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The Hydrograph as a measure of Annual Climate Change

While many modern waterways are controlled by dams and reservoirs, in natural systems the hydrograph provides a climate signature that can be an important way of tracking seasonal fluctuations. The water year starts at the beginning of October and ends at the end of September. The hydrograph below from the United States Geological Survey (USGS) shows the "discharge" or flow of South Boulder Creek in the Rocky Mountains near Boulder, Colorado, which is somewhat controlled by a dam upstream but still shows the basic pattern of a natural system. The unit of measure is in cubic feet per second, with the red line referring to daily mean streamflow.

Note the peak of runoff in June from snowmelt.
Hydrograph of water year on South Boulder Creek
Hydrographs can also be used to compare interannual variability. See Investigating Climatic and Environmental Processes Interannual Hydrograph Signatures. To create your own graphs, go to the USGS Historical Discharge website and locate a stream guage near your region.

View a map from the EPA's Water Academy showing hydrographs from around the U.S. and the regional climate signature they contain.

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