Water Supply in the Conterminous United States, Alaska, Hawaii, and Puerto Rico, Water Years 2010–20, Chapter B of U.S. Geological Survey Integrated Water Availability Assessment—2010–20

The following are the key points of this chapter:

• Throughout much of the Great Plains and Northeast through Midwest aggregated hydrologic regions, low precipitation totals in water years 2011 and 2012 resulted in low streamflow, evapotranspiration, and soil
  moisture, associated with one of the most substantial droughts since the 1930s.
• The highest interannual variability in precipitation was in the California–Nevada, Texas, Southern High Plains, and Southwest Desert hydrologic regions, whereas the lowest interannual variability was in the Florida, Tennessee–Missouri, and Northeast hydrologic regions.
• Among the Western aggregated hydrologic region, where snow is critical for water availability, the California–Nevada hydrologic region had the highest
  interannual variability in maximum snow accumulation with a coefficient of variation (CV) of 0.60, whereas the Columbia–Snake, Pacific Northwest, and Central Rockies hydrologic regions all had a CV of less than 0.36.
• Six of 29 unconfined and 6 of 23 confined principal and regional aquifer systems had current water-level percentiles (median 2010–20) of less than 30 percent of historical water levels (that is, median 2000–20 water levels) including the California Coastal Basin aquifers, the Colorado Plateaus aquifers, and the Central and Southern regions of the High Plains aquifer.
• Hydrologic regions with low precipitation and little storage coincide with aquifer systems that have shown a decline in groundwater levels during water years 2010–20, including the Southern High Plains, Central High Plains, and Texas hydrologic regions.

Companion chapters:

U.S. Geological Survey Integrated Water Availability Assessment—2010–20, Chapter A

Status of Water-Quality Conditions in the United States, 2010–20, Chapter C 

Water Use Across the Conterminous United States, Water Years 2010–20, Chapter D 

Climate Change and Future Water Availability in the United States, Chapter E 

Integrated Water Availability in the Conterminous United States, 2010–20, Chapter F