each phase triggers predictable disruptions of temperature and precipitation. |

Emissions Scenarios

Plausible future atmospheric greenhouse gas concentrations caused by different levels of human greenhouse gas and aerosol emissions. For more information, see []

Environmental Justice

The fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income, with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies. |


The sum of evaporation from the land surface plus transpiration from plants.


The rate and magnitude of climate change that a species or ecosystem is likely to experience. Often measured along with a species' or ecosystem's sensitivity to determine impacts in a climate change vulnerability assessment.


Fire Adapted

Ecosystems or species that can burn in a wildfire and then return to their pre-fire condition prior to the next fire. |


The word “fishery” is used in many ways. It can refer to the occupation, industry, or season for catching fish. It can also refer to the area within the body of water where fish are caught, or the business of catching the fish. |
Image: Boulder Creek, Colo., at Flood Stage


An established gage height for a given location above which a rise in water surface level begins to create a hazard to lives, property, or commerce. |


Geological Carbon Sequestration 

The process of storing carbon dioxide (CO2) in underground geologic formations. The CO2 is usually pressurized until it becomes a liquid, and then it is injected into porous rock formations in geologic basins.
Image: Matanuska Glacier


A large, perennial accumulation of crystalline ice, snow, rock, sediment, and often liquid water that originates on land and moves down slope under the influence of its own weight and gravity.

Global Change

Global-scale changes to the Earth system linked to human activities, including land use changes and climate change.

Greenhouse Gases

Gases in Earth’s atmosphere that trap heat. These gases allow sunlight to pass through the atmosphere, but they prevent the heat that the sunlight brings from leaving the atmosphere. Common greenhouse gasses include carbon dioxide (CO2); methane (CH4); nitrous oxide (N2O); fluorinated gases such as hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride; and water vapor (H2O). Source: NASA Climate Kids



Potential dangers from both natural processes (e.g., earthquakes, floods, and climate change) and human impacts on the environment.
Bathtub rings on rock in Lake Powell where the water has dropped and left minerals behind

Hydrological Drought

A lack of water in the hydrological system, manifesting itself in abnormally low streamflow in rivers and abnormally low levels in lakes, reservoirs, and groundwater. Source: Loon, A. F. 2015. Hydrological drought explained. Wiley Interdisciplinary Reviews Water 2(4): 359-392.


Branch of earth science that deals with water as it occurs in the atmosphere, on the surface of the ground, and underground.


Inland Fish

Fish found in lakes, rivers, streams, canals, reservoirs, and other landlocked waters. Source: USGS/AFS Capitol Hill Roundtable on Extreme Events


Inundation is the total water level that occurs on normally dry ground as a result of a storm, and is expressed in terms of height of water, in feet, above ground level. Source: Defining Storm Surge |

Invasive Species

An organism (disease, parasite, plant, animal, etc.) that is introduced to a new region outside of its historical distribution, begins to spread or expand its range from the site of its original introduction, and has the potential to cause harm to the environment, the economy, or human health.


Keystone Species

Species whose abundance and ecological role has an oversized effect on the other species in an ecosystem, such that their presence helps keep the ecosystem in balance.


La Niña

The cool phase of a recurring climate pattern across the tropical Pacific. The pattern shifts back and forth between El Niño and La Niña irregularly every two to seven years, and each phase triggers predictable disruptions of temperature and precipitation. |

Land Use

The human use of land; can include economic, cultural, and recreational activities. Source: Report on the Environment: Land Use |

Land Use Change

A process by which human activities transform the natural landscape. Often refers to how land has been used, with an emphasis on the functional role of land for economic activities. Source: Paul, B. K. and H. Rashid. (2017). Climatic Hazards in Coastal Bangladesh, Elsevier Inc., via ScienceDirect

Linear Models

Mathematical equation that describes the relationship between two or more quantities as showing a constant rate of change. Shown as: y = a*x1 + b*x2 + c*x3 + ... Source: Linear Models |


Meteorological Drought

A lack of precipitation over an extended period of time (usually a season or more), resulting in a water shortage. Source: Drought Types |


The local climate of a small site or habitat. Source: Microclimate |


Native Species

A species or lower taxon living within its natural range (past or present) including the area which it can reach and occupy using its natural dispersal systems. Source: Native Species |

Natural Resources

Anything naturally occurring that has a beneficial use for humans, including economic, nutritional, recreational, aesthetic, and other benefits.

Non-native Species

Any species that occurs outside its native range as a result of deliberate or accidental introduction by humans. Source: Non-native Species |


Ocean Acidification

Decrease in the pH (that is, increase in acidity) of ocean waters as a result of the increase in atmospheric carbon dioxide concentration.



The study of Earth's climate during the entire history of the Earth. Paleoclimate research uses geologic and biologic evidence (climate proxies) preserved in sediments, rocks, tree rings, corals, ice sheets, and other climate archives to reconstruct past climate in terrestrial and aquatic environments around the world. Paleoclimate reconstructions help us understand what ancient climate and ecosystems looked like.
Paleoclimate Archives and Proxies

Paleoclimate Archives

Geologic (e.g., sediment cores) and biologic (e.g., tree rings) materials that preserve evidence of past changes in climate.
Paleoclimate Archives and Proxies

Paleoclimate Proxies

Physical, chemical, and biological materials preserved within the geologic record (i.e. in paleoclimate archives) that can be analyzed and correlated with climate or environmental parameters in the modern world.

Peak Flow

The maximum rate of discharge during the period of runoff caused by a storm. Source: Peak Flow: Definition and Factors Affecting It |
Ice-rich permafrost bluffs on the bank of the Canning River, Alaska


Any ground that remains completely frozen—32°F (0°C) or colder—for at least two years straight. These permanently frozen grounds are commonly found in regions with high mountains and near the North and South Poles. Source: What is Permafrost? | NASA Climate Kids


The study of plant and animal seasonal cycles (e.g., when plants bloom, animal mating seasons, the timing of migration or hibernation, etc.).
Image: Prescribed Burn

Prescribed Fire

Also known as prescribed burns or controlled burns, they refer to the controlled application of fire by a team of fire experts under specified weather conditions to restore health to ecosystems that depend on fire. Source: Prescribed Fire |


Range Shift

A change in where a species lives. Can result in the species occupying a larger area than before (range expansion), a smaller area (range contraction), or moving to a new location altogether.
Groundwater flow showing natural conditions


The process of adding water to an aquifer. Occurs when precipitation falls on the land surface, infiltrates the soil, and moves through the ground and to the aquifer.

Representative Concentration Pathways

Models predicting future greenhouse gas concentrations, accounting for both natural sources and different potential levels of human emissions. These are frequently used in climate models to project future impacts of climate change. Source:
brown colored stream flowing through green brush with evergreens in background


Lands that occur along the edges of rivers, streams, lakes, and other water bodies. Source: Riparian Zones—It’s all about the Water |


Excess water that flows across the surface of the land and into nearby water bodies. Runoff occurs when there is more water than the land can absorb, and can result from both natural processes (i.e., rainstorms) and human activity (i.e., irrigation).


4 diagrams each show 100 red and blue verticle color stripes representing the average max temperature in Wind Cave National Park

Scenario Planning

A tool to facilitate decision making given uncertain future conditions. In this process, users consider the effects of different plausible future conditions (e.g., future climate conditions) on resources of value and how these impacts might affect management goals and activities.
View of a roadway on a tropical island with palm trees, the area is being overwashed by waves and flooded.

Sea Level Rise

An increase in the ocean’s surface height relative to the land in a particular location. Source: Sea Level Rise |
sea ice in the Nares Strait

Sea ice

Ocean surface water that has frozen. Source: Sea Ice |

Snow Drought

A period of abnormally little snowpack for a specific time of year. Because snowpack acts as a natural reservoir, reduced snowpack storage can impact the amount of water available to communities and ecosystems. Source: What is Snow Drought |

Snow Water Equivalent

A measurement used by hydrologists and water managers to gage the amount of liquid water contained within the snowpack. It is equal to the amount of water that will be released from the snowpack when it melts. Source: What is Snow Water Equivalent |


A seasonal accumulation of slow-melting packed snow. Snowpack acts as a natural reservoir, providing water throughout drier times of the year. Source: Snowpack |


The interactions between humans and the environment

Socioeconomic Drought

Occurs when the demand for an economic good exceeds supply as a result of a weather-related shortfall in water supply. Source: Types of Drought |

Species Status Assessment

An analytical approach developed by the U.S. Fish & Wildlife Service to inform Endangered Species Act (ESA) decisions. Contains three parts: 1) Compilation of the best available information on the species' life history, habitat, and taxonomy; 2) Description of the current condition of the species’ habitat and demographics and probable explanations for past and ongoing changes in abundance and distribution; and 3) Forecast of the species’ response to probable future scenarios of environmental conditions and conservation efforts. Source: Species Status Assessment |

State Wildlife Action Plan

Plans developed by each state, territory, and the District of Columbia that serve as blueprints for conserving fish and wildlife and preventing species from becoming endangered. These plans identify and focus on Species of Greatest Conservation Need and address the full array of wildlife and wildlife-related issues within the state/territory. Source: State Wildlife Action Plans |
Image taken by USGS scientists on Madeira Beach, Florida, during a winter storm event.

Storm Surge

Coastal high water level caused by wind from storms.
River flowing quickly, mountains in the background and streamgage shadow in foreground


The amount of water flowing in a stream or river.


Allen Bondurant measuring the depth to permafrost along a thermokarst lake shore.


A landscape produced by the uneven melting of permafrost that produces irregular surfaces of small hills interspersed with hollows.


The point that must be exceeded for a certain reaction, phenomenon, result, or condition to occur. In a climate context, this could refer to a biological threshold (aka ecological threshold), which is the point at which minor changes in climatic conditions produce disproportionately large and undesirable responses in species or ecosystems. Source: NE CASC Holds "Biological Thresholds" Workshop |

Tipping Point

A critical threshold that, when exceeded, leads to large and often irreversible changes to the system. Source: Tipping Point in the Climate System |

Traditional Knowledge

The knowledge, innovations, and practices of Indigenous and local communities around the world. Developed from experience gained over time immemorial and adapted to the local culture and environment, Traditional Knowledge (TK) is transmitted orally from generation to generation. Source: Definitions of Traditional Knowledge |



Any departure from complete deterministic knowledge of a system. In climate science, specifically refers to ways in which climate projections may diverge from actual, observed climate conditions. Uncertainty in this context is caused by natural variation in climate conditions, incomplete knowledge of the climate system, and/or inherent unknowns in trying to predict the future.
Image: White-Tailed Deer (Odocoileus virginianus)


A hoofed, and typically herbivorous, four-legged mammal such as deer, elephants, horses, etc. Source: Ungulate |


Vulnerability Assessment

A process that seeks to understand the degree to which species, resources, ecosystems, or other features of interest are susceptible to climate change. Includes an analysis of the nature, magnitude, and variability of climate change that the system is exposed to, its sensitivity to changes, and its capacity to adapt to the new climate conditions. Source: Climate Change Vulnerability Assessments |


Components of a simple water budget for part of a watershed


An area of land that channels rainfall and snowmelt to creeks, streams, and rivers, and eventually flows out to places such as reservoirs, bays, and the ocean. Source: Watershed |


The state of the atmosphere at a given point in time and geographic location. Source: Weather and atmosphere |
Fire in Lolo National Forest, Montana


An unplanned fire caused by lightning or other natural causes, by accidental (or arson-caused) human ignitions, or by an escaped prescribed fire. Source: Wildland Fire Program |

Wildland Fire 

An overarching term describing any fire that occurs in vegetation and natural fuels. Wildland fire encompasses both prescribed fire and wildfire. |