Thursday, April 19, 2018

National Drought Mitigation Center


People who study water and how it moves through the environment are called hydrologists. Hydrologists watch streamflow (the amount of water in rivers and streams), lake and reservoir levels, groundwater levels, and even snowpack. They monitor each one of these water sources a little differently, using many different tools. Let’s look at a few of the tools and ways they study water.


Snowpack is very important for hydrologists. The snowpack in the mountains melts in the spring and flows into streams and rivers. During a drought, the snowpack is less than normal. Less snow in the mountains can mean less water in the streams and rivers. 

Hydrologists need to know the snow water equivalent, which is how much water you would get if you were to melt the snow very quickly. They can find this out by measuring the snowpack in several different ways. First, snowpack can be measured by pushing a very long metal tube through the snow until it reaches the ground. The tube is marked like a ruler so you can see the depth of the snow. The snow that gets packed in the middle of the tube is weighed and that weight is the amount of water in the snow. Scientists can also use snow sensors called snow pillows. A snow pillow is basically a scale that is placed on the ground. When snow falls on the snow pillow, the pillow weighs the amount of snow on top of it. This weight tells hydrologists how much water is in the snow.


Hydrologists use stream gauges that they place at different points in rivers and streams to find out how much water is flowing in a river or stream from place to place. During droughts, less water flows, and the water that is in the river or stream will be moving much more slowly than normal. You can find more information about this and even view stream gauges near you on the United States Geologic Survey’s WaterWatch website.


Hydrologists monitor groundwater levels by measuring the distance between the surface of the earth and the surface of water in a well. There are a variety of ways to do this. Sometimes, hydrologists use a simple tape measure. Other times they use high-tech sensors. 

Hydrologists check the groundwater level at different times throughout the year. Taking groundwater measurements helps us know if groundwater levels are changing over a year or over many years. They also help us understand how quickly the groundwater supply is being “recharged.” Surface water (rivers, lakes, streams) and precipitation “recharge” or “refill” groundwater levels. During droughts, groundwater levels may drop because people may be pumping more water out of the ground to water lawns and crops. They may also drop because there is less precipitation and less surface water to refill the groundwater. 

Hydrologists also use the information gained from measuring snowpack, streamflow, and groundwater levels to make computer models. The computer models and information from the measurements we just learned about help us know how much water we have to use during normal years and during drought years.

Hydrology Resources

Click on the links below to see maps and data used by hydrologists.


SNOTEL Data and Products

National Snow Analyses



USGS WaterWatch

Advanced Hydrologic Prediction Service (AHPS)



USGS Active Groundwater Level Network

The National Drought Mitigation Center | University of Nebraska-Lincoln
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