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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

The map depicts streamflow conditions compared to historical streamflow conditions for the day of the year. U.S. Geological Survey stream gages are displayed alongside current drought conditions from the U.S. Drought Monitor. Learn more.

The National Weather Service's Weather Prediction Center (WPC) produces Quantitative Precipitation Forecasts (QPFs) that depict the amount of liquid precipitation expected to fall in a defined period of time. QPFs issued by the WPC are defined as the expected "areal average" (on a 20 x 20 km grid) in inches. This map shows the 7-day total QPF. Learn more.

Streamflow Percentiles

The color with the hex code #ff0000 identifies:
Low
The color with the hex code #b12121 identifies:
Much Below Normal (< 10%)
The color with the hex code #ffa400 identifies:
Below Normal (10% - 24%)
The color with the hex code #00ff00 identifies:
Normal (25% - 75%)
The color with the hex code #40dfd0 identifies:
Above Normal (75% - 90%)
The color with the hex code #0000ff identifies:
Much Above Normal (> 90%)
The color with the hex code #000000 identifies:
High

U.S. Drought Monitor

The color with the hex code #ffff00 identifies:
D0
The color with the hex code #ffcc99 identifies:
D1
The color with the hex code #ff6600 identifies:
D2
The color with the hex code #ff0000 identifies:
D3
The color with the hex code #660000 identifies:
D4

Predicted Inches of Precipitation

The color with the hex code #7fff00 identifies:
0.01
The color with the hex code #00cd00 identifies:
0.1
The color with the hex code #008b00 identifies:
0.25
The color with the hex code #104e8b identifies:
0.5
The color with the hex code #1e90ff identifies:
0.75
The color with the hex code #00b2ee identifies:
1
The color with the hex code #00eeee identifies:
1.25
The color with the hex code #8968cd identifies:
1.5
The color with the hex code #912cee identifies:
1.75

The color with the hex code #8b008b identifies:
2
The color with the hex code #8b0000 identifies:
2.5
The color with the hex code #cd0000 identifies:
3
The color with the hex code #ee4000 identifies:
4
The color with the hex code #ff7f00 identifies:
5
The color with the hex code #cd8500 identifies:
7
The color with the hex code #ffd700 identifies:
10
The color with the hex code #ffff00 identifies:
15
The color with the hex code #ffaeb9 identifies:
20

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