A Tale of Two Basins

  A Tale of Two Basins. This circular chart shows the Upper Colorado River basin and the Lower Colorado River basin side by side. The Upper Colorado basin chart shows that February 4 is the driest day of the year and June 8 is the wettest day of the year. The Lower Colorado basin chart shows that on average October 25 is the driest day of the year and January 8 is the wettest day of the year likely due to a large storm event in 1993. The Upper Colorado chart shows far higher of a flow rate in the summer months compared to the Lower Colorado chart, which does not reach the same high flow in the summer. Average flow rate normalized by basin area (mm per day) for USGS NWIS gages from 1981-2020 in the upper and lower Colorado River Basins. Flow is in mm per day across the entire basin area contributing to each gage.