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.

Figure 1. Annual runoff in the contiguous United States, water years 1930–2019.

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.

Figure 2. Statewide streamflow ranks of the United States for water year 2019 compared to water year 1930–2019 mean annual streamflow.[**For Puerto Rico and the Virgin Islands, 76 years of available data were used and the groupings of ranks were adjusted accordingly.]

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.

Figure 3. Water-resources regions.

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.

Regional streamflow ranks in the United States for water year 2019 compared to water year 1930–2019 mean annual streamflow[**For Puerto Rico and the Virgin Islands, 76 years of available data were used and the groupings of ranks were adjusted accordingly.]

Autumn (October–December 2018) streamflow was ranked much below normal in Colorado (fig. 5). Streamflow was ranked below normal in California, Oregon, and Utah. Above normal streamflow was ranked in Arkansas, Florida, Illinois, Mississippi, and Oklahoma. Much above normal streamflow was ranked in Alabama, Connecticut, Delaware, Georgia, Indiana, Kansas, Kentucky, Massachusetts, Michigan, Minne-sota, Nebraska, New Hampshire, New York, Ohio, South Carolina, South Dakota, Tennessee, Vermont, and West Virginia. Record maximum streamflow was measured in District of Columbia, Iowa, Louisiana, Maryland, New Jersey, North Carolina, Pennsylvania, Rhode Island, Texas, Virginia, and Wisconsin. Nationwide, autumn-season streamflow ranked the highest out of 90 years.

Autumn (October–December 2018) statewide ranks in the United States compared to water year 1930–2019 mean annual streamflow.[**For Puerto Rico and the Virgin Islands, 76 years of available data were used and the groupings of ranks were adjusted accordingly.]

Winter (January–March 2019) streamflow was ranked much below normal in Washington (fig. 6). Streamflow was ranked below normal in Idaho, Oregon, and Puerto Rico and the Virgin Islands. Above normal streamflow was ranked in Alabama, Arizona, California, Connecticut, Delaware, Georgia, Massachusetts, Mississippi, North Carolina, North Dakota, Oklahoma, Pennsylvania, Rhode Island, South Carolina, Texas, and West Virginia. Streamflow was ranked much above normal in Arkansas, District of Columbia, Illinois, Indiana, Kansas, Kentucky, Louisiana, Maryland, Missouri, New Jersey, Ohio, Tennessee, Virginia, and Wisconsin. Record maximum streamflow was measured in Iowa, Minnesota, Nebraska, and South Dakota. Nationwide, winter-season streamflow ranked second highest out of 90 years.

Figure 6. Winter (January–March 2019) statewide ranks in the United States compared to water year 1930–2019 mean annual streamflow.[**For Puerto Rico and the Virgin Islands, 76 years of available data were used and the groupings of ranks were adjusted accordingly.]

Spring (April–June 2019) streamflow was ranked much below normal in Hawaii and Washington (fig. 7). Below normal streamflow was ranked in Puerto Rico and the Virgin Islands. Above normal streamflow was ranked in California, Connecticut, Delaware, Kentucky, Maryland, Nevada, New Jersey, New York, North Carolina, North Dakota, Oregon, Rhode Island, and Utah. Streamflow was ranked much above normal in Arkansas, Indiana, Iowa, Louisiana, Maine, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, Ohio, Oklahoma, Pennsylvania, Texas, and Vermont. Record maximum streamflow was measured in Illinois, Kansas, Michigan, South Dakota, and Wisconsin. Nationwide, spring-season streamflow ranked second highest out of 90 years.

Figure 7. Spring (April–June 2019) statewide ranks in the United States compared to water year 1930–2019 mean annual streamflow.[**For Puerto Rico and the Virgin Islands, 76 years of available data were used and the groupings of ranks were adjusted accordingly.]

Summer (July–September 2019) streamflow was ranked much below normal in Alaska, Arizona, and Washington (fig. 8). Below normal streamflow was ranked in Alabama, Georgia, Hawaii, and South Carolina. Above normal streamflow was ranked in California, Iowa, Louisiana, Michigan, Mississippi, Nevada, Ohio, and Utah. Much above normal streamflow was ranked in Arkansas, Colorado, Illinois, Kansas, Minnesota, Missouri, Nebraska, North Dakota, Oklahoma, and Wisconsin. Record maximum streamflow was measured in South Dakota. Nationwide, summer-season streamflow ranked 14th highest out of 90 years.

Figure 8. Summer (July–September 2019) statewide ranks in the United States compared to water year 1930–2019 mean annual streamflow.[**For Puerto Rico and the Virgin Islands, 76 years of available data were used and the groupings of ranks were adjusted accordingly.]

Assuming individual streamgage data are independent of other streamgage data and are normally distributed, the average streamflow at 5 percent of the streamgages is expected to be high (greater than 95th percentile) and 5 percent is expected to be low (less than the 5th percentile) during any given month. The percentages of streamgages reporting high streamflow in all months of water year 2019 (October 2018–September 2019) were greater than expected (14, 22, 18, 11, 14, 8, 10, 15, 9, 7, 6, and 7 percent, respectively; fig. 9). In contrast, there were no months with a greater-than-expected percentage of streamgages reporting low flow.

Figure 9. Percentage of streamgages with high and low monthly streamflow, October 1999– September 2019.