Climate

The Forest Service is a steward of many of our nation's most treasured landscapes, and within those landscapes are resources that people need and want, such as clean air and water, recreational opportunities and forest products. Impacts from increasing climate variability, extreme weather, and other disturbances – along with changing human demands – challenge our ability to ensure that ecosystems are healthy, resilient, and thus more adaptable to changing conditions. The Office of Sustainability and Climate supports national forests and grasslands with the tools, training, and resources they need to build resiliency into their landscapes in the face of a changing climate.


Historical and Projected Climate Datasets:

The National Forest Climate Change Maps project provides information on projected climate changes at a scale relevant to decision-making process, including forest plans to meet the needs of national forest managers. The maps use the best available science and are available for every national forest with relevant data coverage. The datasets include variables related to precipitation and air temperature, for both historical data and future projections. These datasets were created using 20-model averages of downscaled climate data from MACA-v2METDATA (https://climate.northwestknowledge.net/MACA/) in the contiguous United States, and from SNAP (the Scenarios Network for Alaska and Arctic Planning, https://snap.uaf.edu) datasets in Alaska, where available.

Temperature: Average annual, summer (June-August), and winter (November-March) temperature in the contiguous United States and Alaska, for the historical (1975-2005) and future (2071-2090, RCP 8.5) time periods, and for the absolute change between these. Download; metadata

Precipitation: Average annual, summer (June-August), and winter (November-March) precipitation in the contiguous United States and Alaska, for the historical (1975-2005) and future (2071-2090, RCP 8.5) time periods, and for the absolute and percent change between these. Download; metadata

Snow residence time: Average snow residence time in the contiguous United States, for the historical (1975-2005) and future (2071-2090, RCP 8.5) time periods, and for the absolute and percent change between these. Snow residence time is the estimated number of days between snow accumulation and snow melt. Download; metadata

Snow water equivalent: Average snow water equivalent on April 1st in the contiguous United States, for the historical (1975-2005) and future (2071-2090, RCP 8.5) time periods, and for the absolute and percent change between these. Snow water equivalent is the depth of snow if melted, in mm. Download; metadata

Frost-free days: Average length of the frost-free season in the contiguous United States, for the historical (1975-2005) and future (2071-2090, RCP 8.5) time periods, and for the absolute change between these. Download; metadata

Date of freeze: Average date of freeze (that is, the first day that temperatures drop below zero, ending the annual frost-free season) in the contiguous United States, for the historical (1975-2005) and future (2071-2090, RCP 8.5) time periods, and for the absolute change between these. Download; metadata

Date of thaw: Average date of thaw (that is, the first day that temperatures do not drop below zero at the beginning the annual frost-free season) in the contiguous United States, for the historical (1975-2005) and future (2071-2090, RCP 8.5) time periods, and for the absolute change between these. Download; metadata

Wetting rain days: Absolute change in the average number of wetting rain days (≥0.1 inch [2.54 mm] of precipitation) between the historical (1975-2005) and future (2071-2090, RCP 8.5) time periods in the contiguous United States, for the months of April, May, June, July, August, September, April-June, and May-September. Download; metadata

10-Year Drought: Once-in-a-decade drought, as measured by the number of consecutive days without wetting rain (0.1 inch [2.54 mm] of precipitation) in a summer (May-Sept) in the contiguous United States, for the historical (1975-2005) and future (2071-2090, RCP 8.5) time periods, and for the absolute and percent change between these. This was found by counting the number of days in the longest stretch of consecutive dry days in a summer, repeating this for each year, then calculating the 90th percentile value from this series. Download; metadata

Heat stress index: Heat stress index (HSI), the average number of days per year when the temperature-humidity index (a function of temperature and relative humidity) exceeds the recommended threshold for beef cattle, for the historical (1975-2005) and future (2071-2090, RCP 8.5) time periods, and for the absolute and percent change between these, in the contiguous United States. For more information about these methods, see Reeves and Bagne 2016. Download; metadata


Historical Temperature Trends:

TopoWx ("Topography Weather") temperature data were used to compare historical temperature for two time periods; this dataset provides improved historical temperature data, as compared with other gridded temperature datasets. This dataset represents the average temperature in the contiguous United States in 1948-1968 and 1996-2016, and the absolute change between these. For more information about TopoWx, see http://www.scrimhub.org/resources/topowx/.

Historical temperature: Download; metadata


Drought and Flood Datasets:

Moisture Difference Z-Score 1900-2018
The Moisture Deficit and Surplus map uses moisture difference z-score datasets developed by scientists Frank Koch, John Coulston, and William Smith of the Forest Service Southern Research Station. A z-score is a statistical method for assessing how different a value is from the mean (average). Mean moisture values were derived from historical data on precipitation and potential evapotranspiration, from 1900 to 2018, for the contiguous United States. The greater the z-value, the larger the departure from average conditions, indicating larger moisture deficits or surpluses. Thus, the higher valued areas on these maps indicate a one-, three-, or five-year period with extremely dry or extremely wet conditions, relative to the average conditions over the past century. For further reading on the methodology used to build these maps, click here to access the publication. These data are also featured in the annual national forest health monitoring reports. To analyze changes over time within national forest lands, see the Moisture-Difference Z-Score Drought Summary Tool. Click on a link below for the zipped raster sets for each time period as well as the metadata for each.