REAL-TIME DROUGHT SUMMARIES: ONLINE GRAPHS COMPARING REAL-TIME TO HISTORICAL STREAMFLOW IN COLORADO

During the summer of 2002 when Colorado experienced a severe drought, the U.S. Geological Survey, Colorado Water Science Center developed real-time graphs that were accessible to the public and policymakers on the World Wide Web to show comparisons of current and historical streamflows and volumes. These drought summary graphs were developed as a supplement to the USGS National Drought Watch web page (http://water.usgs.gov/waterwatch/?m=dryw&r=co).

The drought summary graphs are updated daily. For 23 selected streamgaging sites in Colorado, graphs show the following three comparisons:

· Daily mean streamflows for each day of the year to historical median and minimum daily mean streamflows for 2002-2006 by year.

· Total streamflow volume for 2002-2006 to historical mean and previous record-low year streamflow volumes by year.

· Cumulative departure from mean streamflow since January 1, 2000.

For the streamgages in Colorado with 30 years or more of record reporting each day, graphs are shown with the following comparisons:

· Recent daily-average streamflows to historical streamflows for the last twelve months.

· Recent daily-average streamflows to historical streamflows for the period since July 1999.

The Colorado Drought Watch web pages (http://co.water.usgs.gov/drought/index.html) are usually available from April through September each year. Real-time updates to these graphs are suspended for the winter months. Because ice in stream channels can cause major shifts in the relation between stream stage and discharge, manual interpretation of the stage record is required to compute reliable streamflows