Variable: Snow water equivalent

Variable ID: swe

On This Page:

• Identification Information
• Entity and Attribute Information
• Explore Further - Analyses and Findings

Identification Information:

Citation:

Citation Information:

Originator:U.S. Geological Survey

Publication Date:2026

Title:USGS National Water Availability Assessment Data Companion website

Geospatial Data Presentation Form:Digital datasets

Online Linkage:https://water.usgs.gov/nwaa-data/data-file-directory?path=data/water-quantity/wqn-nhmprms-conus-nwaa-v1/swe/

Larger Work Citation(s):

Citation Information:

Originator:Foks, S.S., LaFontaine, J.H., McDonald, R.R., Snyder, A.M., Staub, L.E., Kolb, K.R., LaMotte, A.E., and Viger, R.J.

Publication Date:2024-12-18

Title:Monthly twelve-digit hydrologic unit code aggregations of the National Hydrologic Model Precipitation-Runoff Modeling System version 1.1 forced with CONUS404-BA, 1980-2021 (version 2.0, April 2025)

Geospatial Data Presentation Form:Digital datasets

Online Linkage:https://doi.org/10.5066/P14C5YAP

Publisher:U.S. Geological Survey – ScienceBase

Origin File:huc12_monthly_nhmprms_conus404ba_1980_2021.nc

Origin Variable:nhm_pkwater_equiv_post

Citation Information:

Originator:Regan, R.S., Juracek, K.E., Hay, L.E., Markstrom, S.L., Viger, R.J., Driscoll, J.M., LaFontaine, J.H. and Norton, P.A.

Publication Date:2018-10-31

Title:The U. S. Geological Survey National Hydrologic Model infrastructure: Rationale, description, and application of a watershed-scale model for the conterminous United States

Geospatial Data Presentation Form:Digital datasets

Online Linkage:https://doi.org/10.1016/j.envsoft.2018.09.023

Publisher:Environmental Modelling & Software

Description:

Name:Snow water equivalent

Variable ID:swe

Units:Millimeters (mm)

Summary:

Snow water equivalent (SWE) is the depth of water stored in the snowpack in both liquid and solid forms. Here SWE describes the equivalent depth of liquid water stored on each modeled hydrologic response unit (HRU) as snowpack for each day of the simulation. These daily HRU-based values are then temporally aggregated to monthly time steps and spatially transferred to the 12-digit hydrologic units (HUC12s) for the conterminous United States. This variable is calculated with simulated output from the National Hydrologic Model Application of the Precipitation-Runoff Modeling System.

Technical Description:

A national application of the USGS Precipitation-Runoff Modeling System (PRMS) (Leavesley et al., 1983; Markstrom et al., 2015) was developed using the USGS NHM infrastructure (Regan et al., 2018; Regan et al., 2019). This particular configuration of the NHM-PRMS applied for the CONUS used the Geospatial Fabric for National Hydrologic Modeling version 1.1 (Bock et al., 2020) for modeling units, the WRF-based atmospheric forcing dataset CONUS404-BA (Zhang et al., 2024), and the final parameter database provided in Markstrom et al. (2024).

The PRMS is a process-based, distributed-parameter, daily time step hydrologic simulation code which simulates hydrologic response to various combinations of atmospheric forcings, such as air temperature and precipitation, and landscape characteristics. This application of the PRMS was calibrated using the multi-step process described in Hay et al. (2023). Version 5.2.1 (doi: 10.5066/P9LVUWDC) of the PRMS code was used for this application of the NHM-PRMS.

The Geospatial Fabric for National Hydrologic Modeling (GF) version 1.1 was developed by aggregating NHDPlus version 1 catchments and flowlines for the CONUS, and NHDPlus high-resolution catchments and flowlines for those HUC4 spatial units that cross the Canadian border where NHDPlus version 1 did not have acceptable catchment resolution.

Atmospheric forcings of air temperature and precipitation from the CONUS404-BA dataset were used for this application of the NHM-PRMS. The hourly time step, 1-kilometer gridded variables of air temperature and precipitation from CONUS404-BA were temporally transformed into daily maximum and minimum air temperature and daily precipitation accumulation, and then spatially mapped to the GF v1.1 modeling units, for use in this NHM-PRMS application.

Parent Model:

Name:Hydrologic Model (NHM-PRMS, CONUS NWAA v1)

Model ID:wqn-nhmprms-conus-nwaa-v1

Time Period of Content:

Time Period Information:

Range of Dates/Times:

Start Year/Month:198301

End Year/Month:202109

Status:

Scenario:Historical

Spatial Domain:

Description of Geographic Extent:Lower 48 United States

Bounding Coordinates:

West Bounding Coordinate:-126.0

East Bounding Coordinate:-66.2

North Bounding Coordinate:49.7

South Bounding Coordinate:24.4

Geospatial Data Needed to Map Output:

Description of Spatial Resolution:12-digit hydrologic unit codes

Citation Information:

Title:October 2020 version of the Watershed Boundary Dataset

Online Linkage:https://www.sciencebase.gov/catalog/item/67082a0fd34e969edc5a1cca

Entity and Attribute Information:

Detailed Description:

Entity Type:

Entity Type Label:swe_historical_CONUS_198301-202109_describe.txt

Entity Type Definition:

Text (txt) file containing summary information for the dataset. For each metric (huc12_id, year_month, and swe_mm) it provides the total number of dataset observations, the number of distinct values, and various summary statistics.

Entity Type Definition Source:Producer defined

Entity Type:

Entity Type Label:swe_historical_CONUS_198301-202109_histogram.png

Entity Type Definition:

Portable Network Graphics (PNG) file containing a histogram showing the distribution of data values in the dataset, with values measured in millimeters on the x-axis and the number of occurrences of those values on the y-axis.

Entity Type Definition Source:Producer defined

Entity Type:

Entity Type Label:swe_historical_CONUS_198301-202109_long.csv

Entity Type Definition:

Comma Separated Value (CSV) file containing data for the 1983-2021 period by 12-digit hydrologic unit code (HUC12) and month and year for the Lower 48 United States. The first row is a header row and the data start on the second row. The first column is the 12-digit hydrologic unit code (HUC12) identifier (huc12_id) and the second column is the year and month (year_month). The third column contains the variable data, in millimeters (swe_mm).

Entity Type Definition Source:Producer defined

Entity Type:

Entity Type Label:swe_wqn-nhmprms-conus-nwaa-v1_CONUS_200910-202009_mean_map_1920x1080.png

Entity Type Definition:

Portable Network Graphics (PNG) file containing a map showing snow water equivalent in millimeters averaged from 2009-10 to 2020-09 by 12-digit hydrologic unit code (HUC12) for the Lower 48 United States. This is a 1920x1080 map image with information on the source model and map creation date, as well as a link to the associated data.

Entity Type Definition Source:Producer defined

Entity Type:

Entity Type Label:swe_wqn-nhmprms-conus-nwaa-v1_CONUS_200910-202009_mean_map_4800x2700.png

Entity Type Definition:

Portable Network Graphics (PNG) file containing a map showing snow water equivalent in millimeters averaged from 2009-10 to 2020-09 by 12-digit hydrologic unit code (HUC12) for the Lower 48 United States. This is a 4800x2700 map image with information on the source model and map creation date, as well as a link to the associated data.

Entity Type Definition Source:Producer defined

Entity Type:

Entity Type Label:swe_historical_CONUS_198301-202109_wide.csv

Entity Type Definition:

Comma Separated Value (CSV) file containing data for the 1983-2021 period by month and year for the Lower 48 United States. The first row is a header row and the data start on the second row. The first column is the year and month (year_month). All following columns represent an individual 12-digit hydrologic unit code (HUC12), where the values are the variable data, in millimeters.

Entity Type Definition Source:Producer defined

Explore Further - Analyses and Findings:

National Water Availability Assessment Report Chapter(s):

Chapter:

Title:Chapter A: Executive Summary

Description:

Chapter A introduces the National Water Availability Assessment and provides important background and definitions for how the report characterizes water availability and its components. This chapter also presents the key findings of Chapters B-F and thus acts as a summary of the entire report. The sidebars presented in Chapter A provide context for the datasets and citations that are used throughout the report.

Online Linkage:https://doi.org/10.3133/pp1894A

Chapter:

Title:Chapter B: National Water Supply

Description:

Chapter B (Gorski and others, 2025) is a national assessment of water supply, which is defined as the quantity of water supplied through climatic inputs. The water supply analysis in this chapter includes precipitation (snow or rain), streamflow, soil moisture, snow water equivalent (snowpack), and groundwater levels. This analysis outlines the annual average input and output of water in the U.S. It also includes an assessment of hydrologic regions of the U.S. that have experienced shortages in water supply components between 2010 and 2020, compared to historical conditions.

Online Linkage:https://doi.org/10.3133/pp1894B

Chapter:

Title:Chapter F: Integrated Water availability

Description:

The National Water Availability Assessment Report culminates with Chapter F (Stets and others, 2025), which is an integrated assessment of water availability. A comprehensive description of water availability requires consideration of multiple aspects, such as the amount and conditions of water (quantity and quality), along with the sensitivity of users to those conditions. This chapter uses information from the assessments of water supply, quality, and use to create a more integrated investigation of water availability across CONUS. This investigation includes the use of an index referred to as the surface water-supply and use index (SUI), which determines the relative stress from potential imbalances between water supply and water use.

Online Linkage:https://doi.org/10.3133/pp1894F