The maps and graphs in this summary describe national streamflow conditions for water year 2019 (October 1, 2018, to September 30, 2019) in the context of streamflow ranks relative to the 90-year period of water years 1930–2019, unless otherwise noted. The illustrations are based on observed data (U.S. Geological Survey, 2020a) from the U.S. Geological Survey (USGS) National Streamgage Network (U.S. Geological Survey, 2020b). The period of water years 1930–2019 was evaluated because the number of streamgages in the network before 1930 was too small to provide statistically significant data to compute meaningful statistics in most regions of the country.
In the summary, reference is made to the term “runoff,” which is defined as the amount of water flowing through a stream divided by the drainage basin area of the stream. The value of runoff quantifies the magnitude of water flowing through the Nation’s rivers and streams in measurement units that can be compared from one area to another. In this summary, runoff for a specified period and geographic area is computed from all streamgages with complete streamflow records in the geographic area.
In all the graphics, a rank of 1 indicates the maximum annual flow of all years analyzed and a rank of 90 indicates the minimum annual flow of all years. Rankings of streamflow are grouped into much below normal, below normal, normal, above normal, and much above normal categories based on percentiles of flow (less than 10 percent, 10–24 percent, 25–75 percent, 76–90 percent, and greater than 90 percent, respectively; U.S. Geological Survey, 2020c). Streamflow conditions for States or water-resources regions are presented in the text in order of ranking from maximum to minimum flow; a maximum or minimum flow rank is not shown when there are ties in the rankings. Some of the data used to produce the maps and graphs are provisional and subject to change.
Annual runoff in the Nation’s rivers and streams during water year 2019 (13.62 inches) was much greater than the long-term (1930–2019) mean annual runoff of 9.37 inches for the contiguous United States (fig. 1). Nationwide, the 2019 streamflow ranked the highest out of the 90 years.
Streamflow was much below normal only in Washington (fig. 2). Streamflow was below normal in Alaska, Hawaii, and Oregon. Streamflow was above normal in Alabama, California, Georgia, Maine, Mississippi, Nevada, and Utah. Streamflow was much above normal in Arkansas, Connecticut, Delaware, District of Columbia, Iowa, Kentucky, Louisiana, Massachusetts, Missouri, New Hampshire, New York, North Carolina, North Dakota, Pennsylvania, Tennessee, Texas, Vermont, Virginia, and West Virginia. Record maximum streamflow was measured in Illinois, Indiana, Kansas, Maryland, Michigan, Minnesota, Nebraska, New Jersey, Ohio, Oklahoma, Rhode Island, South Dakota, and Wisconsin.
The United States, Puerto Rico, and the Virgin Islands are divided into 21 large drainages, or waterresources regions (fig. 3). These water-resources regions are based on surface topography and contain the drainage area of a major river; the combined drainage areas of a series of rivers, such as the Texas-Gulf region, which includes several rivers draining into the Gulf of Mexico; or the area of an island or island group. Water-resources regions provide a coherent, watershed-based framework for depicting streamflow variations.
Streamflow was ranked at below normal levels in the Alaska, Hawaii, and Pacific Northwest regions (fig. 4). Streamflow was ranked above normal in the California, Great Basin, Rio Grande, Souris-Red-Rainy, and South Atlantic-Gulf regions. Much above normal streamflow was ranked in the Lower Mississippi, New England, Tennessee, and Texas-Gulf regions. Record maximum streamflow was measured in the Arkansas-White-Red, Great Lakes, Mid-Atlantic, Missouri, Ohio, and Upper Mississippi regions.
The USGS operated a nationwide network of more than 8,200 streamgages in 2018, and almost all USGS streamgages are operated in real time. Current information derived from these streamgages is available at https:// waterwatch.usgs.gov. Tables of data that summarize historical streamflow conditions by State, expressed as runoff, beginning in water year 1901, can be accessed at https://waterwatch.usgs.gov/?id=statesum. These tables are updated every few months to reflect the most current streamflow data.
The streamflow information used to prepare this summary also is used for water management, flood and drought monitoring, bridge design, and several recreational activities. To obtain real-time and archived streamflow data and information, visit the USGS National Water Information System at https://doi.org/10.5066/F7P55KJN (U.S. Geological Survey, 2019c). The National Streamflow Network, which is part of the Groundwater and Streamflow Information Program, is operated primarily by the USGS; however, funding for operating the network is provided by the USGS and about 850 Federal, State, Tribal, regional, and local partners. Access additional streamflow information online at https://www.usgs.gov/ water-resources/groundwater-and-streamflow-information/ streamflow-monitoring?qt-science_support_page_related_ con=0#qt-science_support_page_related_con.
U.S. Geological Survey, 2020a, USGS water data for the Nation: U.S. Geological Survey National Water Information System database, accessed June 2020 at https://doi.org/ 10.5066/ F7P55KJN.
U.S. Geological Survey, 2020b, Groundwater and Streamflow Information Program: U.S. Geological Survey web page, accessed June 2020 at https://www.usgs.gov/ water- resources/ groundwater- and- streamflow- information.
U.S. Geological Survey, 2020c, Map of real-time streamflow compared to historical streamflow for the day of the year (United States): U.S. Geological Survey web page, accessed June 2020 at https://waterwatch.usgs.gov/ ? id= ww_ current.
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