The USGS streamflow monitoring network provides information about hydrologic responses to climate change. Three variables related to climate change are used to evaluate the network: the area of each NOAA climate division (ClimDiv); the area where minimum monthly mean temperature is below freezing (MinTempLT0), and the length of coastal streams (CoastalStreams). Network representation of each climate division is important because climate change affects all areas of the US. Areas where minimum monthly mean temperature is below freezing have the potential for a shift in precipitation from snow to rain or for earlier snowmelt. Coastal streams are likely to have increased flooding because of sea-level rise. Each variable is calculated for incremental gaged areas (IGAs) and, if available, 12-digit hydrologic unit code watersheds (HUC12). Changes in water availability and more extreme events (floods and drought) are likely responses to climate change across the US, but spatial variability in these responses across the US is not assessed as part of the network analysis.
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Three metrics are used to evaluate a monitoring network for each variable: coverage, resolution, and representation. The metrics are calculated from the cumulative distributions of the variables, shown below. Each metric varies from 0 to 1. Metrics are not displayed for multi-category variables (Climate Divisions, Ecoregions, Surficial Geology Types).
Coverage is the fraction of the total value of a variable that is found in areas that are monitored: 0 - none of the variable is in monitored areas; 1 - all of the variable is in monitored areas. Coverage can only be calculate for variables with known values outside of the monitoring network. .
Resolution indicates the deviation of the cumualtive distribution of IGA values from the mean IGA value: 0 - the value of a variable for monitored areas is concentrated entirely in one IGA, 1 - all IGAs have equal value (the mean IGA value of the variable). Resolution can only be calculated for spatially-conserved variables (count, length, area, volume, mass, or fluxes). The resolution of characteristics such as elevation, drainage area, temperature, or fraction of stream length or area with a designation or classification is based on either stream length or land surface area with the characteristic.
Representation indicates whether IGA values are evenly distributed among the decile intervals (0-10%, 10%-20%,...) of a benchmark distribution: 0 - all IGA values are outside the range of the benchmark distribution, 1 - 10% of IGAs are in each of the decile intervals of the benchmark distribution. Typically, HUC12s values are used for the benchmark distribution. If the HUC12 values are unknown, 10% intervals of the IGA range are used to calculate representation: ~0 - nearly all of the total value of a variable is in one interval of the range of values for IGAs, 1 - IGA values are linearly distributed (10% of IGAs are in each of intervals of the range of IGA values). Representation can be calculated for characteristics such as mean elevation or a percent of area in a land cover category, but they must be associated with a spatially-conserved variable such as stream length or land suraface area to create the distributions.
Network objectives can vary for different variables (for example, resolution of streamflow and representation of basin elevation) and should be considered when interpreting these metrics.
IGAs that are important for network coverage, resolution, or representations are designated as priorities to maintain monitoring sites. IGAs and HUC12 where additional gages would substantially improve network coverage, resolution, or representation are designated as priorities to add monitoring sites. IGAs are defined by upstream and downstream sites, so a site is a monitoring priority if it is at the upstream or downstream boundary of a priority IGA. The number of priorities IGAs is not a recommendation about the number of sites needed for monitoring. Indeed, a variable with few priority IGA simply indicates that there are a few areas of particularly high importantce for monitoring and that it may be possible to re-configure - but not eliminate - sites in non-priority IGAs without impacting network performance.
Priority designations are determined by applying consistent rules to the cumulative distributions of each variable. Generally priority areas have higher values of a variable but they may also be part of a variable's distribution that is not well represented by the monitoring network. The cumulative distributions shown for each variable include the specific criteria used for priority designations. Streamflow and material loads are not available for HUC12s, so HUC12s do not have priority designations for these variables. Ungaged areas (shown in the HUC12 layer as orange) can be considered as priorities to add gages for these variables.
Priority areas are not a network design. Network design including the total number of monitoring sites in the network and the specific locations for monitoring sites depends on the objectives and resources available for monitoring and considerations of access and safety. Priority designations are based on the USGS streamflow gaging network active in water year 2020 and could change as sites are added or removed from the network. Priority designations do not reflect legal requirements or local needs for streamflow information at specific locations. Any specific changes to a monitoring network should assess local information needs, access, and safety.
The map viewer has layers with monitoring sites, incremental gaged areas (IGAs), the priority designation of IGAs for individual variables, 12-digit hydrologic unit code watersheds (HUC12s), and the priority designations of HUC12s for individual variables.
Monitoring Sites: USGS gages active in water year 2020 with a pop-up link to the USGS Water Dashboard for each site
Incremental Gaged Areas: IGAs with the values of the variables for each IGA provided in a pop-up window. IGAs have a value of NA if the variable is not available.
IGA Priorities: priority designation of IGAs for each variable.
HUC12: HUC12 watersheds in the major river basin with the values of variables for each HUC12 provided in a pop-up window.
HUC12 Priorities: priority designation of HUC12s in the major river basin for each variable.
Boundaries of IGAs and HUC12s have been simplified for display in the map viewer.
IGAs often extend downstream of gages because they are delineated from National Hydrography Dataset catchments or Watershed Boundary Dataset HUC12s.
Pop-ups are only diplayed for the lowest active layer checked in the control box with data for the feature.
National maps can take a long time to render in the map viewer and only display ungaged HUC12s.
Ungaged areas (shown in orange on the HUC12 layer) are defined as HUC12s with less than half of their area upstream of a gage based on Watershed Boundary Dataset routing (https://www.usgs.gov/national-hydrography/watershed-boundary-dataset).
Data may be missing outside of CONUS where NHD catchments are not available.
Cumulative distributions are generated for each variable to evaluate the network and to identify priority areas for monitoring. Values of a variable for individual IGAs or HUC12s are shown on the horizontal axis. The vertical axis has cumulative values, area, or length depending on the type of variable. Priority areas for maintaining sites are plotted as open blue circles. Priority areas for adding sites are plotted as filled purple circles. The criteria for priority areas are listed at the bottom of each plot. The rules used to define the criteria depend on the type of variable. Missing plots indicate that the variable is not available. IGAs or HUC12 can be identified on the plots by hovering the cursor over a point. Axes can be adjusted with the cursor and reset using the menu at the top of the frame.
Cumulative distributions of the fraction of climate divisions comprised by IGAs that are predominately (more than 90% of their area) in the climate division, the area where mean annual minimum daily temperature is less than 0 C and the length of streams in coastal areas where sea-level rise may affect flooding for incremental gaged areas and 12-digit hydrologic unit code (HUC12) watersheds.
Image source: National Center for Environmental Information, https://www.ncei.noaa.gov/access/monitoring/reference-maps/conus-climate-divisions
Image source: National Center for Environmental Information, https://www.ncei.noaa.gov/access/monitoring/reference-maps/ak-climate-divisions
Alabama (01): 01 Northern Valley, 02 Appalachian Mountain, 03 Upper Plains, 04 Eastern Valley, 05 Piedmont Plateau, 06 Prairie, 07 Coastal Plain, 08 Gulf
Arizona (02): 01 Northwest, 02 Northeast, 03 North Central, 04 East Central, 05 Southwest, 06 South Central, 07 Southeast
Arkansas (03): 01 Northwest, 02 North Central, 03 Northeast, 04 West Central, 05 Central, 06 East Central, 07 Southwest, 08 South Central, 09 Southeast
California (04): 01 North Coast Drainage, 02 Sacramento Drainage, 03 Northeast Interior Basins, 04 Central Coast Drainage, 05 San Joaquin Drainage, 06 South Coast Drainage, 07 Southeast Desert Basins
Colorado (05): 01 Arkansas Drainage, 02 Colorado Drainage, 03 Kansas Drainage, 04 Platte Drainage, 05 Rio Grande Drainage
Connecticut (06): 01 Northwest, 02 Central, 03 Coastal
Delaware (07): 01 Northern, 02 Southern
Florida (08): 01 Northwest, 02 North, 03 North Central, 04 South Central, 05 Everglades and Southwest Coast, 06 Lower East Coast, 07 Keys
Georgia (09): 01 Northwest, 02 North Central, 03 Northeast, 04 West Central, 05 Central, 06 East Central, 07 Southwest, 08 South Central, 09 Southeast
Idaho (10): 01 Panhandle, 02 North Central Prairies, 03 North Central Canyons, 04 Central Mountains, 05 Southwestern Valleys, 06 Southwestern Highlands, 07 Central Plains, 08 Northeastern Valleys, 09 Upper Snake River Plains, 010 Eastern Highlands
Illinois (11): 01 Northwest, 02 Northeast, 03 West, 04 Central, 05 East, 06 West Southwest, 07 East Southeast, 08 Southwest, 09 Southeast
Indiana (12): 01 Northwest, 02 North Central, 03 Northeast, 04 West Central, 05 Central, 06 East Central, 07 Southwest, 08 South Central, 09 Southeast
Iowa (13): 01 Northwest, 02 North Central, 03 Northeast, 04 West Central, 05 Central, 06 East Central, 07 Southwest, 08 South Central, 09 Southeast
Kansas (14): 01 Northwest, 02 North Central, 03 Northeast, 04 West Central, 05 Central, 06 East Central, 07 Southwest, 08 South Central, 09 Southeast
Kentucky (15): 01 Western, 02 Central, 03 Blue Grass, 04 Eastern
Louisiana (16): 01 Northwest, 02 North Central, 03 Northeast, 04 West Central, 05 Central, 06 East Central, 07 Southwest, 08 South Central, 09 Southeast
Maine (17): 01 North, 02 South Interior, 03 Coastal
Maryland (18): 01 Southeastern Shore, 02 Central Eastern Shore, 03 Lower Southern, 04 Upper Southern, 05 Northeastern Shore, 06 North Central, 07 Appalachian Mountains, 08 Allegheny Plateau
Massachusetts (19): 01 West, 02 Central, 03 Coastal
Michigan (20): 01 West Upper, 02 East Upper, 03 Northwest Lower, 04 Northeast Lower, 05 West Central Lower, 06 Central Lower, 07 East Central Lower, 08 Southwest Lower, 09 South Central Lower, 010 Southeast Lower
Minnesota (21): 01 Northwest, 02 North Central, 03 Northeast, 04 West Central, 05 Central, 06 East Central, 07 Southwest, 08 South Central, 09 Southeast
Mississippi (22): 01 Upper Delta, 02 North Central, 03 Northeast, 04 Lower Delta, 05 Central, 06 East Central, 07 Southwest, 08 South Central, 09 Southeast, 010 Coastal
Missouri (23): 01 Northwest Prairie, 02 Northeast Prairie, 03 West Central Plains, 04 West Ozarks, 05 East Ozarks, 06 Bootheel
Montana (24): 01 Western, 02 Southwestern, 03 North Central, 04 Central, 05 South Central, 06 Northeastern, 07 Southeastern
Nebraska (25): 01 Panhandle, 02 North Central, 03 Northeast, 05 Central, 06 East Central, 07 Southwest, 08 South Central, 09 Southeast
Nevada (26): 01 Northwestern, 02 Northeastern, 03 South Central, 04 Extreme Southern
New Hampshire (27): 01 North, 02 South
New Jersey (28): 01 Northern, 02 Southern, 03 Coastal
New Mexico (29): 01 Northwestern Plateau, 02 Northern Mountains, 03 Northeastern Plains, 04 Southwestern Mountains, 05 Central Valley, 06 Central Highlands, 07 Southeastern Plains, 08 Southern Desert
New York (30): 01 Western Plateau, 02 Eastern Plateau, 03 Northern Plateau, 04 Coastal, 05 Hudson Valley, 06 Mohawk Valley, 07 Champlain Valley, 08 St Lawrence Valley, 09 Great Lakes, 01 Central Lakes
North Carolina (31): 01 Southern Mountains, 02 Northern Mountains, 03 Northern Piedmont, 04 Central Piedmont, 05 Southern Piedmont, 06 Southern Coastal Plain, 07 Central Coastal Plain, 08 Northern Coastal Plain
North Dakota (32): 01 Northwest, 02 North Central, 03 Northeast, 04 West Central, 05 Central, 06 East Central, 07 Southwest, 08 South Central, 09 Southeast
Ohio (33): 01 Northwest, 02 North Central, 03 Northeast, 04 West Central, 05 Central, 06 Central Hills, 07 Northeast Hills, 08 Southwest, 09 South Central, 10 Southeast
Oklahoma (34): 01 Panhandle, 02 North Central, 03 Northeast, 04 West Central, 05 Central, 06 East Central, 07 Southwest, 08 South Central, 09 Southeast
Oregon (35): 01 Coastal Area, 02 Willamette Valley, 03 Southwestern Valleys, 04 Northern Cascades, 05 High Plateau, 06 North Central, 07 South Central, 08 Northeast, 09 Southeast
Pennsylvania (36): 01 Pocono Mountains, 02 East Central Mountains, 03 Southeastern Piedmont, 04 Lower Susquehanna, 05 Middle Susquehanna, 06 Upper Susquehanna, 07 Central Mountains, 08 South Central Mountains, 09 Southwest Plateau, 10 Northwest Plateau
Rhode Island (37): 01 Rhode Island
South Carolina (38): 01 Mountain, 02 Northwest, 03 North Central, 04 Northeast, 05 West Central, 06 Central, 07 Southern
South Dakota (39): 01 Northwest, 02 North Central, 03 Northeast, 04 Black Hills, 05 Southwest, 06 Central, 07 East Central, 08 South Central, 09 Southeast
Tennessee (40): 01 Eastern, 02 Cumberland Plateau, 03 Middle, 04 Western
Texas (41): 01 High Plains, 02 Low Rolling Plains, 03 North Central, 04 East Texas, 05 Trans Pecos, 06 Edwards Plateau, 07 South Central, 08 Upper Coast, 09 South, 10 Lower Valley
Utah (42): 01 Western, 02 Dixie, 03 North Central, 04 South Central, 05 Northern Mountains, 06 Uinta Basin, 07 Southeast
Vermont (43): 01 Northeastern, 02 Western, 03 Southeastern
Virginia (44): 01 Tidewater, 02 Eastern Piedmont, 03 Western Piedmont, 04 Northern, 05 Central Mountain, 06 Southwestern Mountain
Washington (45): 01 West Olympic Coast, 02 North East Olympic San Juan, 03 Puget Sound Lowlands, 04 East Olympic Cascade Foothills, 05 Cascade Mountains West, 06 East Slope Cascades, 07 Okanogan Big Bend, 08 Central Basin, 09 Northeastern, 10 Palouse Blue Mountains
West Virginia (46): 01 Northwestern, 02 North Central, 03 Southwestern, 04 Central, 05 Southern, 06 Northeastern
Wisconsin (47): 01 Northwest, 02 North Central, 03 Northeast, 04 West Central, 05 Central, 06 East Central, 07 Southwest, 08 South Central, 09 Southeast
Wyoming (48): 01 Yellowstone Drainage, 02 Snake Drainage, 03 Green and Bear Drainage, 04 Big Horn, 05 Powder, Little Mo and Tongue Drainages, 06 Belle Fourche Drainage, 07 Cheyenne Niobrara Drainage, 08 Lower Platte, 09 Wind River, 10 Upper Platte
Alaska (49): 01 North Slope, 02 West Coast, 03 Central Interior, 04 Northeast Interior, 05 Southeast Interior, 06 Cook Inlet, 07 Bristol Bay, 08 Northwest Gulf, 09 Northeast Gulf, 10 North Panhandle, 11 Central Panhandle, 12 South Panhandle, 13 Aleutians
Konrad, C.P., Anderson, S.W., Restivo, D.E., and David, J.E., 2022, Network Analysis of USGS Streamflow Gages, U.S. Geological Survey Data Release, accessed on August 26, 2022 at https://doi.org/10.5066/P9C8NYTO.
National Oceanic and Atmospheric Administration, 2020, Climate Divisions, accessed on December 21, 2020 at ftp://ftp.ncdc.noaa.gov/pub/data/cirs/climdiv/.
Wieczorek, M.E., Jackson, S.E., and Schwarz, G.E., 2018, Select Attributes for NHDPlus Version 2.1 Reach Catchments and Modified Network Routed Upstream Watersheds for the Conterminous United States (ver. 3.0, January 2021): U.S. Geological Survey data release, accessed on June 16, 2022 at https://doi.org/10.5066/F7765D7V.