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Water Supply

When drought impacts affect the water supply—the water levels in streams, reservoirs, and groundwater—it is known as hydrological drought. Periods of drought can lead to inadequate water supply, threatening the health, safety, and welfare of communities.

Hydrological Drought

Water flowing in a reservoir

 

According to the National Drought Mitigation Center, hydrological drought results from precipitation shortfalls on the surface or subsurface water supply—affecting streamflow, reservoir and lake levels, and groundwater.


 

Data, Maps, and Tools

Streamflow, groundwater, and snowpack data are key to monitoring and forecasting water supply.

U.S. Water Supply Conditions

Streamflow Conditions
Value Map Hex Color Description
Low #ff0000 Record Low Estimated streamflow is the lowest value recorded at this gauge on this day of the year. Learn more.
Much Below #b12121 Much Below Normal ( Estimated streamflow is in the 0–10th percentile of historical streamflow values recorded at this gauge on this day of the year. Learn more.
Below #ffa400 Below Normal (10th–25th Percentile) Estimated streamflow is in the 10th–25th percentile of historical streamflow values recorded at this gauge on this day of the year. Learn more.
Normal #00ff00 Normal (25th–75th Percentile) Estimated streamflow is in the 25th–75th percentile of historical streamflow values recorded at this gauge on this day of the year. Learn more.
Value Map Hex Color Description
Above #40dfd0 Above Normal (75th–90th Percentile) Estimated streamflow is in the 75th–90th percentile of historical streamflow values recorded at this gauge on this day of the year. Learn more.
Much Above #0000ff Much Above Normal (>90th Percentile) Estimated streamflow is in the 90th–100th percentile of historical streamflow values recorded at this gauge on this day of the year. Learn more.
High #000000 Record High Estimated streamflow is the highest value ever measured at this gauge on this day of the year. Learn more.
Not Ranked #ffffff Not Ranked A flow category has not been computed for this gauge, for example due to insufficient historical data or no current streamflow estimates.
Streamflow Conditions
Value Map Hex Color Description
Low #ff0000 Record Low Estimated streamflow is the lowest value recorded at this gauge on this day of the year. Learn more.
Much Below #b12121 Much Below Normal ( Estimated streamflow is in the 0–10th percentile of historical streamflow values recorded at this gauge on this day of the year. Learn more.
Below #ffa400 Below Normal (10th–25th Percentile) Estimated streamflow is in the 10th–25th percentile of historical streamflow values recorded at this gauge on this day of the year. Learn more.
Normal #00ff00 Normal (25th–75th Percentile) Estimated streamflow is in the 25th–75th percentile of historical streamflow values recorded at this gauge on this day of the year. Learn more.
Value Map Hex Color Description
Above #40dfd0 Above Normal (75th–90th Percentile) Estimated streamflow is in the 75th–90th percentile of historical streamflow values recorded at this gauge on this day of the year. Learn more.
Much Above #0000ff Much Above Normal (>90th Percentile) Estimated streamflow is in the 90th–100th percentile of historical streamflow values recorded at this gauge on this day of the year. Learn more.
High #000000 Record High Estimated streamflow is the highest value ever measured at this gauge on this day of the year. Learn more.
Not Ranked #ffffff Not Ranked A flow category has not been computed for this gauge, for example due to insufficient historical data or no current streamflow estimates.
Predicted Inches of Precipitation
Range Map Hex Color
0 - 0.01 #ffffff
0.01 - 0.1 #7fff00
0.1 - 0.25 #00cd00
0.25 - 0.5 #008b00
0.5 - 0.75 #104e8b
0.75 - 1 #1e90ff
1 - 1.25 #00b2ee
1.25 - 1.5 #00eeee
1.5 - 1.75 #8968cd
Range Map Hex Color
1.75 - 2 #912cee
2 - 2.5 #8b008b
2.5 - 3 #8b0000
3 - 4 #cd0000
4 - 5 #ee4000
5 - 7 #ff7f00
7 - 10 #cd8500
10 - 15 #ffd700
15 - 20 #ffff00
20 - #ffaeb9

Impacts and Related Content

Timing

According to the National Drought Mitigation Center, the effects of hydrological drought are usually not seen until much later than those from meteorological and/or agricultural drought, as it takes longer for impacts—such as decreases in groundwater levels—to be seen in the hydrological system.

Competition/Restrictions

Groundwater and surface water from rivers and reservoirs are used in many ways—including electricity generation, recreation, wildlife habitat, flood control, and agricultural irrigation. Drought conditions can exacerbate competition for the use of the depleted resource and trigger restrictions based on prior water rights, creating conflict between water users.

Conjunctive Water Management

To manage for drought and climate extremes, water managers increasingly coordinate the use of both surface water and groundwater to utilize overall water supply more efficiently and diversify water management portfolios. 

By Sector | Water Utilities

Drought impacts on water utility operations range from loss of water supply to increased costs and reduced revenues.

Drought resilience for water utilities includes the ability to respond to immediate water supply threats, as well as considering long-term conditions and planning for permanent solutions.

Forecast-Informed Reservoir Operations (FIRO)

FIRO is a proposed management strategy that uses data from watershed monitoring and modern weather and water forecasting to help water managers selectively retain or release water from reservoirs in a manner that reflects current and forecasted conditions. Western water managers require improved long-range forecasting of precipitation to more effectively manage water resources for both extreme wet and dry conditions. FIRO is being developed and tested as a collaborative effort in the Russian River Basin (Lake Mendocino), the Santa Ana River Basin (Prado Dam), and the Yuba-Feather River Basins.

Lake Meredith National Recreation Area in Texas