This U.S. Geological Survey summary describes the nation's streamflow in water year 2015 (October 1, 2014, to September 30, 2015) against the 86 years from 1930 to 2015, using data from the USGS National Streamflow Information Program. Earlier years are left out because before 1930 there were too few streamgages to represent most regions.
- Runoff is how deep water would stand over an area if all the streamflow in a period were spread evenly across it — a measure that can be compared between places.
- A rank of 1 is the highest flow of all the years. Ranks are grouped by percentile of flow: much below normal (below 10 percent), below normal (10–24), normal (25–75), above normal (76–90) and much above normal (above 90).
- Some of the data are provisional.
The nation
Average runoff in 2015 was 9.07 inches, very close to the 1930–2015 mean of 9.29 inches for the contiguous United States. Nationwide, 2015 ranked 51st of 86 years. (Summaries before 2011 compared median, not average, runoff.)
Annual U.S. runoff, 1930–2015; the horizontal line is the mean, 9.29 inches. USGS.
The states
2015 streamflow rank by state, 1930–2015 (1 = highest, 86 = lowest). Puerto Rico–Virgin Islands was ranked on 72 years of data. USGS.
| Streamflow | States |
|---|---|
| Record low | Alaska |
| Much below normal | California, Nevada, Puerto Rico–Virgin Islands |
| Below normal | Oregon, Idaho, Arizona, South Carolina, North Carolina, Rhode Island |
| Above normal | South Dakota, Iowa, Nebraska, Arkansas, Kentucky, Illinois, Oklahoma, Missouri |
| Much above normal | Texas, Indiana |
Most states were in the normal range.
The regions
The country (with Puerto Rico–Virgin Islands in the Caribbean region and the District of Columbia in the Mid-Atlantic) is divided into 21 water-resources regions, each the basin of a major river such as the Columbia, a group of rivers such as those of the Texas-Gulf region, or an island group. In 2015 the Alaska region hit a record low; California, Great Basin and Caribbean were much below normal; Pacific Northwest and Lower Colorado below normal; Upper Mississippi, Ohio and Arkansas-White-Red above normal; and Texas-Gulf much above normal.
The seasons
| Season | National rank (of 86) | Notable |
|---|---|---|
| Autumn (Oct–Dec 2014) | 41st | Alaska much below normal; Texas and Puerto Rico–Virgin Islands below; ten states above |
| Winter (Jan–Mar 2015) | 67th | New York, California and Hawaii much below normal; twelve states below; Montana much above |
| Spring (Apr–Jun 2015) | 4th | record lows in Oregon and Washington; much below in California, Arizona, Nevada, Idaho, Alaska and Puerto Rico–Virgin Islands; above and much above across twelve central and southern states and the District of Columbia |
| Summer (Jul–Sep 2015) | 22nd | record lows in Washington and Puerto Rico–Virgin Islands; much below or below across the West and Southeast; much above in Arkansas, Hawaii, Oklahoma, Illinois, Iowa, Missouri, Indiana and Kentucky |
Very high and very low flows
In any month, about 5 percent of streamgages would be expected to record very high flow (above the 95th percentile) and 5 percent very low (below the 5th). In 2015, May, June and July had more than the expected share of very high flows (6, 11 and 13 percent), while all eight months from February through September had more than the expected share of very low flows (7, 8, 8, 12, 8, 8, 7 and 6 percent).
Share of streamgages with very high (blue) and very low (red) monthly flow, October 1999–September 2015. USGS.
The network
The USGS runs about 8,100 streamgages nationwide, reporting almost in real time on WaterWatch; historical summaries by state go back to 1900. The data serve water management, flood and drought monitoring, bridge design and recreation. The network is operated mainly by the USGS and funded with about 850 federal, state, tribal, regional and local partners.
Sources
- Xiaodong Jian, David M. Wolock, Harry F. Lins and Steve Brady, Streamflow of 2015 — Water Year National Summary, USGS Fact Sheet 2016–3055. https://doi.org/10.3133/fs20163055
- USGS WaterWatch: http://waterwatch.usgs.gov · National Water Information System: http://waterdata.usgs.gov/nwis
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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